Evaluation of the Biomic V3 microbiology system for identification of selected species on BBL CHROMagar orientation agar and CHROMagar MRSA medium.

The Biomic V3 microbiology system identifies bacteria by reading the color of colonies selected by the user. For CHROMagar orientation, Biomic results agreed with conventional methods for 94% of the strains assayed. For CHROMagar MRSA, Biomic correctly identified 100% of the strains tested and did not misidentify two methicillin-susceptible Staphylococcus aureus strains growing on the plates.

BBL CHROMagar Staph aureus is superior to mannitol salt for detection of Staphylococcus aureus in complex mixed infections.

We used 200 sputum specimens from patients with cystic fibrosis to evaluate BBL CHROMagar Staph aureus medium (CSA; BD Diagnostics, Spark, MD). Samples were inoculated to CSA, trypticase soy blood agar (BA), and Mannitol Salt (MS; BD Diagnostics). After 18 hours of incubation, CSA detected 39 (78%) of 50 Staphylococcus aureus (SA) samples; BA detected 30 (60%); and MS detected 29 (58%). Sensitivity after overnight incubation (at least 18 hours) was 82% for CSA, 72% for BA, and 71% for MS. At 2 days, CSA detected 48 (96%) of the SA. There were 2 false-positive results on CSA (99% specificity). There were 4 (8%) minor and no major or very major discrepancies between minimum inhibitory concentration (MIC) results for isolates grown on CSA and those grown on BA. Even at early reading times, CSA was superior to conventional media for detection of SA in these very complex cultures. MICs from all SA samples can be reported 24 hours sooner, and an additional BA subculture is not needed.

Comparison of rapid intrapartum screening methods for group B streptococcal vaginal colonization.

OBJECTIVE: To compare optical immunoassay (OIA) and rapid polymerase-chain reaction (PCR) with enrichment broth culture for intrapartum detection of vaginal group B streptococcal (GBS) colonization. METHODS: Paired vaginal swabs from 315 consecutive term pregnant women at the time of presentation for delivery to a university medical center were tested for GBS by OIA, PCR, and culture. Sensitivity, specificity, and positive and negative predictive values were calculated. RESULTS: Vaginal colonization was identified by culture in 56 subjects (17.8%). The sensitivity of OIA (7.1%, 95% confidence interval 5.1-9.5%) was significantly less than that of unenhanced rapid PCR (62.5%, 95% CI 48.5-74.8%). CONCLUSIONS: Neither PCR nor OIA is sufficiently sensitive for intrapartum detection of vaginal GBS colonization. Rapid PCR is more sensitive, but further improvements in technique to increase sensitivity will be necessary if PCR is to have a useful role in the management of women at time of presentation for delivery.

Emergence and spread of oseltamivir-resistant A(H1N1) influenza viruses in Oceania, South East Asia and South Africa.

The neuraminidase inhibitors (NAIs) are an effective class of antiviral drugs for the treatment of influenza A and B infections. Until recently, only a low prevalence of NAI resistance (<1%) had been detected in circulating viruses. However, surveillance in Europe in late 2007 revealed significant numbers of A(H1N1) influenza strains with a H274Y neuraminidase mutation that were highly resistant to the NAI oseltamivir. We examined 264 A(H1N1) viruses collected in 2008 from South Africa, Oceania and SE Asia for their susceptibility to NAIs oseltamivir, zanamivir and peramivir in a fluorescence-based neuraminidase inhibition assay. Viruses with reduced oseltamivir susceptibility were further analysed by pyrosequencing assay. The frequency of the oseltamivir-resistant H274Y mutant increased significantly after May 2008, resulting in an overall proportion of 64% (168/264) resistance among A(H1N1) strains, although this subtype represented only 11.6% of all isolates received during 2008. H274Y mutant viruses demonstrated on average a 1466-fold reduction in oseltamivir susceptibility and 527-fold reduction in peramivir sensitivity compared to wild-type A(H1N1) viruses. The mutation had no impact on zanamivir susceptibility. Ongoing surveillance is essential to monitor how these strains may spread or persist in the future and to evaluate the effectiveness of treatments against them.

