Short communicationCharacterization of Escherichia coli O78 from an outbreak of septicemia in lambs in Norway
Introduction
The prevalence of the neonatal loss of lambs in Norwegian sheep husbandries were estimated to 3.3% in 2011 (Ringdal et al., 2011), which equals a loss of approximately 25,000 lambs. Infections caused by Escherichia coli, malnutrition, hypothermia and gastro intestinal diseases, are common causes of death in neonatal lambs.
E. coli are part of the intestinal microbiota in warm blooded animals and man and colonize the neonatal gut soon after birth. Although the majority of E. coli strains are commensals, some strains have the ability to cause disease. The categories of such pathogenic E. coli are divided into two major groups; the diarrhogenic E. coli (DEC) and the extraintestinal pathogenic E. coli (ExPEC). Septicemic E. coli within the ExPEC group are poorly defined regarding pathogenic traits.
A range of molecular and other typing methods are established for deciphering and recognizing pathogenic strains and for source attribution identification during outbreaks of E. coli infections. The resolution and applicability of the methods vary, and often a combination of typing methods is applied for a thorough investigation, serotyping, phylogenetic grouping, pulsed field gel electrophoresis (PFGE), and multi locus sequence typing (MLST).
Virulence factors in E. coli fall into five main categories; iron uptake systems, adhesins, capsular synthesis, invasins and toxins (Russo and Johnson, 2000). Several genes can encode a range of virulence factors within each category. The pangenome of E. coli consists of more than 17,000 unique genes, while individual E. coli genomes consist of about 5000 genes, of which 2000 are conserved and constitute the core genome (Touchon et al., 2009). This illustrates the genomic diversity of E. coli and allows for numerous combinations of virulence genes.
In 2008, a sheep flock on the west coast of Norway experienced neonatal losses due to septicemia. The sheep flock had no previous history of such infections. The lambs underwent post mortem examination and E. coli isolates were grown from internal organs. Little is hitherto known about strains of E. coli causing septicemia in neonatal lambs and the current study intends to characterize the E. coli from an outbreak of septicemia in a Norwegian sheep flock.
Section snippets
Outbreak description and isolation of bacteriological samples
In the spring of 2008, six neonatal lambs in one farm died of septicemia on the west coast of Norway. The sheep flock comprised of 230 ewes and had no known previous history of E. coli septicemia. Four of the septicemic lambs succumbed two to four days post-partum, and were observed paretic and moribund with opisthotonus prior to death. An additional two lambs died three weeks old (Supplementary data, Table S1). Bacterial samples were collected from viscera during post mortem examination.
Genotyping
All eight E. coli isolates from lamb 1–4 and the two isolates from lambs 5 and 6 had identical PTs, designated PT1. The ten controls had eight heterologous PTs, all of which differed from PT1. Of these ten controls, four strains with different PTs were included as controls. The identical PTs of the septicemic E. coli isolates revealed that the E. coli isolates had a clonal appearance, and indicated that the outbreak had a common source of infection. This is further supported by antibiotic
Discussion
In this study, E. coli isolates from an outbreak of septicemia in newborn lambs were shown to be one single clone, suggesting a common source of infection. The clone belonged to serogroup O78, which is frequently encountered as part of the intestinal microbiota of sheep and cattle (Hodgson, 1994). Serogroup O78 is however also the most prevalent serotype isolated from cases of septicemia in lambs, calves, piglets and poultry (Dassouli-Mrani-Belkebir et al., 1988). A survey from the south-west
Acknowledgement
Positive controls for cdtIII, cnf2 and f17b-A (strain no 1404) were kindly provided by Eric Oswald at Ecole Nationale Vétérinaire, Toulouse, France, while positive controls for PAI, traT, bmaE, fimH, kpsMTKI, kpsMTII and fyuA (Strain no FF1-78 and O101) were kindly provided by Toni Chapman at the Immunology and Molecular Diagnostic Research Unit, New South Wales Department of Primary Industries, Australia. This work was funded by the Research Council of Norway (project no. 190217/I10) and the
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