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Latest news on listeriosis
Comp. Immun. Microbiol. infect. Dis. Vol. 14, No. 1, pp. 1-7, 1991 Printed in Great Britain. All rights reserved
0147-9571/91 $3.00+0.00 Copyright © 1991 Pergamon Press plc
REVIEW LATEST NEWS ON LISTERIOSIS A. L. COURTIEU Microbiologie et Hygirne U.F.R. de Mrdecine de Nantes, CHR de Nantes, Centre National de Rrfrrence sur les Listeria, UFR de Nantes, BP 1024, 44035 Nantes Cedex, France Abstract---Emphasis is given essentially to the presentation of recent data in terms of our total knowledge of Listeria and human and animal listeriosis. This disease of extremely varied origin can be studied in terms of two groups of subjects: females in gestation and all other categories of individuals. There was initially only a single species of Listeria, but at least five are known today, only two of which are pathogenic. Their pathogenic power is related essentially to the presence of listerolysin O, although this is not the only factor involved. Identification of Listeria is easy and can be completed with that of its serovar and lysovar. Epidemiological studies have shown that the great majority of listeriosis are anademic. The contamination of receptive subjects is due to certain forms of food. In the absence of efficient vaccination, disease prevention must be obtained by eliminating Listeria from food.
Key words: animal listeriosis, human listeriosis, epidemiology. Rrsum~-A travers un plan reprenant l'ensemble de nos connaissances sur Listeria et les listerioses humaine et animale, on s'attache essentiellement ~i souligner les donnres nouvellement acquises. De maladie fi causes extrrmement multiples, la listeriose se rrsume fi deux groupes de sujets sensibles: les femelles gestantes et les autres catrgories d'individus. D'une esprce initiale, nous en sommes actuellement ~i un minumum de cinq Listeria dont deux seulement sont pathogrnes. Le pouvoir pathogrne est essentiellement 1i6 ~ la prrsence de listeriolysine O, mais ce n'est pas le seul facteur. L'identification des Listeria est aisre. On peut la complrter par celle du srrovar et du lysovar. Nos connaissances en 6pidrmiologie nous montrent que la grande majorit6 des listrrioses observres sont des anadrmies. La contamination des sujets rrceptifs est due ~i certaines formes d'alimentation. En l'absence d'une vaccination efficace, la prrvention doit 6tre assurre par la disparition des Listeria dans les aliments.
Mots-clefs: listeriose animale, listeriose humaine, epidrmiologie.
T h e h i s t o r y o f listeriosis b e g a n officially in 1 9 2 3 - 1 9 2 4 as r e c o u n t e d in a 1926 d e s c r i p t i o n b y M u r r a y et aL [1] o f a n e p i z o o t i c a f f e c t i n g r a b b i t s a n d g u i n e a pigs in t h e e x p e r i m e n t a l a n i m a l c a g e s o f a British u n i v e r s i t y . A n u n k n o w n b a c t e r i a i s o l a t e d in t h e c a d a v e r s o f d i s e a s e d a n i m a l s w a s g i v e n the n a m e Bacterium monocytogenes. It w a s a s m a l l g r a m p o s i t i v e b a c i l l u s w h i c h r e p r o d u c e d t h e s a m e d i s e a s e e x p e r i m e n t a l l y in l a b o r a t o r y r o d e n t s . T h e s e a u t h o r s n o t e d t h a t t h e d i s e a s e d a n i m a l s h a d a m a r k e d i n c r e a s e in b l o o d m o n o c y t e s . A l t h o u g h the first h u m a n c a s e o f listeriosis h a d o c c u r r e d e a r l i e r (1918), it w a s o n l y r e c o g n i z e d in 1942. J. D u m o n t h a d i s o l a t e d a b a c t e r i u m in the c e r e b r o s p i n a l fluid ( C S F ) o f a n I t a l i a n s o l d i e r w h o d i e d o f p u r u l e n t m e n i n g i t i s n e a r the b a t t l e f r o n t . T h i s b a c t e r i u m w a s c o n f i d e d to L. cotoni, a n d t h e c a s e w a s d e s c r i b e d in 1921 by D u m o n t a n d C o t o n i in t h e Annales de l'Institut Pasteur [2] as h a v i n g b e e n d u e to a b a c t e r i u m r e s e m b l i n g the b a c i l l u s o f s w i n e - e r y s i p e l a s . I n 1942, C o t o n i , w h o t o o k a n i n t e r e s t in the m a n y p u b l i c a t i o n s CIMID 14/I--A
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concerning human and animal cases of listeriosis, reexamined in 1918 strain which he had conserved and could then easily identify it. He had not initially observed the mobility of the bacterium, but in view of the new descriptions was able to find it in his strain. He also stressed the facility with which he had been able to conserve the strain in his laboratory for more than 20 years [3]. From 1930 to 1945, there were a number of publications about infections in man and various animals, essentially mammals. Cases of purulent meningitis were especially noted in man and also occurred in animals. The relationship between the disease and gestation were also often mentioned since pregnant women and animals in gestation seemed more often afflicted. Meanwhile, in order to conform to the rules of nomenclature, Listeria replaced the name Listerella [4]. After 1946, there were many cases reported. Bacteriologists became increasingly more knowledgeable of this bacterium and could isolate it easily. Morever, there was a constant increase in the cases observed. Relations between diseased animals and human contamination were sometimes noted, and numerous epidemiologic schemes were elaborated. However, the true epidemiology still remained unknown. It was necessary first to have a better understanding of Listeria in order to extract usable markers from it. It is noteworthy that during the last decade there was considerable development in the spread of disease to the totality of mammals. BACTERIOLOGY Listeria monocytogenes, for a long time the only known species of the genus, is now associated with at least four new species: L. monocytogenes (hemolytic), L. ivanovii (hemolytic), L. seeligeri (hemolytic), L. innocua (nonhemolytic), L. welshimeri (nonhemolytic). Two other less frequent species may also be included: L. grayi (nonhemolytic), L. murrayi (nonhemolytic). Listeria are small gram-positive bacilli which move about at temperatures of around 20 to 30°C by means of a few peritrichous flagella. They may easily be cultured on ordinary media. Seeding should be carried out on blood agars to clearly differentiate the hemolytic strains. Hemolysis is an important characteristic due to production of an enzyme known as listeriolysin O which would seem to be directly related to the pathogenic power of Listeria [5]. Nonhemolytic species can be considered as nonpathogenic. Moreover, initially hemolytic and pathogenic laboratory strains can produce nonhemolytic mutants [6]. However, L. seeligeri is hemolytic and at present also nonpathogenic. Identification of the seven species is easy and can be done by comparing the behavior of the strain on mannitol, D-xylose, nitrate reduction, hemolysis and the CAMP-test (using Rhodoeoccus equi as revealer) [7]. The bacteriologic test thus provides two types of markers: hemolysis which classifies the species as potentially pathogenic or nonpathogenic; and some features determining assignment to one of the five (or seven) species. ANTIGENIC FEATURES As in the case of many genera of gram-positive bacteria, antigenic features are complex. They were for a long time the only usable markers and are still an important element of
