Elsevier

Veterinary Microbiology

Volume 166, Issues 1–2, 27 September 2013, Pages 276-280
Veterinary Microbiology

Short communication
Characterization of Escherichia coli O78 from an outbreak of septicemia in lambs in Norway

https://doi.org/10.1016/j.vetmic.2013.05.004Get rights and content

Abstract

The aim of the study was to characterize isolates of Escherichia coli from an outbreak of septicemia in a Norwegian sheep flock in 2008 with emphasis on virulence, serological grouping, phylogenicity and homology. Six E. coli isolates from succumbed neonatal lambs and four E. coli isolates collected from healthy individuals were analyzed by Pulsed-Field Gel Electrophoresis (PFGE), miniaturized microarray, and polymerase chain reaction (PCR). The septicemic E. coli isolates showed identical pulsotypes (PTs), and belonged to serogroup O78, phylogenetic group A, and MLST ST 369. The virulence genes f17G, bmaE, afaE-VIII, ireA, iroN and iss were detected in the septicemic isolates. The results showed that the E. coli isolates from the septicemic outbreak had a clonal appearance, thus likely originating from a common source. The clone carried genes important for virulence, however, a significant explanation for the high pathogenicity was not revealed.

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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