Columbia blood agar

Bacterial concentrations were determined using standard plating methods and expressed as the number of viable CFUs per milliliter (CFU/mL). Streptococcus dysgalactiae was cultured on Columbia blood agar (Merck, Darmstadt, Germany). All other bacterial species were plated on CASO agar (Merck, Darmstadt, Germany). Samples with an expected count of >100 CFU/mL were inoculated using a spiral plater. Serial ten-fold dilutions of each sample were transferred to agar plates (2 plates/dilution, 50 μL/plate). Samples with an expected count of <100 CFU/mL were cultured using the pour plate method (2 plates/sample, 0.5–1 mL/plate). All agar plates were incubated at 37°C (except for Serratia marcescens, which was incubated at 30°C) for 1–2 days until colonies could be counted.
PC samples collected on day 7 of storage were tested for sterility with the BACT/ALERT 3D 60 Microbial Detection System (bioMérieux, Nuertingen, Germany). Briefly, after the collection of PC samples (20 mL each) under sterile conditions on day 7 of storage, half (10 mL) was injected into a BACT/ALERT SA (aerobic) and SN (anaerobic) culture bottle, respectively, and cultivated under automated blood culture conditions at 36°C in the BACT/ALERT incubator (bioMérieux) for 7 days.

A cross-sectional study was performed on 813 volunteers from November 2011 to May 2012 and was approved by the Ethics Committee of Arak University of Medical Sciences campus after institutional ethical approval (No. 3-143-1392). Students without symptoms or signs of clinical illnesses and antibiotic consumption were enrolled in the study.
Sampling was performed twice within a week on volunteers. The anterior nasal swabs were collected using Transwab (Medical Wire and Equipment Company, Corsham, UK) and were immediately transported to the laboratory. The nasal swabs were enriched with 7.5% salt nutrient broth (Merck, Germany) at 37°C for 2 - 4 hours, then were plated on a Columbia blood agar (Merck, Germany) medium plate and incubated at 37°C for 24 hours. Identification of S. aureus was based on colony morphology and results of Gram staining. The isolated colony was inoculated on sterilized phenol-red mannitol salt agar (MSA) (Merck, Germany) plates and incubated at 37°C for 24 hours. Isolates positive for catalase test, MSA plate, slide coagulase and tube coagulase with human plasma and DNase test and thermostable nuclease, were considered as S. aureus in this study. In addition, all the isolates were checked for the presence of the sa442 gene by PCR (4 (link)) (Table 1).