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Endocarditis caused by Lactococcus lactis subsp. lactis in a patient with atrial myxoma: a case report
Diagnostic Microbiology and Infectious Disease 56 (2006) 325 – 328 www.elsevier.com/locate/diagmicrobio
Endocarditis caused by Lactococcus lactis subsp. lactis in a patient with atrial myxoma: a case report Barbara Zechinia,4, Paola Ciprianib,c, Styliani Papadopoulouc, Giandomenico Di Nuccid, Andrea Petruccac, Antonella Teggia a
Department of Infectious Diseases, II Faculty of Medicine, Sant’Andrea Hospital, University of Rome bLa SapienzaQ, 00189 Rome, Italy b Department of Public Health, II Faculty of Medicine, Sant’Andrea Hospital, University of Rome bLa SapienzaQ, 00189 Rome, Italy c Laboratory of Clinical Microbiology, II Faculty of Medicine, Sant’Andrea Hospital, University of Rome bLa SapienzaQ, 00189 Rome, Italy d Cardiosurgery, II Faculty of Medicine, Sant’Andrea Hospital, University of Rome bLa SapienzaQ, 00189 Rome, Italy Received 27 January 2006; accepted 27 April 2006
Abstract We report a case of subacute endocarditis in a 55-year-old patient affected by left atrial myxoma and with a severe mitral regurgitation. Lactococcus lactis subsp. lactis was isolated from blood cultures and infection was eliminated by treatment with amoxicillin–clavulanic acid. D 2006 Elsevier Inc. All rights reserved. Keywords: Lactococcus lactis subsp. lactis; Endocarditis; Myxoma
The Lactococcus taxonomy has been revised several times during the past 2 decades and in the late 1980s. Lactococcus genus was separated from Streptococcus genus on the basis of DNA–DNA relatedness and phylogenetic analysis of 16S ribosomal RNA (rRNA) sequences (Schleifer et al., 1985). To date, Lactococcus genus comprises 8 species and subspecies; these are Lactococcus lactis subspp. lactis, cremoris, and hordinae, Lactococcus garvieae, Lactococcus plantarum, Lactococcus raffinolactis, and Lactococcus xylosis, all of which are facultative anaerobic, catalase-negative, and Grampositive cocci (Bascomb and Manafi, 1998; Boone et al., 2001; Facklam and Elliott, 1995). These bacteria are very common in the environment and, until recently, were considered as unusual pathogens in humans (Akhaddar et al., 2002; Fefer et al., 1998; Fihman et al., 2006; Halldorsdottir et al., 2002; Koyuncu et al., 2005; Mannion and Rothburn, 1990; Pellizzer et al., 1996; Wood et al., 1985). Here, we report a case of endocarditis caused by L. lactis subsp. lactis. In February 2005, a 55-year-old male was admitted to the Department of Infectious Diseases, Sant’Andrea Hospital, bLa SapienzaQ University, Rome, Italy, with a 5-month history of progressive weakness and fever at 37.5 8C. His 4 Corresponding author. Tel.: +39-6-33775847; fax: +39-6-33775073. E-mail address: [email protected] (B. Zechini). 0732-8893/$ – see front matter D 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.diagmicrobio.2006.04.011
medical history was positive for idiopathic arterial hypertension. In the previous 6 months and 15 days before hospitalization, the patient underwent several dental extractions without antibiotic prophylaxis. On admission, the patient was normotensive, with fever (37.6 8C) and mild dyspnea. The results of the physical examination revealed a grade 3/6 holosystolic murmur at the heart apex radiating to the axilla. No pathologic findings were found on lung examination. No evident mucocutaneous signs of endocarditis or splenomegaly were observed. Routine blood tests were normal, except for an elevated increase of the erythrocyte sedimentation rate (ESR) in the 1st hour (83 mm/h) and a hyposideremic anemia (hemoglobin, 86 g/L). Chest X-ray and electrocardiogram were normal. Transthoracic and transesophageal echocardiography revealed the presence of a large hyperechogenic mass in the left atrium, a large floating vegetation on mitral valve with a severe mitral regurgitation. On admission, 3 sets of blood samples were taken in 2 h and cultured to detect the growth of aerobic and anaerobic microorganisms (Bactec System; Becton Dickinson, Sparks, MD). Only the aerobic blood cultures revealed the presence of a monomicrobic culture constituted by nonhemolytic catalase-negative microorganisms that form small colonies on blood agar. Gram staining revealed the presence of Gram-positive cocci that occur in short chains. A presumptive identification of
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B. Zechini et al. / Diagnostic Microbiology and Infectious Disease 56 (2006) 325–328
Fig. 1. The consensus phylogenetic tree of 16S rDNA sequences of various catalase-negative Gram-positive cocci and of the L. lactis subsp. lactis isolate (GenBank accession no. AM088020) was constructed with the PHYLIP package (version 3.6; neighbor-joining method; http://evolution.genetics. washington.edu/phylip.html). Alignments were performed with the Clustal W program. Genetic distance is indicated on the scale, and bootstrap analysis for nodes values N 70% are shown. GenBank accession numbers of the 16S rDNA sequences are shown (in parentheses).
