Ampicillin-resistant Enterococcus raffinosus in an acute-care hospital: case-control study and antimicrobial susceptibilities

Non-faecium non-faecalis enterococci: a review of clinical manifestations, virulence factors, and antimicrobial resistance

SUMMARYEnterococci are a diverse group of Gram-positive bacteria that are typically found as commensals in humans, animals, and the environment. Occasionally, they may cause clinically relevant diseases such as endocarditis, septicemia, urinary tract infections, and wound infections. The majority of clinical infections in humans are caused by two species: Enterococcus faecium and Enterococcus faecalis. However, there is an increasing number of clinical infections caused by non-faecium non-faecalis (NFF) enterococci. Although NFF enterococcal species are often overlooked, studies have shown that they may harbor antimicrobial resistance (AMR) genes and virulence factors that are found in E. faecium and E. faecalis. In this review, we present an overview of the NFF enterococci with a particular focus on human clinical manifestations, epidemiology, virulence genes, and AMR genes.

Spontaneous resolution or antibiotic effectiveness? Reflection on a case of pediatric urinary tract infections caused by Enterococcus raffinosus

Enterococcus raffinosus, named by Collins et al. in 1989, is a cocci-shaped bacterium that typically appears in pairs or short chains. As a Gram-positive and non-motile bacterium, it grows at 10°C-45°C, exhibiting negative peroxidase activity [1]. It is a normal flora in the oropharynx and gastrointestinal tract of domestic cats [2] and can also be isolated from human rectal swabs [3], it belongs to the same genus Enterococcus as Enterococcus faecalis and Enterococcus faecium. Enterococcus faecalis and Enterococcus faecium constitute 90% of clinically isolated strains. However, the incidence of other enterococci, excluding E. faecalis and E. faecium, is on the rise [4]. In this case report, a patient with pediatric urinary tract infections caused by E. raffinosus was presented, and a summary of relevant literature was provided.

Enterococcal endocarditis revisited

The Enterococcus species is the third main cause of infective endocarditis (IE) worldwide, and it is gaining relevance, especially among healthcare-associated cases. Patients with enterococcal IE are older and have more comorbidities than other types of IE. Classical treatment options are limited due to the emergence of high-level aminoglycosides resistance (HLAR), vancomycin resistance and multidrug resistance in some cases. Besides, few new antimicrobial alternatives have shown real efficacy, despite some of them being recommended by major guidelines (including linezolid and daptomycin). Ampicillin plus ceftriaxone 2 g iv./12 h is a good option for Enterococcus faecalis IE caused by HLAR strains, but randomized clinical trials are essential to demonstrate its efficacy for non-HLAR EFIE and to compare it with ampicillin plus short-course gentamicin. The main mechanisms of resistance and treatment options are also reviewed for other enterococcal species.

Bacteremia caused by non-faecalis and non-faecium enterococcus species at a Medical center in Taiwan, 2000 to 2008

SUMMARY OBJECTIVES

Human infections due to non-faecalis and non-faecium Enterococcus species are emerging but data on the characteristics of these infections are limited.

METHODS

We retrospectively reviewed the computerized database of the bacteriology laboratory at National Taiwan University Hospital from January 2000 through December 2008 to identify patients with non-faecalis and non-faecium enterococcal bacteremia.

RESULTS

Enterococcal bacteremia was diagnosed in 1887 patients during the study period and was caused by non-faecalis and non-faecium enterococci in 182 (9.6%) of these patients. The causative organisms included Enterococcus casseliflavus (n = 59, 3.1%), Enterococcus gallinarum (n = 58, 3.0%), Enterococcus avium (n = 45, 2.4%), Enterococcus hirae (n = 9, 0.5%), Enterococcus raffinosus (n = 9, 0.5%), Enterococcus durans (n = 2, 0.1%), Enterococcus cecorum (n = 2, 0.1%), and Enterococcus canintestini (n = 1, 0.5%). A commercially-available phenotypic identification system misidentified six isolates based upon sequence analysis of 16S and groESL genes. Among the 182 patients, 74 (40.7%) had catheter-associated bloodstream infection and 69 (37.9%) presented with biliary tract infection. Healthcare-associated enterococcal bacteremia comprised 99 (54.4%) episodes and a polymicrobial etiology was found in 106 (58.2%) episodes. The clinical manifestations varied between the infecting Enterococcus species. Multivariate logistic regression showed that immunocompromised status is the only risk factor for the all cause mortality.

