Tunung Robin

Characterisation of L. monocytogenes strains isolated from salad vegetables

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.

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.