Key Words

Lactic acid bacteria Bifidobacteria. Antibiotic resistance Antibiotic resistance genes Multidrug resistance The minimum inhibitory concentrations (MICs) o f 6 different antibiotics (chloramphenicol, clindamycin, erythromycin, streptomycin, tetracycline and vancomycin) were deter-mined for 143 strains of lactic acid bacteria and bifidobacte-ria using the Etest. Different MlCs were found for different species and strains. Based on the distribution o f these MIC values, most o f the strains were either susceptible or intrinsi-cally resistant t o these antibiotics. However, the MIC range of some of these antibiotics showed a bimodal distribution, which suggested that some o f the tested strains possess ac-quired antibiotic resistance. Screening for resistance genes was performed by PCR using specific primers, or using a DNA microarray with around 300 nucleotide probes representing 7 classes o f antibiotic resistance genes.The genes identified encoded resistance t o tetracycline [tet(M), tet(W), tet(0) and tet(OIW)], erythromycin and clindamycin [erm(B)I and strep-tomycin [aph(E) and sat(3)l. Internal portions of some of these determinants were sequenced and found t o be identi-cal t o genes described in other bacteria. All resistance deter-minants were located on the bacterial chromosome, except for tet(M), which was identified o n plasmids in Lactococcus lactis. The contribution o f intrinsic multidrug transporters t o the antibiotic resistance was investigated by cloning and measuring the expression o f Bifidobacterium breve genes in L. /actis. Copyright O 2008 S. Karger A t, Base