CONCLUSIONS

Non-faecalis and non-faecium Enterococcus species can cause protean manifestations which vary with the infecting Enterococcus species. Misidentification of unusual enterococcal species might occur by the commercial identification methods and accurate identification with molecular methods is required.

Matching criteria in case-control studies in the field of antimicrobial resistance

OBJECTIVE

We evaluated the available evidence from case-control studies in the field of antimicrobial resistance to identify the degree that matching was performed and the criteria used to do so.

METHODS

We performed a systematic search of the PubMed database (articles archived by 08/2006) to identify relevant studies. Studies that used the individual matching technique were further analyzed.

RESULTS

115 case-control studies with a focus on antimicrobial resistance were identified: 28 regarding Acinetobacter baumannii, 25 regarding Pseudomonas aeruginosa, and 62 for other bacteria. Individual matching was performed in 32 (27.8%) out of the 115 studies. Age was the most frequently used matching criterion in 22 of 32 (69%) evaluated matched case-control studies, while sex was used in 11 (34%), presence of underlying illness in 8 (25%), site of infection in 5 (16%), and area of residence in 4 studies (12.5%). Other criteria were used in less than 10% of the studies. Analysis of data for matched pairs was performed in 18 of 32 (56.3%) studies that used a matched case-control design.

DISCUSSION

The available evidence from the analyzed data from case-control studies in the field of antimicrobial resistance shows that individual matching is employed only in a proportion of such studies and only for a few characteristics, when it was used. Also, analysis for matched pairs was not used by almost a half of the relevant studies.

First report of vaginal infection caused by Enterococcus raffinosus

The authors have reported the first case of vaginal infection caused by Enterococcus raffinosus. The latter is a rarely identified species, but some of the infections described in the literature should direct some attention to this, often opportunistic pathogen, and its emerging multidrug resistance.

Application of molecular techniques to the study of hospital infection

Nosocomial infections are an important source of morbidity and mortality in hospital settings, afflicting an estimated 2 million patients in United States each year. This number represents up to 5% of hospitalized patients and results in an estimated 88,000 deaths and 4.5 billion dollars in excess health care costs. Increasingly, hospital-acquired infections with multidrug-resistant pathogens represent a major problem in patients. Understanding pathogen relatedness is essential for determining the epidemiology of nosocomial infections and aiding in the design of rational pathogen control methods. The role of pathogen typing is to determine whether epidemiologically related isolates are also genetically related. To determine molecular relatedness of isolates for epidemiologic investigation, new technologies based on DNA, or molecular analysis, are methods of choice. These DNA-based molecular methodologies include pulsed-field gel electrophoresis (PFGE), PCR-based typing methods, and multilocus sequence analysis. Establishing clonality of pathogens can aid in the identification of the source (environmental or personnel) of organisms, distinguish infectious from noninfectious strains, and distinguish relapse from reinfection. The integration of molecular typing with conventional hospital epidemiologic surveillance has been proven to be cost-effective due to the associated reduction in the number of nosocomial infections. Cost-effectiveness is maximized through the collaboration of the laboratory, through epidemiologic typing, and the infection control department during epidemiologic investigations.

Enterococcus raffinosus infection in an immunosuppressed patient: case report and review of the literature

Enterococcus raffinosus rarely occurs in humans. We describe the case of a haematoma infected by E. raffinosus in a 72-year-old patient undergoing immunosuppressive therapy. This study confirms the results of previous reports about the pathogenic potential of this bacterium in humans.

Species identification and antibiotic susceptibility of enterococci isolated from clinical specimens of hospitalized patients