L. lactis was achieved by using the Rapid ID 32 Strep (BioMerieux, Marcy l’Etoile, France) with 98% probability (profile obtained 30333001051) (Bascomb and Manafi, 1998). The results of an additional phenotypic test were susceptibility to vancomycin, positive bile–esculine reaction and leucine–h-naphthylamine hydrolysis, ability to grow at 10 8C but not at 45 8C, and acidification of mannitol broth (Facklam and Elliott, 1995). To unambiguously identify the bacterial isolate at species level, we analyzed the 16S rRNA sequence by automated DNA sequencing (ABI 310; Applied Biosystem, Foster City, CA) (Tabacchioni et al., 1995). The 16S ribosomal DNA (rDNA) sequence of the bacterial isolate (GenBank accession no. AM088020) was undertaken using 3 different Web-based alignment tools: i) BLAST analysis (http:// www.ncbi.nlm.nih.gov/BLAST), ii) RDP II project (http:// rdp.cme.msu.edu/index.jsp), and iii) BiBi Bio-informatic Bacterial Identification analysis (http://pbil.univ-lyon1.fr/ bibi/query.php). All 3 different sequence analysis tools applied in this study showed an optimum alignment (N 99% identity) with the 16S rDNA sequence of the L. lactis subsp. lactis reference strain IL1403 (GenBank accession no.
X64887). Signature sequences of L. lactis, present within variable regions of 16S rDNA sequence, show all the 9 critical positions described by Ward et al. (1998), which specifically characterized L. lactis subsp. lactis and differentiated it from closely related L. lactis subspecies. Furthermore, to definitively asses our bacterial identification, we amplified the acmA gene by polymerase chain reaction and we performed a phylogenetic analysis based on the 16S rDNA sequence (Ennahar et al., 2003; Garde et al., 1999). Deoxyribonucleic acid fragments with a molecular mass of about 1100 and 700 bp, consistent with the expected L. lactis subsp. lactis acmA pattern, were successfully amplified with the primer pair PALA-4/PALA-14 (data not shown) (Garde et al., 1999). Phylogenetic analysis, based on 16S rDNA sequences of various catalase-negative Gram-positive cocci, indicated that the clinical isolate belonged to the L. lactis subsp. lactis (Fig. 1) (Ennahar et al., 2003; Fihman et al., 2006). These findings made us conclude that the clinical isolate was unambiguously identified as L. lactis subsp. lactis. The L. lactis subsp. lactis isolate was susceptible to amoxicillin/clavulanate, ampicillin, clindamycin, erythro-
B. Zechini et al. / Diagnostic Microbiology and Infectious Disease 56 (2006) 325–328
mycin, ciprofloxacin, tetracycline, and trimethoprim/sulfamethoxazole as assessed using agar dilution technique of the National Committee of Clinical Laboratory Standard for streptococci (NCCLS, 2006; Koyuncu et al., 2005). The susceptibility breakpoints considered in this study for trimethoprim/sulfamethoxazole were that described by Elliot and Facklam (1996). Before microbiologic identification, an empiric antimicrobial therapy with amoxicillin–clavulanic acid (2.2 g tid, iv) was started. The patient was treated with amoxicillin– clavulanic acid for 4 weeks, following improvement of general health conditions and fever, and dyspnea disappearing on the 3rd day of treatment. After the therapy, the patient was treated by surgical excision of the mass and of the mitral valve followed by the replacement of mechanic valve for the persistence of severe mitral regurgitation. Histologic features of the mass were consistent with a diagnosis of a myxoma without signs of inflammation, whereas the