Characterisation of avian isolates of Staphylococcus aureus
The main part of the work was to develop PCR techniques for identification and typing of avian S. aureus. Different primer sets were applied in order to generate reproducible profiles of the PCR amplimers. Of the 86 avian S. aureus studied, 12, 7, 4 and 5 groups were recognised by the use of ribosomal, REP, coagulase gene and protein A gene primers respectively. PCR-ribotyping (method 1) produced a relatively simple pattern which was used for rapid identification of these isolates and for differentiation of these isolates from each other. These PCR fingerprinting methods were simple to perform and reproducible. The majority (80%) of the strains even from different geographical locations had similar “typical avian” profiles whereas 20% had atypical avian profiles. Results showed that many of the virulence factors characterised in this study in avian S. aureus were likely to be regulated by the agr and sar loci. Sequencing of the agrD region in selected strains suggested that 80% of avian (typical avian) isolates belonged to agr specificity group II and the other (20%) (atypical avian) stains belonged to agr specificity groups I or III. An investigation by multiplex PCR for eight toxin genes (encoding enterotoxins A-E, exfoliative toxins A-B and toxic shock syndrome toxin-1) revealed that only 5% of the avian isolates produced one or more of these toxin genes and all were atypical by other criteria. A multiplex PCR developed to detect haemolysin (a, g and d) genes showed that all the 86 avian S. aureus isolates had the a and d-haemolysin genes and a majority (86%) of the strains also had the g-haemolysin gene. Many of those that lacked the g-haemolysin gene were atypical by other criteria. Only 5% of the avian S. aureus strains possessed the b-haemolysin gene and, again, these isolates were atypical by other criteria.