SOURCE:

Faculty: Biosences
Department: Applied Microbiology And Brewing

CONTRIBUTORS:

Okafor, A. C.
Ogbo, F. C.

ABSTRACT:

Edible land snail is high in protein, as well as in essential amino acids, iron and vitamins needed for human nutrition. However, they may serve as source of bacterial pathogens in the food chain because of their habitat, which is often associated with wastes, including faecal matter. Data on various bacterial hazards associated with edible snails are needed for making legislations that will improve food safety and protect public health. The aim of this study is to assess bacterial hazards associated with edible land snails (Achatina achatina) in three major markets in South East, Nigeria. The objectives are to: determine the viable counts, prevalence of virulence potentials and antibiotic resistance among presumptive pathogenic bacteria in edible land snails; identify bacterial pathogens using 16S rRNA gene sequencing technique; detect toxin genes in pathogenic isolates, and determine the processing method that will reduce the bacterial load of snail meat. This study focused on three markets serving as the largest platforms for the sale of A. achatina in South East, Nigeria. Three hundred edible snails were procured from Igboukwu market in Anambra State (n = 100), Abakaliki meat market in Ebonyi State (n = 100) and Ogbete main market in Enugu State (n = 100). Samples were aseptically collected into sterile plastic containers and quickly transported to the laboratory. They were analysed for various bacterial counts on selective and differential media that are specific for various bacterial pathogens. The prevalence of virulence associated properties and antibiotic resistance among presumptive bacterial pathogens were determined using phenotypic tests. Bacterial isolates were selected based on virulence associated properties and identified using 16S rRNA gene sequencing technique. Staphylococcus and Bacillus strains were screened for the presence of some toxin-coding genes by polymerase chain reaction using specific primers. The bacterial load of snail meat for each processing method was determined using plate count method. Bacterial counts in Log CFU/g of snail samples ranged from 8.43 to 9.61 (aerobic plate count), 6.84 to 8.18 (coliform), 6.04 to 7.51 (Citrobacter), 3.32 to 5.18 (Shigella), 5.32 to 7.38 (E. coli), 3.94 to 5.38 (Staphylococci), 3.04 to 5.61 (Aeromonas) and 3.08 to 4.65 (Bacillus). Haemolysin production and biofilm formation were the most common virulence associated properties. Isolates displayed multidrug resistance in the order: Abakaliki isolates > Igboukwu isolates > Ogbete isolates. The 16S rRNA gene sequencing revealed that the most important pathogenic isolates present were Escherichia fergusonii, Citrobacter freundii, Bacillus cereus, Bacillus thuringiensis, Staphylococcus sciuri, Staphylococcus arlettae and Aeromonas hydrophila. An enterotoxin gene (sea) was detected in Staphylococcus sciuri strain NEDU181 (GenBank accession number: MK518066). Bacillus thuringiensis strain NEDU186 (MK530172) was found to possess four (hbla, nhea, nheb and cytk) out of the five toxin genes examined in this study. Also, results showed that reduction in mean bacterial loads of snail meat was achieved with each processing method in the order: Wood ash (3.57 Log CFU/g) > Potassium alum (4.64 Log CFU/g) > Lime (4.81 Log CFU/g) > Cassava-retting water (5.06 Log CFU/g) > Garri (6.61 Log CFU/g). The edible snails were contaminated with high loads of bacterial indicators and pathogens. Staphylococcus and Bacillus strains contaminating edible snails haboured enterotoxin genes. Therefore, they may be considered a neglected source of foodborne bacterial pathogens in the food chain if not properly handled and prepared. The findings of the study highlight the need for regulations and education for proper handling of snails to minimize cross contamination of bacterial pathogens to other foods during retail and adequate cooking before consumption.