histologic examination of the valve revealed signs of chronic inflammation with giant cells, neoangiogenesis, and polymorphonuclear neutrophil cell infiltration. The research of the bacterium in the mitral valve and in the myxoma evaluated by staining with Brown–Brenn stain (a tissue Gram stain) resulted negative. At 3 months of followup, the patient was symptom free. Bacterial endocarditis caused by members of the Lactococcus genus is unusual, with only a few cases described in literature (Fefer et al., 1998; Fihman et al., 2006; Halldorsdottir et al., 2002; Koyuncu et al., 2005; Mannion and Rothburn, 1990; Pellizzer et al., 1996; Wood et al., 1985). In our case report, Rapid ID 32 Strep identifies our clinical isolate simply L. lactis, but in consequence of a similar morphology and phenotypic characteristics with Enterococcus spp., it is difficult to discriminate strains of lactococci from enterococci only on the basis of phenotypic tests (Bascomb and Manafi, 1998; Facklam and Elliott, 1995; Fihman et al., 2006). Moreover, commercial identification systems based on phenotypic tests are not able to differentiate, at subspecies level, L. lactis subsp. lactis and L. lactis subsp. garvieae (the 2 species more frequently isolated from human infection) (Elliot et al., 1991). Thus, endocarditis due to lactococci may indeed be underdiagnosed (Mannion and Rothburn, 1990). Even if we did not establish the source of infection, we hypothesize that dental extractions without antibiotic prophylaxis might have induced invasions of the bloodstream by bacteria from the local flora. These bacteremias, in the presence of preexisting cardiac lesions resulting from the atrial myxoma and mitral valve dysfunction, could have favored the development of endocarditis. The amoxicillin– clavulanic acid antimicrobial therapy administrated to our patient was able to improve his general health condition and to restore normal ESR value, thus, indicating that the detected isolate was indeed responsible for the infection. In our case, the infection showed a subacute time course and was paucisymptomatic, with mild hematochemical
327
signs of inflammation in the presence of severe anatomic and histologic findings. The antibiotic therapy was quickly effective, also because the antibiotic susceptibility test of L. lactis did not show resistance to different antibiotics, in particular, to penicillin. Nevertheless, the surgical treatment was needed because of the presence of left atrial myxoma and of the mechanic mitral valve dysfunction. The histologic examination excluded the presence of signs of inflammation in the myxoma, as frequently reported in literature (Gregory et al., 2004). Further studies are needed to clarify whether specific virulence factors are carried and expressed by the L. lactis subsp. lactis clinical isolates, conferring to these strains the specific ability to cause infection in humans. We report the 4th case of endocarditis described in literature caused by members of the L. lactis group and the 1st case of endocarditis due to L. lactis subsp. lactis. This case report also highlights the importance of the use of molecular techniques for rapid and correct identification of members of the Lactococcus genus (Fihman et al., 2006; Garde et al., 1999; Ward et al., 1998). References Akhaddar A, El Mostarchid B, Garraz M, Boucetta M (2002) Cerebellar abscess due to Lactococcus lactis. A new pathogen. Acta Neurochir 144:305 – 306. Bascomb S, Manafi M (1998) Use of enzyme tests in characterization and identification of aerobic and facultatively anaerobic gram-positive cocci. Clin Microbiol Rev 11:318 – 340. Boone DR, Castenholz RW, Garrity GM (2001) Bergey’s manual of systematic bacteriology. 