Relapsing endocarditis caused by Enterococcus faecalis forming small colony variants

Microdiversity of Enterococcus faecalis isolates in cases of infective endocarditis: selection of non-synonymous mutations and large deletions is associated with phenotypic modifications

Context: Today, infective endocarditis (IE) caused by Enterococcus faecalis represents 10% of all IE and is marked by its difficult management and the frequency of relapses. Although the precise reasons for that remain to be elucidated, the evolution of the culprit strain under selective pressure through microdiversification could be, at least in part, involved. Material and methods: To further study the in situ genetic microdiversity and its possible phenotypic manifestations in E. faecalis IE, we sequenced and compared multiple isolates from the valves, blood culture and joint fluid of five patients who underwent valvular surgery. Growth rate and early biofilm production of selected isolates were also compared. Results: By sequencing a total of 58 E. faecalis genomes, we detected a considerable genomic microdiversity, not only among strains from different anatomical origins, but also between isolates from the same studied cardiac valves. Interestingly, deletions of thousands of bases including the well-known virulence factors ebpA/B/C, and srtC, as well as other large prophage sequences containing genes coding for proteins implicated in platelet binding (PlbA and PlbB) were evidenced. The study of mutations helped unveil common patterns in genes related to the cell cycle as well as central metabolism, suggesting an evolutionary convergence in these isolates. As expected, such modifications were associated with a significant impact on the in-vitro phenotypic heterogeneity, growth, and early biofilm production. Conclusion: Genome modifications associated with phenotypic variations may allow bacterial adaptation to both antibiotic and immune selective pressures, and thus promote relapses.

Development of the Bacterial Spectrum and Antimicrobial Resistance in Surgical Site Infections of Trauma Patients

Background: While ubiquitously multi-resistant bacteria are on the rise, peri-operative antimicrobial prophylaxis in trauma and near-to-bone surgical procedures has only been changed slightly during the last 25 years. Recent clinical studies concerning the bacterial spectrum and efficacy of antimicrobial treatment in infected trauma surgical patients are rare. The aim of the study was analysis of the contemporary bacterial spectrum and its antimicrobial resistance including the assessment of the appropriateness of peri-operative antimicrobial prophylaxis with cefuroxime. Methods: Patients of a level-I academic trauma center who underwent open or arthroscopic surgery because of a recent trauma necessitating the use of bone-near metal implants were included in the study. All patients in whom a surgical site infection (SSI) had developed during six weeks post-operatively necessitating surgical debridement and had positive microbiologic culture results from an intra-operative surgical site swab were analyzed, retrospectively. In particular, age, gender, date and duration of surgical interventions, and patient's related risk factors were collected, and infecting agents and their minimum inhibitory concentration values for 34 selected antimicrobial agents were evaluated. An SSI occurring later than 6 weeks post-operatively and patients with chronic and septic wounds were excluded. Statistical analysis was performed with SPSS^® (IBM, Armonk, NY). Results: There were 438 pathogens cultured in specimens from 303 enrolled patients (female = 140, male = 163). The most frequent pathogens were Staphylococcus aureus (27.1%), S. epidermidis (20.6%), Enterococcus faecalis (13.6%), Escherichia coli (5.1%), and Pseudomonas aeruginosa (3.7%) accounting for 303 isolates. Of those, 89 (29.4%) were multi-resistant. Of the S. epidermidis isolates, 79.8% (n = 71) were resistant against Oxacillin and thus against most beta-lactam antibiotic agents. Altogether, only 44.1% of the infecting organisms were susceptible to cefuroxime, the antimicrobial agent most often being used for prophylactic purposes. Conclusion: Standardized antimicrobial prophylaxis with cephalosporins has to be reconsidered critically. Multi-resistant species such as S. epidermidis are an increasing challenge in trauma operations.

Proliferation rate and penicillin binding of enterococcal isolates from patients with immunosupression

Low proliferation rate of bacterial populations was recently assumed to be a reason for higher resistance to antibiotics and appearance of many chronic infections. Slowly growing populations, called 'small colony variants' (SCVs) have been described in many bacterial species to make from as low as 0·02% up to 46% of population. Thirty enterococcal strains from urine and faeces of renal transplant recipients with asymptomatic, insignificant bacteriuria were studied. Growth characteristics were estimated by microculture and OD reading after 1, 3 and 5 h of culture. At the same time, penicillin binding and changes of aggregation of the cells were analysed by flow cytometry. The results of our study showed high diversity of the proliferation rates among studied isolates. Based on proliferation rates and aggregation, six of studied strains (20%) could be considered as SCVs-like. Significantly lower binding of penicillin was also observed for these SCV-like strains. SIGNIFICANCE AND IMPACT OF THE STUDY: This study provides relevant information about prevalence of enterococcal strains with low proliferation rate (likely small colony variant (SCV)) among kidney transplant recipients. Percentage of such strains in this cohort was relatively high (20%). Additionally, penicillin binding of these strains measured even at the beginning of proliferation (after 1 and 3 h of incubation), was significantly lower than among other strains. Finally, all of them were determined as penicillin resistant, with minimal inhibitory concentration value above 256 μg ml^-1 . As the risk of systemic infections caused by such strains is probably higher than in case of other strains, screening for the SCVs in this group of patients should be recommended.

Dwarfs in disguise: multiple spinal abscesses and spondylodiscitis caused by an Enterococcus faecium small-colony variant

Small-colony variants are slow-growing subpopulations of bacteria known to be involved in latent or recurrent infections, especially in deep-seated foci. Their atypical growth in small colonies can hamper prompt and correct identification in clinical specimens. Here, we present the first case of multiple spinal abscesses and spondylodiscitis associated with an Enterococcus faecium small-colony-variant in an immunocompetent patient. This case demonstrates the diagnostic challenges when encountering this phenotype in the diagnostic laboratory.

First Japanese case of infectious endocarditis due to Enterococcus faecalis small-colony variants

A male patient was admitted to our hospital due to infectious endocarditis. He had been treated with levofloxacin for 6 weeks, sulbactam/cefoperazone for 4 weeks, and benzylpenicillin for 2 days prior to valve replacement surgery. Gram-positive cocci, with morphology consistent with γ-Streptococcus, were detected in blood cultures obtained at admission, as well as in vegetation obtained from the aortic valve. However, the strain could not be identified using biochemical methods. Sequencing of the 16S rRNA gene indicated that the culture was a small-colony variant of Enterococcus faecalis. This is the first case in Japan of infectious endocarditis due to E. faecalis small-colony variants. Small-colony variants are subpopulations of bacteria with slow growth, reduced sugar fermentation, and unstable phenotype. As a result, these strains tend to be misidentified. Further, small-colony variants are associated with recurrent and persistent infections such as prosthetic joint infection and infectious endocarditis. These strains are found in various bacterial species, including Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, and Pseudomonas aeruginosa, but rarely in Enterococcus species. The case highlights the need to be vigilant of E. faecalis small-colony variants, especially in patients who received long-term courses of antibiotics.

Enterococcus faecium small colony variant endocarditis in an immunocompetent patient

Small colony variants (SCV) are slow-growing subpopulations of bacteria usually associated with auxotrophism, causing persistent or recurrent infections. Enterococcus faecalis SCV have been seldom described, and only one case of Enterococcus faecium SCV has been reported, associated with sepsis in a leukaemia patient. Here we report the first case described of bacteraemia and endocarditis by SCV E. faecium in an immunocompetent patient.