The species accuracy of the Most Probable Number (MPN) European Union reference method for enumeration of Escherichia coli in marine bivalves

Continuous European Union programmes with specified methods for enumeration of Escherichia coli in bivalves for human consumption are currently running. The objective of this research was to examine the species accuracy of the five times three tube Most Probable Number (MPN) EU reference method used for detection of E. coli in marine bivalves. Among 549 samples of bivalves harvested from Norwegian localities during 2014 and 2015, a total number of 200 bacterial isolates were prepared from randomly selected culture-positive bivalves. These presumptive E. coli isolates were characterized biochemically by the Analytical Profile Index (API) 20E, as well as by Matrix Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS). The majority of isolates (90%) were identified as E. coli, by both API 20E and MALDI-TOF MS. Ten isolates (5%) were identified as Klebsiella pneumoniae, while one isolate was identified as K. oxytoca by both methods, whereas three isolates were identified as Acinetobacter baumannii, Citrobacter braakii, and Enterobacter cloacae, respectively. The identification of the remaining six isolates were not in compliance between the two methods.

An interlaboratory study to find an alternative to the MPN technique for enumerating Escherichia coli in shellfish

Nine laboratories in eight countries tested 16 batches of common mussels (Mytilus edulis) over a 32 week period in order to find an alternative to the Most Probable Number (MPN) technique to enumerate E. coli. The alternatives investigated included the 3M Petrifilm system, the Merck Chromocult agar method and a Malthus conductance technique. The Petrifilm was found to be unsuitable and was subsequently dropped from the trial. After 669 analyses, a correlation of 0.83 was observed for log E. coli counts between the MPN and Chromocult methods and there was no significant evidence that either method tended to give higher readings than the other. The MPN was slightly better than the Chromocult method for repeatability but the Chromocult was slightly better for reproducibility. However, the observed differences are probably too small to be of practical importance. On the basis of these data therefore, the two methods appear equally suitable for E. coli enumeration in shellfish. There were poor correlations between these methods and the Malthus technique. A small but significant number of samples tested positive on the Malthus instrument but were recorded negative on the MPN and Chromocult tests. Subsequent analysis positively identified E. coli from these Malthus assays. After statistical analysis, errors were noted in both the MPN and Chromocult methods but it was found that there would be no statistical differences if the Chromocult agar were used as an alternative to the MPN technique.

Microbes in food processing technology

There is an increasing understanding that the microbial quality of a certain food is the result of a chain of events. It is clear that the microbial safety of food can only be guaranteed when the overall processing, including the production of raw materials, distribution and handling by the consumer are taken into consideration. Therefore, the microbiological quality assurance of foods is not only a matter of control, but also of a careful design of the total process chain. Food industry has now generally adapted quality assurance systems and is implementing the Hazard Analysis Critical Control Point (HACCP) concept. Rapid microbiological monitoring systems should be used in these cases. There is a need for rapid and simple microbiological tests which can be adapted to the technology and logistics of specific production processes. Traditional microbiological methods generally do not meet these high requirements. This paper discusses the tests, based on molecular biological principles, to detect and identify microbes in food-processing chains. Tests based on DNA technology are discussed, including in vitro DNA amplification like the polymerase chain reaction (PCR) method and identifications based on RFLP, RAPD and DNA fingerprinting analysis. PCR-based methodology can be used for the rapid detection of microbes in food manufacturing environments. In addition, DNA fingerprinting methods are suitable for investigating sources and routes of microbial contamination in the food cycle.

Immunochemical probes for food proteins after heat processing

While better hygiene controls and vaccinations have diminished the occurrence of infectious diseases in humans, food-borne diseases have increased. Thus sterilization of food products is of prime importance. The introduction of new technologies applied to food has necessitated new methods for the control of food safety and food quality. This review aims to point out the importance of immunochemistry in the identification of structural changes induced in food proteins during food processing. New technologies have introduced the use of additives in food products, therefore it is important to identify and quantify such additives, even after complete hear denaturation. Toxic chemicals, toxins and pesticides which can contaminate food products before or during processing should also be identified. Finally, the use of immunochemical tests as a control of sterilization procedures in heterogeneous foodstuffs is discussed.