2nd ed. Springer7 New York. Elliot JA, Facklam R (1996) Antimicrobial susceptibilities of Lactococcus lactis and Lactococcus garvieae and a proposed method to discriminate between them. J Clin Microbiol 34:1296 – 1298. Elliot JA, Collins MD, Pigott NE, Facklam R (1991) Differentiation of Lactococcus lactis and Lactococcus garvieae from humans by comparison of whole-cell protein patterns. J Clin Microbiol 22: 880 – 881. Ennahar S, Cai Y, Fujita Y (2003) Phylogenetic diversity of lactic acid bacteria associated with paddy rice silage as determined by 16S ribosomal DNA analysis. Appl Environ Microbiol 69:444 – 451. Facklam R, Elliott JA (1995) Identification, classification, and clinical relevance of catalase-negative, gram-positive cocci, excluding the streptococci and enterococci. Clin Microbiol Rev 8:479 – 495. Fefer JJ, Ratzan KR, Sharp SE, Saiz E (1998) Lactococcus garvieae endocarditis: report of a case and review of the literature. Diagn Microbiol Infect Dis 32:127 – 130. Fihman V, Raskine L, Barrou Z, Kiffel C, Riahi J, Bercot B, Sanson-Le Pors MJ (2006) Lactococcus garvieae endocarditis: identification by 16S rRNA and sodA sequence analysis. J Infect 52:e3 – e6. Garde S, Babin M, Gaya P, Nunez M, Medina M (1999) PCR amplification of the gene acma differentiates Lactococcus lactis subsp. lactis and L. lactis subsp. cremoris. Appl Environ Microbiol 65:5151 – 5153. Gregory SA, O’Byrne III WT, Fan P (2004) Infected cardiac myxoma. Echocardiography 21:65 – 67. Halldorsdottir HD, Halldorsdottir V, Bodvarsson A, Thorgeirsson G, Kristjansson M (2002) Endocarditis caused by Lactococcus cremoris. Scand J Infect Dis 34:205 – 206. Koyuncu M, Acuner IC, Uyar M (2005) Deep neck infection due to Lactococcus lactis subsp. cremoris: a case report. Eur Arch Otorhinolaryngol 262:719 – 721.
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B. Zechini et al. / Diagnostic Microbiology and Infectious Disease 56 (2006) 325–328
Mannion PT, Rothburn MM (1990) Diagnosis of bacterial endocarditis caused by Streptococcus lactis and assisted by immunoblotting of serum antibodies. J Infect 21:317 – 318. National Committee of Clinical Laboratory Standards (2006) Performance standards for antimicrobial susceptibility testing; sixteenth information supplement, M100-S16. Clinical and Laboratory Standard Institute, Wayne, Pennsylvania, USA. Pellizzer G, Benedetti P, Biavasco F, Manfrin V, Franzetti M, Scagnelli M, Scarparo C, de Lalla F (1996) Bacterial endocarditis due to Lactococcus lactis subsp. cremoris: case report. Clin Microbiol Infect 2:230 – 232.
Schleifer KH, Kraus J, Dvorak C, Kilpper-Balz R, Collins MD, Fischer W (1985) Transfer of Streptococcus lactis and related streptococci to the genus Lactococcus gen. nov. Syst Appl Microbiol 6:183 – 195. Tabacchioni S, Visca P, Chiarini L, Bevivino A, Di Serio C, Fancelli S, Fani R (1995) Molecular characterization of rhizosphere and clinical isolates of Burkholderia cepacia. Res Microbiol 146:531 – 542. Ward LJH, Brown JCS, Davey GP (1998) Two methods for the genetic differentiation of Lactococcus lactis subsp. lactis and cremoris based on differences in the 16S rRNA gene sequence. FEMS Microbiol Lett 166:15 – 20. Wood HF, Jacobs K, McCarty M (1985) Streptococcus lactis isolated from a patient with subacute bacterial endocarditis. Am J Med 18:345 – 347.
