Cultural and molecular diagnosis of staphylococcus aureus in clinical and subclinical mastitis and determination of antibiotic susceptibility of isolates

In addition to S. aureus, the following species were identified: Streptococcus spp., E. coli, Bacillus spp. and yeast. A conventional PCR study was performed in order to confirm the identification of the isolates as Staphylococcus spp. For this purpose, genus-specific primers (756 bp) were used. As a result of the phenotypic identification of the isolates used in the study, 100% of all Staphylococcus spp. suspected isolates were identified as S. aureus. The identification of all isolates as Staphylococcus spp. was confirmed by determining the 16S rRNA (gene (756 bp) value. A total of 24 S. aures strains were isolated and produced (McFarland No: 0.5) in brain heart infusion broth (BHIB) (1.10493.0500, Merck) and an antibiogram test was performed on Mueller-Hinton agar (MHA) (1.05437.0500, Merck). The test was performed according to the Kirby-Bauer disk diffusion method (Bauer et al., 1966). The test was performed with cefoperazone (75 μg, Oxoid), amoxicillin/clavulanic acid (20/10 μg, Oxoid), oxytetracycline (30 μg, Oxoid), penicillin G (10 μg, Oxoid), sulfamethoxazole/trimethoprim (2 5 μg, Oxoid), enrofloxacin (5 μg, Oxoid), vancomycin (30 μg, Oxoid), gentamicin (10 μg, Oxoid), erythromycin (15 μg, Oxoid) and cephalothin (30 μg, Oxoid) were used (CLSI, 2017). The zone diameters of the isolates as a result of the antibiotic test were evaluated in accordance with CLSI (2019). The isolates exhibited varying degrees of resistance to the different antibiotics. The highest resistance was determined to be to penicillin G, with 80.76% (n=21) of the isolates being resistant. This was followed by erythromycin, with 73.07% (n=19) of the isolates being resistant. Other antibiotics that were effective against the isolates included gentamicin, with 65.38% (n=17) of the isolates being resistant, enrofloxacin, with 46.15% (n=12) of the isolates being resistant, and oxytetracycline, with 42.30% (n=11) of the isolates being resistant. The antibiotic to which the isolates demonstrated the greatest sensitivity was identified as cefoperazone, with 69.23% (n=18) of isolates exhibiting sensitivity to this agent. This was followed by cephalothin with 65.38% (n=17), amoxicillin/clavulanic acid with 61.53% (n=16), vancomycin and trimethoprim/sulfamethoxazole with 53.84% (n=14). It was determined that four of the 26 S. aureus waters isolated in the study (15.38%) exhibited multiple antibiotic resistance. Of the 3 isolates exhibiting resistance to three different antibiotic classes, one isolate demonstrated resistance to four different antibiotics. Concurrent studies are being conducted on a total of 22 isolates that do not demonstrate multiple antibiotic resistance. Key Words: Cattle, mastitis, pathogen, isolation, identification.