Acquired antibiotic resistance in lactic acid bacteria from food

Acquired antibiotic resistance, i.e. resistance genes located on conjugativ e or mobilizable plasmids and transposons can be found in species living in habitats (e.g. human and animal intestines) which are regularly challenged with antibiotics. Most data are available for enterococci and enteric lact obacilli. Raw material from animals (milk and meat) which are inadvertantly contaminated with fecal matters during production will carry antibiotic re sistant lactic acid bacteria into the final fermented products such as raw milk cheeses and raw sausages. The discovered conjugative genetic elements of LAB isolated from animals and food are very similar to elements studied previously in pathogenic streptococci and enterococci, e.g. theta-type repl icating plasmids of the pAM beta 1, pIP501-family, and transposons of the T n916-type. Observed resistance genes include known genes like tetM, ermAM, cat, sat and vanA. A composite 29'871 bp resistance plasmid detected in Lac tococcus lactis subsp. lactis isolated from a raw milk soft cheese contains tetS previously described in Listeria monocytogenes, cat and str from Stap hylococcus aureus. Three out of five IS elements on the plasmid are almost or completely identical to IS1216 present in the vanA resistance transposon Tn1546. These data support the view that in antibiotic challenged habitats lactic acid bacteria like other bacteria participate in the communication systems which transfer resistance traits over species and genus borders. Th e prevalence of such bacteria with acquired resistances like enterococci is high in animals (and humans) which are regularly treated with antibiotics. The transfer of antibiotic resistant bacteria from animals into fermented and other food can be avoided if the raw substrate milk or meat is pasteuri zed or heat treated. Antibiotic resistance traits as selectable markers in genetic modification of lactic acid bacteria for different purposes are pre sently being replaced, e.g. by metabolic traits to generate food-grade vect ors.