Abstract
Escherichia coli is an important cause of bovine mastitis and can cause both severe inflammation with a short-term transient infection, as well as less severe, but more chronic inflammation and infection persistence. E. coli is a highly diverse organism that has been classified into a number of different pathotypes or pathovars, and mammary pathogenic E. coli (MPEC) has been proposed as a new such pathotype. The purpose of this study was to use genome sequence data derived from both transient and persistent MPEC isolates (two isolates of each phenotype) to construct a genome-based phylogeny that places MPEC in its phylogenetic context with other E. coli pathovars. A subsidiary goal was to conduct comparative genomic analyses of these MPEC isolates with other E. coli pathovars to provide a preliminary perspective on loci that might be correlated with the MPEC phenotype. Both concatenated and consensus tree phylogenies did not support MPEC monophyly or the monophyly of either transient or persistent phenotypes. Three of the MPEC isolates (ECA-727, ECC-Z, and ECA-O157) originated from within the predominately commensal clade of E. coli, referred to as phylogroup A. The fourth MPEC isolate, of the persistent phenotype (ECC-1470), was sister group to an isolate of ETEC, falling within the E. coli B1 clade. This suggests that the MPEC phenotype has arisen on numerous independent occasions and that this has often, although not invariably, occurred from commensal ancestry. Examination of the genes present in the MPEC strains relative to the commensal strains identified a consistent presence of the type VI secretion system (T6SS) in the MPEC strains, with only occasional representation in commensal strains, suggesting that T6SS may be associated with MPEC pathogenesis and/or as an inter-bacterial competitive attribute and therefore could represent a useful target to explore for the development of MPEC specific inhibitors.
Highlights
Dairy cattle mastitis, or inflammation of the mammary gland, is the dominant bovine health disorder affecting milk production worldwide, with reported annual losses exceeding two billion dollars in the United States dairy industry [1,2,3]
E. coli is a highly diverse organism that has been classified into a number of different pathotypes or pathovars, including adherent-invasive E. coli (AIEC), avian pathogenic E. coli (APEC), enteroaggregative E. coli (EAEC), enterohemorrageic E. coli (EHEC), enteropathogenic E. coli (EPEC), enterotoxigenic E. coli (ETEC), extra-intestinal pathogenic E. coli (ExPEC), and uropathogenic E. coli (UPEC)
We have developed a collection of E. coli isolates that can be divided into two distinct groups: those isolated from intramammary infections (IMI) displaying transient infection characteristics and those isolated from IMI associated with persistently infected mammary glands
Summary
Inflammation of the mammary gland, is the dominant bovine health disorder affecting milk production worldwide, with reported annual losses exceeding two billion dollars in the United States dairy industry [1,2,3]. There is no published E. coli phylogeny that includes MPEC isolates in a comparative dataset that encompasses representative isolates of the various E. coli pathovars. There are studies involving MPEC isolates that employ a PCR based test [12] to assess E. coli phylogroup membership, this is not a phylogenetic analysis, and provides no information on relative relationships of the isolates within each phylogroup. This PCR based test has been shown to provide unreliable designations for certain phylogroups [13], and in particular, that group (phylogroup A) to which MPEC isolates are most typically assigned
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