A 3-year long study of Staphylococcus aureus isolates from subclinical mastitis in three Azawak zebu herds at the Sahelian experimental farm of Toukounous, Niger

bovine mastitis. The aim of the present work was to follow in three herds and
during the 3 years the clonality of S. aureus isolated from California Mastitis
Test (CMT)-positive cows at the experimental station of Toukounous (Niger)
by (i) comparing their pulsed field gel electrophoresis (PFGE) fingerprints, (ii)
identifying their virulotypes by PCR amplification and (iii) assessing the
production of capsule and the formation of biofilm. The 88 S. aureus isolates
belonged to 14 different pulsotypes, 3 of them being predominant: A (30 %),
D (27 %), B (15 %). A and B pulsotypes had the highest profile similarity
coefficient (94 %), while others had similarity coefficients under 60 %.
Seventy-five S. aureus isolates were further studied for their virulotypes,
capsular antigens and biofilm production. Most surface factor-, leukocidin- and
haemolysin-, but not the enterotoxin-encoding genes were detected in the
majority (>75 %) of the isolates and were evenly distributed between the A, B
and D pulsotype isolates. The majority of the 72 S. aureus positive with the
cap5H or cap8H PCR produced the CP5 (82 %) or the CP8 (88 %) capsular
antigen, respectively. Biofilm production by the 57 icaA-positive isolates was
strong for 8 isolates, moderate for 31 isolates but weak for 18 isolates,
implying that the icaA gene may not be expressed in vitro by one third of the
positive isolates. Similar to other studies, those results confirm that a
restricted number of S. aureus clones circulate within the three herds at
Toukounous and that their specific virulence-associated properties must still be
further studied