a b s t r a c tA 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%.

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 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 <3 up to >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.

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.

Seventy-one strains of L. monocytogenes isolated from raw salad vegetables consumed in the minimally processed state in Malaysia were characterised by serotyping, random amplified polymorphic DNA-polymerase chain reaction analysis (RAPD-PCR) and antimicrobial susceptibility testing. Based on serotyping, only one strain belonged to serotype 4 while the rest were from serotype 1. RAPD-PCR typing was carried out using two primers, i.e., OPAR-8 and GEN 1-50-09. Based on RAPD-PCR fingerprinting, the strains could be grouped into six composite profile groups and a solitary isolate. The isolates were also evaluated against 16 antibiotics. Excluding nalidixic acid and oxacillin for which L. monocytogenes has natural resistance, the highest prevalence of resistance was against cephalexin. None of the isolates were resistant against imipenem and kanamycin. The multiple antibiotic resistance index (MARI) ranged from 0.06 to 0.63. It was found that most (82%) isolates were susceptible to antibiotics commonly used in veterinary and human listeriosis treatment.