Over a 4-month period, a total of 315 enterococci were isolated from various clinical specimens of hospitalized patients. By applying an array of biochemical tests, all strains were accurately identified to the species level, and their susceptibilities to clinically relevant antibiotics were determined by a standardized agar dilution technique. E. faecalis and E. faecium accounted for 87.3% and 9.2% of isolates, respectively. E. avium (1%), E. gallinarum (1%), E. durans (0.6%), E. hirae (0.6%), and E. casseliflavus (0.3%) isolates were also identified. Eleven strains of E. faecium and 1 E. hirae isolate were resistant to ampicillin, but none of the isolates produced beta-lactamase. Twenty-three E. faecium and 3 E. faecalis strains as well as 1 E. hirae isolate revealed imipenem resistance. A total of 25.4% enterococci (60 E. faecalis and 19 E. faecium isolates, 1 E. hirae strain) were erythromycin-resistant. Twelve strains (11 E. faecium and 1 E. avium) exhibited ciprofloxacin resistance. High-level resistance to streptomycin was found in 58 (21.1%) E. faecalis, 9 (31%) E. faecium, and both E. hirae strains, whereas high-level gentamicin resistance (HLGR) was exclusively seen in the species E. faecalis (11.6% of isolates belonging to this species). A simple agar screening test containing 500 micrograms of gentamicin per ml proved to be highly reliable for detection of HLGR. The structural gene coding for HLGR was specifically amplified by the polymerase chain reaction in all isolates showing this resistance trait. Moreover, the gene was specifically detected by a nonradioactively labelled oligonucleotide probe in colony blot hybridization assays, indicating the potential application of these molecular approaches as a diagnostic tool.

DNA hybridization and contour-clamped homogeneous electric field electrophoresis for identification of enterococci to the species level

In this study, 113 Enterococcus faecium, 37 Enterococcus faecalis, 24 Enterococcus gallinarum, 15 Enterococcus raffinosus, and 13 Enterococcus casseliflavus clinical isolates and American Type Culture Collection (ATCC) strains were evaluated by contour-clamped homogeneous electric field electrophoresis. Thirty-one of the E. faecium, 22 of the E. faecalis, 24 of the E. gallinarum, 15 of the E. raffinosus, and 13 of the E. casseliflavus isolates were also evaluated by DNA-DNA hybridization. Genomic DNAs from type strains E. faecalis ATCC 19433, E. faecium ATCC 19434, E. gallinarum ATCC 49573, E. raffinosus ATCC 49427, and E. casseliflavus ATCC 25788 were labeled with biotin for use as probes. E. faecalis differed from all other species in always having a largest fragment of > 400 kb. E. gallinarum was different from all other species in having all SmaI fragments of < 200 kb. Biotin-labeled probes showed a high degree of hybridization with genomic DNA from the same species and a low degree of hybridization when hybridized to genomic DNA from different species for all isolates tested except for four isolates identified as E. faecium by conventional biochemical methods. The DNA from these four isolates hybridized strongly to DNA from E. gallinarum ATCC 49573 and weakly to E. faecium ATCC 19434 DNA and had all SmaI fragments of < 200 kb in size. These data suggest that these isolates are nonmotile E. gallinarum. DNA from each ATCC type strain hybridized strongly with itself and had only a low degree of hybridization with DNA from other ATCC type strains tested. These results suggest that contour-clamped homogeneous electric field electrophoresis patterns and DNA-DNA hybridization with biotin-labeled probes may be of use for species differentiation of some enterococci.

Virulence of enterococci

Enterococci are commensal organisms well suited to survival in intestinal and vaginal tracts and the oral cavity. However, as for most bacteria described as causing human disease, enterococci also possess properties that can be ascribed roles in pathogenesis. The natural ability of enterococci to readily acquire, accumulate, and share extrachromosomal elements encoding virulence traits or antibiotic resistance genes lends advantages to their survival under unusual environmental stresses and in part explains their increasing importance as nosocomial pathogens. This review discusses the current understanding of enterococcal virulence relating to (i) adherence to host tissues, (ii) invasion and abscess formation, (iii) factors potentially relevant to modulation of host inflammatory responses, and (iv) potentially toxic secreted products. Aggregation substance, surface carbohydrates, or fibronectin-binding moieties may facilitate adherence to host tissues. Enterococcus faecalis appears to have the capacity to translocate across intact intestinal mucosa in models of antibiotic-induced superinfection. Extracellular toxins such as cytolysin can induce tissue damage as shown in an endophthalmitis model, increase mortality in combination with aggregation substance in an endocarditis model, and cause systemic toxicity in a murine peritonitis model. Finally, lipoteichoic acid, superoxide production, or pheromones and corresponding peptide inhibitors each may modulate local inflammatory reactions.

