Modelling the effect of water activity and temperature on growth rate and aflatoxin production by two isolates of Aspergillus flavus on paddy.

AIMS: This study was conducted to characterize the growth of and aflatoxin production by Aspergillus flavus on paddy and to develop kinetic models describing the growth rate as a function of water activity (a(w)) and temperature. METHODS AND RESULTS: The growth of A. flavus on paddy and aflatoxin production were studied following a full factorial design with seven a(w) levels within the range of 0·82-0·99 and seven temperatures between 10 and 43°C. The growth of the fungi, expressed as colony diameter (mm), was measured daily, and the aflatoxins were analysed using HPLC with a fluorescence detector. The maximum colony growth rates of both isolates were estimated by fitting the primary model of Baranyi to growth data. Three potentially suitable secondary models, Rosso, polynomial and Davey, were assessed for their ability to describe the radial growth rate as a function of temperature and a(w). Both strains failed to grow at the marginal temperatures (10 and 43°C), regardless of the a(w) studied, and at the a(w) level of 0·82, regardless of temperature. Despite that the predictions of all studied models showed good agreement with the observed growth rates, Davey model proved to be the best predictor of the experimental data. The cardinal parameters as estimated by Rosso model were comparable to those reported in previous studies. Toxins were detected in the range of 0·86-0·99 a(w) with optimal a(w) of 0·98 and optimal temperature in the range of 25-30°C. CONCLUSIONS: The influences of a(w) and temperature on the growth of A. flavus and aflatoxin production were successfully characterized, and the models developed were found to be capable of providing good, related estimates of the growth rates. SIGNIFICANCE AND IMPACT OF THE STUDY: The results of this study could be effectively implemented in minimizing the risk of aflatoxin contamination of the paddy at postharvest.

Transfer of Campylobacter jejuni from raw to cooked chicken via wood and plastic cutting boards.

AIMS: We quantified Campylobacter jejuni transferred from naturally contaminated raw chicken fillets and skins to similar cooked chicken parts via standard rubberwood (RW) and polyethylene cutting boards (PE). METHODS AND RESULTS: RW and PE cutting boards (2.5 × 2.5 cm(2)) were constructed. RW surfaces were smooth and even, whereas PE was uneven. Scoring with scalpel blades produced crevices on RW and flaked patches on the PE boards. Raw chicken breast fillets or skin pieces (10 g) naturally contaminated with Camp. jejuni were used to contaminate the cutting boards (6.25 cm(2)). These were then briefly covered with pieces of cooked chicken. Campylobacter jejuni on raw chicken, the boards, and cooked chicken pieces were counted using a combined most-probable-number (MPN)-PCR method. The type of cutting board (RW, PE; unscored and scored) and temperature of cooked chicken fillets and skins were examined. Unscored PE and RW boards were not significantly different in regards to the mean transfer of Camp. jejuni from raw samples to the boards. The mean transfer of Camp. jejuni from scored RW was significantly higher than from scored PE. When the chicken fillets were held at room temperature, the mean transfer of Camp. jejuni from scored RW and PE was found to be 44.9 and 40.3%, respectively. CONCLUSIONS: RW and PE cutting boards are potential vehicles for Camp. jejuni to contaminate cooked chicken. Although cooked chicken maintained at high temperatures reduced cross-contamination via contaminated boards, a risk was still present. SIGNIFICANCE AND IMPACT OF THE STUDY: Contamination of cooked chicken by Camp. jejuni from raw chicken via a cutting board is influenced by features of the board (material, changes caused by scoring) and chicken (types of chicken parts and temperature of the cooked chicken).

Occurrence of thermophilic Campylobacter spp. contamination on vegetable farms in Malaysia.

The aim of the present study was to examine the prevalence of thermophilic Campylobacter spp. (Campylobacter jejuni and Campylobacter coli) in soil, poultry manure, irrigation water, and freshly harvested vegetables from vegetable farms in Malaysia. C. jejuni was detected in 30.4% and 2.7% of the soil samples, 57.1% and 0% of the manure samples, and 18.8% and 3% of the vegetable samples from farm A and farm B, respectively, when using the MPNPCR method. Campylobacter spp. was not found in any of the irrigation water samples tested. Therefore, the present results indicate that the aged manure used by farm A was more contaminated than the composted manure used by farm B. Mostly, the leafy and root vegetables were contaminated. C. coli was not detected in any of the samples tested in the current study. Both farms tested in this study were found to be contaminated by campylobacters, thereby posing a potential risk for raw vegetable consumption in Malaysia. The present results also provide baseline data on Campylobacter contamination at the farm level.

Colonization of streptomycin-treated mice by Aeromonas species.

Streptomycin-treated adult mice were investigated as a possible model for studying the enteropathogenicity of Aeromonas species. C57BL mice pre-treated with streptomycin (5.0 g/L drinking water, 48 hours) received a single intragastric dose (10(10) bacteria /10.5 mL) of one of six well-characterized, toxin-producing, human diarrhoeal isolates of A. veronii biovar sobria (n = 3) or A. hydrophila (n = 3). Their faeces were examined for Aeromonas for 10 days post-challenge. All strains colonized the antibiotic-treated mice. Colonization did not occur in mice which did not receive streptomycin. Strains of A. hydrophila were recovered in greater numbers than strains of A. veronii biovar sobria, and colonized ( > or = 10(3) cfu/g of faeces) a greater proportion of mice at day 10. Strains of the latter species, however, were more adherent in cell line assays used as models of intestinal adhesion. A. hydrophila strains localized in the large intestine and appeared not to be cell associated. This study, therefore, points to species-related differences in intestinal colonization mechanisms. The streptomycin-treated adult mouse model may prove useful for further investigation of some of these mechanisms. Diarrhoeal symptoms were, however, not produced in this model.