Assessment of antibiotic susceptibilities, genotypic characteristics and biofilm-forming abilities of Staphylococcus aureus and Salmonella Typhimurium
This study was designed to evaluate the antibiotic susceptibilities, genotypic characteristics and biofilm formation abilities of antibiotic-sensitive Staphylococcus aureus KACC 13236 (SAS), multiple antibiotic-resistant S. aureus CCARM 3080 (SAR), antibiotic-sensitive Salmonella Typhimurium KCCM 40253 (STS) and multiple antibiotic-resistant Salmonella Typhimurium CCARM 8009 (STR) cultured in various levels of pHs (4.0, 5.5 and 7.3) and temperatures (4, 20 and 37°C). The SAS biofilm cells were highly resistant to ampicillin, cephalothin, oxacillin and piperacillin (MIC90 >256 μg/ml) compared with the SAS planktonic cells. The STR strain was less susceptible to cephalothin, oxacillin and piperacillin than the STS. The SAR strain was positive for the staphylococcal enterotoxin genes (sec, seg, sei, sel, sem, sen and seo). The highest biofilm formation index (BFI) was 2.07 for the SAR biofilm cells cultured at 37°C and pH 5.5. The antibiotic-resistant pathogens showed multiple antibiotic resistance, genotypic heterogeneity and cross-protective responses to low pH in the form of biofilms. This study provides useful information for the comparison of antibiotic resistance patterns and biofilm formation abilities between antibiotic-sensitive and resistant pathogens in planktonic and biofilm cells.
Key words: Antibiotic resistance, Staphylococcus aureus, Salmonella Typhimurium, biofilm formation, crossprotection.