The pure colonies isolated from the horse blood agar plates tested for oxidase reduction (oxidase strips, Fort Richards, Auckland), indicated by a purple colouration, were transferred to 1 mL of 2% (weight/volume) Chelex solution (Sigma-Aldrich) in distilled water and boiled at 100°C on heating blocks for 10 minutes. These were then cooled to room temperature, centrifuged at 13,000 rpm for 10 minutes and the supernatants were collected in fresh sterile eppendorf tubes and stored at -20°C