Genomic and Phenomic Study of Mammary Pathogenic Escherichia coli.

Shlomo E Blum,Nir Edery,Gabriel Leitner,Daniel Elad,Shlomo Sela,Elimelech D Heller,Chitrita Debroy

doi:10.1371/journal.pone.0136387

Shlomo E Blum, Nir Edery + Show 5 more

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https://doi.org/10.1371/journal.pone.0136387

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Abstract

Escherichia coli is a major etiological agent of intra-mammary infections (IMI) in cows, leading to acute mastitis and causing great economic losses in dairy production worldwide. Particular strains cause persistent IMI, leading to recurrent mastitis. Virulence factors of mammary pathogenic E. coli (MPEC) involved pathogenesis of mastitis as well as those differentiating strains causing acute or persistent mastitis are largely unknown. This study aimed to identify virulence markers in MPEC through whole genome and phenome comparative analysis. MPEC strains causing acute (VL2874 and P4) or persistent (VL2732) mastitis were compared to an environmental strain (K71) and to the genomes of strains representing different E. coli pathotypes. Intra-mammary challenge in mice confirmed experimentally that the strains studied here have different pathogenic potential, and that the environmental strain K71 is non-pathogenic in the mammary gland. Analysis of whole genome sequences and predicted proteomes revealed high similarity among MPEC, whereas MPEC significantly differed from the non-mammary pathogenic strain K71, and from E. coli genomes from other pathotypes. Functional features identified in MPEC genomes and lacking in the non-mammary pathogenic strain were associated with synthesis of lipopolysaccharide and other membrane antigens, ferric-dicitrate iron acquisition and sugars metabolism. Features associated with cytotoxicity or intra-cellular survival were found specifically in the genomes of strains from severe and acute (VL2874) or persistent (VL2732) mastitis, respectively. MPEC genomes were relatively similar to strain K-12, which was subsequently shown here to be possibly pathogenic in the mammary gland. Phenome analysis showed that the persistent MPEC was the most versatile in terms of nutrients metabolized and acute MPEC the least. Among phenotypes unique to MPEC compared to the non-mammary pathogenic strain were uric acid and D-serine metabolism. This study reveals virulence factors and phenotypic characteristics of MPEC that may play a role in pathogenesis of E. coli mastitis.

Highlights

Mastitis, the inflammation of the mammary gland, is one of the most economically important diseases affecting dairy production [1,2]
Published E. coli genomes used for intra-species genomic comparisons were selected to represented different E. coli pathotypes, namely avian pathogenic E. coli (APEC), uropathogenic E. coli (UPEC); neonatal meningitis E. coli (NMEC), enteropathogenic E. coli (EPEC), enterohemorrhagic E. coli (EHEC), adherent-invasive E. coli (AIEC), enteroaggregative E. coli (EAEC), enteroinvasive E. coli (EIEC), enterotoxigenic E. coli (ETEC) and Shigella spp
The murine model of intra-mammary infection has been widely used for the research of pathogenesis, immune response, treatment and prevention of mastitis, but only in a few instances it was used for comparison between the pathogenicity of different strains of the same pathogen species [47]

Summary

Introduction

The inflammation of the mammary gland, is one of the most economically important diseases affecting dairy production [1,2]. Economic losses directly caused by mastitis in dairy farms include treatment expenses, lower milk yield and value, and culling of severely affected animals. Bovine mastitis is typically caused by infection of the mammary gland by pathogenic microorganisms present in the environment, skin or teat apex of dairy animals. In many cases, there are long term detrimental effects on mammary gland health and milk quality following an episode of E. coli mastitis, and in some cases the mammary gland does not fully recover [7]. Persistent E. coli infections in the mammary gland causing recurrent episodes of mastitis have long been documented [8]. Persistent infections may represent about 4.8% of clinical cases of E. coli mastitis [9], and are being increasingly recognized [5,7,10,11]

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