Antibiotic resistance in Leuconostoc isolates of cheese origin

Abstract

Leuconostoc spp. are widely distributed in dairy environments, mostly as adjunct cultures and non-starter lactic acid bacteria. In order to gain Qualified Presumption of Safety status, bacteria must not carry transferable resistance to antibiotics. Although members of lactic acid bacteria are recognized as safe, constant monitoring of antibiotic resistance is recommended by European Food Safety Authority. The aim of this study was to evaluate antibiotic resistance in Leuconostoc isolates of cheese origin. This study was conducted on 20 Leuconostoc isolates belonging to two species: Leuconostoc mesenteroides (n=18) and Leuconostoc pseudomesenteroides (n=2). All investigated isolates originated from Serbian traditional raw milk cheeses – Zlatar, Sjenica and Homolje cheese. Minimum inhibitory concentrations were determined by broth microdilution method for 8 antibiotics and results were interpreted according to European Food Safety Authority guidance. Most prevalent resistance phenotype was resistance to kanamycin (n=15), following with resistance to chloramphenicol (n=6), and streptomycin (n=5). One Ln. mesenteroides isolate showed multiresistance, with resistance to 7 out of 8 investigated antibiotics. Genetic basis of tetracycline resistance (tet(A), tet(B), tet(C), tet(K), tet(L), tet(M), tet(O) and tet(W) genes) was analyzed by PCR method in all isolates. None of the analyzed genes was found in any of the isolates. According to the results of this study Leuconostoc isolates are not a reservoir of tetracycline resistance. However, determining genetic basis of antibiotic resistance is necessary for the complete risk assessment regarding transferable antibiotic resistance in the isolates.