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Detection of Vibrio Spp., Salmonella Spp., and Shigella Spp. Among the Frozen Food Samples Employing Enrichment Culture Technique

Tahmina Shammi
Department of Microbiology, Stamford University Bangladesh, 51 Siddeswari Road, Dhaka-1217, Bangladesh

Abstract/ Executive Summary:

Freezing has long been an established method for food preservation. Freezing temperature may act as a stress factor for microbial cells, transforming the cells into injured or dormant state. Upon inoculation, these debilitated cells cannot grow on solid media and hence produce false negative results. Foods contaminated with injured cells of pathogenic bacterial strains are of potential health risk. Employing enrichment cultivation technique, present study attempted to detect such injured, dormant or viable but non culturable (VBNC) cells in different frozen food samples, collected from local markets and super-shops of Dhaka metropolis. Compared to the conventional cultivation means, the enrichment procedure revealed a significant increase in bacterial burden as well as increase in the pathogenic load. A maximum of 3 log increase in case of total bacterial load while 4 log, 5 log and 2 log increase in case of Vibrio spp., Salmonella spp. and Shigella spp., consecutively were observed. These findings clearly demonstrated the presence of injured cells in frozen foods which could be lethal under normal condition thereby posing public health risk.

Keywords: Frozen food, Injured cells, Viable but non-culturable (VBNC) cells, Pathogenic microorganisms, Enrichment cultivation procedure, Public health

Location: Department of Microbiology, Stamford University Bangladesh, 51 Siddeswari Road, Dhaka-1217, Bangladesh

Start Date:

End Date:

Program Area: Quality and Nutrition

Commodity: Fresh and processed food

Objectives:

Objective of the study was to determine the frozen food samples employing enrichment culture technique

Methodology:

Sampling, sample processing and enrichment of samples: Collection of samples was performed aseptically in the month of September 2014 from different places of New market, Malibag, Siddeswari and Mogbazar area in the Dhaka city of Bangladesh. Eight Samples of different categories including meat, fish, shrimp, squid, poultry and processed frozen foods (one chicken ball and one mutton roll) were collected and quickly transported to laboratory keeping in an ice box maintaining the temperature at 4°C. Ten gm of each sample was weighed and added in a sterile homogenizing beaker containing 90 ml of sterile normal saline, and then homogenized to prepare 100 ml sample suspension for microbiological examinations. As it is normally assumed that Salmonella spp., Shigella spp. and Vibrio spp. remain in viable but non-culturable (VBNC) state or in stressed condition in the environment therefore, enrichment technique was employed for the isolation and identification of these bacteria. One ml sample was added to 9 ml selenite cysteine broth (SCB) (Difco Laboratories, Detroit, Mich.) and alkaline peptone water (APW) (Difco Laboratories, Detroit, Mich.), respectively. Culture suspensions were incubated for 4 hours at 37ºC with shaking at 100 rpm. A series of 10 fold serial dilutions were made up to 10-6 for both non-enriched and enriched samples. Then 0.1 mL from each of the enriched broth was spread over Salmonella-Shigella agar (SSA) and Thioglycollate citrate bile salt (TCBS) agar respectively. Moreover, nutrient agar plates were also used for the determination of total viable bacteria and for the detection of psychrophiles by incubating the respective agar plates at 37°C for 12-24 hours and at 2-7ºC for 14 days. Detection of Vibrio spp., Salmonella spp., and Shigella spp. Thiosulfate Citrate Bile Salt Sucrose (TCBS) (Difco Laboratories, Detroit, Mich.) agar plates were used to quantify the contaminating Vibrio spp. within the samples. While Salmonella-Shigella (SS) agar (Difco Laboratories, Detroit, Mich.) was used both for the isolation and quantification of Salmonella spp. and Shigella spp. After incubation at 37ºC for 24 hours, characteristic colonies were detected and enumerated. Yellow colored colony on TCBS is characteristic of Vibrio spp. while the black centered colony on Salmonella/Shigella agar was considered as Salmonella spp. and the colorless colony on the same agar plates was noted as Shigella spp. A deduction of the pre-enriched bacterial load from the enriched ones detected the amount of injured cells of Vibrio spp., Salmonella spp., and Shigella spp. in all the samples examined. Finally, a series of biochemical tests were performed following the standard method to confirm the presence of these isolate

Source of Information: Stamford Journal of Microbiology, 2015. Vol. 5, Issue 1, 26-29; ISSN: 2074-5346

Article Link (Online Journal): http://www.banglajol.info/index.php/SJM/article/view/26917/17973

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

An array of frozen foods contributes largely to the economy of Bangladesh, and it also serves as popular food items; therefore studies relating to disease onset, respective of storage, are required for the maintenance of national health and safety. Frozen meat, poultry especially shrimp which is a prime export product of Bangladesh have been studied previously. In this study, it was attempted to detect microbiological quality as well as pathogenic load of different frozen foods, meat, poultry, shrimp with some processed frozen food and frozen squid which has recently been introduced to the urban consumer’s of Bangladesh, This study focused on enrichment is not suitable for enumeration rather a presence absence test, that future study may include establishment of quantitative method for injured cell analysis and risk assessment of different pathogens commonly observed in frozen food products.

Knowledge Management: Journal