Mechanical prevention of virulent Vibrio cholerae bacteria in some commercially dried fishes through cumin seed (Nigella sativa) extracts

Abstract

The present study was designed to investigate the antibacterial activity of black cumin seed extracts with the aim at inhibiting of the growth of pathogenic bacteria, Vibrio cholerae on three different dried fishes named Loitta (Harpodon nehereus),Shrimp (Penaeus monodon) and Churi (Trichiurus haumela). Two different extracts with ethanol and acetone solvents were prepared separately. The antibacterial activities of these extracts were determined by three different methods; i. enumerating the bacterial load before and after extracts treatment, ii. Disc diffusion method, iii. Tube dilution method. A total of ten samples were taken for each method with three replicates. The selective Thiosulfate-citrate-bile salts-sucrose agar media (T.C.B.S Cholera) was used for isolation of V. cholerae from the dried fish tissue. The average loads of the V. cholerae in Loitta and Shrimp were 3.1×104 CFU/g and 2.67×103 CFU/g respectively while no V. cholerae was detected in dried Churi fish. Though both extracts showed strong sensitivity to the isolated bacteria, but acetone extract of black cumin was found to be more effective than ethanol extract. The Minimum Inhibitory Concentrations (MIC) value of acetone and ethanol extracts in inhibiting the growth of V. cholerae was 25% and 30% respectively. This result suggests that, black cumin seed extract can be used as an alternative medicine to prevent the enteric disease of consumers associated with dried fish consumption.