The performance of a rapid penicillin-binding protein 2a (PBP2a) detection assay, the Alere PBP2a Culture Colony Test, was evaluated for identification of PBP2a-mediated beta-lactam resistance in human and animal clinical isolates of Staphylococcus intermedius group, Staphylococcus lugdunensis, and Staphylococcus schleiferi. The assay was sensitive and specific, with all PBP2a-negative and -positive strains testing negative and positive, respectively.

BACKGROUND: Of the 13 US vancomycin-resistant Staphylococcus aureus (VRSA) cases, 8 were identified in southeastern Michigan, primarily in patients with chronic lower-extremity wounds. VRSA infections develop when the vanA gene from vancomycin-resistant enterococcus (VRE) transfers to S. aureus. Inc18-like plasmids in VRE and pSK41-like plasmids in S. aureus appear to be important precursors to this transfer. OBJECTIVE: Identify the prevalence of VRSA precursor organisms. DESIGN: Prospective cohort with embedded case-control study. PARTICIPANTS: Southeastern Michigan adults with chronic lower-extremity wounds. METHODS: Adults presenting to 3 southeastern Michigan medical centers during the period February 15 through March 4, 2011, with chronic lower-extremity wounds had wound, nares, and perirectal swab specimens cultured for S. aureus and VRE, which were tested for pSK41-like and Inc18-like plasmids by polymerase chain reaction. We interviewed participants and reviewed clinical records. Risk factors for pSK41-positive S. aureus were assessed among all study participants (cohort analysis) and among only S. aureus-colonized participants (case-control analysis). RESULTS: Of 179 participants with wound cultures, 26% were colonized with methicillin-susceptible S. aureus, 27% were colonized with methicillin-resistant S. aureus, and 4% were colonized with VRE, although only 17% consented to perirectal culture. Six participants (3%) had pSK41-positive S. aureus, and none had Inc18-positive VRE. Having chronic wounds for over 2 years was associated with pSK41-positive S. aureus colonization in both analyses. CONCLUSIONS: Colonization with VRSA precursor organisms was rare. Having long-standing chronic wounds was a risk factor for pSK41-positive S. aureus colonization. Additional investigation into the prevalence of VRSA precursors among a larger cohort of patients is warranted.

Data on the interaction between methicillin-resistant Staphylococcus aureus (MRSA) colonization and clinical infection are limited. During 2007-2008, we enrolled HIV-infected adults in Atlanta, Georgia, USA, in a prospective cohort study. Nares and groin swab specimens were cultured for S. aureus at enrollment and after 6 and 12 months. MRSA colonization was detected in 13%-15% of HIV-infected participants (n = 600, 98% male) at baseline, 6 months, and 12 months. MRSA colonization was detected in the nares only (41%), groin only (21%), and at both sites (38%). Over a median of 2.1 years of follow-up, 29 MRSA clinical infections occurred in 25 participants. In multivariate analysis, MRSA clinical infection was significantly associated with MRSA colonization of the groin (adjusted risk ratio 4.8) and a history of MRSA infection (adjusted risk ratio 3.1). MRSA prevention strategies that can effectively prevent or eliminate groin colonization are likely necessary to reduce clinical infections in this population.

We compared recovery of Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) from nasal and groin swabs of 600 HIV-infected outpatients by selective and non-selective direct plating and broth enrichment. Swabs were collected at baseline, 6-month and 12-month visits, cultured by direct plating to Mannitol Salt Agar (MSA), CHROMagar MRSA (CM), and overnight broth enrichment with sub-culture to MSA (Broth). MRSA isolates were characterized by pulsed-field gel electrophoresis (PFGE), SCCmec typing and PCR for the Panton-Valentine leukocidin. At each visit 13-15% of patients were colonized with MRSA and 30-33% with methicillin-susceptible S. aureus (MSSA). Broth, CM and MSA detected 95%, 82% and 76% of MRSA-positive specimens, respectively. MRSA recovery was significantly higher from Broth compared to CM (p ≤ 0.001) or MSA (p ≤ 0.001); there was no significant difference in recovery between MSA and CM. MSSA recovery also increased significantly using Broth compared to MSA (p ≤ 0.001). Among specimens collected from the groin, Broth, CM, and MSA detected 88%, 54%, and 49% of the MRSA-positive isolates, respectively. Broth enrichment had a greater impact on recovery of MRSA from the groin than from the nose compared to both CM (p ≤ 0.001) and MSA (p ≤ 0.001). Overall, 19% of MRSA-colonized patients would have been missed with nasal culture only. USA500/Iberian and USA300 were the most common MRSA strains recovered, and USA300 was more likely than other strain types to be recovered from the groin than from the nose (p=0.05).

