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Chemical sporicidal agents
Journal of Hospital Infection (1983) 4, 87-94
Letters to the Editor Sir, Chemical
sporicidal
agents
In July 1982, the Society for Applied Bacteriology held a symposium on the revival of injured microbes. A part of that meeting was devoted to the revival of bacterial spores injured by chemical and physical agents. Spore destruction is an important consideration in hospital infection as well as in the food industry. Consequently, increasing knowledge of the chemistry, structure and properties of spores, together with an understanding of their response to, and repair of injury from, exposure to chemical or physical agents can only be beneficial. The properties of sporicidal chemicals have been discussed in detail by Russell (1982) and Waites (1982). Gaseous compounds include ethylene oxide, and formaldehyde, but generally their action tends to be slow and their efficiency is subject to important environmental factors, notably relative humidity and temperature. They may, moreover, be highly toxic to personnel. (Christensen and Kristensen, 1982). No significant additions have been made in recent years to the list of liquid chemical sporicides, of which the most important are the aldehydes (glutaraldehyde, formaldehyde), halogens (chlorine, hypochlorites, iodine, iodophors) and hydrogen peroxide. The antimicrobial properties of these agents have been considered by Hugo and Russell (1982) and Waites (1982). Most preservative or disinfectant type agents such as phenols and cresols, alcohols, quaternary ammonium compounds, biguanides (e.g. chlorhexidine) and organic mercury compounds are bactericidal and not sporicidal at ordinary temperatures, although they are potent inhibitors of spore germination and/or outgrowth (Russell, 1982). In the United Kingdom, some members of this latter group may be employed in conjunction with heat as a means of sterilizing certain parenteral and eye preparations (British Pharmacopoeia, 1980). In this context, it is also of interest to note the development of low-temperature steam with formaldehyde as a means of sterilizing heat-sensitive materials for hospital use (Alder and Simpson, 1982). Despite the comparatively small number of chemical sporicides, information continues to be gleaned on the nature of their lethal effect, together with a better understanding of the mechanisms of spore resistance and how it develops during sporulation. For example, Waites and Bayliss (1979) have demonstrated that alteration of the spore coat of some, but not all, types of bacterial spores renders them sensitive to some but not all chemical agents. Further work along these lines will obviously lead to a better understanding of resistance and possibly of ways in which this can be overcome, which could be of value in hospitals and elsewhere. Certainly, potentiation of action may be achieved by appropriate means; for example, a buffered methanol/sodium hypochlorite mixture kills 87
88
Letters to the Editor
spores more rapidly than does buffered hypochlorite alone. This is claimed to result from an effect of the alcohol on spore coats (Coates and Death, 1978; Death and Coates, 1979). In the testing of sporicides, due attention should be paid to the prevention of sporistasis occurring in subculture (counting) media consequent upon the presence of low but inhibitory concentrations of chemical agent, and to the realization that injured spores may require long periods of incubation before germination and outgrowth can take place (Russell, 1982). A recent important finding is the post-treatment neutralization of glutaraldehyde by glycine (Gorman and Scott, 1976; Cheung and Brown, 1982; Gorman et al., 1982). Other workers have shown that a post-treatment heating of formaldehyde-exposed spores stimulates germination of the injured spores (Spicer and Peters, 1981). These findings are of interest, and should stimulate further research into mechanisms of revival of injured spores. Despite the importance of sporicides in some specific cases, e.g. the use of glutaraldehyde, ethylene oxide or low temperature steam plus formaldehyde in sterilizing certain types of medical equipment, it must, in conclusion be emphasized that thermal or irradiation methods are more reliable sterilization procedures. Furthermore, heat is the preferred method of disinfecting medical equipment whenever possible (Ayliffe and Collins, 1982), although other methods, such as formaldehyde (Babb et al., 1982) remain of value. Welsh School of Pharmacy, University of Wales Institute of Science and Technology, Cathays Park, Card# CFI 3NU
