Evaluation of in vitro susceptibility trends to vancomycin and daptomycin by strain type of Staphylococcus aureus causing bloodstream infections.

In total, 718 consecutive clinical meticillin-resistant Staphylococcus aureus (MRSA) isolates from 2006 to 2010 and 417 clinical meticillin-susceptible S. aureus (MSSA) isolates from mid-2007 to 2010 were evaluated. Isolates were from blood cultures obtained from separate patients in Detroit, MI, and were tested for in vitro susceptibility trends to vancomycin and daptomycin by molecular strain type. The MRSA pulsed-field gel electrophoresis (PFGE) results showed that 290 (40.4%) were USA100, 296 (41.2%) were USA300 and the remaining isolates were non-USA100/300. Vancomycin minimum inhibitory concentrations (MICs) by Etest [mean±standard deviation (S.D.) 1.55±0.26mg/L] in MRSA isolates showed no significant change over the 5-year period within all strain types, whilst daptomycin MICs by Etest (mean±S.D. 0.51±0.25mg/L) showed a significant downward trend across time (r=-0.243; P<0.001), with this trend occurring among all PFGE groups. For MSSA, a significant decrease in MICs to vancomycin was found by Etest (r=-0.160; P=0.001) and conversely a significant increase in daptomycin MICs by Etest was found (r=0.146; P=0.028). The results of this study showed that changes in MIC were not specific to strain molecular type. For vancomycin, there was no change in MRSA MICs and a decrease in MSSA MICs for blood isolates. For daptomycin, MICs decreased in MRSA and increased in MSSA blood isolates over the study period.

Characterization of vancomycin-resistant Enterococcus faecium isolated from swine in three Michigan counties.

Vancomycin-resistant enterococci are a major cause of nosocomial infections but are rarely found in humans in the community and have not been identified in food animals in the United States. We evaluated a total of 360 fecal specimens from humans and their animals being raised for exhibit at three county fairs in Michigan. Fecal samples from 158 humans, 55 swine, 50 cattle, 25 horses, 57 sheep, 14 goats, and 1 llama were obtained and plated onto Enterococcosel agar containing 16 µg/ml of vancomycin. Vancomycin-resistant Enterococcus faecium (VREF) was isolated from six pigs but not from humans or any animal other than pigs. All six VREF isolates had a MIC to vancomycin of ≥256 µg/ml and contained the vanA gene. Pulsed-field gel electrophoresis (PFGE) patterns of the six VREF isolates were ≥80% similar. Multilocus sequence typing (MLST) revealed sequence type 5 (ST5) (n = 2), ST6 (n = 3), and ST185 (n = 1), which are E. faecium sequence types belonging to clonal complex 5 (CC5). These findings show the dissemination of VREF strains among pigs in three Michigan counties. This is the first report of VRE found in food animals in the United States.

Comparative evaluation of epidemiology and outcomes of methicillin-resistant Staphylococcus aureus (MRSA) USA300 infections causing community- and healthcare-associated infections.

Methicillin-resistant Staphylococcus aureus (MRSA) USA300 clone is commonly found in the community and is being increasingly reported in the healthcare setting. A retrospective analysis was conducted to compare the epidemiology and outcomes between community-associated (CA) and healthcare-associated (HA) USA300 MRSA infections. The study enrolled 160 subjects with USA300 MRSA infections (47.5% CA-MRSA and 52.5% HA-MRSA). Failure in the HA group was higher (38.1%) compared with the CA group (23.7%) (P=0.05). Predictors of failure included male gender, age, presence of any co-morbidity, coronary artery disease, chronic kidney disease, history of MRSA, previous admission, fluoroquinolone exposure, HA infection and osteomyelitis (P

Molecular epidemiology of methicillin-resistant Staphylococcus aureus bloodstream isolates in urban Detroit.

