Week 11 Food Microbiology PDF

 MIC60104 Introduction to Microbiology By Dr Lee Khai Wooi Food and industrial microbiology Food microbiology 1. Food spoilage 2. Microbial toxins 3. Microorganisms in fermented foods Food microbiology Foods are nutritious to humans but also are ideal culture media for m...

 MIC60104 Introduction to Microbiology By Dr Lee Khai Wooi Food and industrial microbiology Food microbiology 1. Food spoilage 2. Microbial toxins 3. Microorganisms in fermented foods Food microbiology Foods are nutritious to humans but also are ideal culture media for microbial growth Microbial growth in food can result in either preservation or spoilage Contamination by disease-causing microorganisms can occur during food-handling sequence  Intrinsic factors  pH, moisture, water activity, [O]-[N] potential, physical structure, nutrients, natural antimicrobial agents  Extrinsic factors  Environmental temperature, humidity, gases, types of microorganism present in food Differences in spoilage processes in relation to food characteristics Approximate minimum water activity relationships of microbial groups and specific organism of important in food spoilage Intrinsic factors 1. Carbohydrates: spoilage does not result major odors  Breads, jams, fruits 2. Proteins &/ fats: Foul odors (amine compounds)  Meat, butter, eggs Putrefaction-proteolysis & anaerobic breakdown of proteins  Cadaverine Degradation of fats to short-chained fatty acids  Rancidity 3. Low pH favors the growth of yeasts and molds 4. Neutral to high pH favors the growth of bacteria 5. Water availability is measured by water activity (aw)- microbes dehydrated by hypertonic conditions  Osmophiles- adapted to environment with high solutes/high [osmotic]  Xerophiles- survive dry/low water activity environment 6. [O]-[N] potential (Redox)  Fresh fruits are in their reduced state  O2 will diffuse and oxidize dead cells (No respiration)  Cooking will increase/decrease reducing compounds Cut, shredded, ground or minced 7. Physical structure  Grinding/mixing (Increased surface area) 8. Antimicrobial substances in foods  Coumarins in fruits & vegetables  Lysozyme in eggs  Tabasco/hot red pepper sauces 9. Herbs & spices  antimycotic aldehydes and phenols Phytochemicals-allicin, eugenol, rosmarinic acid  E.g. Sage, rosemary, cinnamon, mustard, oregano, garlic, cloves, basil 10. Polyphenol contents in green & black teas Extrinsic factors 1. Temperature 2. Humidity 3. Storage atmosphere Eliminate surface-associated microorganism that are sensitive to O2/CO2  Shrink/vacuum-packaging Atmospheric modified  Modified atmosphere storage packaging ( 60% CO2 inhibits spoilage fungi) Vacuum- Shrink-packaging packaging Food spoilage Rapid microbial growth Attractive appealing food  sour, foul-smelling, fungus-covered 1. Spoilage of unpasteurized milk Stage 1: Acid production by Lactococcus lactis (Sour) Stage 2: Growth of acidophilic Lactobacillus (Sour) Stage 3: Yeasts & molds degrade lactic acids Stage 4: Bacteria digest proteins (Alkaline-putrid odor, bitter flavor) 2. Spoilage of fruits/vegetables Stage 1: Molds penetrate cell wall/skins with exoenzymes Stage 2: Soft rot by Erwinia carotovora bacteria (Hydrolytic enzymes) Stage 3: Decomposition-High redox potential/lack of reduced conditions permit growth of aerobes and facultative anaerobes Ergotism Claviceps purpura grows on grains and produce toxic ergotamines (Hallucinogenic alkaloids) Ergotamines constrict blood vessels and cause the muscle of the uterus to contract Altered behavior, abortion, death Claviceps purpura grows on grains Aflatoxins Aspergillus flavus grows on moist grains and nuts Fungus-derived hepatocarcinogens- DNA intercalating agent  frameshift mutation AF-B1 is the most potent AF-B1 & B2 ingested and converted by lactating animals to AF-M1 & M2 Fumonicins Fusarium moniliforme grows on moist grains and nuts Disrupt synthesis & metabolism of sphingolipids Often contaminate