Food, water and public health microbiology

39. Food, water and public health microbiology




Questions


image How do food products become contaminated with microorganisms?

image How can contamination be prevented?

image What is the role of public health in the prevention of infection?

Our food, water and air can harbour a number of potential pathogens that cause a range of infections including gastroenteritis, septicaemia and respiratory infections (Fig. 3.39.1). The advent of penicillin and other antibiotics, or even vaccination, have not been the main factors responsible for reducing the prevalence and incidence of such infections. It is mainly a consequence of the substantial improvement in environmental hygiene.


image

Fig. 3.39.1 Environmental sources of infection.



Food microbiology


Fresh food is easily contaminated by potential pathogens. Vegetables and fruit have soil contamination and even after washing they may harbour microbes if they were washed in faecally contaminated water. Outbreaks of hepatitis A or Salmonella spp. have occurred with imported fruit and other food stuff that has been washed in ‘river’ water or produced with contaminated ingredients. Shellfish pose a particular hazard if grown in sewage-contaminated waters as they filter-feed and concentrate microbes. Some raw meats have been found to contain pathogens such as Escherichia coli O157:H7 in burgers or Salmonella and Campylobacter in poultry, which are often from the animal’s gut.


Refrigeration at ≤ 4°C retards bacterial growth, although those that are ‘cold-loving’ (psychrophiles) such as Listeria monocytogenes, Yersinia enterocolitica and Aeromonas hydrophila can survive and eventually cause infection if consumed. There are a number of other measures utilized to preserve food for longer. Food may be ‘cook-chilled’ (cooked then rapidly frozen), canned (at temperatures of 115°C for 24–100min intervals), lyophilized (water removal from food), irradiated (ultraviolet or gamma irradiation), pasteurized (e.g. low heat at 63°C for 30min), chemically treated (nitrates, organic acids) or preserved by using sugar or salt to decrease water availability.


Although not possible for all foods, the safest approach to preventing food poisoning is adequate cooking, as pathogens do not survive sustained high temperatures. Cooking may be compromised by poor handling so that the food is then recontaminated. Catering services that provide food for patients have to ensure that the food is safe to eat in order to minimize the risk of food-borne infection. Most establishments have a food safety programme based on the hazard analysis of critical control point (HACCP), which focuses on areas that are critical to food safety (e.g. temperature control for cooking and refrigeration).


Control of food that is sold is regulated under the Food Safety Act 1990 (and other more specific legislation) in the UK or similar legislation in many other countries.

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Jul 3, 2016 | Posted by in MUSCULOSKELETAL MEDICINE | Comments Off on Food, water and public health microbiology

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