d-Haemolysin assay. TheS.aureusaccessorygeneregulator (agr) activity was measured by d-haemolysin production on Trypticase soy agar containing 5 % sheep blood using S. aureus strain RN4220, as described previously (Traber et al., 2008). Evidence of enhanced haemolysis between RN4220 and a test isolate was considered positive for d-haemolysin production. Repression of agr was defined as an absence of d-haemolysin production.