Antibiotic susceptibility of Lactobacillus rhamnosus strains isolated from Parmigiano Reggiano cheese

This work aimed to evaluate the antibiotic susceptibility of 63 Lactobacillus rhamnosus strains isolated from Parmigiano Reggiano cheese, of Lactobacillus GG and of the type strain L. rhamnosus DSM 20021. Antimicrobial susceptibility was determined by the disc diffusion method on 41 antibiotics. Inhibition zone diameter was carefully measured and the results (the mean of four determinations) were expressed in terms of resistance or susceptibility. All the strains isolated from cheese showed resistance to six antibiotics (cefixime, vancomycin, neomycin, enoxacin, pefloxacin and sulphamethoxazole plus trimethoprim). The strain DSM 20021T was resistant to nine antibiotics (the previous six plus cephalexin, bacitracin and lincomycin), while the commercial strain L. GG showed resistance to eighteen antibiotics. A high strain-specific resistance to different antibiotics was ascertained in Lactobacillus rhamnosus isolated from cheese. The results obtained in this study confirm that antibiotic resistance is a very important feature in the selection of potentially probiotic lactic acid bacteria.