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differentiation. In France, they were determined by the Centre national de rrfrrences des Listeria (National Listeria Reference Center) of the College of Medicine of the University of Nantes. The species L. monocytogenes has a dozen different serovars, whereas L. ivanovii has only serovar 5. It is to be noted that some serovars are found in two different species. There may be other as yet unidentified antigens involved, and antigen associations not corresponding to the general scheme have also been observed. OTHER MARKERS It is likely that Listeria will benefit from the current progress in molecular biology which has not yet been extensively applied to this bacterial genus. In the meantime, a procedure referred to as lysotyping has been developed in Nantes by A. Audurier [8] which is a useful complement to the characterization of serovars. In the most frequent serovars (1/2a, l/2b, 1/2c and 4b), it enables very characteristic lysovars to be identified. This determination has proved to be quite useful in the study of some recent epidemics in human populations. LISTERIOSIS Reference works published before 1960 indicate that manifestations of listerial infection were numerous and of quite varied clinical form. In time, these conceptions were simplified, so that today it may be considered that there are only two forms of listeriosis; fetomaternal listeriosis and listeriosis not related to gestation. Although this division is a bit schematic, it is useful for both animals and man. 1. Fetomaternal listeriosis This is usually a disease of pregnant women and animals in gestation. In women it is often characterized by a short acute episode of pseudogrippal type. The cure can be spontaneous. If hemoculture is performed at the time of temperature rise, L. monocytogenes can often be isolated in the blood. However, this episode can cause abortion or premature delivery depending on gestational age. The fetus or infant may appear to be in good health but is often infected, in which case multinodular listeriosis with microabscesses disseminated in various viscera can be involved. This is the granulomatosis infanti septica described by German authors. L. monocytogenes abounds in these abscesses, and there are very often lesions of the uterine side of the placenta, with presence of Listeria. Infants can be born prematurely with no signs of infection. If bacteriologic examinations are performed, L. monocytogenes may be found in gastric fluid and/or in the meconium. This bacterial "carrier" condition may be of no consequence, but in any event the attending physician systematically prescribes associated antibiotic therapy. It would seem that this particular sensitivity in women and animals in gestation is due to major disturbances of the immune state. An analogy may be found with listeriosis unrelated to gestation and occurring in immunosuppressed subjects. With (or without) treatment, women are normally cured; however, the fetus (especially) and the infant are severely affected (lethality of around 25% in France). Some children born viable can be afflicted with listerial meningitis in the days following delivery. They are generally included in the fetomaternal listeriosis category, although probably infected only at the time of delivery by direct contamination from the mother. The
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infrequent cases of newborn infants contaminated directly or indirectly by being kept in a room recently exposed to fetomaternal listeriosis can also be included in this category.
2. Listerioses unrelated to gestation Consideration of the previous cases serves as a transition to this category for which the name of the disease has been given in the plural. In effect, the clinical forms are numerous both in man and animals. Meningitis and meningoencephalitis. These are the best known and also the most severe manifestations, affecting all human age groups but especially young children and the elderly. Two-thirds of the victims are male (but women with fetomaternal listeriosis are excluded from this figure). Mortality is high, becoming greater with age and/or the existence of one or more associated risk factors (cancer, hemopathy, diabetes, acquired or passive immunosuppression, nephropathy, etc.). Endocarditis. Although this form is not very frequent (34 cases worldwide in 1988) [9], it is of interest for consideration. Many cases o f infectious endocarditis in man are due to the action of human saprophyte bacteria such as streptococci and enterococci. It is generally considered that these bacteria fix on already diseased heart or aortic valves during transient bacteremia (e.g. dental avulsions). The same reasoning can be applied to the case of Listeria behaving similarly with respect to a bacteremia of gastrointestinal origin at the time of an intestinal transit of some importance. Endocarditis also affects prosthetic heart valves (8 out of the 34 cases reported). Overall mortality is 50%). Diverse suppurative forms. All sorts of localizations have been described. Infections of arterial aneurysms may be cited first since they are similar to endocarditis, but one also finds pleuropulmonary suppurations, abscesses of different viscera and the genital organs, subcutaneous abscesses, etc. There are also septicemias which can be related to the existence of a suppurative localization, including meningitis. They can also be primary as in the case of the pregnant woman.
