Microbial flora of food
It is important to be able to distinguish food poisoning from food spoilage. The former is when food is eaten which looks normal, smells normal and tastes normal. Hence you eat enough to make you ill from the ingested pathogens or toxins. Spoiled food does not normally cause food poisoning because it is rejected by the consumer before ingestion. In order to help determine if food is spoiled please note the list below ;-
Food Spoilage Test (sense of humour required...)
But more seriously....
Ready-to-eat food guidelines and surveillance studies
The HPA (UK) guidelines for ready-to-eat foods (Section 6.11, p288) were updated at the end of 2009. You can down load a .pdf file version by going to the HPA (UK) web site. These were released just at the final stages of the book being complied and so are only briefly referred to, but the main detail is on the previous similar 2000 version.
The USA are collecting baseline data of microorganisms in food (FSIS). Meanwhile there are a number of microbiological surveillance studies that have been published on various ready-to-eat foods, assessed according to criteria such as the HPA(UK) RTE guidelines. These include:
- Ice cream
- Stuffing (Richardson & Stevens 2003 J Appl Microbiol 94, 733-737)
- Organic vegetables (Sagoo et al. 2001 Lett Appl Microbiol 33, 434-439)
- Meat and meat products (Joint Food Safety and Standards Group, UK, Number 9)
- Burgers (Little et al. 2001 Commun Dis Public Health 4, 293-9)
- Cooked rice (Nichols et al. 1999 J Food Protect 62, 877-882)
- Chicken sandwiches (Little et al. 2002 Commun Dis Public Health 5, 289-98)
- Foods from sandwich bars and take-aways
- Quiche (Gillespie et al. 2001 Commun Dis Public Health 4, 53-9)
- Salmonella and Campylobacter contamination of fresh & frozen chicken
These studies help to shows the proportion of foods containing pathogenic bacteria (not viruses or toxins), and contribute towards the microbiological risk assessment of such foods.
Dairy products, lactic acid bacteria and probiotics
Lactic acid bacteria have been used for centuries to preserve various food products (Overview).
More recently there has been considerable interest in the use of lactic acid bacteria and related organisms in the production of probiotics (p134). Below is a list of web sites some of which are commercial which sell probiotic cultures for a range of purposes. Look trough the sites and decide which tests you would carry out to determine the efficacy of these products. Firstly consider the number of organisms that would survive the stomach (lactic acid bacteria will be acid resistant) and the number of bacteria already colonising the intestinal tract.
In the first edition (2000) I introduced the potential applications of DNA arrays, etc as I believed modern food microbiologists should be aware of these developments, even if they do not have access/direct use of them. Since then the complete genomes of many important foodborne pathogens have been released and a number are listed in Table 2.15, (p89). Of particular relevance here is the sequence analysis of Bifidobacterium longum (PNAS article) as well as Lactococcus lactis has been published (Genome Research). There is a Lactic Acid Bacterium Genome Consortium (see NEWS) who worked on the genomes of nine organisms. Their work was published in PNAS and this may assist in our understanding of probiotics.
- WHO draft guidelines on the evaluation of probiotics (May 2002)
- Lactic acid bacteria description
- Lactobacillus description
- Wakunaga products
- Candida and probiotics
- Living Well with Probiotics
- Custom probiotics
- Dr Ohhira's original probiotic culture !
Food additives are used for a variety of purposes, including preservation. A useful site which can be used to search for data on food additives has been compiled by the Nordic Working Group on Food Toxicology (Nordic Food Additive database).
If you are looking for useful pictures of food matrix and micro-organisms a useful site is Foods under the microscope
A couple of web sites I have just picked up on eggs are good at explaining the egg structure and associated microbial hazards:
- Egg guide
- CDC site on Salmonella Enteritidis and eggs
Section 7.5 has simple diagrams on microbial biofilms. There is also a very descriptive article on biofilms in an issue of Emerging Infectious Diseases (Sept, 2002)
Please visit the ''Poetic Justice' site for a break!