Detection of Listeria monocytogenes in foods

Listeria monocytogenes is a gram positive, facultative intracellular pathogen with the capacity to cause food poisoning outbreaks as well as severe illness in vulnerable human population groups. It can cause a rare but serious disease called listeriosis with high fatality rates (20–30%) compared with other foodborne microbial pathogens. Although Listeria monocytogenes is infective to all human population groups, it is more likely to cause severe problems among pregnant women, immunocompromised individuals, the elderly and neonates. There are a variety of phenotyphic and genotyphic methods for the detection of Listeria monocytogenes in foods. Recent technological advances have increased the ability of scientists to detect Listeria monocytogenes. The purpose of this review is to discuss molecular characteristics of the Listeria monocytogenes pathogen, standard detection methods of this pathogen in foods based on culture methods, confirmation of species and subtyping based on phenotypic and genotyphic methods

Prevalence and quantification of Vibrio parahaemolyticus in raw salad vegetables at retail level

The purpose of this study was to investigate the biosafety of Vibrio parahaemolyticus in raw salad vegetables at wet markets and supermarkets in Malaysia. A combination of the most probable number -polymerase chain reaction (MPN- PCR) method was applied to detect the presence of V. parahaemolyticus and to enumerate their density in the\ud food samples. The study analyzed 276 samples of common vegetables eaten raw in Malaysia (Wild cosmos=8; Japanese parsley=21; Cabbage=30; Lettuce=16; Indian pennywort=17; Carrot=31; Sweet potato=29; Tomato=38; Cucumber=28; Four-winged bean=26; Long bean=32). The samples were purchased from two supermarkets (A and B) and two wet markets (C and D). The occurrence of V. parahaemolyticus detected was 20.65%, with a higher frequency of V. parahaemolyticus in vegetables obtained from wet markets (Wet market C=27.27%; Wet Market D=32.05%) compared with supermarkets (Supermarket A=1.64%; Supermarket B=16.67%). V. parahaemolyticus was most prevalent in Indian pennywort (41.18%). The density of V. parahaemolyticus in all the samples ranged from 2,400 MPN/g, mostly <3 MPN/g concentration. Raw vegetables from wet markets contained higher levels of V. parahaemolyticus compared with supermarkets. Although V. parahaemolyticus was present in raw vegetables, its numbers were low. The results suggest that raw vegetables act as a transmission route for V. parahaemolyticus. This study will be the first biosafety assessment of V. parahaemolyticus in raw vegetables in Malaysia

Listeria monocytogenes in raw salad vegetables sold at retail level in Malaysia.

A range of commercially available vegetables (n = 306) that are consumed in the minimally processed state in Malaysia was examined for the presence of Listeria spp. and Listeria monocytogenes to provide information on the occurrence of such organisms in these vegetables. Analysis was carried out using the most probable number–polymerase chain reaction (MPN–PCR) method. It was found that Listeria spp. and L. monocytogenes could be detected in 33.3% and 22.5% of the vegetables respectively. L. monocytogenes was more frequently detected in Vigna unguiculata (Japanese parsley) at 31.3% and Oenanther stolonifera (yardlong bean) at 27.2%

Quantitative risk assessment of acquiring listeriosis from consumption of minimally processed vegetables

Listeriosis is a serious invasive disease with high fatality rates especially among the vulnerable population. Although the causative pathogen had been detected in several foods in Malaysia, there have so far been no reported cases of listeriosis in Malaysia. The aim of this study was to carry out a quantitative risk assessment to estimate the risk of acquiring listeriosis through the consumption of minimally processed salad vegetables in Malaysia. The probability of illness per serving was calculated using an exponential dose-response model for high-risk and low-risk groups of consumer using the stochastic approach. The risk estimate of acquiring listeriosis for the healthy population was 1.98 × 10–4 per 100,000 population. For susceptible population, the risk estimate was considerably higher, i.e., 0.172 per 100,000 population for AIDS patients, 0.00496 per 100,000 population for diabetics and 0.149 per 100,000 for the elderly population

Evaluation of Listeria spp. and Listeria monocytogenes in selected vegetable farms

The aim of the study was to examine the prevalence of Listeria spp. and Listeria monocytogenes in soil, poultry manure, irrigation water, and freshly harvested vegetables from three vegetable farms in Cameron Highlands. A total of 177 samples including environmental and vegetable samples were collected. Among the environmental samples (n = 94), poultry manure was found to have a higher prevalence of Listeria spp. and L. monocytogenes at 77.8% and 61.1% respectively using the MPN-PCR analysis procedure. Soil samples were also found to harbour Listeria spp. and L. monocytogenes at 47.6% and 38.1% respectively. Irrigation water sampled from the farms were found to be free from Listeria spp. Both Listeria spp. and L. monocytogenes were also detected in 24% and 12% of swabs done at the three farms respectively. Among the freshly harvested vegetables, Listeria spp. was detected in cabbages (30%), cucumber (20%), yardlong beans (10%) and carrots (10%) whereas L. monocytogenes was detected in cabbages (10%), yardlong beans (10%) and carrots (10%) using the MPN-PCR analysis procedure. The present results signify that Listeria spp. poses a potential risk for raw vegetable consumption in Malaysia. The study also provides baseline data on Listeria spp. contamination at farm level

Assessment of Listeria monocytogenes in salad vegetables through kitchen stimulation study

This study was to investigate the occurrence of cross-contamination and decontamination in the kitchen via Listeria monocytogenes contaminated vegetables during salad preparation. In this study, naturally contaminated produce were used to provide realistic quantitative data as opposed to information obtained through artificial inoculation. The study was designed to simulate the real preparation of salad in kitchens in Malaysia which simply involved washing the vegetables in tap water and cutting them on a chopping board prior to serving. It was found that the mean percentage of transfer rates for L. monocytogenes from vegetables to wash water was 32.4–60.2%; from wash water to cucumber 24.9–66.3%; from vegetables to chopping board 18.9–32.2%; from chopping board to cucumber 5.4–75.3%. Washing of the vegetables in tap water caused a 0.3-log reduction of L. monocytogenes attached to the vegetables