3. Frequency of human listeriosis in France The Direction grnrrale de la Sant~ and the Laboratoire national de la Sant6 (two organizations concerned with human health) contribute to the monitoring of human listeriosis in France through collaboration with laboratories of large hospitals (university or nonuniversity) and the Centre national de rrfrrence des Listeria. In 1987, the frequency of the disease was estimated at a little less than 1000 cases per year [10] on the basis of 651 cases reported directly by bacteriologists. There were about as many cases of fetomaternal listeriosis as of the other category. Lethality was 34%. LABORATORY DIAGNOSIS Listeriosis is rarely detected during clinical examination. However, if the obstetrician is aware of the existence of a febrile state during pregnancy, he automatically prescribes a hemoculture. Listerial meningitis is not especially distinguishable from other forms of bacterial meningitis except at the beginning when a lymphocytic and/or monocytic reaction can be noted in CSF. The diagnosis of listeriosis is thus based essentially on bacteriologic examination of a suitable specimen. Culturing is easy and without complications unless the specimen is contaminated. If it is, recourse to the customary techniques (enrichment, selective media)
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is necessary. Once isolated colonies have been obtained, identification of the genus is rapid: small gram-positive bacilli mobile at 25°C, hemolytic colonies and fast hydrolysis of esculin are indicative of Listeria. Determination of bacterial sensitivity to antibiotics is not urgent. Listeria do not seem to be greatly affected by acquisition of resistance. Descriptions are rare but have been carefully presented. A serological examination may be performed on a subject with suspected listeriosis as there are antigens for seroagglutination or complement fixation. Unfortunately, the results of these reactions are difficult to interpret: positivity with no proven listeriosis; negativity during follow-up of listeriosis confirmed by bacteriologic examination. EPIDEMIOLOGY For a long time it was difficult to find explanations relative to the spread of the disease. The relation between diseased animals and human infection has been described several time, for instance by Hyslop and Osborn [11]. In 1959, these authors drew attention to the risk of human infection from animal listeriosis. Moreover, they also reported listeriosis in gravid rabbits after absorption of milk from a diseased cow. Epidemics in cattle and especially sheep farms have been reported more and more frequently. Diverse concentrations of cases in man have been reported in France by Burdin [12] and Humbert [13]. The first great concentration was reported by Carbonnelle [14]: more than 150 cases during a 3-year period in the area between Angers and Laval. At the time of this study, the authors indicated that they found 7% listerial placentas during systematic research in cases of abortion. They also found a high concentration of Listeria in the water purification facility in Angers: 61% of positive samples at the outlet of the facility. Veterinarians provided the first explanations concerning the origin of some listeriosis in food. In 1985, at an international symposium on listeriosis in Nantes, France, Nicolas [15] reviewed the important role played by highly contaminated ensilage in the development of listeriosis in animals consuming it. When consumption was stopped, there was a rapid decline in the appearance of new cases. Such cases would seem to be due to contamination from a common source (anademic) and not from animal to animal. Although the latter possibility may exist, it is apparently not very important (cf. the possibilities of interhuman contamination with respect to perinatal listeriosis). Veritable epidemics with bacteriologic proof have been described, and a review of these was published in 1988 by Kvenberg [16]. Three of these cases shall be considered here. In 1979, in Nova Scotia, Canada, there was an epidemic especially affecting pregnant women (34 perinatal and 7 adult cases). The food incriminated was cabbage which had been contaminated by sheep manure. In 1985, near Los Angeles, California, there were more than 100 cases and 30 deaths due to cheeses prepared in California according to a Mexican recipe and in conformity with Food and Drug Adminsitration standards. From 1983 to 1987, there were more than 120 cases in the canton of Vaud, Switzerland, due to consumption of a cheese (vacherin) produced in the Jura. The cases were equally distributed between fetomaternal listeriosis and listeriosis unrelated to pregnancy. There have been no evident descriptions of human contamination by meat products. However, many controls have shown that numerous preparations are more or less contaminated: pork products (sausage, etc.), beef and pork, fowl, etc. Some checks have shown the presence of Listeria in nearly half of the samples studied [17].