Plasma cefazolin levels during cardiovascular surgery: effects of cardiopulmonary bypass and profound hypothermic circulatory arrest.

OBJECTIVES: We sought to assess the effects of cardiopulmonary bypass and profound hypothermic circulatory arrest on plasma cefazolin levels administered for antimicrobial prophylaxis in cardiovascular surgery. METHODS: Four groups (10 patients per group) were prospectively studied: vascular surgery without cardiopulmonary bypass (group A), cardiac surgery with a cardiopulmonary bypass time of less than 120 minutes (group B), cardiac surgery with a cardiopulmonary bypass time of greater than 120 minutes (group C), and cardiac surgery with cardiopulmonary bypass and profound hypothermic circulatory arrest (group D). Subjects received cefazolin at induction and a second dose before wound closure. Arterial blood samples were obtained preceding cefazolin administration, at skin incision, hourly during the operation, and before redosing. Cefazolin plasma concentrations were determined by using a radial diffusion assay, with Staphylococcus aureus as the indicator microorganism. Cefazolin plasma concentrations were considered noninhibitory at 8 microg/mL or less, intermediate at 16 mug/mL, and inhibitory at 32 microg/mL or greater. RESULTS: In group A cefazolin plasma concentrations remained greater than 16 microg/mL during the complete surgical procedure. In group B cefazolin plasma concentrations diminished to 16 microg/mL or less in 30% of the patients but remained greater than 8 microg/mL. In group C cefazolin plasma concentrations decreased to less than 16 microg/mL in 60% of patients and were less than 8 microg/mL in 50% of patients. In group D cefazolin plasma concentrations reached 16 microg/mL in 66% of the patients but decreased to 8 microg/mL in only 1 patient. CONCLUSIONS: For patients undergoing cardiac surgery with a cardiopulmonary bypass time of greater than 120 minutes, a single dose of cefazolin before skin incision with redosing at wound closure does not provide targeted antimicrobial cefazolin plasma levels during the entire surgical procedure. Patients undergoing profound hypothermic circulatory arrest are better protected, but the described protocol of prophylaxis is not optimal.

Practical bench comparison of BBL CHROMagar Orientation and standard two-plate media for urine cultures.

A total of 1023 urine samples sent for routine culture were plated onto sheep blood and MacConkey agars and a BBL CHROMagar Orientation (CO; Becton Dickinson, Cockeysville, Md.) plate, and the results were compared. Of these, 250 urine samples (24%) grew >10000 CFU of one or two putative pathogens/ml and 773 showed no growth (NG), mixed growth of <10000 CFU/ml, or three or more strains (mixed). The CO and conventional medium results agreed completely for 595 cultures with NG or <10000 CFU/ml. An additional 178 urine samples yielded clinically insignificant differences. Both medium sets essentially agreed on quantities and identification for 400 single-pathogen cultures and 9 mixed cultures. With the caveat that CO cannot differentiate Klebsiella, Enterobacter, and Serratia spp., enteric pathogens were identified only by morphology and color on CO. Direct visual differentiation of group B streptococci from lactobacilli is not possible, but lactobacillus cells always exhibited easily recognizable morphology on Gram stain. Of 108 paired organism susceptibility results encompassing 2268 drug-pathogen combinations, there were 3% errors and only 1% very major errors. Use of CO allowed a >50% reduction in inoculation time and a >20% reduction in work-up time. For our laboratory, with 50% "no growth" and ca. 25% significant results (50% Escherichia coli), CO allowed time and workup cost savings for a majority of cultures. A cost analysis (time and supplies for our laboratory) showed that if CO is used alone, the break-even level for CO pricing is US dollars 1.78; if CO and blood agar are both used, the break-even pricing for CO is US dollars 1.53.