Research – Evaluation of ceftazidime as an antibiotic supplement of mannitol-yolk-polymyxin B agar used for the enumeration of Bacillus cereus in ready-to-eat vegetables

Journal of Food Protection


Bacillus cereus, which causes foodborne disease, is detected using selective media. However, competing flora is the most common factor preventing the correct enumeration of B. cereus on selective agars. In this study, we aimed to improve the selectivity of mannitol-yolk-polymyxin B agar (MYPA) and its modified version containing trimethoprim (mMYPA) developed in our previous study by supplementation with ceftazidime (16 μg/mL). Ceftazidime-supplemented MYPA (C-MYPA16) and mMYPA (C-mMYPA16) were evaluated for bacteria recoverability and selectivity using three types of ready-to-eat vegetables. Four B. cereus and one B. thuringiensis strains were mixed and artificially inoculated into vegetable salad, radish sprouts, and sprout mix, and then recovered using MYPA, mMYPA, C-MYPA16, and C-mMYPA16. In all tested vegetables, mMYPA, C-MYPA16, and C-mMYPA16 exhibited similar recoverability of B. cereus / thuringiensis ( p > 0.05), whereas MYPA showed undistinguishable colonies in case of radish sprouts and sprout mix. At the same time, C-mMYPA16 provided the best selectivity compared with the other agars because it eliminated most of competing flora in the tested vegetables, especially in sprouts, without negatively affecting the recovery of B. cereus / thuringiensis . Our results indicate that the supplementation of mMYPA with ceftazidime may improve medium selectivity for B. cereus / thuringiensis in food testing.

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