Endocarditis caused by Lactococcus lactis subsp. lactis in a patient with atrial myxoma: a case report Barbara Zechinia,4, Paola Ciprianib,c, Styliani Papadopoulouc, Giandomenico Di Nuccid, Andrea Petruccac, Antonella Teggia a
Department of Infectious Diseases, II Faculty of Medicine, Sant’Andrea Hospital, University of Rome bLa SapienzaQ, 00189 Rome, Italy b Department of Public Health, II Faculty of Medicine, Sant’Andrea Hospital, University of Rome bLa SapienzaQ, 00189 Rome, Italy c Laboratory of Clinical Microbiology, II Faculty of Medicine, Sant’Andrea Hospital, University of Rome bLa SapienzaQ, 00189 Rome, Italy d Cardiosurgery, II Faculty of Medicine, Sant’Andrea Hospital, University of Rome bLa SapienzaQ, 00189 Rome, Italy Received 27 January 2006; accepted 27 April 2006
Abstract We report a case of subacute endocarditis in a 55-year-old patient affected by left atrial myxoma and with a severe mitral regurgitation. Lactococcus lactis subsp. lactis was isolated from blood cultures and infection was eliminated by treatment with amoxicillin–clavulanic acid. D 2006 Elsevier Inc. All rights reserved. Keywords: Lactococcus lactis subsp. lactis; Endocarditis; Myxoma
The Lactococcus taxonomy has been revised several times during the past 2 decades and in the late 1980s. Lactococcus genus was separated from Streptococcus genus on the basis of DNA–DNA relatedness and phylogenetic analysis of 16S ribosomal RNA (rRNA) sequences (Schleifer et al., 1985). To date, Lactococcus genus comprises 8 species and subspecies; these are Lactococcus lactis subspp. lactis, cremoris, and hordinae, Lactococcus garvieae, Lactococcus plantarum, Lactococcus raffinolactis, and Lactococcus xylosis, all of which are facultative anaerobic, catalase-negative, and Grampositive cocci (Bascomb and Manafi, 1998; Boone et al., 2001; Facklam and Elliott, 1995). These bacteria are very common in the environment and, until recently, were considered as unusual pathogens in humans (Akhaddar et al., 2002; Fefer et al., 1998; Fihman et al., 2006; Halldorsdottir et al., 2002; Koyuncu et al., 2005; Mannion and Rothburn, 1990; Pellizzer et al., 1996; Wood et al., 1985). Here, we report a case of endocarditis caused by L. lactis subsp. lactis. In February 2005, a 55-year-old male was admitted to the Department of Infectious Diseases, Sant’Andrea Hospital, bLa SapienzaQ University, Rome, Italy, with a 5-month history of progressive weakness and fever at 37.5 8C. His 4 Corresponding author. Tel.: +39-6-33775847; fax: +39-6-33775073. E-mail address: [email protected] (B. Zechini). 0732-8893/$ – see front matter D 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.diagmicrobio.2006.04.011
medical history was positive for idiopathic arterial hypertension. In the previous 6 months and 15 days before hospitalization, the patient underwent several dental extractions without antibiotic prophylaxis. On admission, the patient was normotensive, with fever (37.6 8C) and mild dyspnea. The results of the physical examination revealed a grade 3/6 holosystolic murmur at the heart apex radiating to the axilla. No pathologic findings were found on lung examination. No evident mucocutaneous signs of endocarditis or splenomegaly were observed. Routine blood tests were normal, except for an elevated increase of the erythrocyte sedimentation rate (ESR) in the 1st hour (83 mm/h) and a hyposideremic anemia (hemoglobin, 86 g/L). Chest X-ray and electrocardiogram were normal. Transthoracic and transesophageal echocardiography revealed the presence of a large hyperechogenic mass in the left atrium, a large floating vegetation on mitral valve with a severe mitral regurgitation. On admission, 3 sets of blood samples were taken in 2 h and cultured to detect the growth of aerobic and anaerobic microorganisms (Bactec System; Becton Dickinson, Sparks, MD). Only the aerobic blood cultures revealed the presence of a monomicrobic culture constituted by nonhemolytic catalase-negative microorganisms that form small colonies on blood agar. Gram staining revealed the presence of Gram-positive cocci that occur in short chains. A presumptive identification of
326
B. Zechini et al. / Diagnostic Microbiology and Infectious Disease 56 (2006) 325–328
Fig. 1. The consensus phylogenetic tree of 16S rDNA sequences of various catalase-negative Gram-positive cocci and of the L. lactis subsp. lactis isolate (GenBank accession no. AM088020) was constructed with the PHYLIP package (version 3.6; neighbor-joining method; http://evolution.genetics. washington.edu/phylip.html). Alignments were performed with the Clustal W program. Genetic distance is indicated on the scale, and bootstrap analysis for nodes values N 70% are shown. GenBank accession numbers of the 16S rDNA sequences are shown (in parentheses).