corn and corn-based feeds & foods Leukoencephalomalacia in horses, pulmonary edema in pigs, esophageal cancer in humans  Algal toxins Syndrome Causative organisms Primary vector Toxin type Parasitic shellfish poisoning Alexandrium spp. Shellfish Saxitoxins Gymnodinium spp. Pyrodinium spp. Neurotoxic Gymnodinium breve Brevitoxins Ciguatera fish poisoning Gambierdiscus toxicus Reef fish Ciguatoxins Amnesic shellfish poisoning Pseudo-nitzchia spp. Shellfish Domoic acid Diarrhetic shellfish poisoning Dinophysis spp. Dinophysistoxins Prorocentrum spp. Okadaic acid Estuary syndrome Pfiesteria piscicida Water Unknown  Food-borne infection Involves: 1. Ingestion of pathogen 2. Growth of pathogen in host 3. Tissue invasion &/or toxin release) Typical incubation period of infection  Food-borne intoxication Symptoms appear as soon as contaminated food in consumed Growth of microorganism is not required Toxins produced can be associated with microbial cells or released to/from the cells Infections Intoxications Bacteria, viruses, parasites protozoa Toxins Invade &/ multiply in lining of intestine No invasion or multiplication Incubation period: hours-days Incubation period: minutes to hours Diarrhea, nausea, vomiting, abdominal Vomitting, nausea, diarrhea, weakness, craps, fever respiratory failure, numbness, sensory/motor dysfunction Communicable Not communicable Inadequate cooking, cross Inadequate cooking, cross contamination, poor personal hygiene, contamination, poor personal hygiene, food handling food handling  Major food-borne infectious diseases Disease Organism Incubation period & characteristics Major foods involved Salmonellosis S. typhimurium, 8-48 h; Enterotoxin & cytotoxins Meats, poultry, fish, eggs, S. enteritidis dairy products Acrobacter A. butzleri Severe diarrhea, recurrent cramps Meat products, especially diarrhea poultry Campylobacteriosis Campylobacter jejuni Usually 2-10 days; Most toxins are heat labile Milk, pork, poultry products, water Listeriosis L. monocytogenes Varying periods, related to meningitis & Meat products, especially abortion; new-borns & elderly are more pork & milk susceptible Escherichia coli E. coli, including 24-72 h. Enterotoxigenic positive & negative Undercooked ground diarrhea & colitis serotype O157:H7 strains; Haemorrhagic colitis beef, raw milk Shigellosis S. sonnei, S. flexneri 24-72 h Egg products, puddings Yersiniosis Y. enterocolitica 16-48 h; Some heat-stable toxins Milk, meat products, tofu Plesiomonas P. shigelloides 1-2 h Uncooked molluscs & diarrhea foreign travel Vibrio V. parahaemolyticus 16-48 h Seafood, shellfish gastroenteritis Salmonellosis Salmonella ingested in food or water invades phagocytes and grows as an intracellular pathogen. Replicates and spread to adjacent cells Combination of endotoxins, enterotoxins and cytotoxins are produced to kill host cell Salmonella- containing vacuole (SCV) Infection landscapes of E. coli 1. Enterotoxigenic (ETEC) 2. Enteropathogenic (EPEC) 3. Enteroinvasive (EIEC) 4. Enterohemorrhagic (EHEC, e.g.O157:H7) Enterotoxigenic E. coli (ETEC): Adheres to small intestine enterocytes using its fimbriae. Not causing severe cell damage Produces heat labile (LT) and heat stable (ST) toxins, which increase host cell cyclic AMP and cyclic GMP, respectively. As a result, chloride secretion is enhanced; sodium chloride adsorption is inhibited  Secretion of water into the lumen of the gut Travelers' diarrhea (under developed countries) *The LT toxin produced by ETEC is closely related to the cholera toxin produced by Vibrio cholerae. Enteropathogenic E. coli (EPEC): Bacteria to adhere to enterocytes, using adhesin (intimin) molecule. EPEC produces proteins that manipulate actin in the enterocyte, changing the structure of the cell.  