ant(6)-I Genes Encoding Aminoglycoside O-Nucleotidyltransferases Are Widely Spread Among Streptomycin Resistant Strains of Campylobacter jejuni and Campylobacter coli

Abstract

Thermotolerant <i>Campylobacter</i> species <i>C. jejuni</i> and <i>C. coli</i> are actually recognized as the major bacterial agent responsible for food-transmitted gastroenteritis. The most effective antimicrobials against <i>Campylobacter</i> are macrolides and some, but not all aminoglycosides. Among these, susceptibility to streptomycin is reduced by mutations in the ribosomal RPSL protein or by expression of ANT(6)-I aminoglycoside O-nucleotidyltransferases. The presence of streptomycin resistance genes was evaluated among streptomycin-resistant <i>Campylobacter</i> isolated from humans and animals by using PCR with degenerated primers devised to distinguish <i>ant(6)-Ia</i>, <i>ant(6)-Ib</i> and other <i>ant</i>-like genes. Genes encoding ANT(6)-I enzymes were found in all possible combinations with a major fraction of the isolates carrying a previously described <i>ant</i>-like gene, distantly related and belonging to the new <i>ant(6)-I</i> sub-family <i>ant(6)-Ie</i>. Among <i>Campylobacter</i> isolates, <i>ant(6)-Ie</i> was uniquely found functional in <i>C. coli</i>, as shown by gene transfer and phenotype expression in <i>Escherichia coli</i>, unlike detected coding sequences in <i>C. jejuni</i> that were truncated by an internal frame shift associated to RPSL mutations in streptomycin resistant strains. The genetic relationships of <i>C. coli</i> isolates with ANT(6)-Ie revealed one cluster of strains presented in bovine and humans, suggesting a circulation pathway of <i>Campylobacter</i> strains by consuming contaminated calf meat by bacteria expressing this streptomycin resistance element.