L. lactis was achieved by using the Rapid ID 32 Strep (BioMerieux, Marcy l’Etoile, France) with 98% probability (profile obtained 30333001051) (Bascomb and Manafi, 1998). The results of an additional phenotypic test were susceptibility to vancomycin, positive bile–esculine reaction and leucine–h-naphthylamine hydrolysis, ability to grow at 10 8C but not at 45 8C, and acidification of mannitol broth (Facklam and Elliott, 1995). To unambiguously identify the bacterial isolate at species level, we analyzed the 16S rRNA sequence by automated DNA sequencing (ABI 310; Applied Biosystem, Foster City, CA) (Tabacchioni et al., 1995). The 16S ribosomal DNA (rDNA) sequence of the bacterial isolate (GenBank accession no. AM088020) was undertaken using 3 different Web-based alignment tools: i) BLAST analysis (http:// www.ncbi.nlm.nih.gov/BLAST), ii) RDP II project (http:// rdp.cme.msu.edu/index.jsp), and iii) BiBi Bio-informatic Bacterial Identification analysis (http://pbil.univ-lyon1.fr/ bibi/query.php). All 3 different sequence analysis tools applied in this study showed an optimum alignment (N 99% identity) with the 16S rDNA sequence of the L. lactis subsp. lactis reference strain IL1403 (GenBank accession no.
X64887). Signature sequences of L. lactis, present within variable regions of 16S rDNA sequence, show all the 9 critical positions described by Ward et al. (1998), which specifically characterized L. lactis subsp. lactis and differentiated it from closely related L. lactis subspecies. Furthermore, to definitively asses our bacterial identification, we amplified the acmA gene by polymerase chain reaction and we performed a phylogenetic analysis based on the 16S rDNA sequence (Ennahar et al., 2003; Garde et al., 1999). Deoxyribonucleic acid fragments with a molecular mass of about 1100 and 700 bp, consistent with the expected L. lactis subsp. lactis acmA pattern, were successfully amplified with the primer pair PALA-4/PALA-14 (data not shown) (Garde et al., 1999). Phylogenetic analysis, based on 16S rDNA sequences of various catalase-negative Gram-positive cocci, indicated that the clinical isolate belonged to the L. lactis subsp. lactis (Fig. 1) (Ennahar et al., 2003; Fihman et al., 2006). These findings made us conclude that the clinical isolate was unambiguously identified as L. lactis subsp. lactis. The L. lactis subsp. lactis isolate was susceptible to amoxicillin/clavulanate, ampicillin, clindamycin, erythro-
B. Zechini et al. / Diagnostic Microbiology and Infectious Disease 56 (2006) 325–328
mycin, ciprofloxacin, tetracycline, and trimethoprim/sulfamethoxazole as assessed using agar dilution technique of the National Committee of Clinical Laboratory Standard for streptococci (NCCLS, 2006; Koyuncu et al., 2005). The susceptibility breakpoints considered in this study for trimethoprim/sulfamethoxazole were that described by Elliot and Facklam (1996). Before microbiologic identification, an empiric antimicrobial therapy with amoxicillin–clavulanic acid (2.2 g tid, iv) was started. The patient was treated with amoxicillin– clavulanic acid for 4 weeks, following improvement of general health conditions and fever, and dyspnea disappearing on the 3rd day of treatment. After the therapy, the patient was treated by surgical excision of the mass and of the mitral valve followed by the replacement of mechanic valve for the persistence of severe mitral regurgitation. Histologic features of the mass were consistent with a diagnosis of a myxoma without signs of inflammation, whereas the