Changes in cell signal transduction: Causes lesions that lead to the secretion of water into the gut Triggers of inflammation & permeability at tight junction. Enteroinvasive E. coli (EIEC): EIEC employ virulence factors known as invasins that allow the organisms to penetrate the enterocytes of the intestine. EIEC replicates inside the host cell and invade neighboring host cells, leading to tissue damage & inflammation. The pathogenesis is very similar to shigellosis. Enterohemorrhagic E. coli (EHEC): A.k.a. Shiga toxin producing E. coli (STEC) EHEC adheres to enterocytes like EPEC The major difference between EHEC and EPEC is the production of Shiga-toxins (STx) STx is closely related to the toxin produced by Shigella dysenteriae STx inhibits protein synthesis by cleaving an adenine residue from the 28s rRNA component of ribosomes. Stx stimulates inflammation and gain access to the circulation at the breached epithelium, causing vascular damage in gut, kidneys and the central nervous system E. coli O157:H7 is an STEC Others 1. Staphylococcus (Toxic shock syndrome) Enterotoxins of S. aureus classified as superantigens that induce severe T cell response (Release intercellular mediators called cytokines, the inflammatory response). Toxic shock syndrome toxin 1 (TSST-1)  Sudden, potentially fatal condition 2. Clostridium botulinum (Botulinum toxin) Botulinum toxin is a neurotoxin Affects the autonomic nerves that control respiration and heart beat Can be destroyed by heat (80°C, 10 min) Destroy SNARE proteins  Inhibits fusion of synaptic vesicle at the axon terminal  No acetylcholine release at synaptic junction  Microorganism and food product Winery: Cheese: Yoghurt: Saccharomyces cerevisiae Leuconostocs Streptococcus thermophilus Saccharomyces carlsbergensis Lactobacillus casei Lactobacillus bulgaricus Zymomonas mobilis Streptococcus thermophilus Lactobacillus casei Lactobacillus bulgaricus Penicillium roqueforti Microorganisms used in cheese Cheese Contributing microorganisms (Country of origin) Earlier stages of production Later stages of production Soft, un-ripened Cottage Lactococcus lactis Leuconostoc cremoris Cream L. cremoris, L. diacetylactis, S. thermophilus, L. bulgaricus Mozzarella (Italy) S. thermophilus, L. bulgaricus Soft, ripened Brie Lactococcus lactis, L. cremoris Penicillium camemberti (France) P. Candidum Brevibacterium linens Camembert Lactococcus lactis, L. cremoris Penicillium camemberti (France) Brevibacterium linens Semisoft Blue, Roquefort (France) Lactococcus lactis, L. cremoris Penicillium roqueforti Brick, Muenster (US) Lactococcus lactis, L. cremoris Brevibacterium linens Limburger (Belgium) Lactococcus lactis, L. cremoris Brevibacterium linens Hard, ripened Cheddar, Colby (Britain) Lactococcus lactis, L. cremoris Lactobacillus casei, L. plantarum Swiss (Switzerland) L. lactis, L. helveticus, Propionibacterium shermanii, S. thermophilus P. freudenreichii Very hard, ripened Parmesan (Italy) Lactococcus lactis, L. cremoris, Lactobacillus bulgaricus S. thermophilus  Fermented foods Foods (Area) Raw ingredients Fermenting microorganisms Coffee Coffee beans Erwinia dissolvens, Saccharomyces spp. (Brazil, Congo, Hawaii, India) Gari (West Africa) Cassava Corynebacterium mnihot, Geotrichum spp. Kenkey (Ghana, Nigeria) Corn Aspergillus spp., Penicillium spp., Lactobacilli, yeasts Kimchi (Korea) Cabbage Lactic acid bacteria Miso (Japan) Soybeans Aspergillus oryzae, Zygosaccharomyces rouxii Ogi (Nigeria) Corn Lactobacillus plantarum, L. lactis, Zygosaccharomyces rouxii Olives Green olives Leuconostoc mesenteroides, L. plantarum, Neurospora (Worldwide) sitophila Ontjom (Indonesia) Peanut presscake Neurospora sitophila Peujeum (Indonesia) Cassava Molds Pickles (Worldwide) Cucumbers Pediococcus cerevisiae, L. plantarum Poi (Hawaii) Taro roots Lactic acid bacteria Sauerkraut (Worldwide) Cabbage L. mesenteroides, L. plantarum Soy sauce (Japan) Soybeans Aspergillus oryzae/soyae, Z. rouxii, Lactobacillus delbrueckii Sufu (China) Soybeans Mucor spp. Tao-si (China) Soybeans A. oryzae Tempeh (Indonesia) Soybeans Rhizopus oligosporus, R. oryzae