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In recent years, there have been a large number of publications concerning the results of Listeria research in food products for human (and even in some cases animal) consumption. Listeria were frequent, especially nonhemolytic ones and L. seeligeri. L. ivanovii was very rare. However, various serovars of L. monocytogenes were also found, including 4b and the serogroup 1/2 (a, b and c). Certain authors now tend to consider that if a product contains a species of Listeria it can also contain a lower concentration of L. monocytogenes. The apparent conclusion to be drawn from these epidemiological considerations is that, owing to the small number of cases described, the interindividual epidemic must be nonexistent. Conversely, the epidemic develops mainly according to the anademic mode, and the most usual source in both man and the animal is food. PROPHYLAXIS Vaccination trials have been carried out in animals, but none has proved to be truly convincing. Based on acquired knowledge, much effort has been directed at eliminating Listeria from food. Prophylaxis thus begins with the animal. Ensilage must be done correctly since Listeria develop easily in " p o o r " silage with an alkaline tendency. Good feeding practices will limit the spread of Listeria in animal farms. Milk will be less often contaminated and meat will be more wholesome. Absence of Listeria should be ensured in the preparation of food for human consumption involving high risk of Listeria propagation (especially cheeses and pork products to be eaten uncooked). During production all possible causes of recontamination should be eliminated. In France, the dairy industry has understood this requirement. The organization of new production processes in suitable premises is being implemented even before the probable publication of official texts to regulate the distribution of products. Public services and packages are paying particular attention to new forms f o r distribution of food products to prevent them from being another source of Listeria (as was the Canadian cabbage). THERAPEUTICS Like all bacteria, Listeria are sensitive to various antibiotics. They behave like most gram-positive bacteria and are ordinarily sensitive to penicillins (aminopenicillins), aminoglycosides and macrolides. They are comparatively less sensitive to cephalosporins, particularly to those referred to as third-generation. They are only slightly sensitive to the new quinolones. PeniciUins, aminoglycosides and quinolones have very marked killing power which is however sometimes unstable at low concentrations. Conversely, their associations are rapidly and definitively bactericidal: aminopenicillin with quinolone or aminoglycoside; aminoglycoside with quinolone. Practically all species behave in the same way. In medicine one of these associations is often used. The use of tetracycline in human listeriosis was never highly developed. Recent publications giving sensitivity statistics no longer even mention this antibiotic. Over the years, no significant increase has been noted in rates of resistance to antibiotics, There are however strains which are resistant to one or more antibiotics, and it has been
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s u g g e s t e d t h a t p l a s m i d s m a y b e r e s p o n s i b l e f o r this. S o m e p l a s m i d s m a y e v e n b e c a p a b l e of interchanges between streptococci or enterococci and Listeria. REFERENCES I. Murray E. G. D., Webb R. A. and Swann M. B. R. A disease of rabbits characterised by a large mononuclear leucocytosis, caused by a hitherts undescribed bacillus Bacterium monocytogenes (n.sp.). J. Path. Baeteriol. 29, 407-439 (1926). 2. Dumont P. et Cotoni L. Bacille semblable au rouget du proc, recontr6 dans le L.C.R. d'une m6ningite. Ann. Inst. Pasteur 35, 625~33 (1921). 3. Cotoni L. A propos des bact6ries d6nomm6es Listerella. Rappel d'un observation ancienne de m6ningite chez l'homme. Ann. Inst. Pasteur 68, 92-95 (1942). 4. Pirie J. H. H. Listeria: change of name for a genus of bacteria. Nature 145, 264 (1940). 5. Rocourt J. and Berche P. Third Forum in microbiology virulence Listeria monocytogenes. Ann. Inst. Pasteur/Microbiol. 138, 241-284 (1987). 6. Pine L., Weaver R. E., Carlone G. M. et al. Listeria monocytogenes ATCC 35152 and NCTC 7973 contain a nonhemolytic, nonvirulent variant. J. olin. Mierobiol. 25, 2247-2251 (1987). 7. Rocourt J., Schrettenbrunner A. et Seeliger H. R. P. Differenciation biochimique des groupes g6n6miques de Listeria monocytogenes (sensu lato). Ann. microbiol. (Inst. Pasteur) 134A, 65-71 (1983). 8. Audurier A., Rocourt J. et Courtieu A. L. Isolement et caract6risation de bact6riophages de Listeria monocytogenes. Ann. Microbiol. (Inst. Pasteur) 128A, 185-198 (1978). 9. Gallacher P. G. and Watanakunakorn C. Listeria monocytogenes endocarditis: a review of the literature 1950-1986. Scand. J. infect. Dis. 20, 359 368 (1988). 10. Goulet V., Lemagny F., Rebiere I. et Espaze E. P. La list6riose en France en 1987. Etude r&rospective fi partir d'un 6chantillon d'h6pitaux publics. Bull. bpid~miol, hebdo. 12, 45-46 (1989). 1 I. Hyslop N. S. G. and Osborne A. D. Listeriosis: a potential danger to public health. Vbtbrin. Rec. 71, 1082-1095 (1959). 12. Burdin J. C., Weber M. et Martin F. Etude 6pid6miologique de la list6riose humaine en France ~ propos de 62 cas observ6s en Lorraine. Rev. Epidemiol. Med. soc. Sant~ 22, 279-302 (1974). 13. Humbert G., Duval C., Fessard C., Meunier M. et Ledoux A. Les list6rioses en France. R6sultats d'une enqu6te national (824 cas). Med. real. infect. 6, Suppl. list6rioses, 60 70 (1976). 14. Carbonnelle B., Cottin J., Parvery F., Kouyoumdjian S., Le Lirzin M., Cordier G. et Vincent F. Epid6mie de list6riose dans l'Ouest de la France (1975-1976). Rev. Epid~miol. Santb 26, 451-467 (1978). 15. Nicolas J. A. et Vidaud N. Contribution ~ l'6tude des Listeria pr6sentes dans les denr6es d'origine animale destin6es fi la consommation humaine. In Listkrioses, Listeria, Listeriosis 1985-1986(Edited by Courtieu A. L., Espaze E. P. et Reynaud A. E.) pp. 330-338. Universit6 de Nantes (1986). 16. Kuenberg J. E. Outbreaks of listeriosis/Listeria--contaminated foods. Microbiol. Sci. 5, 355 358 (1988). 17. Rocourt J. List6riose humaine: aspects cliniques et 6pid6miologiques. R61e de l'alimentation. Le Biologieste 23, 29-40 (1989).