A. D. Russell
References Alder, V. G. & Simpson, R. A. (1982). Sterilisation and disinfection by heat methods. In Principles and Practice of Disinfection, Preservation and Sterilisation (Ed. Russell, A. D., Hugo, W. B. & Ayliffe, G. A. J.) pp. 433-453. Blackwell Scientific Publications, Oxford. Ayliffe, G. A. J. & Collins, B. J. (1982). Problems of disinfection in hospitals. In Principles and Practice of Disinfection, Preservation and Sterilisation (Ed. Russell, A. D., Hugo, W. B. & Ayliffe, G. A. J.) pp. 244-261. Blackwell Scientific Publications, Oxford. Babb, J. R., Bradley, C. R. & Ayliffe, G. A. J. (1982). A formaldehyde disinfection unit. Journal of Hospital Infection 3, 193-197. British Pharmacopoeia (1980). London: H.M.S.O. Cheung, H. Y. & Brown, M. R. W. (1982). Evaluation of glycine as an inactivator of glutaraldehyde. Journal of Pharmacy and Pharmacology 34, 211-214. Christensen, E. A. & Kristensen, H. (1982). Gaseous sterilisation. In Principles and Practice of Disinfection, Preservation and Sterilisation (Ed. Russell, A. D., Hugo, W. B. & Ayliffe, G. A. J.) pp. 548-568. Blackwell Scientific Publications, Oxford. Coates, D. & Death, J. E. (1978). Sporicidal activity of mixtures of alcohols and hypochlorite. Journal of Clinical Pathology 31, 148-152. Death, J. E. & Coates, D. (1979). Effect of pH on sporicidal and microbicidal activity of buffered mixtures of alcohol and sodium hypochlorite. Journal of Clinical Pathology 32, 148-153.
Letters
89
to the Editor
Gorman, S. P. & Scott, E. M. (1976). Evaluation of potential inactivators of gluaraldehyde in disinfection studies with Escherichiu coli. Microbios Letters 1, 197-204. Gorman, S. P., Hutchinson, E. P., Scott, E. M. & McDermott, L. M. (1982). Death, injury and revival of chemically-treated Bacillus subtilis spores. Journal of Applied Bacteriology 53 (in press). Hugo, W. B. & Russell., A. D. (1982). Types of antimicrobial agents. In Principles and Practice of Disinfectron, Presemation and Sterilisation (Ed. Russell, A. D., Hugo, W. B. & Ayliffe, G. A. J.) pp. 8-106. Blackwell Scientific Publications. Russell, A. D. (1982). The Destruction of Bacteria2 Spores. London: Academic Press. Spicher, G. & Peters, J. (1981). Heat activation of bacterial spores after inactivation by formaldehyde. Dependence of heat activation on temperature and duration of action. Zentralblatt fiir Bakteriologie, Parasitenkunde, Infektionshrankheiten und Hygiene, I. Abteilang Originale Reihe B 173, 188-196 (in German). Wakes, W. M. (1982). Resistance of bacterial spores. In Principles and Practice of Disinfection, Presetwation and Sterilisation (Ed. Russell, A. D., Hugo, W. B. & Ayliffe, G. A. J.) pp. 207-220. Blackwell Scientific Publications, Oxford. Waites, W. M. & Bayliss, C. E. (1979). The effect of changes in spore coat on the destruction of Bacillus cereas spores by heat and chemical treatments. Journal of A plied Biochemistry 1, 71-76.
Sir, Blood culture
procedure
and contamination
with Klebsiella
We read with interest the letter by Haji and his colleagues (Haji et al., 1982) and we would like the opportunity to make some observations. Whilst agreeing in principle with the possibility ‘that this problem is more common in the summer time’, in our own ‘outbreak’ (Willson, Petts and Baker, 1981) we believe the reason for the increased rate of pseudobacteraemia from January to April was due to obtaining ESR bottles from a different manufacturer. Those obtained throughout much of 1980 and early 1981 appeared to be very heavily contaminated with mixed non-fermentative Gram-negative bacilli and ampicillin-sensitive KZebsieZZu aerogenes. Since April 1981 we have reverted back to the original ESR bottle manufacturer and have had no further isolates of ampicillin-sensitive K. aerogenes.
