Analysis of Morphologically Similar Staphylococcus aureus Colonies for Assessment of Phenotypic and Genotypic Correlation

摘要

Once parents or guardians consented to the TREAT PARENTS trial, swab samples were collected from the nares, throat, groin, and perianal region to screen for the presence of S. aureus. The samples were collected with the Copan Eswab transport system (Copan, Murrieta, CA). For each sample, 10 μl was aliquoted onto a quarter of one S. aureus selective chromogenic agar (SASelect; Bio-Rad, Hercules, CA) plate and one 5% sheep blood agar (SBA; Remel, Lenexa, KS) plate and incubated at 37°C for 16 to 24 h. At the same time, 100 μl of each sample was aliquoted into tryptic soy broth containing 6.5% sodium chloride (Bio-Rad, Hercules, CA) and incubated at 37°C for 16 to 24 h. After incubation, 10 μl of each broth was plated on SASelect medium and 5% SBA, streaked for isolation, and incubated at 37°C for 16 to 24 h. The colonies had to have the same color, size, consistency, and entirety to be called identical. Two medical technologists independently read the plates, and there were no inconsistencies between them in the determination of identical versus different morphologies on the basis of the criteria described. For each S. aureus morphology on every positive plate, five separate colonies were individually subcultured on 5% SBA and then frozen. These isolates were analyzed by pulsed-field gel electrophoresis (PFGE) and antimicrobial susceptibility testing (AST) with standard antistaphylococcal agents.