To gain a better understanding of epidemiology of resistance in Staphylococcus aureus, we describe the molecular epidemiology of methicillin-resistant Staphylococcus aureus bloodstream isolates in urban Detroit. Bloodstream isolates from July 2005 to February 2007 were characterized. Two hundred ten bloodstream isolates from 201 patients were evaluated. Patient characteristics were as follows: median age, 54 years; 56% male; and 71% African-American. Seventy-six percent of infections were health care associated, with 55% being community-onset infections and 21% hospital acquired, and 24% were community associated. The most common sources were skin/wound (25%), central venous catheters (24%), unknown source (20%), and endocarditis (9%). Ninety percent and 5% of isolates had a MIC of vancomycin of or=1.5 mg/liter. Results of pulsed-field gel electrophoresis showed 17 strain types. The predominant strains were USA100 (104 isolates) and USA300 (74 isolates). Forty-nine percent of the isolates had staphylococcal cassette chromosome mec II, and 56% had agr II. All USA300 isolates were positive for the Panton-Valentine leukocidin toxin genes and agr I. Forty-seven percent of USA300 bloodstream infections were health care associated (35% community onset and 12% hospital onset). USA300 strains were more common in injection drug users with skin/wound as the predominant source of infection. Thirty percent of the USA100 strains were closely related to vancomycin-resistant Staphylococcus aureus isolates. The results of this study show that vancomycin MICs using automated dilution testing with Vitek-2 and E-test were highly discordant. Most methicillin-resistant S. aureus strains causing bacteremia are health care associated, commonly have MICs of vancomycin that are high within the susceptible range are not detected by routine automated dilution testing, and have significant diversity of molecular characteristics. USA100 strains that are closely related to vancomycin-resistant S. aureus (VRSA) isolates and USA300 strains are common as causes of both hospital and community-onset infection. Infection control measures should focus not only on prevention of the spread of community strains in the hospital but also prevention of the spread of hospital strains associated with VRSA into the community.

Heterogeneity of vat(E)-carrying plasmids in Enterococcus faecium recovered from human and animal sources.

In this study, quinupristin/dalfopristin (Q/D)-resistant Enterococcus faecium isolates (33 from poultry farms and 1 from a human outpatient) with Q/D minimal inhibitory concentrations ranging from 4 microg/mL to 32 microg/mL were analysed. Polymerase chain reaction detected the presence of vat(E) in all isolates. Using pulsed-field gel electrophoresis (PFGE), 14 distinct PFGE patterns were identified. The human E. faecium isolate was distinguishable from the 33 farm isolates by PFGE. Southern hybridisation localised the vat(E) gene to an 11 kb plasmid and resulted in five plasmid hybridisation types. The vat(E)-carrying plasmid from the human isolate showed a nearly identical hybridisation pattern to a plasmid from a farm isolate. This study showed that the vat(E) gene, conferring resistance to Q/D, was carried on different plasmids in a heterogeneous group of E. faecium, some of which may be acquired by E. faecium capable of infecting humans.

Epidemiology of antimicrobial resistance in enterococci of animal origin.

OBJECTIVE: We evaluated the epidemiology of antimicrobial resistance in enterococci from animal farms and the potential relation of resistance to antimicrobial use. METHODS: Enterococci from faecal samples from 18 beef cattle, 18 dairy cattle, 18 swine, 13 chicken, and eight turkey farms were prospectively evaluated over a 6 year period from 1998 to 2003. RESULTS: We evaluated 1256 isolates of Enterococcus faecium and 656 isolates of Enterococcus faecalis. None was vancomycin resistant. Quinupristin/dalfopristin, gentamicin and ciprofloxacin resistance rates in E. faecium were 2%, 0% and 55% in beef cattle, 8%, 7% and 47% in dairy cattle, 21%, 1% and 47% in swine, 85%, 12% and 23% in chicken, and 52%, 13% and 24% in turkey isolates, respectively. For E. faecalis, gentamicin resistance rates were 0% in beef cattle, 24% in dairy cattle, 37% in swine, 32% in chicken, and 29% in turkey isolates, whereas 12%, 9%, 21%, 64% and none of isolates from beef, dairy, swine, chicken, and turkey farms, respectively, were resistant to ciprofloxacin. Quinupristin/dalfopristin resistance in E. faecium was more common on chicken and turkey farms using virginiamycin (P<0.0001 for both) compared with farms not using a streptogramin, gentamicin resistance was more common on dairy farms using gentamicin (P<0.0001) compared with farms not using this antibiotic, and ciprofloxacin resistance was more common on turkey and dairy farms using enrofloxacin compared with those with no enrofloxacin use (P=0.02 and P=0.04, respectively). For E. faecalis, gentamicin resistance was more frequently detected on dairy and swine farms using gentamicin (P<0.0001 and P=0.0052, respectively) and ciprofloxacin resistance was more common on beef farms using enrofloxacin (P<0.0001) compared with farms not using these antimicrobials. PFGE showed multiple strain types with some clones common between animals of the same animal species. CONCLUSIONS: This study shows the presence of a significant reservoir of antibiotic-resistant enterococci among farm animals. Resistance was more common on farms using antimicrobial agents.

