A-046. Dissemination of Bacitracin Resistance in Enterococcal Isolates

R. Matos, V. V. Pinto, M. S. Lopes;
ITQB/IBET, Oeiras, PORTUGAL.

The enterococci are part of the natural microbiota of the gastro-intestinal tract, being also found in other environments, such as food, sands and waters. During many years these microorganisms have been considered harmless to man, however, this vision has been changing, since they are now the second cause of cirurgical and urinary tract infections and the third cause of bacteremia. The antibiotic use as growth promoters in animal feeding was, together with its application in clinical therapy, one of the main responsible factors for the increase in infections caused by multiresistant enterococci. In 1999, bacitracin was banished from animal feeding by the EU, and had since been only used in therapy. Almost one decade later, enterococci of different origins had shown to be resistant to bacitracin, a polypeptidic antibiotic targeted at the bacterial cell wall-synthesis. In the present work, 58 enterococcal isolates with distinct MIC for bacitracin, were chosen from five different environments. Screening of the operon bcrABDR genes, responsible for bacitracin resistance in enterococci, revealed its dissemination in all environments, and its association with resistant phenotypes. Of the two mechanisms coded by this operon, the ABC transporter is the most disseminated. Undecaprenol-kinase appears associated with Enterococcus faecalis isolates from clinical origin and with HLBR phenotype. The regulator gene, bcrR, is not essential for the bacitracin resistance and when absent the operon are constitutively expressed. The bacitracin resistance genes were transferable by conjugation and are thus associated with mobile elements of the genome. The dissemination of these genes among different strains and environments becomes thus expectable.