0147-9571/91 $3.00+0.00 Copyright © 1991 Pergamon Press plc
REVIEW LATEST NEWS ON LISTERIOSIS A. L. COURTIEU Microbiologie et Hygirne U.F.R. de Mrdecine de Nantes, CHR de Nantes, Centre National de Rrfrrence sur les Listeria, UFR de Nantes, BP 1024, 44035 Nantes Cedex, France Abstract---Emphasis is given essentially to the presentation of recent data in terms of our total knowledge of Listeria and human and animal listeriosis. This disease of extremely varied origin can be studied in terms of two groups of subjects: females in gestation and all other categories of individuals. There was initially only a single species of Listeria, but at least five are known today, only two of which are pathogenic. Their pathogenic power is related essentially to the presence of listerolysin O, although this is not the only factor involved. Identification of Listeria is easy and can be completed with that of its serovar and lysovar. Epidemiological studies have shown that the great majority of listeriosis are anademic. The contamination of receptive subjects is due to certain forms of food. In the absence of efficient vaccination, disease prevention must be obtained by eliminating Listeria from food.
Key words: animal listeriosis, human listeriosis, epidemiology. Rrsum~-A travers un plan reprenant l'ensemble de nos connaissances sur Listeria et les listerioses humaine et animale, on s'attache essentiellement ~i souligner les donnres nouvellement acquises. De maladie fi causes extrrmement multiples, la listeriose se rrsume fi deux groupes de sujets sensibles: les femelles gestantes et les autres catrgories d'individus. D'une esprce initiale, nous en sommes actuellement ~i un minumum de cinq Listeria dont deux seulement sont pathogrnes. Le pouvoir pathogrne est essentiellement 1i6 ~ la prrsence de listeriolysine O, mais ce n'est pas le seul facteur. L'identification des Listeria est aisre. On peut la complrter par celle du srrovar et du lysovar. Nos connaissances en 6pidrmiologie nous montrent que la grande majorit6 des listrrioses observres sont des anadrmies. La contamination des sujets rrceptifs est due ~i certaines formes d'alimentation. En l'absence d'une vaccination efficace, la prrvention doit 6tre assurre par la disparition des Listeria dans les aliments.
Mots-clefs: listeriose animale, listeriose humaine, epidrmiologie.
T h e h i s t o r y o f listeriosis b e g a n officially in 1 9 2 3 - 1 9 2 4 as r e c o u n t e d in a 1926 d e s c r i p t i o n b y M u r r a y et aL [1] o f a n e p i z o o t i c a f f e c t i n g r a b b i t s a n d g u i n e a pigs in t h e e x p e r i m e n t a l a n i m a l c a g e s o f a British u n i v e r s i t y . A n u n k n o w n b a c t e r i a i s o l a t e d in t h e c a d a v e r s o f d i s e a s e d a n i m a l s w a s g i v e n the n a m e Bacterium monocytogenes. It w a s a s m a l l g r a m p o s i t i v e b a c i l l u s w h i c h r e p r o d u c e d t h e s a m e d i s e a s e e x p e r i m e n t a l l y in l a b o r a t o r y r o d e n t s . T h e s e a u t h o r s n o t e d t h a t t h e d i s e a s e d a n i m a l s h a d a m a r k e d i n c r e a s e in b l o o d m o n o c y t e s . A l t h o u g h the first h u m a n c a s e o f listeriosis h a d o c c u r r e d e a r l i e r (1918), it w a s o n l y r e c o g n i z e d in 1942. J. D u m o n t h a d i s o l a t e d a b a c t e r i u m in the c e r e b r o s p i n a l fluid ( C S F ) o f a n I t a l i a n s o l d i e r w h o d i e d o f p u r u l e n t m e n i n g i t i s n e a r the b a t t l e f r o n t . T h i s b a c t e r i u m w a s c o n f i d e d to L. cotoni, a n d t h e c a s e w a s d e s c r i b e d in 1921 by D u m o n t a n d C o t o n i in t h e Annales de l'Institut Pasteur [2] as h a v i n g b e e n d u e to a b a c t e r i u m r e s e m b l i n g the b a c i l l u s o f s w i n e - e r y s i p e l a s . I n 1942, C o t o n i , w h o t o o k a n i n t e r e s t in the m a n y p u b l i c a t i o n s CIMID 14/I--A
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concerning human and animal cases of listeriosis, reexamined in 1918 strain which he had conserved and could then easily identify it. He had not initially observed the mobility of the bacterium, but in view of the new descriptions was able to find it in his strain. He also stressed the facility with which he had been able to conserve the strain in his laboratory for more than 20 years [3]. From 1930 to 1945, there were a number of publications about infections in man and various animals, essentially mammals. Cases of purulent meningitis were especially noted in man and also occurred in animals. The relationship between the disease and gestation were also often mentioned since pregnant women and animals in gestation seemed more often afflicted. Meanwhile, in order to conform to the rules of nomenclature, Listeria replaced the name Listerella [4]. After 1946, there were many cases reported. Bacteriologists became increasingly more knowledgeable of this bacterium and could isolate it easily. Morever, there was a constant increase in the cases observed. Relations between diseased animals and human contamination were sometimes noted, and numerous epidemiologic schemes were elaborated. However, the true epidemiology still remained unknown. It was necessary first to have a better understanding of Listeria in order to extract usable markers from it. It is noteworthy that during the last decade there was considerable development in the spread of disease to the totality of mammals. BACTERIOLOGY Listeria monocytogenes, for a long time the only known species of the genus, is now associated with at least four new species: L. monocytogenes (hemolytic), L. ivanovii (hemolytic), L. seeligeri (hemolytic), L. innocua (nonhemolytic), L. welshimeri (nonhemolytic). Two other less frequent species may also be included: L. grayi (nonhemolytic), L. murrayi (nonhemolytic). Listeria are small gram-positive bacilli which move about at temperatures of around 20 to 30°C by means of a few peritrichous flagella. They may easily be cultured on ordinary media. Seeding should be carried out on blood agars to clearly differentiate the hemolytic strains. Hemolysis is an important characteristic due to production of an enzyme known as listeriolysin O which would seem to be directly related to the pathogenic power of Listeria [5]. Nonhemolytic species can be considered as nonpathogenic. Moreover, initially hemolytic and pathogenic laboratory strains can produce nonhemolytic mutants [6]. However, L. seeligeri is hemolytic and at present also nonpathogenic. Identification of the seven species is easy and can be done by comparing the behavior of the strain on mannitol, D-xylose, nitrate reduction, hemolysis and the CAMP-test (using Rhodoeoccus equi as revealer) [7]. The bacteriologic test thus provides two types of markers: hemolysis which classifies the species as potentially pathogenic or nonpathogenic; and some features determining assignment to one of the five (or seven) species. ANTIGENIC FEATURES As in the case of many genera of gram-positive bacteria, antigenic features are complex. They were for a long time the only usable markers and are still an important element of
