ABSTRACT
Fish forms a much-cherished delicacy, which cuts across different barriers such as age and other sociodemographic factors. Smoking is one of the traditional processing methods aimed at preventing or reducing postharvest losses. This study aimed to evaluate pathogenic Staphylococcus spp. from smoked fish sold in Benin City, Nigeria. Three hundred and thirty smoked fish samples were obtained from open markets in four Local Government Areas in Edo South Senatorial District. The smoked fish samples were sorted and separated on the basis of the local parlance (Scomber or Titus fish (Scombar scombrus), Hake or Meluza (Merluccius merluccius), Catfish (Clarias gariepinus), Sese or Horse Mackerel (Trachurus trachurus) and Herring or Shawa (Clupea harengus)). A structured questionnaire was administered to the fish vendors for evaluation of processing practices before sampling. Standard bacteriological methods were employed for isolation, enumeration and characterization of Staphylococcal isolates. Phenotypic virulence properties of the isolates were evaluated using the production of DNAse, hemolysin, gelatinase and lipase. Antibiotic sensitivity test was carried out using the Kirby-Bauer disc diffusion method, and multiple antibiotic resistance index was evaluated. Polymerase chain reaction was used to identify Staphylococcus aureus and evaluate virulence and resistance genes. The quantitative microbial risk assessment of S. aureus from smoked fish was evaluated using Firth’s model, and the probability of infection was established. Data were analyzed using Microsoft Excel and r-programming software. The results revealed that most of the fishes evaluated in the study were Scomber (40.32%), Meluza (33.87%), Herring (17.74%), and Sese (4.84%). Most (93.33%) of the fish vendors participated in the smoking process, while wood combustion (95.12%) was the most predominant smoking material used. Most (64.44%) of the smoked fish evaluated in the study were processed on the same day, while 28.89% of the fish were processed a day before. The coagulase-positive staphylococcal counts of smoked fish samples ranged from log10 1.54 ± 1.57 cfu/g to log10 3.45 ± 0.44 cfu/g. The mean coagulase-positive Staphylococcal counts of Scomber, Sese and Meluza were log10 2.62 ± 1.42 cfu/g, log10 2.04 ± 1.60 cfu/g and log10 4.90 ± 0.46 cfu/g respectively. The mean coagulase-positive Staphylococcal counts of smoked fish samples processed and purchased same day were log10 2.19 ± 1.48 cfu/g, while the counts of smoked fish samples processed a day and two days before evaluation were log10 2.70 ± 1.76 cfu/g and log10 3.52 ± 0.40 cfu/g respectively. The phenotypic virulence properties of the Staphylococcal isolates revealed that all coagulase- positive isolates (100%) had DNAse, gelatinase and lipase. The antibacterial sensitivity profile (%) revealed that all isolates were sensitive to meropenem and ciprofloxacin (100%), and notable sensitivity was observed for gentamicin and colistin (80% apiece). The distribution of Staphylococcal virulence genes revealed that 100% (n =20) of the isolates possessed seA and agrA genes, which codes for the production of heat-stable enterotoxin and expression of staphylococcal virulence, respectively. Genes for resistance to antibiotics genes like beta-lactam (blaZ; 60%), tetracyclines (tetM; 80%), macrolides (ermA; 90) and aminoglycosides (aacA; 70%) were found. The probability of infection as per consumption of high doses (quantity) of smoked fish contaminated with Staphylococcus was 0.98. The findings emphasize the need for enhanced consumer education, better preservation practices, and stricter regulations in the handling and storage of smoked fish to mitigate the risk of staphylococcal foodborne illnesses.
