Virulence related sequences; insights provided by comparative genomics of Streptococcus uberis of differing virulence

Abstract

BackgroundStreptococcus uberis, a Gram-positive, catalase-negative member of the family Streptococcaceae is an important environmental pathogen responsible for a significant proportion of subclinical and clinical bovine intramammary infections. Currently, the genome of only a single reference strain (0140J) has been described. Here we present a comparative analysis of complete draft genome sequences of an additional twelve S. uberis strains.ResultsPan and core genome analysis revealed the core genome common to all strains to be 1,550 genes in 1,509 orthologous clusters, complemented by 115-246 accessory genes present in one or more S. uberis strains but absent in the reference strain 0140J. Most of the previously predicted virulent genes were present in the core genome of all 13 strains but gene gain/loss was observed between the isolates in CDS associated with clustered regularly interspaced short palindromic repeats (CRISPRs), prophage and bacteriocin production. Experimental challenge experiments confirmed strain EF20 as non-virulent; only able to infect in a transient manner that did not result in clinical mastitis. Comparison of the genome sequence of EF20 with the validated virulent strain 0140J identified genes associated with virulence, however these did not relate clearly with clinical/non-clinical status of infection.ConclusionThe gain/loss of mobile genetic elements such as CRISPRs and prophage are a potential driving force for evolutionary change. This first “whole-genome” comparison of strains isolated from clinical vs non-clinical intramammary infections including the type virulent vs non-virulent strains did not identify simple gene gain/loss rules that readily explain, or be confidently associated with, differences in virulence. This suggests that a more complex dynamic determines infection potential and clinical outcome not simply gene content.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1512-6) contains supplementary material, which is available to authorized users.

Application of a Dot Blot Hybridization Platform to Assess Streptococcus uberis Population Structure in Dairy Herds

“…The virulence-related genes hasA (probe V7), hasC (V1), gapC (V2), oppF (V3), sua (V4), and pauA (V6) were present in most of the S. uberis tested causing recurring infections, suggesting their importance for efficient S. uberis colonization. The majority of isolates contained the genes hasC (V1) and hasA (V7), associated with hyaluronic capsule production, corresponding to the typical pattern of genes hasABC found in fully sequenced strains (Hossain et al, 2015). Nevertheless, in five isolates from Barcelos the hasA (probe V7) gene was not detected.…”

“…Efficient colonization and survival can also be attributed to the protein SUAM ( Streptococcus uberis adhesion molecule), which plays a role in adherence to the bovine mammary epithelial cells (Almeida et al, 2006); to the ability of this species to produce an hyaluronic acid capsule, which confers resistance to phagocytosis and desiccation in the environment (Ward et al, 2001; Field et al, 2003); and to a glyceraldehyde-3-phosphate dehydrogenase (GAPDH) able to bind host proteins and protect against reactive oxygen species (Reinoso et al, 2011). The first fully sequenced genome of S. uberis (strain 0140J) confirmed the presence of several genes consistent with an organism capable of surviving in several environmental niches (Ward et al, 2009) and opened the possibility of using comparative genomic analyses to identify further virulence factors (Hossain et al, 2015). …”

An update on environmental mastitis: Challenging perceptions

“…Strain‐specific virulence can be replicated in vivo (Hill, ; Tassi et al., ) and is associated with differences in uptake and killing by neutrophils or monocytes in vitro (Hill, ; Tassi et al., ). There is, however, no obvious association between outcome of infection and gene content (Hossain et al., ). Strain‐specific virulence has also been documented for E. faecium (Petersson‐Wolfe et al., ).…”

Symposium review: Intramammary infections—Major pathogens and strain-associated complexity

“…Within each of the major bovine IMI pathogen species, a diversity of strains and lineages (see Table 1) exists, each with a potentially unique repertoire of virulence factors and immune-stimulatory antigens (Budd et al, 2015;Hossain et al, 2015;Keane, 2016). Strain typing of E. coli, Strep.…”

“…uberis IMI has proven difficult to elucidate. Despite the differences between strain 0140J and EF20 in ability to induce IMI, whole-genome analysis of these strains, along with other strains associated with clinical and subclinical infection, failed to illuminate an obvious genetic reason for this difference (Hossain et al, 2015). Further research is required to reveal the virulence factors necessary for Strep.…”