histologic examination of the valve revealed signs of chronic inflammation with giant cells, neoangiogenesis, and polymorphonuclear neutrophil cell infiltration. The research of the bacterium in the mitral valve and in the myxoma evaluated by staining with Brown–Brenn stain (a tissue Gram stain) resulted negative. At 3 months of followup, the patient was symptom free. Bacterial endocarditis caused by members of the Lactococcus genus is unusual, with only a few cases described in literature (Fefer et al., 1998; Fihman et al., 2006; Halldorsdottir et al., 2002; Koyuncu et al., 2005; Mannion and Rothburn, 1990; Pellizzer et al., 1996; Wood et al., 1985). In our case report, Rapid ID 32 Strep identifies our clinical isolate simply L. lactis, but in consequence of a similar morphology and phenotypic characteristics with Enterococcus spp., it is difficult to discriminate strains of lactococci from enterococci only on the basis of phenotypic tests (Bascomb and Manafi, 1998; Facklam and Elliott, 1995; Fihman et al., 2006). Moreover, commercial identification systems based on phenotypic tests are not able to differentiate, at subspecies level, L. lactis subsp. lactis and L. lactis subsp. garvieae (the 2 species more frequently isolated from human infection) (Elliot et al., 1991). Thus, endocarditis due to lactococci may indeed be underdiagnosed (Mannion and Rothburn, 1990). Even if we did not establish the source of infection, we hypothesize that dental extractions without antibiotic prophylaxis might have induced invasions of the bloodstream by bacteria from the local flora. These bacteremias, in the presence of preexisting cardiac lesions resulting from the atrial myxoma and mitral valve dysfunction, could have favored the development of endocarditis. The amoxicillin– clavulanic acid antimicrobial therapy administrated to our patient was able to improve his general health condition and to restore normal ESR value, thus, indicating that the detected isolate was indeed responsible for the infection. In our case, the infection showed a subacute time course and was paucisymptomatic, with mild hematochemical
327
signs of inflammation in the presence of severe anatomic and histologic findings. The antibiotic therapy was quickly effective, also because the antibiotic susceptibility test of L. lactis did not show resistance to different antibiotics, in particular, to penicillin. Nevertheless, the surgical treatment was needed because of the presence of left atrial myxoma and of the mechanic mitral valve dysfunction. The histologic examination excluded the presence of signs of inflammation in the myxoma, as frequently reported in literature (Gregory et al., 2004). Further studies are needed to clarify whether specific virulence factors are carried and expressed by the L. lactis subsp. lactis clinical isolates, conferring to these strains the specific ability to cause infection in humans. We report the 4th case of endocarditis described in literature caused by members of the L. lactis group and the 1st case of endocarditis due to L. lactis subsp. lactis. This case report also highlights the importance of the use of molecular techniques for rapid and correct identification of members of the Lactococcus genus (Fihman et al., 2006; Garde et al., 1999; Ward et al., 1998). References Akhaddar A, El Mostarchid B, Garraz M, Boucetta M (2002) Cerebellar abscess due to Lactococcus lactis. A new pathogen. Acta Neurochir 144:305 – 306. Bascomb S, Manafi M (1998) Use of enzyme tests in characterization and identification of aerobic and facultatively anaerobic gram-positive cocci. Clin Microbiol Rev 11:318 – 340. Boone DR, Castenholz RW, Garrity GM (2001) Bergey’s manual of systematic bacteriology. 