3. The differences in antibiotic susceptibility between pH 5.5 and 7.3 were especially noticeable for the biofilm cells of S. aureus KACC13236. However, the antibiotic resistance patterns of S. aureus CCARM 3080 were not significantly different between the biofilm cells at pH 5.5 and 7.3, showing
MIC values of 128 μg mL−1 to more than 256 μg mL−1. As shown in Table 5, the planktonic and biofilm cells of S. Typhimurium JQ1 nmr CCARM 8009 were more likely to be resistant to most antibiotics when compared to S. aureus KACC13236. Similarly, the biofilm cells of S. Typhimurium were more resistant to antibiotics compared with the planktonic cells. According to the results of the susceptibility of selected foodborne pathogens, the strains of S. aureus KACC13236, S. aureus CCARM 3080, S. Typhimurium KCCM 40253, and S. Typhimurium CCARM 8009 were assigned to antibiotic-susceptible S. aureus (S. aureusS), multiple antibiotic-resistant S. aureus (S. aureusR), antibiotic-susceptible S. Typhimurium (S. TyphimuriumS), multiple antibiotic-resistant S. Typhimurium
(S. TyphimuriumR), respectively. The gene expression patterns were evaluated in the antibiotic-susceptible (S. aureusS and S. TyphimuriumS) and multiple antibiotic-resistant strains (S. aureusR and S. TyphimuriumR) anaerobically cultured in TSB adjusted to pH 5.5 and 7.3 during the planktonic-to-biofilm transition for 48 h at 37 °C (Figs 1 and 2). The relative expression of norB, norC, mdeA, sec, seg, sei, sel, sem, sen, and seo genes was observed in the planktonic and biofilm cells of S. aureusS and S. aureusR (Fig. 1). The norB and mdeA genes
Belnacasan were overexpressed at the planktonic cells of both Selleck Docetaxel S. aureusS and S. aureusR grown in TSB at pH 5.5 after 48-h incubation (Fig. 1a). The relative expression level of norC gene was increased 2.8-fold in S. aureusS. The relative gene expression levels of sel and sem were increased 5.0- and 3.0-fold, respectively, in the planktonic cells of S. aureusR grown in TSB at pH 5.5. As shown in Fig. 1b, the relative gene expression of norC and mdeA was stabilized in the planktonic cells of both S. aureusS and S. aureusR grown in TSB at pH 7.3. The relative expression levels of norB, seg, and sei genes were increased 52.6-, 2.6-, and 5.9-fold, respectively, in the planktonic cells of S. aureusR grown in TSB at pH 7.3. Unlike the planktonic cells, all genes were stable in the biofilm cells of S. aureusR grown in TSB at pH 5.5 and pH 7.3, except for the sec gene in S. aureusR biofilm cells formed in TSB at pH 5.5 (Fig. 1c,d). The relative gene expression levels of norB and mdeA were increased 1.9- and 2.0-fold, respectively, in the biofilm cells of S. aureusS grown in TSB at pH 5.5 (Fig. 1c). The highest expression level (116.6-fold) was observed at the norB gene in the S. aureusR biofilm cells grown in TSB at pH 5.5. As shown in Fig. 1d, the norB, norC, and mdeA genes were stable in the biofilm cells of both S. aureusS and S. aureusR grown in TSB at pH 7.3.