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differentiation. In France, they were determined by the Centre national de rrfrrences des Listeria (National Listeria Reference Center) of the College of Medicine of the University of Nantes. The species L. monocytogenes has a dozen different serovars, whereas L. ivanovii has only serovar 5. It is to be noted that some serovars are found in two different species. There may be other as yet unidentified antigens involved, and antigen associations not corresponding to the general scheme have also been observed. OTHER MARKERS It is likely that Listeria will benefit from the current progress in molecular biology which has not yet been extensively applied to this bacterial genus. In the meantime, a procedure referred to as lysotyping has been developed in Nantes by A. Audurier [8] which is a useful complement to the characterization of serovars. In the most frequent serovars (1/2a, l/2b, 1/2c and 4b), it enables very characteristic lysovars to be identified. This determination has proved to be quite useful in the study of some recent epidemics in human populations. LISTERIOSIS Reference works published before 1960 indicate that manifestations of listerial infection were numerous and of quite varied clinical form. In time, these conceptions were simplified, so that today it may be considered that there are only two forms of listeriosis; fetomaternal listeriosis and listeriosis not related to gestation. Although this division is a bit schematic, it is useful for both animals and man. 1. Fetomaternal listeriosis This is usually a disease of pregnant women and animals in gestation. In women it is often characterized by a short acute episode of pseudogrippal type. The cure can be spontaneous. If hemoculture is performed at the time of temperature rise, L. monocytogenes can often be isolated in the blood. However, this episode can cause abortion or premature delivery depending on gestational age. The fetus or infant may appear to be in good health but is often infected, in which case multinodular listeriosis with microabscesses disseminated in various viscera can be involved. This is the granulomatosis infanti septica described by German authors. L. monocytogenes abounds in these abscesses, and there are very often lesions of the uterine side of the placenta, with presence of Listeria. Infants can be born prematurely with no signs of infection. If bacteriologic examinations are performed, L. monocytogenes may be found in gastric fluid and/or in the meconium. This bacterial "carrier" condition may be of no consequence, but in any event the attending physician systematically prescribes associated antibiotic therapy. It would seem that this particular sensitivity in women and animals in gestation is due to major disturbances of the immune state. An analogy may be found with listeriosis unrelated to gestation and occurring in immunosuppressed subjects. With (or without) treatment, women are normally cured; however, the fetus (especially) and the infant are severely affected (lethality of around 25% in France). Some children born viable can be afflicted with listerial meningitis in the days following delivery. They are generally included in the fetomaternal listeriosis category, although probably infected only at the time of delivery by direct contamination from the mother. The
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infrequent cases of newborn infants contaminated directly or indirectly by being kept in a room recently exposed to fetomaternal listeriosis can also be included in this category.
2. Listerioses unrelated to gestation Consideration of the previous cases serves as a transition to this category for which the name of the disease has been given in the plural. In effect, the clinical forms are numerous both in man and animals. Meningitis and meningoencephalitis. These are the best known and also the most severe manifestations, affecting all human age groups but especially young children and the elderly. Two-thirds of the victims are male (but women with fetomaternal listeriosis are excluded from this figure). Mortality is high, becoming greater with age and/or the existence of one or more associated risk factors (cancer, hemopathy, diabetes, acquired or passive immunosuppression, nephropathy, etc.). Endocarditis. Although this form is not very frequent (34 cases worldwide in 1988) [9], it is of interest for consideration. Many cases o f infectious endocarditis in man are due to the action of human saprophyte bacteria such as streptococci and enterococci. It is generally considered that these bacteria fix on already diseased heart or aortic valves during transient bacteremia (e.g. dental avulsions). The same reasoning can be applied to the case of Listeria behaving similarly with respect to a bacteremia of gastrointestinal origin at the time of an intestinal transit of some importance. Endocarditis also affects prosthetic heart valves (8 out of the 34 cases reported). Overall mortality is 50%). Diverse suppurative forms. All sorts of localizations have been described. Infections of arterial aneurysms may be cited first since they are similar to endocarditis, but one also finds pleuropulmonary suppurations, abscesses of different viscera and the genital organs, subcutaneous abscesses, etc. There are also septicemias which can be related to the existence of a suppurative localization, including meningitis. They can also be primary as in the case of the pregnant woman.
