Kinetics of growth and inactivation of Salmonella enterica serotype Typhimurium DT104 in pasteurised liquid egg products

The potential impact of post-pasteurisation contamination of liquid egg products with the multi-antibiotic resistant pathogen Salmonella enterica serotype Typhimurium definitive type 104 (DT104) was assessed by determining the viability of this bacterium in whole egg, albumen and 10% w/w sugared and salted yolk incubated at 4–42 °C. Results indicated that populations of S. Typhimurium DT104 were slowly inactivated in all four products when stored at 4 °C. However, based on the typical shelf-lives of cold-stored liquid egg, less than 0.6 log-kill would be achieved in those products prior to their use. Incubation at temperatures pertaining to abuse situations (10, 15, 20 and 25 °C) revealed an increasing potential for growth of S. Typhimurium DT104 in whole egg, albumen and sugared yolk, as indicated by trends in growth rate, lag duration and maximum population density. At even higher temperatures (30, 37 and 42 °C), growth rates of S. Typhimurium DT104 in whole egg and sugared yolk continued to increase. The same was true for S. Typhimurium DT104 in albumen except that growth was not observed at 42 °C and instead populations were inactivated within 30 h. At no temperature tested was S. Typhimurium DT104 able to grow in salted yolk. The influence of these growth and inactivation patterns on the risk of salmonellosis in relation to product type and storage temperature is discussed.     

Detection of salmonellae using accelerated methods

During the last two decades, a substantial increase in salmonellae surveillance of foods and feeds by the food industry and regulatory authorities has occured. This exposed the many limitations of the conventional cultural methods for salmonellae detection as these methods are, inherently, cumbersome, labour intensive, costly and time consuming. Inevitably, considerable research has been conducted to develop simpler and more rapid methods. This review brings together reported accelerated methods which were either developed specifically for salmonellae or may be adapted for salmonellae detection. These methods include fluorescent-antibody staining, enrichment serology, radiometric, bacteriophage, immunoassay as well as other methods.     

不同沙门氏菌及干扰菌的分离鉴定

使用3种沙门氏菌(猪霍乱沙门氏菌、鼠伤寒沙门氏菌、甲型副伤寒沙门氏菌)和2种干扰菌(弗氏柠檬酸杆菌和奇异变形杆菌)分别接种分离培养基,观察生长和显色情况。研究沙门氏菌和干扰菌在常规分离培养基BS、XLD、DHL、HE、BGA和显色培养基CAS上的形态特征及生化试验结果,比较分离鉴别效果。研究发现甲型副伤寒沙门氏菌具有延迟产H2S特性,弗氏柠檬酸杆菌和奇异变形杆菌均有产H2S现象,显色培养基CAS的鉴别效果最好,BGA的分离鉴别效果最差。在实际检测工作中,不能以是否产H2S作为鉴定沙门氏菌的唯一依据,利用显色培养基可以显著提高检测效率和准确度。     

The contamination of a major water supply by gulls (Larus sp.): A study of the problem and remedial action taken

In recent years one of the storage reservoirs supplying Loch Katrine water to Glasgow exhibited a serious deterioration in bacterial quality. This was associated with the winter nocturnal roosting habits of gulls (Larus sp.) on the reservoir. Investigations showed a significant correlation between the numbers of gulls roosting and the numbers of E. coli present in the water. Salmonellae organisms of identical serotypes were isolated from the gulls, from the untreated water and, on three occasions, from the treated water. Broadcasting species specific distress calls of Larus gulls proved to be an effective measure for discouraging gulls from roosting on the reservoir. The routine use of this bio-acoustic method of gull scaring reduced the bacteria in the water to numbers typical of an upland unpolluted reservoir.     

Bacteriological Quality of Freshly Processed Broiler Chickens as Affected by Carcass Pretreatment and Gamma Irradiation

Chicken carcasses dipped in whey fermented by Streptococcus thermophilus, lactic acid solution or water and irradiated at 2.5 kGy by ⁶⁰Co were evaluated for bacteriological quality on day-1, day-3 and at 3-day intervals for an 18-day storage (4°C) period. Unirradiated carcasses treated similarly were used as control. Gram negative bacteria, Yersinia and Campylobacter counts were significantly (p<0.01) lower in irradiated samples, but no significant (p>0.05) differences were observed among the dipping solutions. Salmonellae were completely eliminated in irradiated samples. Whey fermented by 5. thermophilus reduced the proportion of Salmonella contaminated carcasses from 67% to 20%. As evidenced by the bacterial counts the shelf-life was found to be 15 days for irradiated carcasses compared to about 6 days for the unirradiated samples.     

Efficacy of heat treatment in the reduction of salmonellae and Escherichia coli O157:H– on alfalfa, mung bean and radish seeds used for sprout production

We studied the effect of hot-water treatment at various time/temperature regimes to design a decontamination process which is consistent with the recommendation of the National Advisory Committee on Microbiological Criteria for Foods (NACMCF) to reduce pathogens on seeds by 5log cfu/g. Alfalfa, mung bean and radish seeds were inoculated by immersion with more than 10⁷ cfu/g of enterobacteria (Salmonella Senftenberg W775, S. Bovismorbificans and Escherichia coli O157:H^–), dried and stored at 2 °C. The numbers of salmonellae and E. coli O157:H^– on these seeds remained unchanged during storage for 8 weeks. To achieve sprouting rates of more than 95%, time-temperature regimes were defined. The thermal treatment of contaminated mung bean (2–20 min for 55–80 °C), radish and alfalfa seeds 0.5–8 min (53–64 °C) reduced all pathogens by more than 5log cfu/g. For S. Senftenberg W775 on radish seeds, D values of 3.2, 1.9 and 0.6 min were determined for exposure at 53, 55 and 58 °C and a z value of 6.2 °C was calculated. For alfalfa seeds, the respective D values were 3.0, 1.6, and 0.4 min and the z value was the same as that determined for radish seeds.