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TAMU FSTC 326 - Food Microbiology Test 2

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B. Aerobic or facultatively anaerobic sporeformers1. Genus Bacillus (“Small Staff”)(B. cereus, B. subtilis, B. anthracis) family bacilliaceaea) Foodborne pathogen: B. cereus (foodborne intoxication; most common amongst Bacillus foodborne disease)spore does not distend the mother cell(1) B. mycoides: enterotoxin-producing species associated mainly with milk; pasteurized milk unproperly stored temperature wise, cross-contaminationB. thuringiensis: may produce disease via enterotoxin secretion; toxico-infection; some are plant pathogens but some strains are known to secrete enterotoxinsVery similar to B. cereus(2) Toxins produced: enterotoxin, emetic toxin(a) Chemical similarity to Clostridium perfringens toxins(b) Hemolysin BL (HBL): primary diarrheal toxin(c) Diarrheal disease (Enterotoxin):i) Short duration, generally without feverii) Foodborne transmission: cereals, meats, dairy, grainsiii) Some vomiting, diarrhea, crampingEnterotoxin (toxico-infection)(d) Emetic toxin (intoxication)i) More severe symptoms: severe vomitingii) 1-6 hr incubation period post ingestioniii) similar to Staphylococcal GI intoxication symptomsiv) Chinese rice syndrome: loss of hot holding capacity in foods on buffets(1) Organism contaminate post-cooking; if temperature drops during holding, surviving cells synthesize toxin(2) Food intoxicationB. cereus Heavily underreported pathogenb) Non-pathogenic Bacillus species (spoilage concerns)Psychrotolerant: B. weihenstephanesis (pasteurizd milk spoilage can cause “sweet curdling of milk”- no souring effect; while under refrigeration- does not have to include temp abuse)B. subtilis: spoilage of cooked plant/grain foodsSome species of Bacillus relevant to food spoilage now moved to genus Paenibacillus (“Like a Bacillus”)P. pectinolyticus (pectin destroying;produce spoilage)P. polymyxa (much slime)P. macerans (cleavage)These are non-pathogenic but cause severe visual and textural defects(1) Mesophilic and thermophilic species: spoilage of low-acid canned foods(a) Canned vegetables, meats, etc.(b) Spore survives processing, germinates, and growsi) Acid fermented from sugarsii) Little or no gas production (flat sour)(2) Mesophilic: B. polymyxa, B. macerans, B. subtilis, B. licheniformis(3) Thermophilics: Geobacillus stearothermophilus (formerly B. stearothermophilus)plant derived foodsthermophilic flat sour spoilage, canned low-acid foodscanning can kill the vegetative cells but some spores will not be killedvisual and textural defectsmostly problematic in high starch, neutral pH, plant derived foodsC. Obligately anaerobic sporeformers1. Genus Clostridium (C. botulinum, C. perfringens)a) C. botulinum: Causative agent, foodborne botulism (as well as other forms of botulism)obligate, strict anaerobic fermentative rodsmesophilic, thermophilic, psychrotrophic species and strains exist in genusspore distends mother cell“sausage disease/death” - botulism first described in early 1200’s associated with euro style blood sausages(1) Strains are classified based on neurotoxin synthesis (7 toxin serotypes: A, B, C, D, E, F, G)Toxin type A is most problematic for human disease(a) Group I: proteolytic strains (mostly prob. for meats)(b) Group II: non-proteolytic strains(c) Group III: toxin types C, D(d) Group IV: toxin type G(2) Microbe growth:(a) Nutritionally Fastidious with respect to nutrients: complex nutrients must be provided by environment/food for growth, toxin production in simple form(b) Temperatures: 10-50°C observed as optimal, but environment has impact on growth (No growth at refrigeration!)most wont grow below 10 C, but some are thermotolerant/thermophilicToxin types B, E,F isolates: minimum growth temp. 3 CProteolytic and non-proteolytic strains identified(c) No growth at pH < 4.5 (Low acid canned foods most problematic!); threshold 4.6 up to pH 7 for low-acid canned foods(d) Minimum water activity for growth: 0.94water activity is an indicator of the availability of water; not a measure of total water(3) Not effective competitor in various foods/toxin production most problematic in heated foods where microbes are killed(4) Foodborne adult botulism: intoxication (extremely potent; Lethal Dose .1 - 1 ng/kg body weight) with consumption of preformed neurotoxinhas been explored for weaponizing and now commercialized into a therapy use as botox: is a purified botulinum toxinbefore commercial use, was used for therapeutic aid for people with muscle glitches; was a highly controlled injection; very little was used(a) Absorption of toxins through intestinal walls leads to muscle paralysis(b) Neurotoxin-secreting: induces flaccid paralysis (binding to nerve synapses inhibits acetylcholine release)prevents acetylcholine release at neuromuscular junctions, skeletal musclesprevent muscle contraction/activationflaccid paralysis (permanent relaxation of muscle), descendingDroopiness of eyelids, slurred speechDescending paralysis of smooth muscles: diaphragm! – inability to control respirationiii) Toxin is heat sensitive: 80°C, 10 min; boiling waterToxin is heat liable (sensitive) and may be destroyed by cooking/boiling, irradiation, or other processesLots of issues with improper home canningIncubation period: 12 hr – 36 hr (may be shorter depending on the toxin type and dose)Groupings:1 (proteolytic): high protein meat2 (non-paralytic)3 (toxin types C,D)4(toxin type G)(c) Symptoms:i) Droopiness of eyelidsii) Chronic fatigueiii) GI symptoms: diarrhea, nausea, vomitingiv) Fatal if not treated (3-5 days)v) Onset: 12-72 hr post-ingestionthere are treatments but cant clear it(d) Foods of concern: (not high acid foods)heated foods temperature abused after cookingprocessed/fully cooked meat/poultry – improper cooling post-cooking allows spores to germinate, secrete toxini) Heat processed low-acid canned foods: meats, produce(1) Under-processing (Currently processed to 12-D)(2) Anaerobic environment in food created from heating(3) No other competitors post-processingii) Controlling synthesis of toxin in foods:(1) Acidification; pH reductionproblematic for canned tomato products, despite acid content so have more severe canning procedure because botulinum can grow in it(2) Addition of curing agents to inhibit spore germinationoutbreaks in various meat dishes: vacuum-sealed smoked salmon(3) Refrigerated storage: 2011 outbreak of botulism in OH, GA (2 cases)2011: Potato soup, cooked but left unrefrigerated for weeks2009 Georgia: vegetable juice left out


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