Antibiotic resistance patterns of lactic acid bacteria isolated from Nigerian grown salad vegetables

The reports on some foodborne lactic acid bacteria (LAB) possessing antibiotic resistance (AR) genes on mobile genetic elements are on the increase. In Nigeria, such information is rare. This study was therefore designed to determine the presence and locations of AR genes in LAB isolated from locally grown salad vegetables. The LAB used in this study were previously isolated from Nigerian grown cabbage, carrot, cucumber and lettuce and identified by partial sequencing of their 16S rRNA gene. The AR and integrons (intl1, 2, 3) genes were detected using polymerase chain reaction after phenotypic agar disc diffusion assay of 20 antibiotics. Extraction and curing of plasmids were performed using standard methods. Univariate analysis was performed to determine resistance to ≥ 2 antibiotics, while multinomial logistic regression was conducted to determine association of resistance patterns with vegetable sources/ types and LAB strains at 95% confidence interval (CI). The entire LAB were phenotypically resistant to ≥2 antibiotics, while uncultured Solibacillus clone RBL-135 was resistant to all and possessed the 454 bp vancomycin (vanX) gene on chromosomes. Three others, Lactobacillus plantarum YML 007 (lettuce), Lactobacillus plantarum TCP 008 (cabbage) and Weissella cibaria PON 10339 (carrot), also amplified this gene while Weissella confusa SJL 602 (lettuce) amplified resistance gene for beta lactam (blaZ). This gene (blaZ) was also detected in three other LAB but with size corresponding to 500 bp. None of the tetracycline ribosomal protection protein, tet(M), (S), (W), efflux tet(K), (L), aminoglycoside acetyltransferase and phosphotransferase encoding gene, aac(61)- aph(21), integrons (intl 1,2,3) were detected. The plasmid cured LAB exhibited same resistance patterns as their wild derivatives. The naturally occurring LAB in the study vegetables are phenotypically multidrug resistant, a few possessing vanX and blaZ resistance genes on chromosomes. Hence, they lack potentials to transfer AR through plasmids and integrons.