The Hyaluronic Acid Capsule of Streptococcus uberis Is Not Required for the Development of Infection and Clinical Mastitis

Abstract

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. The virulence of a mutant strain of S. uberis (TRF0-6) that lacked the ability to produce a hyaluronic acid capsule due to an insertion within its single copy of hasA ( ) was compared to that of the capsular parental strain (0140J). Strains TRF0-6 and 0140J infected all mammary gland quarters following experimental challenge. The wild type and the mutant induced overt signs of disease in four out of four and in six out of eight mammary gland quarters, respectively. Both the wild type and the hasA mutant were resistant to killing by bovine neutrophils following cultivation in bovine milk. The ability to withstand the bactericidal action of neutrophils following growth in milk was therefore independent of the capsule and coincided with the ability of supernatants from such cultures to prevent the bactericidal action of neutrophils. This investigation revealed that, in the absence of the capsule, S. uberis is able to withstand the bactericidal effect of bovine neutrophils and induce mastitis in dairy cows.

Application of Streptococcus uberis Multilocus Sequence Typing: Analysis of the Population Structure Detected among Environmental and Bovine Isolates from New Zealand and the United Kingdom

“…Previous analysis of the 160 United Kingdom isolates (which were all milk isolates) had shown a correlation between hasA carriage and clinical mastitis (4), in line with a previous study of Danish isolates (7). For comparison, we analyzed the hasA carriage of the 77 New Zealand milk isolates relative to the disease status of the cows (Table 6).…”

“…The significance of hasA gene carriage is unclear. The presence of capsule is not thought to play a direct role in pathogenicity, since mutation of hasA did not reduce pathogenicity in experimental infections (7). In addition, a few clinical isolates are hasA-negative.…”

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

“…The ability to produce mutations at random within S. uberis has been exploited for identification of genes responsible for capsulation (48) and has enabled the role of capsule to be investigated in vivo in the target species (11). A mutant strain that was unable to utilize specific tri-and oligopeptides as sources of essential amino acids due to an insertion within oppF (encoding an ATPase associated with the oligopeptide permease operon of S. uberis) was found to grow poorly in milk compared to its isogenic parent (42).…”

The Activation of Bovine Plasminogen by PauA Is Not Required for Virulence of Streptococcus uberis

“…The plasmid was cured from PauA mutants by repeated subculturing at 28°C and analysis for loss of erythromycin resistance at 37°C, as described previously (5,19) for other mutants of S. uberis. All subsequent analyses were performed with a cured derivative of a single pauA mutant, PNW-001.…”

“…The protocol used was that reported previously for analysis of a hasA mutant of S. uberis (5). In brief, approximately 10 3 CFU of each strain in 1 ml of pyrogen-free saline was infused into the mammary gland after the evening milking through the teat duct.…”