Retrospectively examining our blood culture isolates from 1976 until just before the ‘outbreak’, we conclude that there were many incidents of unrecognized pseudobacteraemia mainly due to non-fermentative Gram-negative bacilli, which showed no such summer time increase, although it is possible that venepuncture techniques improved for a short period following each investigation by the Microbiology Department. Prospectively and retrospectively examining our blood culture isolates after the ‘outbreak’ we found in many cases an ESR investigation was also carried out on the same day. We refer to these below as ‘citrate associated’ regardless of the order of inoculation of the various specimen bottles. Our findings are:
Letters to the Editor Sir, Chemical
sporicidal
agents
In July 1982, the Society for Applied Bacteriology held a symposium on the revival of injured microbes. A part of that meeting was devoted to the revival of bacterial spores injured by chemical and physical agents. Spore destruction is an important consideration in hospital infection as well as in the food industry. Consequently, increasing knowledge of the chemistry, structure and properties of spores, together with an understanding of their response to, and repair of injury from, exposure to chemical or physical agents can only be beneficial. The properties of sporicidal chemicals have been discussed in detail by Russell (1982) and Waites (1982). Gaseous compounds include ethylene oxide, and formaldehyde, but generally their action tends to be slow and their efficiency is subject to important environmental factors, notably relative humidity and temperature. They may, moreover, be highly toxic to personnel. (Christensen and Kristensen, 1982). No significant additions have been made in recent years to the list of liquid chemical sporicides, of which the most important are the aldehydes (glutaraldehyde, formaldehyde), halogens (chlorine, hypochlorites, iodine, iodophors) and hydrogen peroxide. The antimicrobial properties of these agents have been considered by Hugo and Russell (1982) and Waites (1982). Most preservative or disinfectant type agents such as phenols and cresols, alcohols, quaternary ammonium compounds, biguanides (e.g. chlorhexidine) and organic mercury compounds are bactericidal and not sporicidal at ordinary temperatures, although they are potent inhibitors of spore germination and/or outgrowth (Russell, 1982). In the United Kingdom, some members of this latter group may be employed in conjunction with heat as a means of sterilizing certain parenteral and eye preparations (British Pharmacopoeia, 1980). In this context, it is also of interest to note the development of low-temperature steam with formaldehyde as a means of sterilizing heat-sensitive materials for hospital use (Alder and Simpson, 1982). Despite the comparatively small number of chemical sporicides, information continues to be gleaned on the nature of their lethal effect, together with a better understanding of the mechanisms of spore resistance and how it develops during sporulation. For example, Waites and Bayliss (1979) have demonstrated that alteration of the spore coat of some, but not all, types of bacterial spores renders them sensitive to some but not all chemical agents. Further work along these lines will obviously lead to a better understanding of resistance and possibly of ways in which this can be overcome, which could be of value in hospitals and elsewhere. Certainly, potentiation of action may be achieved by appropriate means; for example, a buffered methanol/sodium hypochlorite mixture kills 87
88
Letters to the Editor
spores more rapidly than does buffered hypochlorite alone. This is claimed to result from an effect of the alcohol on spore coats (Coates and Death, 1978; Death and Coates, 1979). In the testing of sporicides, due attention should be paid to the prevention of sporistasis occurring in subculture (counting) media consequent upon the presence of low but inhibitory concentrations of chemical agent, and to the realization that injured spores may require long periods of incubation before germination and outgrowth can take place (Russell, 1982). A recent important finding is the post-treatment neutralization of glutaraldehyde by glycine (Gorman and Scott, 1976; Cheung and Brown, 1982; Gorman et al., 1982). Other workers have shown that a post-treatment heating of formaldehyde-exposed spores stimulates germination of the injured spores (Spicer and Peters, 1981). These findings are of interest, and should stimulate further research into mechanisms of revival of injured spores. Despite the importance of sporicides in some specific cases, e.g. the use of glutaraldehyde, ethylene oxide or low temperature steam plus formaldehyde in sterilizing certain types of medical equipment, it must, in conclusion be emphasized that thermal or irradiation methods are more reliable sterilization procedures. Furthermore, heat is the preferred method of disinfecting medical equipment whenever possible (Ayliffe and Collins, 1982), although other methods, such as formaldehyde (Babb et al., 1982) remain of value. Welsh School of Pharmacy, University of Wales Institute of Science and Technology, Cathays Park, Card# CFI 3NU
