First detection of infectious spleen and kidney necrosis virus (ISKNV) associated with massive mortalities in farmed tilapia in Africa.

In late 2018, unusual patterns of very high mortality (>50% production) were reported in intensive tilapia cage culture systems across Lake Volta in Ghana. Samples of fish and fry were collected and analysed from two affected farms between October 2018 and February 2019. Affected fish showed darkening, erratic swimming and abdominal distension with associated ascites.

Vru (Sub0144) controls expression of proven and putative virulence determinants and alters the ability of Streptococcus uberis to cause disease in dairy cattle.

The regulation and control of gene expression in response to differing environmental stimuli is crucial for successful pathogen adaptation and persistence. The regulatory gene vru of Streptococcus uberis encodes a stand-alone response regulator with similarity to the Mga of group A Streptococcus. Mga controls expression of a number of important virulence determinants.

Identification of motifs of Burkholderia pseudomallei BimA required for intracellular motility, actin binding, and actin polymerization.

Actin-based motility of the melioidosis pathogen Burkholderia pseudomallei requires BimA (Burkholderia intracellular motility A). The mechanism by which BimA mediates actin assembly at the bacterial pole is ill-defined. Toward an understanding of the regions of B.

Actin-based motility of Burkholderia thailandensis requires a central acidic domain of BimA that recruits and activates the cellular Arp2/3 complex.

Burkholderia species use BimA for intracellular actin-based motility. Uniquely, Burkholderia thailandensis BimA harbors a central and acidic (CA) domain. The CA domain was required for actin-based motility, binding to the cellular Arp2/3 complex, and Arp2/3-dependent polymerization of actin monomers.

Sortase anchored proteins of Streptococcus uberis play major roles in the pathogenesis of bovine mastitis in dairy cattle.

Streptococcus uberis, strain 0140J, contains a single copy sortase A (srtA), encoding a transamidase capable of covalently anchoring specific proteins to peptidoglycan. Unlike the wild-type, an isogenic mutant carrying an inactivating ISS1 insertion within srtA was only able to infect the bovine mammary gland in a transient fashion. For the first 24 h post challenge, the srtA mutant colonised at a similar rate and number to the wild type strain, but unlike the wild type did not subsequently colonise in higher numbers.

Evidence for niche adaptation in the genome of the bovine pathogen Streptococcus uberis.

Background: Streptococcus uberis, a Gram positive bacterial pathogen responsible for a significant proportion of bovine mastitis in commercial dairy herds, colonises multiple body sites of the cow including the gut, genital tract and mammary gland. Comparative analysis of the complete genome sequence of S. uberis strain 0140J was undertaken to help elucidate the biology of this effective bovine pathogen.

Identification of multiple linear epitopes of the plasminogen activator A (PauA) of Streptococcus uberis with murine monoclonal antibodies.

Streptococcus (S.) uberis is a common cause of mastitis in cattle. A protein (PauA) secreted by this bacterium is capable of activating plasminogen from sheep and cattle.

Complex interactions between bovine plasminogen and streptococcal plasminogen activator PauA.

The interactions between bovine plasminogen and the streptococcal plasminogen activator PauA that culminate in the generation of plasmin are not fully understood. Formation of an equimolar activation complex comprising PauA and plasminogen by non-proteolytic means is a prerequisite to the recruitment of substrate plasminogen; however the determinants that facilitate these interactions have yet to be defined. A mutagenesis strategy comprising nested deletions and random point substitutions indicated roles for both amino and carboxyl-terminal regions of PauA and identified further essential residues within the alpha domain of the plasminogen activator.

The activation of bovine plasminogen by PauA is not required for virulence of Streptococcus uberis.

A mutant of Streptococcus uberis carrying a single copy of ISS1 within pauA was unable to activate bovine plasminogen. Contrary to a hypothesis postulated previously, this mutation did not alter the ability of the bacterium to grow in milk or to infect the lactating bovine mammary gland.

MtuA, a lipoprotein receptor antigen from Streptococcus uberis, is responsible for acquisition of manganese during growth in milk and is essential for infection of the lactating bovine mammary gland.

A mutant strain of Streptococcus uberis (AJS001) that was unable to grow in bovine milk was isolated following random insertional mutagenesis. The level of growth in milk was restored to that of the parental strain (strain 0140J) following addition of MnSO(4) but not following addition of other metal ions. The mutant contained a single insertion within mtuA, a homologue of mtsA and psaA, which encode metal-binding proteins in Streptococcus pyogenes and Streptococcus pneumoniae, respectively.

The hyaluronic acid capsule of Streptococcus uberis is not required for the development of infection and clinical mastitis.

The frequency at which the genes responsible for capsule biosynthesis occurred in field isolates of Streptococcus uberis was determined. Of the two genotypes detected (hasABC and hasC), the capsular genotype (hasABC) was more common. This genotype was present at a higher frequency in a population isolated from mastitis cases than in a population isolated from cattle bedding.