Twenty-four hour isolation and confirmation of Bacillus cereus in foods

An existing Bacillus cereus isolation medium (PEMBA composed of polymyxin, pyruvate, egg yolk, mannitol, bromthymol blue and agar) has been modified and its comparative performance evaluated. Bromthymol blue was replaced with bromcresol purple, hence the new medium was designated PEMPA. The advantage of this modification was decreased incubation time (from 48 h to 22 h) and an increased ability to recognize presumptive isolates. Recoveries of 20 reference strains of B. cereus inoculated into rice and tested on three selective media (PEMPA, PEMBA and MYP composed of mannitol, egg yolk and polymyxin) compared favorably. Additionally, quantitation of B. cereus from 23 naturally contaminated foods on MYP, PEMBA and PEMPA, and from 39 naturally contaminated foods on PEMBA and PEMPA gave comparable results.