Mary Beth Perri

Plasmid-associated hemolysin and aggregation substance production contribute to virulence in experimental enterococcal endocarditis.

A rabbit endocarditis model was utilized to evaluate the virulence conferred by the conjugative plasmid pAD1 with the following strains: Enterococcus faecalis plasmid-free FA2-2 and FA2-2 containing plasmids pAD1 (hemolysin and aggregation substance positive), pAM9058 (insertional inactivation of hemolysin), and pAM944 or pAM947 (insertional inactivation of aggregation substance). All isolates were similar in ability to produce endocarditis. Mean vegetation weight was greater in animals inoculated with strains that produced aggregation substance (P < 0.01). Mortality was significantly increased in animals given FA2-2 containing pAD1 compared with those given all other strains (P < 0.01). These results suggest that the combination of hemolysin and aggregation substance is associated with increased mortality and that vegetation weight is associated with production of aggregation substance in experimental E. faecalis endocarditis.

Characterization of antimicrobial resistance in enterococci of animal origin.

Among 97 enterococci cultured from animals, gentamicin MICs were > or = 2,000 micrograms/ml for 9 isolates and between 250 and 1,024 micrograms/ml for 6 isolates. For two isolates tested (gentamicin MICs, 256 and 512 micrograms/ml, respectively), there was no in vitro synergy with penicillin plus gentamicin, resistance was transferable, and there was no hybridization with a probe specific for 6-aminoglycoside acetyltransferase-2-aminoglycoside phosphotransferase. The results of the study indicate the presence of a unique gentamicin resistance genotype in enterococci of animal origin.

Role of Environmental Surveillance in Determining the Risk of Hospital-Acquired Legionellosis: A National Surveillance Study With Clinical Correlations

OBJECTIVEnHospital-acquired Legionella pneumonia has a fatality rate of 28%, and the source is the water distribution system. Two prevention strategies have been advocated. One approach to prevention is clinical surveillance for disease without routine environmental monitoring. Another approach recommends environmental monitoring even in the absence of known cases of Legionella pneumonia. We determined the Legionella colonization status of water systems in hospitals to establish whether the results of environmental surveillance correlated with discovery of disease. None of these hospitals had previously experienced endemic hospital-acquired Legionella pneumonia.nnnDESIGNnCohort study.nnnSETTINGnTwenty US hospitals in 13 states.nnnINTERVENTIONSnHospitals performed clinical and environmental surveillance for Legionella from 2000 through 2002. All specimens were shipped to the Special Pathogens Laboratory at the Veterans Affairs Pittsburgh Medical Center.nnnRESULTSnLegionella pneumophila and Legionella anisa were isolated from 14 (70%) of 20 hospital water systems. Of 676 environmental samples, 198 (29%) were positive for Legionella species. High-level colonization of the water system (30% or more of the distal outlets were positive for L. pneumophila) was demonstrated for 6 (43%) of the 14 hospitals with positive findings. L. pneumophila serogroup 1 was detected in 5 of these 6 hospitals, whereas 1 hospital was colonized with L. pneumophila serogroup 5. A total of 633 patients were evaluated for Legionella pneumonia from 12 (60%) of the 20 hospitals: 377 by urinary antigen testing and 577 by sputum culture. Hospital-acquired Legionella pneumonia was identified in 4 hospitals, all of which were hospitals with L. pneumophila serogroup 1 found in 30% or more of the distal outlets. No cases of disease due to other serogroups or species (L. anisa) were identified.nnnCONCLUSIONnEnvironmental monitoring followed by clinical surveillance was successful in uncovering previously unrecognized cases of hospital-acquired Legionella pneumonia.

Plasmid Content of a Vancomycin-Resistant Enterococcus faecalis Isolate from a Patient Also Colonized by Staphylococcus aureus with a VanA Phenotype

ABSTRACT Vancomycin-resistant Enterococcus faecalis coisolated with vancomycin-resistant (VanA) Staphylococcus aureus was found to contain two plasmids, designated pAM830 (45 kb) and pAM831 (95 kb). pAM830, found to be conjugative and closely related to the Inc18 family of broad-host-range conjugative plasmids, encodes resistances to vancomycin (via a Tn1546-like element) and erythromycin; pAM831 encodes resistances to gentamicin, streptomycin, and erythromycin.

Comparative in vitro and bactericidal activity of oxazolidinone antibiotics against multidrug-resistant enterococci.

Increasing resistance among enterococci poses a considerable therapeutic problem. In this study, we evaluated the comparative in vitro activity of two investigational oxazolidinone antibiotics, eperezolid and linezolid, versus clinical isolates of multidrug-resistant enterococci. One hundred isolates (16 Enterococcus faecalis, 69 E. faecium, 10 E. gallinarum, 2 E. casseliflavus, 1 E. avium, 1 E. hirae, and 1 E. raffinosus) evaluated were collected from diverse geographic areas in North America and Europe from 1991 to 1995. Eperezolid MIC50 and MIC90 were 1.0 microgram/mL and 2.0 micrograms/mL (1.0-2.0 micrograms/mL range). Linezolid MIC50 and MIC90 were 2.0 micrograms/mL and 2.0 micrograms/mL (0.5-2.0 micrograms/mL range), respectively. MICs were the same at 10(3) CFU/mL and 10(8) CFU/mL initial inoculum. In time-kill experiments using 10 strains and concentrations of 4 micrograms/mL, 8 micrograms/mL, and 16 micrograms/mL (achievable serum concentrations) of eperezolid and linezolid there was a 2 log10 reduction of growth for 2 of 10 isolates tested using eperezolid and a 1 log10 reduction for 50% of isolates with both agents. There was indifferent bactericidal killing when either oxazolidinone was combined with gentamicin, ampicillin, or streptomycin for isolates lacking these resistances. This study demonstrates these oxazolidinone agents to have excellent in vitro activity versus multidrug-resistant enterococci.

