Infective endocarditis caused by USA300 methicillin-resistant Staphylococcus aureus (MRSA).

We report seven cases of infective endocarditis caused by USA300 methicillin-resistant Staphylococcus aureus (MRSA) at an urban, tertiary care, academic institution. Five strains were community associated and two were healthcare associated. All patients were injection drug users. Staphylococcus aureus isolates were characterised as USA300-type MRSA using pulsed-field gel electrophoresis. Five cases were right-sided endocarditis and two cases were left-sided. The mean length of in-hospital antimicrobial therapy was 23 days and the mean length of total antibiotic therapy was 55 days. Complications included heart failure resulting in valve replacement in one patient as well as death in that patient. As USA300 strains of MRSA continue to increase in prevalence, clinicians must be aware of the increasing spectrum of illness in considering management and prevention strategies.

Epidemiology and outcomes of community-associated methicillin-resistant Staphylococcus aureus infection.

Over a 2-year period (2003 to 2005) patients with community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) and community-acquired methicillin-susceptible Staphylococcus aureus (CA-MSSA) infections were prospectively identified. Patients infected with CA-MRSA (n = 102 patients) and CA-MSSA (n = 102 patients) had median ages of 46 and 53 years, respectively; the most common sites of infection in the two groups were skin/soft tissue (80 and 93%, respectively), respiratory tract (13 and 6%, respectively), and blood (4 and 1%, respectively). Fourteen percent of patients with CA-MRSA infections and 3% of patients with CA-MSSA infections had household contacts with similar infections (P < 0.01). Among the CA-MRSA isolates, the pulsed-field gel electrophoresis (PFGE) groups detected were USA300 (49%) and USA100 (13%), with 27 PFGE groups overall; 71% of the isolates were staphylococcal chromosome cassette mec (SCCmec) type IV, 29% were SCCmec type II, and 54% had the Panton-Valentine leucocidin (PVL) gene. Among the CA-MSSA isolates there were 33 PFGE groups, with isolates of the USA200 group comprising 11%, isolates of the USA600 group comprising 11%, isolates of the USA100 group comprising 10%, and isolates of the PVL type comprising 10%. Forty-six and 18% of the patients infected with CA-MRSA and CA-MSSA, respectively, were hospitalized (P < 0.001). Fifty percent of the patients received antibiotic therapy alone, 5% received surgery alone, 30% received antibiotics and surgery, 3% received other therapy, and 12% received no treatment. The median durations of antibiotic therapy were 12 and 10 days in the CA-MRSA- and CA-MSSA-infected patients, respectively; 48 and 56% of the patients in the two groups received adequate antimicrobial therapy, respectively (P < 0.001). The clinical success rates of the initial therapy in the two groups were 61 and 84%, respectively (P < 0.001); recurrences were more common in the CA-MRSA group (recurrences were detected in 18 and 6% of the patients in the two groups, respectively [P < 0.001]). CA-MRSA was an independent predictor of clinical failure in multivariate analysis (odds ratio, 3.4; 95% confidence interval, 1.7 to 6.9). In the community setting, the molecular characteristics of the S. aureus strains were heterogeneous. CA-MRSA infections were associated with a more adverse impact on outcome than CA-MSSA infections.

Quinupristin-dalfopristin resistance in Enterococcus faecium isolates from humans, farm animals, and grocery store meat in the United States.

Three hundred sixty-one quinupristin-dalfopristin (Q-D)-resistant Enterococcus faecium (QDREF) isolates were isolated from humans, turkeys, chickens, swine, dairy and beef cattle from farms, chicken carcasses, and ground pork from grocery stores in the United States from 1995 to 2003. These isolates were evaluated by pulsed-field gel electrophoresis (PFGE) to determine possible commonality between QDREF isolates from human and animal sources. PCR was performed to detect the streptogramin resistance genes vatD, vatE, and vgbA and the macrolide resistance gene ermB to determine the genetic mechanism of resistance in these isolates. QDREF from humans did not have PFGE patterns similar to those from animal sources. vatE was found in 35%, 26%, and 2% of QDREF isolates from turkeys, chickens, and humans, respectively, and was not found in QDREF isolates from other sources. ermB was commonly found in QDREF isolates from all sources. Known streptogramin resistance genes were absent in the majority of isolates, suggesting the presence of other, as-yet-undetermined, mechanisms of Q-D resistance.