Molecular and clinical epidemiology of vancomycin-resistant Enterococcus faecalis.

OBJECTIVES: With the recent emergence of vancomycin-resistant (VR) Staphylococcus aureus, subsequent to the suggested transfer of the vanA resistance gene from Enterococcus faecalis, we sought to determine risk factors for acquisition of VR E. faecalis and to evaluate the molecular epidemiology of this less-prevalent and less-studied species of VR enterococcus. METHODS: We compared clinical isolates of VR E. faecalis from 71 patients, collected over 12 years in a large community teaching hospital, with isolates from 126 patients with vancomycin-susceptible E. faecalis. RESULTS: Risk factors for VR E. faecalis acquisition by multivariate analysis were nursing home residence (P = 0.0005), haemodialysis (P = 0.009), decubitus ulcers (P = 0.03) and receipt of parenteral vancomycin (P = 0.0002). Twenty-one percent of VR E. faecalis demonstrated vanA and 79% vanB resistance. The number of VanA isolates increased over time. Molecular analysis showed vanA or vanB in multiple PFGE groups. CONCLUSIONS: The results of this study suggest gene dissemination among some isolates and intra-hospital spread of other isolates. The risk factors identified clearly suggest that VR E. faecalis is a nosocomial pathogen and should be considered in infection control practices. Further surveillance of VR E. faecalis is warranted, due to the potential spread of vancomycin resistance among enterococci and staphylococci.

Plasmid content of a vancomycin-resistant Enterococcus faecalis isolate from a patient also colonized by Staphylococcus aureus with a VanA phenotype.

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.

Comparison of microscan broth microdilution, synergy quad plate agar dilution, and disk diffusion screening methods for detection of high-level aminoglycoside resistance in enterococcus species.

We compared the dried MicroScan microdilution panel, Synergy Quad plate agar dilution, and high-potency disk diffusion screening methods for the detection of high-level aminoglycoside resistance in 815 enterococcal bloodstream isolates. Agreement between the three methods was 99% when testing for high-level gentamicin resistance and 96% when testing for high-level streptomycin resistance.

Multiplex PCR for detection of aminoglycoside resistance genes in enterococci.

A multiplex PCR procedure for detecting the aminoglycoside resistance genes aac(6')-Ie-aph(2")-Ia, aph(2")-Ib, aph(2")-Ic, aph(2")-Id, aph(3')-IIIa, and ant(4')-Ia was evaluated and found to determine accurately the presence of these genes in enterococci.

Molecular analysis of vancomycin-resistant Enterococcus faecalis from Michigan hospitals during a 10 year period.

We evaluated the molecular relatedness of 47 clinical isolates of vancomycin-resistant Enterococcus faecalis collected from 15 Michigan hospitals from 1991 to 2000. There were 17 PFGE strain types for the 47 isolates. Ten of 15 hospitals demonstrated interhospital, and three of 15 intrahospital, dissemination of some isolates. Forty-two isolates (89.4%) demonstrated vanB resistance. All vanA isolates comprised unique PFGE groups, suggesting transposon dissemination or the presence of a similar plasmid. The results of this study suggest inter- and intrahospital dissemination of strains of vancomycin-resistant E. faecalis during a 10 year period in Michigan.