Isolation of Food-Borne Microorganisms from Atlantic Mackerel and Disinfection of the Raw Fish by Radiation, Low Temperature and Combination Treatments

Abstract

An investigation was undertaken for the isolation and identification of fish-borne microorganisms from mackerel fish (Scomberomorus guttatus) collected from Savar Bazar. Radiation, low temperature (-20°C) and combination treatments were then applied for the decontamination of associated organisms. The ranges of total viable bacterial count, total coliform count, total faecal coliform count and total staphylococcal count varied from 6.5 x 10⁴ to 1.04 x 10⁵, 2 x 10² to 4.0 x 10², 0 to 1 x 10² and 4.4 x 10⁴ to 3.8 x 10⁴ cfu/g respectively, while the total fungal count was nil. Sixty-four bacterial isolates were identified including Staphylococcus (19%), Micrococcus (11%), Enterobacter (8%), Klebsiella (17%), Bacillus (19%), Escherichia (17%) and Pseudomonas (9%). To disinfect the microorganisms, the samples were irradiated at different doses (0-10.0 kGy) of gamma irradiation. Total coliform and total faecal coliform bacteria were inactivated below the detectable level at 2.5 kGy of irradiation. The number of total viable bacteria decreased by three logs when irradiated at 5.0 kGy and the number of Staphylococcus bacteria were eliminated completely after the irradiation dose of 5.0 kGy. During frozen storage, the total viable bacterial counts were gradually declined in all the samples. After six months of storage the bacterial counts were decreased about one log in all of the samples. It has been observed that combination treatments (irradiation and freezing) are more effective than the single treatment for eliminating the fish-borne bacteria.

Keywords: Mackerel fish; Microbial contamination; Irradiation; Low temperature

DOI: http://dx.doi.org/10.3329/bjm.v25i2.4871

Bangladesh J Microbiol, Volume 25, Number 2, December 2008, pp 105-109