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Consequences of γ-irradiation on the Dissemination of Microorganisms Among Sea Fish in Bangladesh

Mrityunjoy Acharjee
Department of Microbiology, Stamford University Bangladesh, Dhaka, Bangladesh

Rabeya Sultana
Department of Microbiology, Stamford University Bangladesh, Dhaka, Bangladesh

Rashed Noor*
School of Life Sciences (SLS), Independent University Bangladesh (IUB), Bashundhara, Dhaka, Bangladesh

Abstract/ Executive Summary:

In a cohort with our earlier investigation, the present study attempted to evaluate the existence and survival of spoilage microorganisms in five common sea fishes (Scomber colias, Lates calcarifer, Tenualosa ilisha, Pandalus borealis, Colossoma macropomum) available in Bangladesh and also optimized the doses of γ-irradiations to reduce the proliferation of the bacterial pathogens. Total 75 samples of 5 categories (n = 15) sea fishes were collected from the super shops in Dhaka city, and each sample was subjected to γ-irradiation (6 kGy and 8 kGy). Both samples (non-irradiated and irradiated) were analyzed for the existence of pathogenic bacteria through the conventional cultural techniques and the confirmative biochemical identification procedures. The response of the microbial isolates against different drugs was also investigated. Most of the non-irradiated samples were found to harbor a huge population of microorganisms up to 1.5 × 108 cfu/g or cfu/mL including the fecal coliforms ranging up to 106 cfu/g or cfu/mL. Several specific bacterial species like Salmonella spp., Shigella spp., Staphylococcus spp., Pseudomonas spp., Vibrio spp. and Listeria spp. were noticed to be present in a titer of 107 cfu/mL or cfu/g. Moreover, the identified isolates were found to be resistant against single or multiple antibiotics tested. Thus, the incidence of coliforms and other harmful bacteria together with their drug-resistance traits may be considered as a serious threatening to the public health upon consumption of such fishes. When subjected to γ-irradiation, the propagation rate of pathogens was reduced up to 4 logs with the irradiation dose of 6 kGy; however, 100% reduction was observed when 8 kGy was applied.

Keywords: Gamma (γ) Irradiation; 6 kGy and 8 kGy; Sea Fish; Pathogens; Antibiotic Resistance; Microbiological Quality

Location: Different supper shop in Dhaka city

Start Date: 00-01-2017

End Date: 00-04-2017

Program Area: Risk Management in Agriculture

Commodity: Fish

Objectives:

To achieve the total reduction of microorganisms among the fishes, the present study was further designed not only to detect the microbial prevalence and drug-resistant pathogens but also to establish the efficacy of ionizing radiation (γ -irradiation) of varying doses (6 kGy and 8 kGy) for the commercial supply of popular fishes free of microbial contamination.

Methodology:

Study area and sampling: Total 75 samples of 5 categories of fishes were studies. Fifteen (15) samples of Scomber Colias (chub mackerel), 15 Lates calcarifer (Koral), 15 Tenualosa Ilisha (hilsha), 15 Pandalus Borealis (shrimp), 15 Colossoma macropomum (rupchanda) were collected from different supper shop in Dhaka city within a time frame of January, 2017 to April 2017. All the samples were collected aseptically and transported immediately to the laboratory by using sterile polyethylene bags with ice. Sample processing, irradiation and microbiological analysis The appropriate length and weight of each fish sample were measured and cut into 3 pieces and then the samples were washed out with distilled water. Each piece of samples was put in separate sterile polythene packets (irradiation by at 15 kGy), and sealed properly. Two pieces of the samples were irradiated separately at 6 kGy and 8 kGy using 60 cobalt radiation sources (provided by the Board of Radiation and Isotope Technology, India) for 20 minutes, and the remaining half (i.e., non-irradiated) were subjected to pathogenic study. Then the packets of both fresh (non-irradiated) and irradiated samples were washed with peptone buffer water and each piece of both irradiated fish was homogenized with normal saline. The packet-washed water and the fish blend samples were then serially diluted up to 10-5 for microbiological analysis. As described earlier, according to the information provided by the Institute of Food and Radiation Biology (IFRB), Bangladesh Atomic Energy Commission (BAEC), Dhaka, Bangladesh, current study implemented gamma irradiation on different sea fish samples (Supplement 1). Estimation of total viable bacteria (TVB), total fecal coliform (TFC), staphylococcal and fungi In order to detect the presence (as well as the quantification) of the total viable bacteria (TVB), total fecal coliform (TFC), Fungal count and Staphylococcus aureus, 0.1 ml of suspension from each dilution of the samples was spread out onto Nutrient agar, Membrane Fecal Coliform (mFC) agar, Sabouraud Dextrose Agar (SDA) and Manitol Salt Agar (MSA) plates, consecutively [3,29]. For TVB and Staphylococcal assay, plates were incubated at 37°C for 24 hours while for estimating the fecal coliforms, plates were incubated at 44.5°C for 24 hours. The SDA plates were incubated at 25°C for 48 hours for the determination of fungal count. Detecting the presence of Salmonella spp., Shigella spp., Vibrio spp. Pseudomonas spp and Listeria spp. Since Salmonella spp., Shigella spp., Vibrio spp. Pseudomonas spp and Listeria spp. may survive in the natural environment (for example, within the fish samples tested) but their presence can be often misguided by their viable but nonculturable (VBNC) state and thereby imparting false-negative results in vitro. The fish samples were further subjected to enrichment for the isolation and identification of such VBNC bacteria. One ml of each sample was added to selenite cystein broth (SCB) and alkaline peptone water (APW) and incubated at 37ºC for 6 hours, and then 0.1 ml of suspension was spread onto Salmonella Shigella (SS) agar and Thiosulphate Citrate Bile Salt Sucrose (TCBS) agar media, for the assay of Salmonella spp., Shigella spp., and Vibrio spp., consecutively. For the isolation of Listeria spp. and Pseudomonas spp., 0.1 ml of suspension was spread onto Listeria identification media and Cetrimide agar respectively. Then the plates were incubated at 37°C for 24 hours. Finally, the confirmation of all the isolates was examined by the standard biochemical tests. Statistical analysis All the experiments were performed three times. Statistical analyses were performed by determining the p-value through a t-test. Errors were also calculated.

Source of Information: Microbiology 15.8 (2019): 784-794.

Article Link (Online Journal):

Funding Source:

1.

Budget:

Total Budget (Tk.) :

Achievement/Findings:

An array of experimental and suggestive data unraveled the fact that different foods including sea fishes may serve are a good reservoir of microbial agents, sometimes the pathogenic activity of those microorganisms may responsible for food-borne disease outbreaks. The virulence genes of these pathogens may create not only infection of the fish but also become fatal for the consumers. While in Bangladesh the genetic analysis of the export quality shrimp has been performed by our group; however, still the other sea fishes need to be analyzed for the possible expression of the virulent genes. Apart from molecular study, the present research successfully (1) portrayed the pathogenic profile of popular and export quality sea fishes of Bangladesh, (2) figured out the drug-resistance trait of the isolated pathogens which in turn may help the clinical professionals to further work on these isolates to know the molecular mechanism of the drug-resistance gene transmission; and (3) finally the study clearly demonstrated the irradiation dose possessing the bactericidal and fungicidal activity within the fish samples tested. The efficacy of the radiation dose 6 kGy and 8 kGy on microbial reduction is expected to improve the shelf-life as well as the public health of the consumers. Such findings may also help to meet the high export demand of our sea fishes.

Knowledge Management: Journal