micro and food poisoning

7/28/2019 Micro and Food Poisoning

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Presence of microorganisms in food may lead to:

1. Food spoilage i

Food spoilage occurs because of the biochemical activity of microorganisms as they grow

in the food, and manifests usually by changes in the food’s appearance, odor, texture, or taste, typically when the spoilage microflora exceeds about 107 organisms/g of food.Spoilage characteristics develop in food as microorganisms digest the food to support their growth.

a. Sugar fermentation with acid production. As bacteria metabolize pentoses andhexoses for energy production, it yields lactic acid causing a sour taste in the food.

b. Sugar fermentation with gas production.The catabolism of hexoses byfermentative yeasts produces ethanol and carbon dioxide. Relatively low pH andhigh sugar-containing products would support this type of spoilage. The typical

yeast spoilage defect in products such as sugar syrups and tomato products inhermetically sealed packages is caused by gas production.

c. Protein hydrolysis.Many spoilage bacteria produce proteolytic enzymes thathydrolyze proteins in foods such as milk, meat, poultry, and seafood products. Anaerobic proteolysis byClostridiumspp. can result in a noxious putrefaction of the food. Pseudomonads can carry the proteolysis one step further bymetabolizing amino acids to produce very foul-smelling compounds, such as theaptly named putrescine and cadaverine.

d. Digestion of complex carbohydrates.Produce spoilage can be caused by bacteriaand molds that produce pectinases which digest the pectin layer between the plantcell walls, resulting in a soft or mushy texture. When accompanied by proteolyticactivity, mushy produce will also develop a foul odor. Amylolytic enzymesproduced by molds and several bacteria digest starches to polysaccharides andsimple sugars, destroying the viscosity of products in which starches are used asthickening agents, such as gravies and pie fillings.

e. Lipolysis. A wide variety of microorganisms, including pseudomonads, molds, andstaphylococci, produce lipolytic enzymes that hydrolyze lipids, producing readilyoxidizable substrates that have a rancid odor.

f. Oxidation of organic acids and alcohols.Many molds and oxidative yeasts can

grow on acidified foods and metabolize the organic acid, raising the pH of thefood high enough to permit the growth of other types of spoilage organisms.

g. Guaiacol production. Alicyclobacilli can grow in some fruit or vegetable juices,metabolizing vanillin and other precursor molecules to guaiacol, a product with anasphalt-like or phenolic odor.



Surface growth.Most groups of microorganisms can spoil food by growing on the surface, causingslimy or sticky to the touch, and color changes in food.

2. Severe or other forms of illness ii,iiiresulting from food poisoning. Some are:

a. Campylobacteriosis caused by Campylobacter jejuni , an invasive organism infectingchickens, cows & swine, can lead to such complications as urinary tract infectionsand reactive arthritis, meningitis, recurrent colitis, acute cholecystitis, andGuillain-Barre syndrome , a rare disease that affects the nerves of the bodybeginning several weeks after the diarrheal illness. This disease occurs when aperson’s immune system is triggered to attack the body’s own nerves, and can lead toparalysis that last several weeks and usually require intensive care. Deaths, also rare,have been reported.

b. Specifically,L. monocytogenes is recognized as a human pathogen that causeslisteriosis. Listeriosis primarily affects newborn infants, pregnant women, the elderlyand those with compromised immune systems – cancer patients, leukemic patiens,and AIDS patients.

In a healthy non-pregnant person, listeriosis may occur as a mild illness with fever,headaches, nausea and vomiting. Among pregnant women,intrauterine or cervicalinfections may result in spontaneous abortion or still birth. Infants born alivemay develop meningitis and mortality.

c. One strain of E. coli, theE. coli O157:H7, causes a distinctive and sometimes deadlydisease.

This pathogen produces several virulence factors that causesevere damage to thelining of the intestine, acute renal failure (children and elderly), hemolysis,thrombocytopenia, and neurological problems (the last three occur mainly inadults). All EHEC, includingE. coli O157:H7, produce Shiga toxins which targets thehuman kidney, particularly the cortical region which is rich in Gb3 receptors for thetoxin.

Symptoms begin with non-bloody diarrhea one to five days after eating contaminated food, andprogress to bloody diarrhea (hemorrhagic diarrhea), severe abdominal pain and moderatedehydration. In young children,hemolytic uremic syndrome (HUS) is a serious complication

that can lead to renal failure and death. In the elderly, the complications sometimes lead tothrombocytopenic purpura (TPP), characterized by cerebral nervous system deterioration,seizures and strokes .

i Sperber and Doyle, Compendium of the Microbiological Spoilage of Foods and Beverages 2009,p. 10-12



ii Entry for Public Health Veterinarian/Food Safety: Overview of Food Microbiology, 2008, p. 15-25

iiiColorado State University Extension, Bacterial Food-borne Illness, No. 9.300,http://www.ext.colostate.edu/index.html

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