BACKGROUND: Recent outbreaks in ambulatory care settings have highlighted infection control breaches as risk factors for disease transmission. In May 2009, 3 patients were hospitalized with severe methicillin-susceptible Staphylococcus aureus (MSSA) infections after receiving epidural injections at a West Virginia outpatient pain clinic. METHODS: We conducted a retrospective cohort study evaluating clinic patients who received injections during a 3-week period. A case was defined as laboratory-confirmed infection or clinical evidence of infection ≤ 14 days after a patient received an injection. Infection control procedures were assessed. MSSA isolates from patient infections and clinic staff nasal swabs were genotyped by using pulsed-field gel electrophoresis. RESULTS: Eight (7%) of 110 cohort patients met the case definition; 6 (75%) cases were laboratory confirmed. Eight (12%) of 69 patients who received epidural injections were case patients compared with none of the other 41 patients (P = .02). During procedures, staff use of face masks and preparation of patient skin were suboptimal; epidural injection syringes were reused to access shared medication vials. MSSA isolates from 2 patients and 1 staff member were indistinguishable by pulsed-field gel electrophoresis. CONCLUSION: Infection control breaches likely facilitated MSSA transmission to patients receiving epidural injections. Adhering to correct infection control practices in ambulatory care settings is critical to prevent disease transmission.

Utility of Etest for antimicrobial susceptibility testing of Yersinia pestis was evaluated in comparison with broth microdilution and disk diffusion for eight agents. Four laboratories tested 26 diverse strains and found Etest to be reliable for testing antimicrobial agents used to treat Y. pestis, except for chloramphenicol and trimethoprim-sulfamethoxazole. Disk diffusion testing is not recommended.

Although high rates of clinical infection with methicillin-resistant Staphylococcus aureus (MRSA) have been reported in HIV-infected adults, data on MRSA colonization are limited. We enrolled HIV-infected adults receiving care at the Atlanta VA Medical Center. Swabs from each participant's nares and groin were cultured with broth enrichment for S. aureus. Of 600 HIV-infected adults, 79 (13%) were colonized with MRSA and 180 (30%) with methicillin-susceptible S. aureus. MRSA pulsed-field gel electrophoresis types USA300 (n=44, 54%) and USA500/Iberian (n=29, 35%) predominated. Inclusion of groin swabs increased MRSA detection by 24% and USA300 detection by 38%. In multivariate analysis, MRSA colonization compared to no MRSA colonization was associated with a history of MRSA clinical infection, rarely or never using condoms, and contact with prisons and jails. In summary, the prevalence of MRSA colonization was high in this study of HIV-infected adults and detection of USA300 was enhanced by groin culture.

We compared the results obtained with six commercial MIC test systems (Etest, MicroScan, Phoenix, Sensititre, Vitek Legacy, and Vitek 2 systems) and three reference methods (agar dilution, disk diffusion, and vancomycin [VA] agar screen [VScr]) with the results obtained by the Clinical and Laboratory Standards Institute broth microdilution (BMD) reference method for the detection of VA-intermediate Staphylococcus aureus (VISA). A total of 129 S. aureus isolates (VA MICs by previous BMD tests, <or=1 microg/ml [n = 60 strains], 2 microg/ml [n = 24], 4 microg/ml [n = 36], or 8 microg/ml [n = 9]) were selected from the Centers for Disease Control and Prevention strain collection. The results of BMD with Difco Mueller-Hinton broth were used as the standard for data analysis. Essential agreement (percent +/-1 dilution) ranged from 98 to 100% for all methods except the method with the Vitek Legacy system, for which it was 90.6%. Of the six commercial MIC systems tested, the Sensititre, Vitek Legacy, and Vitek 2 systems tended to categorize VISA strains as susceptible (i.e., they undercalled resistance); the MicroScan and Phoenix systems and Etest tended to categorize susceptible strains as VISA; and the Vitek Legacy system tended to categorize VISA strains as resistant (i.e., it overcalled resistance). Disk diffusion categorized all VISA strains as susceptible. No susceptible strains (MICs <or= 2 microg/ml) grew on the VScr, but all strains for which the VA MICs were 8 microg/ml grew on the VScr. Only 12 (33.3%) strains for which the VA MICs were 4 microg/ml grew on VScr. The differentiation of isolates for which the VA MICs were 2 or 4 microg/ml was difficult for most systems and methods, including the reference methods.