Assessment of the alteration in phage adsorption rates of antibiotic-resistant Salmonella typhimurium.

This study was designed to evaluate the phage-binding receptors on the surface of antibiotic-sensitive Salmonella typhimurium (ASST) and antibiotic-resistant S. typhimurium (ARST). The antibiotic susceptibilities of plasmid-cured ASST and ARST were evaluated against ampicillin, cephalothin, ciprofloxacin, kanamycin, penicillin, and tetracycline. The capsular polysaccharides (CPSs) and lipopolysaccharides (LPSs) were quantified using carbazole assay and HPLC, respectively. The amounts of CPSs and LPSs in ARST were decreased from 108 to 62 μg/ml and 284-111 ng/ml, respectively, after plasmid curing. The adsorption rates of P22, PBST10, and PBST13 to plasmid-uncured and plasmid-cured ASST and ARST were decreased after proteinase K and periodate treatments. The highest reduction in phage adsorption rate was observed for P22 to the plasmid-cured ARST treated with periodate (71%). The relative expression levels of btuB, fhuA, and rfaL were decreased by more than twofold in the plasmid-cured ASST, corresponding to the decrease in the adsorption rates of P22 and PBST10. The plasmid-cured ARST lost the ability to express the β-lactamase gene, which was related to the loss of resistance to ampicillin, cephalothin, kanamycin, penicillin, and tetracycline. The results provide valuable insights into understanding the interaction between phage and antibiotic-resistant bacteria.