Occurrence of weak mutators among avian pathogenic Escherichia coli (APEC) isolates causing salpingitis and peritonitis in broiler breeders.
A collection of 46 avian pathogenic Escherichia coli (APEC) isolates was examined for the presence of mutators by determining the rate of mutation to rifampicin resistance. The collection included 34 E. coli isolates obtained in pure culture from chronic lesions of salpingitis and peritonitis in 34 broiler breeders, of which 12 were associated with the development of secondary septicemia. Twelve additional isolates were obtained from a clonal outbreak (ST95) of E. coli peritonitis syndrome (EPS), the lesions of which changed gradually over time into a subacute/chronic form. The hypothesis of the present study was that mutation rates would be higher for chronic infection isolates than for isolates from acute infections/exacerbations. The distribution of mutation rates followed a pattern similar to that found for other clinical isolates of E. coli, with a modal/median value of 1.47 × 10(-8). Of the 46 isolates, 24% (n=11) were weakly hypermutable (2.00 × 10(-8) ≤ μ<2.00 × 10(-7)), however, no strong mutators were detected (μ ≥ 2.00 × 10(-7)). Chronic salpingitis isolates had the highest proportion (45%, P=0.001) of weak mutators and also, significantly higher mutation rates (P=0.003) compared to isolates that caused septicemia (4%). In addition, mutation rates were significantly lower among ST95 isolates (P<0.0005), and among isolates from the same clonal group as ST95 (P=0.027), when compared to isolates from other groups. Although a clear association with the time phase of infection (as lesions of EPS became more chronic) could not be observed (ρ=0.523, P=0.081), a higher frequency of weak mutators among chronic infection isolates suggests that increased mutation rates play a role in adaptation of APEC to long-term persistence in an infected host environment.
Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Stigbøjlen 4, 1870 Frederiksberg, Denmark. Electronic address: tpiresantos@life.ku.dk.
Teresa
T
Pires-dos-Santos
Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Stigbøjlen 4, 1870 Frederiksberg, Denmark.
Magne
M
Bisgaard
Danish Health and Medicines Authorities, Danish Medicines Agency, University of Copenhagen, Denmark.
Niels
N
Kyvsgaard
Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Stigbøjlen 4, 1870 Frederiksberg, Denmark.
Henrik
H
Christensen
D000818:Animals; D002645:Chickens; D002908:Chronic Disease; D024881:Drug Resistance, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics*; D004927:Escherichia coli Infections / Q000382:microbiology / Q000662:veterinary*; D005260:Female; D009154:Mutation / Q000235:genetics; D059645:Mutation Rate; D010538:Peritonitis / Q000382:microbiology / Q000662:veterinary*; D011201:Poultry Diseases / Q000382:microbiology*; D012488:Salpingitis / Q000382:microbiology / Q000662:veterinary*
Avian pathogenic Escherichia coli (APEC); Broiler breeders; Mutation rates; Salpingitis; Weak mutators