2nd ed. Springer7 New York. Elliot JA, Facklam R (1996) Antimicrobial susceptibilities of Lactococcus lactis and Lactococcus garvieae and a proposed method to discriminate between them. J Clin Microbiol 34:1296 – 1298. Elliot JA, Collins MD, Pigott NE, Facklam R (1991) Differentiation of Lactococcus lactis and Lactococcus garvieae from humans by comparison of whole-cell protein patterns. J Clin Microbiol 22: 880 – 881. Ennahar S, Cai Y, Fujita Y (2003) Phylogenetic diversity of lactic acid bacteria associated with paddy rice silage as determined by 16S ribosomal DNA analysis. Appl Environ Microbiol 69:444 – 451. Facklam R, Elliott JA (1995) Identification, classification, and clinical relevance of catalase-negative, gram-positive cocci, excluding the streptococci and enterococci. Clin Microbiol Rev 8:479 – 495. Fefer JJ, Ratzan KR, Sharp SE, Saiz E (1998) Lactococcus garvieae endocarditis: report of a case and review of the literature. Diagn Microbiol Infect Dis 32:127 – 130. Fihman V, Raskine L, Barrou Z, Kiffel C, Riahi J, Bercot B, Sanson-Le Pors MJ (2006) Lactococcus garvieae endocarditis: identification by 16S rRNA and sodA sequence analysis. J Infect 52:e3 – e6. Garde S, Babin M, Gaya P, Nunez M, Medina M (1999) PCR amplification of the gene acma differentiates Lactococcus lactis subsp. lactis and L. lactis subsp. cremoris. Appl Environ Microbiol 65:5151 – 5153. Gregory SA, O’Byrne III WT, Fan P (2004) Infected cardiac myxoma. Echocardiography 21:65 – 67. Halldorsdottir HD, Halldorsdottir V, Bodvarsson A, Thorgeirsson G, Kristjansson M (2002) Endocarditis caused by Lactococcus cremoris. Scand J Infect Dis 34:205 – 206. Koyuncu M, Acuner IC, Uyar M (2005) Deep neck infection due to Lactococcus lactis subsp. cremoris: a case report. Eur Arch Otorhinolaryngol 262:719 – 721.
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B. Zechini et al. / Diagnostic Microbiology and Infectious Disease 56 (2006) 325–328
Mannion PT, Rothburn MM (1990) Diagnosis of bacterial endocarditis caused by Streptococcus lactis and assisted by immunoblotting of serum antibodies. J Infect 21:317 – 318. National Committee of Clinical Laboratory Standards (2006) Performance standards for antimicrobial susceptibility testing; sixteenth information supplement, M100-S16. Clinical and Laboratory Standard Institute, Wayne, Pennsylvania, USA. Pellizzer G, Benedetti P, Biavasco F, Manfrin V, Franzetti M, Scagnelli M, Scarparo C, de Lalla F (1996) Bacterial endocarditis due to Lactococcus lactis subsp. cremoris: case report. Clin Microbiol Infect 2:230 – 232.
Schleifer KH, Kraus J, Dvorak C, Kilpper-Balz R, Collins MD, Fischer W (1985) Transfer of Streptococcus lactis and related streptococci to the genus Lactococcus gen. nov. Syst Appl Microbiol 6:183 – 195. Tabacchioni S, Visca P, Chiarini L, Bevivino A, Di Serio C, Fancelli S, Fani R (1995) Molecular characterization of rhizosphere and clinical isolates of Burkholderia cepacia. Res Microbiol 146:531 – 542. Ward LJH, Brown JCS, Davey GP (1998) Two methods for the genetic differentiation of Lactococcus lactis subsp. lactis and cremoris based on differences in the 16S rRNA gene sequence. FEMS Microbiol Lett 166:15 – 20. Wood HF, Jacobs K, McCarty M (1985) Streptococcus lactis isolated from a patient with subacute bacterial endocarditis. Am J Med 18:345 – 347.