Chapman agar

This study investigated 33 clinical strains of S. aureus obtained from the sputum samples of patients with known CF treated at the Department of Microbiology, National Tuberculosis and Lung Diseases Research Institute (Warsaw, Poland). All study participants provided informed consent to collect samples. Cultures of S. aureus were grown in Columbia Blood Agar with 5% sheep blood (bioMérieux, Marcy-l’Etoile, France) and Chapman Agar (bioMérieux, Marcy-l’Etoile, France) at 37 °C for 24–48 h in aerobic atmosphere. Antimicrobial susceptibility testing was performed using the standardized disk diffusion method and gradient method with Mueller-Hinton Agar (Oxoid, France). The results were interpreted according to the European Committee of Antimicrobial Susceptibility Testing (EUCAST) [44 ] breakpoints against the following antibiotics: cefoxitin, gentamycin, tobramycin, ciprofloxacin, levofloxacin, erythromycin, clindamycin, tetracycline, trimethoprim/sulfamethoxazole, linezolid, teicoplanin, and vancomycin. All the strains were stored frozen at −70 °C in Lysogeny broth medium (LB) (Sigma-Aldrich, St Louis, MO, USA) with 2% glycerol prior to the study.

The study was carried out on 110 strains of S. aureus isolated from oral samples of patients with symptoms of oral infections in 2016–2018. Oral swabs were analyzed at the Laboratory of Oral Microbiology of the Medical University of Gdansk in accordance with routine laboratory procedures. The analyzed staphylococcal strains were not specifically isolated for this research; they were part of the diagnostic laboratory procedure and no humans were involved in the experiments.
The materials were streaked onto blood agar and Chapman agar (bioMerieux) and were incubated 18–24 h at 37 °C. After incubation, colonies with typical staphylococcal morphology (size, shape, or pigmentation) were identified biochemically with the API ID32 STAPH test (bioMerieux), and uncertain identification was additionally confirmed by the MALDI-TOF MS method.
After final identification, the isolates were stored at −80 °C in Trypticase Soy Broth (Becton Dickinson, Franklin Lakes, NJ, USA) supplemented with 20% glycerol for further use.

Following the analysis of the Gram stain slides, a 10 μL sample from the ETA was inoculated onto corresponding culture media for bacterial isolation. The following media were used: sheep blood agar, chocolate agar, MacConkey agar, Chapman agar, and Sabourad dextrose agar (bioMerieux, Marcy-l’Étoile, France). The plates were incubated at 37 °C for 24 h. The bacterial growth was assessed according to the number of colony-forming units (CFU)/mL. A threshold of 10⁵ CFU/mL was set for positive samples.
A VITEK^® 2 (bioMerieux, Marcy-l’Étoile, France) antibiotic susceptibility testing system was used. A well-isolated bacterial colony was selected from the culture plate and emulsified in a sterile saline tube. The bacterial suspension was transferred onto specific cassettes following the manufacturer’s instructions, and automated susceptibility testing was performed. Antimicrobial testing was interpreted according to the Clinical and Laboratory Standards Institute (CLSI) [47 (link)].