Localization of MtuA, an LraI homologue in Streptococcus uberis

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Abstract

Aims

To determine the localization of MtuA, an LraI lipoprotein within Streptococcus uberis and assess whether the protein was able to induce an antibody response capable of growth inhibition.

Methods and Results

Immunoblots and ELISAs were performed on S. uberis cell fractions to localize the protein. The strongest reactivity was within the membrane-enriched fraction. Electron micrographs also showed labelling consistent with a location within the membrane. Specific antibodies from both rabbits and calves were unable to inhibit the growth of S. uberis in milk. In addition, MtuA was not detectable in a whole-cell ELISA and whole bacterial cells were unable to adsorb specific antibodies from antiserum raised against MtuA.

Conclusions

The MtuA protein appears to be located within the cell membrane and is not on the bacterial surface and thus not available for interaction with potentially growth-inhibiting antibodies.

Significance and Impact of the Study

Unlike PsaA of S. pneumoniae and MtsA of S. pyogenes, MtuA of S. uberis does not appear to be located at the cell surface. Therefore, in contrast to studies with other similar proteins, MtuA is unlikely to be a good vaccine candidate.

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