Abstract
Thermotolerant Campylobacter species C. jejuni and C. coli are actually recognized as the major bacterial agent responsible for food-transmitted gastroenteritis. The most effective antimicrobials against Campylobacter 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 Campylobacter isolated from humans and animals by using PCR with degenerated primers devised to distinguish ant(6)-Ia, ant(6)-Ib and other ant-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 ant-like gene, distantly related and belonging to the new ant(6)-I sub-family ant(6)-Ie. Among Campylobacter isolates, ant(6)-Ie was uniquely found functional in C. coli, as shown by gene transfer and phenotype expression in Escherichia coli, unlike detected coding sequences in C. jejuni that were truncated by an internal frame shift associated to RPSL mutations in streptomycin resistant strains. The genetic relationships of C. coli isolates with ANT(6)-Ie revealed one cluster of strains presented in bovine and humans, suggesting a circulation pathway of Campylobacter strains by consuming contaminated calf meat by bacteria expressing this streptomycin resistance element.
Highlights
Campylobacteriosis is the main cause of foodborne diseases in the UE and in the United States [Collective Eurosurveillance Editorial Team, 2015; (Accessed March 2018)1]
The minimal inhibitory concentrations (MICs) for STR, ERY, gentamicin (GEN), CIP, and tetracycline (TET) were determined by agar dilution methods according to the guidelines of CLSI (Clinical and Laboratory Standards Institute [CLSI], 2010), including Campylobacter jejuni ATCC 33560 as the reference strain
Resistance was determined according to the EUCAST2, by using cut-off values [ecological cut-off value (ECOFF)] of 4 mg/L for STR, 4 mg/L (C. jejuni) or 8 mg/L (C. coli) for ERY, 2 mg/L for GEN, 0.5 mg/L for CIP, and 1 mg/L (C. jejuni) or 2 mg/L (C. coli) for TET
Summary
Campylobacteriosis is the main cause of foodborne diseases in the UE and in the United States [Collective Eurosurveillance Editorial Team, 2015; (Accessed March 2018)1]. Aminoglycosides, the third class of antimicrobials used worldwide after sulfonamides and beta-lactams, are a recommended alternative for the treatment of difficult infections caused by thermotolerant Campylobacter spp. The advantages of using aminoglycosides compared to other antimicrobials are their concentration-dependent bactericidal activity and relatively predictable pharmacokinetics, and synergism with other antibiotics (Vakulenko and Mobashery, 2003). When antibiotic resistance appears it is due to target modification of ribosomal components, antimicrobial modification, or lowering drug accumulation in the cell (Vakulenko and Mobashery, 2003). Mutation K43R of S12 protein, a component of the 30S ribosomal subunit encoded by the rpsL gene, confers high-level of STR resistance in Campylobacter (Olkkola et al, 2010). An additional role in STR resistance of ANT-like protein has been suggested in C. coli (Olkkola et al, 2016)
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