In vitro susceptibility of vancomycin-resistant enterococci (VRE) to fosfomycin.

We evaluated the in vitro activity of fosfomycin against 75 clinical isolates of vancomycin-resistant enterococci (VRE). Using the NCCLS breakpoint for susceptibility of urinary tract isolates to fosfomycin (MIC > or = 256), 51 out of 52 Enterococcus faecium and all Enterococcus faecalis isolates tested were susceptible or intermediate to fosfomycin.

Comparative in vitro activity of quinupristin/dalfopristin against multidrug resistant : Enterococcus faecium

The in vitro susceptibilities of 82 strains of vancomycin resistant Enterococcus faecium (VREF), (49 vanA and 33 vanB) from over 13 hospitals in Europe and United States were studied. The MIC for several antibiotics showed high levels of resistance to vancomycin, ampicillin, gentamicin, and imipenem. All VREF strains were highly susceptible to quinupristin/dalfopristin with a MIC 90% of 0.5 microgram/ml for both vanA and vanB phenotypes. Time-kill and synergy studies of VREF for quinupristin/dalfopristin alone and quinupristin/dalfopristin in combination with several antibiotics (ampicillin, gentamicin, ciprofloxacin, rifampin and novobiocin) did not show bactericidal activity. In induction experiments using SF6550, (VREF, a vanA strain), quinupristin/dalforpristin showed a delay in the expression of vancomycin resistance by 2.5 hours. The results of this study show quinupristin/dalfopristin to have excellent in vitro activity versus multiple resistant E. faecium.

High vancomycin serum trough is not associated with reduction of mortality in methicillin-resistant Staphylococcus aureus bloodstream infections

The current Infectious Diseases Society of America (IDSA) and the American Society of Health-System Pharmacists (ASHP) guidelines recommend a vancomycin serum trough concentration of 15 to 20 mg/L in patients with methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infection (BSI). The objective of this study was to evaluate the mortality difference in MRSA BSI pre and post hospital-wide implementation of higher serum trough concentration per IDSA/ ASHP guidelines. This was a retrospective cohort study performed in an integrated hospital health system (2238 beds) in Southeast Michigan. We evaluated 1173 consecutive individual patients with MRSA BSI over a 9-year period. The vancomycin minimum inhibitory concentrations (MICs) were determined by Etest method for all isolates. Attainment of vancomycin serum trough concentration per IDSA/ASHP guidelines was implemented in January 2010 by clinical pharmacist as part of the antimicrobial stewardship program. During the study period, the mean vancomycin MIC was 1.57 ± 0.26 mg/L, the percentage of MRSA isolates with vancomycin MIC ≥ 2 mg/L was 17.5%, and the 30-day all-cause mortality was 16.5%. There was no difference in mortality during the 9-year period (p=0.193). There was no change in all-cause mortality for MRSA BSI after the hospital-wide implementation of higher vancomycin dose and serum trough concentration per IDSA/ ASHP guidelines. Prospective multicenter, controlled studies evaluating optimal dosing strategies for vancomycin are warranted. Correspondence to: Marcus J. Zervos, Division Head, Infectious Diseases, Henry Ford Health System, Professor of Medicine, Wayne State University School of Medicine, Detroit, MI 48202, USA, Tel: +1-313-916-2573; Fax: +1-313-9162993; E-mail: mzervos1@hfhs.org

Risk factors associated with vancomycin-resistant enterococcus (VRE) and methicillin-resistant Staphylococcus aureus (MRSA) co-infection

A retrospective case control study evaluated risk factors for co-infection with methicillin resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE). Over an 8-year period, 111 patients with MRSA and VRE were identified as cases and 1077 patients with MRSA alone were controls. The variables collected were age, gender, previous antibiotic administration, bacterium strain type and underlying comorbidities. Independent risk factors of co-infection were exposure to vancomycin (OR=3.70), quinolones (OR=3.09) and cephalosporins (OR=2.03) up to 3 months before bacterial isolation, neurologic disease (OR=2.22), gastrointestinal disease (OR=1.95), respiratory disease (OR=2.00) renal disease (OR=1.67), diabetes (OR=1.83) and dialysis (OR=1.92). The results of the study will have important implications for control interventions. Correspondence to: Katherine Reyes, Henry Ford Health System, Division of Infectious Diseases, 2799 West Grand Blvd CFP3, Henry Ford Health System, Detroit, MI, 48202, USA, Tel: 313-916-2573; E-mail: kreyes1@hfhs.org