The incidence of outbreaks of foodborne listeriosis has indicated the need for a reliable and rapid detection of the microbe in different foodstuffs. A method combining redox potential measurement and real-time polymerase chain reaction (PCR) was developed to detect Listeria monocytogenes in artificially contaminated raw milk and soft cheese. Food samples of 25 g or 25 ml were homogenised in 225 ml of Listeria Enrichment Broth (LEB) with Oxford supplement, and the redox potential measurement technique was applied. For Listeria species the measuring time was maximum 34 h. The absence of L. monocytogenes could reliably be proven by the redox potential measurement method, but Listeria innocua and Bacillus subtilis could not be differentiated from L. monocytogenes on the basis of the redox curves. The presence of L. monocytogenes had to be confirmed by real-time PCR. The combination of these two methods proved to detect < 10 cfu/g of L. monocytogenes in a cost-and time-effective manner. This method can potentially be used as an alternative to the standard nutrient method for the rapid detection of L. monocytogenes in food.
The aim of this study was to investigate the occurrence of Salmonella enterica and its most important serovars Salmonella Infantis, Salmonella Enteritidis, Salmonella Typhimurium, and Campylobacter spp. in the broiler meat production chain. Altogether 110 pooled samples were analysed; environment, cloaca, body surface at the farm, then carcass, offal, and packed meat from the slaughterhouse. The combination of redox potential measurement and realtime PCR was used for the detection of the microbes.
At the farm, the first Salmonella positive result came from the water system, then it appeared in most of the samples. In contrast to the absence of Salmonella on the birds’ body surface before transportation, by the end of the processing it had reached 100%, with the only identifiable serovar being S. Infantis (65%). All packed meat samples showed positivity, from which 70% was S. Infantis.
Campylobacter appeared at the farm on the 3rd week and remained significant during the breeding. After the slaughtering process, the contamination was 100% in the carcass, offal, and packaged meat samples.
Our results demonstrated the success of the Salmonella control program, by the low prevalence of S. Typhimurium and Enteritidis.
The rapid detection of Campylobacter spp. is of utmost importance for the reduction of infections in humans by contaminated food products. The standard culturing method (ISO 10272-1:2006) involves a high time and labour demand. In this paper, we present a method that reduces the detection time of Campylobacter spp. to or below one third as compared to the ISO method, at a reduced cost per test. We used redox potential change of enrichment cultures (Bolton broth with Bolton selective supplement) for reliably selecting Campylobacter-contaminated raw milk and broiler meat samples. Identification of Campylobacter spp. in the contaminated samples was done by real-time PCR method. Culturing time to conclusive redox monitoring varied between 6 and 24 h for positive samples, depending on the contamination rate, in contrast to 136 h with the standard culturing process. However, now the Campylobacter-negative majority of food samples will not need to be tested by real-time PCR because redox potential monitoring can identify them in the selective enrichment phase. This method could be potentially used as a faster alternative to the current standard ISO 10272-1:2006, for nonregulatory monitoring purposes.
The potential effect of doxycycline on the microbial activity was investigated in three types of soil. Soil samples were spiked with doxycycline, incubated at 25°C and tested at 0, 2, 4 and 6 days after treatment. The microbiological activity of the soil was characterized by the viable count determined by plate pouring and by the time necessary to reach a defined rate of the redox-potential decrease termed as time to detection (TTD).The viable count of the samples was not changed during the storage. The TTD values, however exhibited a significant increase in the 0.2-1.6 mg/kg doxycycline concentration range compared to the untreated samples indicating concentration-dependent inhibitory effect on microbial activity. The potency of the effect was different in the 3 soil types. To describe the combined effect of the doxycycline concentration and time on the biological activity of one type of soil a mathematical model was constructed and applied.The change of microbial metabolic rate could be measured also without (detectable) change of microbial count when the traditional microbiological methods are not applicable. The applied new redox potential measurement-based method is a simple and useful procedure for the examination of microbial activity of soil and its potential inhibition by antibiotics.
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