3. Frequency of human listeriosis in France The Direction grnrrale de la Sant~ and the Laboratoire national de la Sant6 (two organizations concerned with human health) contribute to the monitoring of human listeriosis in France through collaboration with laboratories of large hospitals (university or nonuniversity) and the Centre national de rrfrrence des Listeria. In 1987, the frequency of the disease was estimated at a little less than 1000 cases per year [10] on the basis of 651 cases reported directly by bacteriologists. There were about as many cases of fetomaternal listeriosis as of the other category. Lethality was 34%. LABORATORY DIAGNOSIS Listeriosis is rarely detected during clinical examination. However, if the obstetrician is aware of the existence of a febrile state during pregnancy, he automatically prescribes a hemoculture. Listerial meningitis is not especially distinguishable from other forms of bacterial meningitis except at the beginning when a lymphocytic and/or monocytic reaction can be noted in CSF. The diagnosis of listeriosis is thus based essentially on bacteriologic examination of a suitable specimen. Culturing is easy and without complications unless the specimen is contaminated. If it is, recourse to the customary techniques (enrichment, selective media)
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is necessary. Once isolated colonies have been obtained, identification of the genus is rapid: small gram-positive bacilli mobile at 25°C, hemolytic colonies and fast hydrolysis of esculin are indicative of Listeria. Determination of bacterial sensitivity to antibiotics is not urgent. Listeria do not seem to be greatly affected by acquisition of resistance. Descriptions are rare but have been carefully presented. A serological examination may be performed on a subject with suspected listeriosis as there are antigens for seroagglutination or complement fixation. Unfortunately, the results of these reactions are difficult to interpret: positivity with no proven listeriosis; negativity during follow-up of listeriosis confirmed by bacteriologic examination. EPIDEMIOLOGY For a long time it was difficult to find explanations relative to the spread of the disease. The relation between diseased animals and human infection has been described several time, for instance by Hyslop and Osborn [11]. In 1959, these authors drew attention to the risk of human infection from animal listeriosis. Moreover, they also reported listeriosis in gravid rabbits after absorption of milk from a diseased cow. Epidemics in cattle and especially sheep farms have been reported more and more frequently. Diverse concentrations of cases in man have been reported in France by Burdin [12] and Humbert [13]. The first great concentration was reported by Carbonnelle [14]: more than 150 cases during a 3-year period in the area between Angers and Laval. At the time of this study, the authors indicated that they found 7% listerial placentas during systematic research in cases of abortion. They also found a high concentration of Listeria in the water purification facility in Angers: 61% of positive samples at the outlet of the facility. Veterinarians provided the first explanations concerning the origin of some listeriosis in food. In 1985, at an international symposium on listeriosis in Nantes, France, Nicolas [15] reviewed the important role played by highly contaminated ensilage in the development of listeriosis in animals consuming it. When consumption was stopped, there was a rapid decline in the appearance of new cases. Such cases would seem to be due to contamination from a common source (anademic) and not from animal to animal. Although the latter possibility may exist, it is apparently not very important (cf. the possibilities of interhuman contamination with respect to perinatal listeriosis). Veritable epidemics with bacteriologic proof have been described, and a review of these was published in 1988 by Kvenberg [16]. Three of these cases shall be considered here. In 1979, in Nova Scotia, Canada, there was an epidemic especially affecting pregnant women (34 perinatal and 7 adult cases). The food incriminated was cabbage which had been contaminated by sheep manure. In 1985, near Los Angeles, California, there were more than 100 cases and 30 deaths due to cheeses prepared in California according to a Mexican recipe and in conformity with Food and Drug Adminsitration standards. From 1983 to 1987, there were more than 120 cases in the canton of Vaud, Switzerland, due to consumption of a cheese (vacherin) produced in the Jura. The cases were equally distributed between fetomaternal listeriosis and listeriosis unrelated to pregnancy. There have been no evident descriptions of human contamination by meat products. However, many controls have shown that numerous preparations are more or less contaminated: pork products (sausage, etc.), beef and pork, fowl, etc. Some checks have shown the presence of Listeria in nearly half of the samples studied [17].
