Prevalence of Aspergillus species in Smoke-Dried Fish from Selected Markets in Uyo, Akwa Ibom State, Nigeria

Consumption of smoked and smoke-dried fish is common in Nigeria as smoking is one of the common methods of preserving fish. Sadly, due to unhygienic handling and processing techniques, coupled with poor storage facilities and sanitary conditions in the market environments, majority of the fish sold in markets are laden with fungal contaminants of the genus, Aspergillus. The purpose of this study was to determine the prevalence of Aspergillus species among the smoke-dried fish sold in Uyo markets. A total of 360 samples of smoke-dried fish from five breeds of fish were randomly collected from six Uyo markets for study. The samples were aseptically cultured and assayed for the presence of Aspergillus species in Obong University Microbiology Laboratory. Each of the fish samples was blended and 1g suspended in 9ml of sterile distilled water, and 10-fold serial dilutions were made to produce graded concentrations ranging from 10-1 to 10-9. About 1ml of each dilution was spread on the surfaces of triplicate potato dextrose agar plates supplemented with 0.05 mg/ml of chloramphenicol and gentamicin and incubated at 25 ± 2°C for 7 days. Representative colonies of Aspergillus species on PDA were sub-cultured on sterile PDA plates to obtain pure colonies, and were further confirmed by microscopic examination. The microbial colonies in each plate were counted and the average number of colonies in the triplicate was calculated. Out of the 360 samples collected, Aspergillus was isolated from 51 samples, resulting in a prevalence of 14.2%. Four species of Aspergillus isolated from this study were 22 isolates of A. fumigatus, 13 isolates of A. niger, 12 isolates of A. flavus and 4 isolates of A. ochraceus. A. fumigatus was the most encountered species of Aspergillus in each market while A. ochraceus was the least. Urua Ekpa market had the highest number of isolates of Aspergillus species, with 12 isolates, followed by Itam market with 10 isolates. According to the order of magnitude, catfish was the most contaminated fish samples, followed by mackerel (Titus), tilapia, Asa fish and finally, Shawa fish. The result also revealed the rich microbial population of Aspergillus species from the various breeds of fish samples with mean values ranging from 1.9 x 102 cfu/g to 2.4 x 102 cfu/g. The result obtained from this study shows that a lot of fish sold in Uyo markets are contaminated with Aspergillus fungi which are opportunistic pathogens of public health importance. Therefore, to cub the menace of aspergillosis in Akwa Ibom state and possibly in Nigeria at large, fish contaminations should be avoided by employing appropriate professional techniques of fish processing and storage. This is the first systematic report on the prevalence and diversity of Aspergillus species in smoke-dried fish sold in Uyo, Akwa Ibom State. It provides baseline data for surveillance of fungal contamination in smoked fish and highlights the need for improved food hygiene in Uyo markets.