Assessment of antibiotic susceptibilities, genotypic characteristics and biofilm-forming abilities of Staphylococcus aureus and Salmonella Typhimurium

Abstract

This study was designed to evaluate the antibiotic susceptibilities, genotypic characteristics and biofilm formation abilities of antibiotic-sensitive Staphylococcus aureus KACC 13236 (SA^S), multiple antibiotic-resistant S. aureus CCARM 3080 (SA^R), antibiotic-sensitive Salmonella Typhimurium KCCM 40253 (ST^S) and multiple antibiotic-resistant Salmonella Typhimurium CCARM 8009 (ST^R) cultured in various levels of pHs (4.0, 5.5 and 7.3) and temperatures (4, 20 and 37°C). The SA^S biofilm cells were highly resistant to ampicillin, cephalothin, oxacillin and piperacillin (MIC₉₀ >256 μg/ml) compared with the SA^S planktonic cells. The ST^R strain was less susceptible to cephalothin, oxacillin and piperacillin than the ST^S. The SA^R 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 SA^R 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.