Detection of Non-Aureus Staphylococci and Mammaliicocci from Ready-To-Eat Food Retailed in Lagos, Nigeria

Abstract

Non-aureus staphylococci (NAS) and mammalicocci (collectively NASM) are coagulase-negative staphylococci, though they are less well-known than Staphylococcus aureus . Certain species within the NASM group have been associated with foodborne illnesses due to their ability to produce enterotoxins that are similar to those produced by S. aureus . In this study, 180 samples of ready-to-eat foods were examined, including 30 samples each of soybean cheese, cow milk cheese, yogurt, and meat pie, along with 60 samples of mixed vegetables. Isolation of the bacteria was performed using selective culture media technique, followed by biochemical testing, including a coagulase test. The taxonomic characterization of NASM was carried out using 16S rRNA gene sequencing, and antibiotic susceptibility was done using the Kirby-Bauer disk diffusion method. Of the total samples examined, 133 exhibited bacterial growth on Mannitol Salt Agar. This included samples of soybean 27 (15%), cow milk cheese 30 (16.67%), mixed vegetables 39 (21.67%), yogurt 27 (15%), and meat pie 10 (5.56%). Among these isolates, 20 (15.037%) displayed nonpigmented characteristic growth on nutrient agar and were subsequently subjected to biochemical testing. Specifically,9 (45%) of the isolates were identified as M. sciuri , 2 (10%) as S. edaphicus , 3 (15%) as S. arlettae , 1 (5%) as S. hominis , 2 (10%) as S. gallinarum , and 3 (15%) as S. ureilyticus. Approximately 90% of the isolates showed resistance to three or more antibiotics, with isolates 11, 16, and 21 showing resistance to five or more antibiotics. The result indicated M. scuiri as a frequent contributor to ready-to-eat food contamination, and three of the strains showed multidrug resistance. Although the risk of foodborne illness may be relatively low in NASM, the potential for the spread of antibiotic resistance genes to more pathogenic species of the family Staphylococcaceae such as S. aureus remains a significant concern.