The antibiotic susceptibility pattern of Listeria monocytogenes isolated from mixed vegetable salad collected in Permanent Site of Olabisi Onabanjo University, Ago-iwoye, Ogun state was investigated using standard microbiological standards. Twenty five (25) samples of mixed vegetable salad were purchased from eight (8) different locations. The total aerobic plate counts, total coliform count and total Listeria plate count were determined by the spread plate method on Nutrient Agar, MacConkey Agar and Brilliance Listeria Agar respectively. The antimicrobial susceptibility of the isolated Listeria spp. to antibiotics was determined by the disk diffusion method on Muellar Hinton Agar.
The mean aerobic plate count obtained from the samples was 4.63 x 105 cfu/g and ranged from 3.0 x 105 to 1.6 x 106 cfu/g. Also mean total coliform count obtained from the samples was 4.32 x 105 and ranged from 3.0 x 105 to 1.92 x 105 cfu/g. The mean count for total Listeria spp. count was 5.2 x 101 cfu/g and ranged from 3.0 x 101 cfu/g – 1.91 x 102 cfu/g.
A total of twenty four (24) isolates was recovered from the 25 samples of mixed salads examined, 20 (83.4) were positive for Listeria spp. out of which 10(41.7%) were positive for Listeria monocytogenes. All Listeria monocytogenes strains were susceptible to Gentamycin. However, there was 100% resistant to Thrimethoprim and Oxacillin. Listeria monocytogenes were susceptible to Vancomycin 10 (40%), Ampicillin 12(48%), and Amoxicillin 6 (24%). Resistant to Amoxicillin was encountered in 18(72%) which represent the highest resistant
The study recommended that vegetable handlers should make sure that fresh vegetables are transported and stored in hygienic condition. Consumers of fresh vegetables should ensure vegetables are in good condition before being prepared for food.