In vitro activity of sparfloxacin and clinafloxacin against multidrug-resistant enterococci

We evaluated the in vitro susceptibility of 140 clinical enterococcal isolates to the quinolones sparfloxacin and clinafloxacin. Isolates included Enterococcus faecalis (107), Enterococcus faecium (29), Enterococcus raffinosus (3), and one Enterococcus gallinarum. There were 111 isolates that showed high-level [minimum inhibitory concentrations (MICs) > or = 2000 micrograms/ml] resistance to gentamicin and were resistant to high levels of all other aminoglycosides; five isolates produced beta-lactamase; 21 isolates were resistant (MIC > or = 16 micrograms/ml) to ampicillin and were not beta-lactamase producers; and 13 strains were resistant (MIC > or = 32 micrograms/ml) to vancomycin. Most strains were susceptible to low concentrations of sparfloxacin and clinafloxacin, with MIC90S of 0.6 microgram/ml and 0.5 micrograms/ml, respectively. There were no inoculum effects. Time-kill experiments were performed with 22 strains; using 2 x MIC at 24 h, a > or = 2 log10 reduction in growth was observed with sparfloxacin and clinafloxacin for 14 and 17 strains, respectively. Time-kill synergism experiments were performed with 15 strains lacking high-level aminoglycoside resistance. In vitro bacterial synergism with the combination of sparfloxacin or clinafloxacin with streptomycin or gentamicin was observed for five and 12 isolates, respectively. The bactericidal activity of sparfloxacin and clinafloxacin suggest that these antibiotics may prove useful for therapy of multidrug resistant enterococci.

Clonal spread of vancomycin-resistant Enterococcus faecium between patients in three hospitals in two states

The DNAs of 3* vancomycin-resistant Enterococcus faecium isolates from five hospitals in three states were analyzed by contour-clamped homogeneous electric field electrophoresis and plasmid analysis. There were 22 strain types. One strain type was common to patients in three hospitals in two states. These results suggest the apparent intra- and interhospital spread of vancomycin-resistant E. faecium.

Molecular typing of ampicillin-resistant, non-beta-lactamase-producing Enterococcus faecium isolates from diverse geographic areas

Molecular typing methods were compared by using 66 ampicillin-resistant, non-beta-lactamase-producing Enterococcus faecium clinical isolates from diverse geographic areas. Whole-plasmid analysis, restriction enzyme analysis of plasmid DNA with EcoRI and HindIII, and contour-clamped homogeneous electric field electrophoresis with digestion by SmaI and ApaI were performed on all isolates. Whole-plasmid analysis identified 47 different groups. Restriction enzyme analysis of plasmid DNA identified 50 groups when EcoRI was used and 51 groups when HindIII was used. Results with EcoRI and HindIII differed in 9 of 66 isolates. Grouping results with whole-plasmid analysis differed from results of restriction enzyme analysis of plasmid DNA (combining EcoRI and HindIII) in 20 of 66 isolates. Contour-clamped homogeneous electric field electrophoresis identified 46 groups when SmaI was used and 44 groups when ApaI was used. Results with SmaI and ApaI differed in 3 of 66 isolates. Grouping results with contour-clamped homogeneous electric field electrophoresis (combining SmaI and ApaI) differed from results of restriction enzyme analysis of plasmid DNA (combining EcoRI and HindIII) in 17 of 66 isolates. The combined use of whole-plasmid analysis, restriction enzyme analysis of plasmid DNA with two enzymes, and contour-clamped homogeneous electric field electrophoresis with two restriction enzymes should be considered when E. faecium is typed for epidemiologic investigation.

Emergence and nosocomial transmission of ampicillin-resistant enterococci

Between 1986 and 1988, the incidence of ampicillin-resistant enterococci increased sevenfold at a university-affiliated hospital. Forty-three patients acquired nosocomial infections with ampicillin-resistant enterococci, most of which were also resistant to mezlocillin, piperacillin, and imipenem. An analysis of plasmid and chromosomal DNAs of isolates revealed that the increase was due to an epidemic of 19 nosocomial infections that yielded closely related strains of Enterococcus faecium and to a significant increase in the incidence of nonepidemic, largely unrelated strains of ampicillin-resistant enterococci. The nonepidemic strains were identified as E. faecium, E. raffinosus, E. durans, and E. gallinarum. A logistic regression analysis revealed that patients with nonepidemic resistant strains were 16 times more likely than controls to have received preceding therapy with imipenem. In our institution, the increase in the incidence of ampicillin-resistant enterococci appears to be due to the selection of various strains of resistant enterococci by the use of imipenem and to the nosocomial transmission of E. faecium and E. raffinosus.