Abstract

Ready-to-eat foods are those that do not require preparation by heat employment before being ingested by the consumer. The present study focused to assess the occurrence of L. monocytogenes in ready-to-eat food products available in the local markets in Chikkaballapura, Karnataka, and to improve the basic knowledge of the incidence and characteristics of L. monocytogenes. Samples comprising of locally prepared and sold ready-to-eat packed food products being consumed by Childrens were collected and subjected to serial dilution and inoculated to nutrient agar medium, Palcam selective agar base medium and Tryptic soy broth. The growth with the typical colony characteristics were further identified up to species level based on their morphological and biochemical characteristics. The bacteria isolated from different ready-to-eat food products was found to be gram-positive bacilli, motile. The results of biochemical assay of bacteria isolated from different ready-to-eat food products showed positive for catalase, oxidase, methyl red, Voges Proskauer, and CAMP tests. Whereas, isolated strains were negative for indole and citrate utilization tests. Based on the morphological and biochemical characterization, isolated strain was identified as L. monocytogenes. In conclusion, results of the presented study suggested that L. monocytogenes is prevalent in ready-to-eat food products and sheds new light on the growth of food pathogens and spoilage microbes in a variety of ready-to-eat food products. These findings could be considered in estimating the risks associated with the production and consumption of ready-to-eat food products.

Description

Listeriosis has been recognized in the 1920s as an infection caused by a Gram-positive bacterium later called Listeria monocytogenes. In 1981, an outbreak in Canada was first associated with the presence of this pathogen in foods, encouraging the development of research on the ubiquitous features of the microorganism and its pathogenicity.1 Since then, it is considered an important bacterium in public health, responsible for foodborne disease that despite the low incidence, has a high mortality rate among affected individuals. L. monocytogenes is extensively distributed in a wide range of agricultural environment such as soil, manure, and water.2 This pathogen is generally transmitted to human through contaminated food and water. It is found as a saprotroph in soil, but it can transform into a pathogenic form when enters into the animal or human cell.3 One of the possible sources of contamination of L. monocytogenes in food products and food industry is due to the cross contamination. L. monocytogenes is one of very few pathogenic organisms which can grow at refrigerated temperatures. The bacterium is widespread in nature and can survive and grow under low temperatures and pH, high concentrations of salt or bile, oxidative stress, carbon starvation, and other adverse conditions making it a potential hazard in foods.4 Listeriosis in human is very often associated with very high mortality which may be as high as 30%.5 In USA, approximately 1,591 cases of listeriosis in human have been reported in a year and it contributes to about 0.1% of total food-borne illnesses, but is responsible for 2.6% of hospitalizations and 18.87% of the deaths caused by food-borne illnesses.6 Both the outbreaks and sporadic human listeriosis is caused by transmission of this pathogen through contaminated food and the involvement of a wide variety of foods has been reported throughout the world.7,8 In USA, the recent multistate outbreak of L. monocytogenes apparently through consumption of contaminated cantaloupe has drawn worldwide attention. A total of 146 persons were infected and 33 deaths were reported in this outbreak in which multiple states of USA were affected.9 Considering its immense pathogenic potentiality and high mortality rate, different regulatory agencies including USFDA have imposed zero tolerance for this pathogen in ready-toeat food products.10 The most widely used techniques for identifying L. monocytogenes are the conventional methods, which depend on the use of microbiological media to cultivate and count this pathogen in a targeted manner. These techniques yield both qualitative and quantitative results, are affordable, and are sensitive. There have also been reports of clinical cases of listeriosis in humans brought on by L. monocytogenes from Delhi and Karnataka states of India