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In recent years, there have been a large number of publications concerning the results of Listeria research in food products for human (and even in some cases animal) consumption. Listeria were frequent, especially nonhemolytic ones and L. seeligeri. L. ivanovii was very rare. However, various serovars of L. monocytogenes were also found, including 4b and the serogroup 1/2 (a, b and c). Certain authors now tend to consider that if a product contains a species of Listeria it can also contain a lower concentration of L. monocytogenes. The apparent conclusion to be drawn from these epidemiological considerations is that, owing to the small number of cases described, the interindividual epidemic must be nonexistent. Conversely, the epidemic develops mainly according to the anademic mode, and the most usual source in both man and the animal is food. PROPHYLAXIS Vaccination trials have been carried out in animals, but none has proved to be truly convincing. Based on acquired knowledge, much effort has been directed at eliminating Listeria from food. Prophylaxis thus begins with the animal. Ensilage must be done correctly since Listeria develop easily in " p o o r " silage with an alkaline tendency. Good feeding practices will limit the spread of Listeria in animal farms. Milk will be less often contaminated and meat will be more wholesome. Absence of Listeria should be ensured in the preparation of food for human consumption involving high risk of Listeria propagation (especially cheeses and pork products to be eaten uncooked). During production all possible causes of recontamination should be eliminated. In France, the dairy industry has understood this requirement. The organization of new production processes in suitable premises is being implemented even before the probable publication of official texts to regulate the distribution of products. Public services and packages are paying particular attention to new forms f o r distribution of food products to prevent them from being another source of Listeria (as was the Canadian cabbage). THERAPEUTICS Like all bacteria, Listeria are sensitive to various antibiotics. They behave like most gram-positive bacteria and are ordinarily sensitive to penicillins (aminopenicillins), aminoglycosides and macrolides. They are comparatively less sensitive to cephalosporins, particularly to those referred to as third-generation. They are only slightly sensitive to the new quinolones. PeniciUins, aminoglycosides and quinolones have very marked killing power which is however sometimes unstable at low concentrations. Conversely, their associations are rapidly and definitively bactericidal: aminopenicillin with quinolone or aminoglycoside; aminoglycoside with quinolone. Practically all species behave in the same way. In medicine one of these associations is often used. The use of tetracycline in human listeriosis was never highly developed. Recent publications giving sensitivity statistics no longer even mention this antibiotic. Over the years, no significant increase has been noted in rates of resistance to antibiotics, There are however strains which are resistant to one or more antibiotics, and it has been
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s u g g e s t e d t h a t p l a s m i d s m a y b e r e s p o n s i b l e f o r this. S o m e p l a s m i d s m a y e v e n b e c a p a b l e of interchanges between streptococci or enterococci and Listeria. REFERENCES I. Murray E. G. D., Webb R. A. and Swann M. B. R. A disease of rabbits characterised by a large mononuclear leucocytosis, caused by a hitherts undescribed bacillus Bacterium monocytogenes (n.sp.). J. Path. Baeteriol. 29, 407-439 (1926). 2. Dumont P. et Cotoni L. Bacille semblable au rouget du proc, recontr6 dans le L.C.R. d'une m6ningite. Ann. Inst. Pasteur 35, 625~33 (1921). 3. Cotoni L. A propos des bact6ries d6nomm6es Listerella. Rappel d'un observation ancienne de m6ningite chez l'homme. Ann. Inst. Pasteur 68, 92-95 (1942). 4. Pirie J. H. H. Listeria: change of name for a genus of bacteria. Nature 145, 264 (1940). 5. Rocourt J. and Berche P. Third Forum in microbiology virulence Listeria monocytogenes. Ann. Inst. Pasteur/Microbiol. 138, 241-284 (1987). 6. Pine L., Weaver R. E., Carlone G. M. et al. Listeria monocytogenes ATCC 35152 and NCTC 7973 contain a nonhemolytic, nonvirulent variant. J. olin. Mierobiol. 25, 2247-2251 (1987). 7. Rocourt J., Schrettenbrunner A. et Seeliger H. R. P. Differenciation biochimique des groupes g6n6miques de Listeria monocytogenes (sensu lato). Ann. microbiol. (Inst. Pasteur) 134A, 65-71 (1983). 8. Audurier A., Rocourt J. et Courtieu A. L. Isolement et caract6risation de bact6riophages de Listeria monocytogenes. Ann. Microbiol. (Inst. Pasteur) 128A, 185-198 (1978). 9. Gallacher P. G. and Watanakunakorn C. Listeria monocytogenes endocarditis: a review of the literature 1950-1986. Scand. J. infect. Dis. 20, 359 368 (1988). 10. Goulet V., Lemagny F., Rebiere I. et Espaze E. P. La list6riose en France en 1987. Etude r&rospective fi partir d'un 6chantillon d'h6pitaux publics. Bull. bpid~miol, hebdo. 12, 45-46 (1989). 1 I. Hyslop N. S. G. and Osborne A. D. Listeriosis: a potential danger to public health. Vbtbrin. Rec. 71, 1082-1095 (1959). 12. Burdin J. C., Weber M. et Martin F. Etude 6pid6miologique de la list6riose humaine en France ~ propos de 62 cas observ6s en Lorraine. Rev. Epidemiol. Med. soc. Sant~ 22, 279-302 (1974). 13. Humbert G., Duval C., Fessard C., Meunier M. et Ledoux A. Les list6rioses en France. R6sultats d'une enqu6te national (824 cas). Med. real. infect. 6, Suppl. list6rioses, 60 70 (1976). 14. Carbonnelle B., Cottin J., Parvery F., Kouyoumdjian S., Le Lirzin M., Cordier G. et Vincent F. Epid6mie de list6riose dans l'Ouest de la France (1975-1976). Rev. Epid~miol. Santb 26, 451-467 (1978). 15. Nicolas J. A. et Vidaud N. Contribution ~ l'6tude des Listeria pr6sentes dans les denr6es d'origine animale destin6es fi la consommation humaine. In Listkrioses, Listeria, Listeriosis 1985-1986(Edited by Courtieu A. L., Espaze E. P. et Reynaud A. E.) pp. 330-338. Universit6 de Nantes (1986). 16. Kuenberg J. E. Outbreaks of listeriosis/Listeria--contaminated foods. Microbiol. Sci. 5, 355 358 (1988). 17. Rocourt J. List6riose humaine: aspects cliniques et 6pid6miologiques. R61e de l'alimentation. Le Biologieste 23, 29-40 (1989).