Antimicrobial resistance in veal calves in the Netherlands occurs frequently. The way this resistance arises and the mechanisms of resistance present are mostly unknown. In his thesis Joost Hordijk determined the prevalence and resistance mechanisms of quinolone resistance and resistance to Extended Spectrum Cephalosporins (ESC). Both antimicrobial classes are considered to be of critical importance for humans, but are also used in animals. Resistance to these antimicrobial classes may cause therapeutic failure.
Of all fecal samples collected for monitoring of antimicrobial resistance, 14% harbored E. coli resistant to quinolones. Resistance to quinolones is caused by either alteration or protection of the drug target. From these resistant E. coli, all isolates harbored one or more mutations in the gyrA gene. Furthermore, approximately 50% of the resistant isolates harbored additional mutations in the parC and/or parE gene. Resistance due to these mutations can only be spread by cell division. In veal calves, the first quinolone resistance gene that can potentially be transferred directly between bacteria was found in 2009. Transferrable resistance genes have the potential to spread relatively fast. However, this was not observed for qnr genes in veal calves.
Resistance to ESC is mainly caused by Extended Spectrum ß-lactamases (ESBL) or AmpC ß-lactamases. These are enzymes that degenerate ß-lactam antimicrobials (penicillins, cephalosporins). ESBL/AmpC’s are often located on plasmids and are therefore transferrable between bacteria. In a retrospective study from 1997 to 2010 it was shown that the prevalence of ESBL/AmpC producing E. coli increased. The prevalence varied greatly between farms, but also within farms the prevalence of different ESBL/AmpC genes varied greatly in time.
28 februari 2013 om 12.45 uur, Academiegebouw Utrecht
Promotor 1: Prof.dr. D.J. Mevius, Promotor 2: Prof.dr. J.A. Wagenaar
Titel proefschrift Joost Hordijk: Quinolone resistance and ESBL/AmpC’s in commensal Escherichia coli in veal calves