Abstract:
BACKGROUND : Coagulase-negative staphylococci (CoNS) are among the leading bacterial causes of bovine mastitis
in many dairy-producing countries. Among the challenges associated with the specific diagnosis of CoNS infections
is the biochemical heterogeneity of the species in the genus and the unavailability of accurate, cost-effective and
up-to-date diagnostic tests. A previous study investigating the diversity of CoNS associated with cases of bovine
mastitis in South Africa, resulted in six CoNS isolates which could not be identified despite the use of a
combination of different molecular assays. The identification and characterisation of the isolates was pursued
further in this study.
RESULTS : The six CoNS isolates in question were identified by sequencing multiple housekeeping genes (dnaJ,
hsp60, rpoB, 16S rRNA) and characterized through the use of matrix-assisted laser/desorption ionization time of
flight mass spectrometry (MALDI-TOF MS) and the Biolog GEN III Microplate™ bacterial identification system.
Sequencing of housekeeping genes identified the isolates as S. devriesei. This Staphylococcus species was only
described in 2010 and this is the first report documenting the isolation of S. devriesei from cases of bovine IMIs in
South Africa. Analysis of mass spectra generated by the six isolates showed intra-species variation which was also
observed when evaluating the metabolic profiles of the isolates using the Biolog GEN III system. Neither the MALDITOF
MS nor the Biolog database are currently populated with data relating to S. devriesei, resulting in the isolates
not being identified, in the case of MALDI-TOF MS analysis, or mis-identified as was observed with the Biolog GEN
III system.
CONCLUSIONS : The phenotyping data collected during this investigation provides useful information concerning
Staphylococcus devriesei which could be used to populate user system databases thereby ensuring the accurate
identification of isolates in future. The availability of improved diagnostics will in turn facilitate studies to elucidate
the epidemiology, pathogenicity and true prevalence of this species in dairy herds.
