Phenotypical and genotypical investigation of the antimicrobial resistance profile and biofilm formation of Staphylococcus aureus isolates from ground beef and meatballs

Staphylococcus aureus (S. aureus) is a bacterium that threatens public health because it causes infections and food intoxications. The formation of antibiotic-resistant microorganisms and the ability of bacteria to form biofilms have become a major problem in foodborne infections. For this reason, within the scope of the thesis study, it was aimed to determine the presence of S. aureus, antibiotic resistance profiles and biofilm formation in ground beef and meatball samples consumed in Amasya. For this purpose, 60 meat samples (30 ground beef, 30 meatballs) presented for consumption in Amasya between February 2022 and July 2022 were used as material. First, decimal dilutions of the samples were made with peptone water (0.1%), inoculated on Baird Parker agar plates containing egg yolk tellurite and incubated at 35 °C for 24-48 hours. After incubation, suspicious colonies were selected and evaluated as Staphylococcus sp. S. aureus isolates were phenotypically confirmed by tests such as Gram stain, catalase test, growth on mannitol-only agar, and coagulase. Secondly, DNA isolation was performed from the isolates by boiling method. The isolates were genotypically confirmed to be S. aureus with genus specific (16S rRNA) and species specific (nuc) gene regions by PCR. Thirdly, the resistance profiles of the isolates against gentamicin, tobramycin, levofloxacin, piperacillin-tazobactam, imipenem, chloramphenicol, penicillin, methicillin, and erythromycin antibiotics were determined by disk diffusion test. Finally, biofilm production of isolates was determined phenotypically by Congo red agar (CRA) and microtitration plate method. In addition, PCR testing targeting the icaA and icaD genes was performed to genotypically confirm biofilm formation. From the samples examined, 297 Staphylococcus sp. were isolated and 58 of these isolates were determined to be S. aureus phenotypically and genotypically. Disk diffusion results showed that all of the isolates were susceptible to imipenem and piperacillin-tazobactam, but resistant to methicillin %43.10 (25/58), erythromycin %41.37 (24/58), penicillin %58.62 (34/58), gentamicin %10.34 (6/58), chloramphenicol %17.24 (10/58), tobramycin %6.89 (4/58), and levofloxacin %1.72 (1/58). Biofilm formation was determined as 58.62% (34/58) in CRA and 58.62% (34/58) in microtitration plate method. In PCR analysis, icaD gene in 7 isolates and icaA gene in 2 isolates were evaluated as positive. In conclusion, detection of S. aureus in ground meat and meatballs, development of antibiotic resistance and biofilm production of isolates mean that this bacterium poses a potential risk for public health. For this reason, it is important for public health to take the necessary measures to reduce the risk of S. aureus contamination that may occur during the purchase, processing, transportation and sale of foods.