A. D. Russell
References Alder, V. G. & Simpson, R. A. (1982). Sterilisation and disinfection by heat methods. In Principles and Practice of Disinfection, Preservation and Sterilisation (Ed. Russell, A. D., Hugo, W. B. & Ayliffe, G. A. J.) pp. 433-453. Blackwell Scientific Publications, Oxford. Ayliffe, G. A. J. & Collins, B. J. (1982). Problems of disinfection in hospitals. In Principles and Practice of Disinfection, Preservation and Sterilisation (Ed. Russell, A. D., Hugo, W. B. & Ayliffe, G. A. J.) pp. 244-261. Blackwell Scientific Publications, Oxford. Babb, J. R., Bradley, C. R. & Ayliffe, G. A. J. (1982). A formaldehyde disinfection unit. Journal of Hospital Infection 3, 193-197. British Pharmacopoeia (1980). London: H.M.S.O. Cheung, H. Y. & Brown, M. R. W. (1982). Evaluation of glycine as an inactivator of glutaraldehyde. Journal of Pharmacy and Pharmacology 34, 211-214. Christensen, E. A. & Kristensen, H. (1982). Gaseous sterilisation. In Principles and Practice of Disinfection, Preservation and Sterilisation (Ed. Russell, A. D., Hugo, W. B. & Ayliffe, G. A. J.) pp. 548-568. Blackwell Scientific Publications, Oxford. Coates, D. & Death, J. E. (1978). Sporicidal activity of mixtures of alcohols and hypochlorite. Journal of Clinical Pathology 31, 148-152. Death, J. E. & Coates, D. (1979). Effect of pH on sporicidal and microbicidal activity of buffered mixtures of alcohol and sodium hypochlorite. Journal of Clinical Pathology 32, 148-153.
Letters
89
to the Editor
Gorman, S. P. & Scott, E. M. (1976). Evaluation of potential inactivators of gluaraldehyde in disinfection studies with Escherichiu coli. Microbios Letters 1, 197-204. Gorman, S. P., Hutchinson, E. P., Scott, E. M. & McDermott, L. M. (1982). Death, injury and revival of chemically-treated Bacillus subtilis spores. Journal of Applied Bacteriology 53 (in press). Hugo, W. B. & Russell., A. D. (1982). Types of antimicrobial agents. In Principles and Practice of Disinfectron, Presemation and Sterilisation (Ed. Russell, A. D., Hugo, W. B. & Ayliffe, G. A. J.) pp. 8-106. Blackwell Scientific Publications. Russell, A. D. (1982). The Destruction of Bacteria2 Spores. London: Academic Press. Spicher, G. & Peters, J. (1981). Heat activation of bacterial spores after inactivation by formaldehyde. Dependence of heat activation on temperature and duration of action. Zentralblatt fiir Bakteriologie, Parasitenkunde, Infektionshrankheiten und Hygiene, I. Abteilang Originale Reihe B 173, 188-196 (in German). Wakes, W. M. (1982). Resistance of bacterial spores. In Principles and Practice of Disinfection, Presetwation and Sterilisation (Ed. Russell, A. D., Hugo, W. B. & Ayliffe, G. A. J.) pp. 207-220. Blackwell Scientific Publications, Oxford. Waites, W. M. & Bayliss, C. E. (1979). The effect of changes in spore coat on the destruction of Bacillus cereas spores by heat and chemical treatments. Journal of A plied Biochemistry 1, 71-76.
Sir, Blood culture
procedure
and contamination
with Klebsiella
We read with interest the letter by Haji and his colleagues (Haji et al., 1982) and we would like the opportunity to make some observations. Whilst agreeing in principle with the possibility ‘that this problem is more common in the summer time’, in our own ‘outbreak’ (Willson, Petts and Baker, 1981) we believe the reason for the increased rate of pseudobacteraemia from January to April was due to obtaining ESR bottles from a different manufacturer. Those obtained throughout much of 1980 and early 1981 appeared to be very heavily contaminated with mixed non-fermentative Gram-negative bacilli and ampicillin-sensitive KZebsieZZu aerogenes. Since April 1981 we have reverted back to the original ESR bottle manufacturer and have had no further isolates of ampicillin-sensitive K. aerogenes.
Retrospectively examining our blood culture isolates from 1976 until just before the ‘outbreak’, we conclude that there were many incidents of unrecognized pseudobacteraemia mainly due to non-fermentative Gram-negative bacilli, which showed no such summer time increase, although it is possible that venepuncture techniques improved for a short period following each investigation by the Microbiology Department. Prospectively and retrospectively examining our blood culture isolates after the ‘outbreak’ we found in many cases an ESR investigation was also carried out on the same day. We refer to these below as ‘citrate associated’ regardless of the order of inoculation of the various specimen bottles. Our findings are: