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153 Cards in this Set
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Gram (+) Bacteria |
Cytoplasmic membrane Thick peptidoglycan Teichoic acids strengthen cell structure |
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Gram (-) Bacteria |
Cytoplasmic membrane Thin peptidoglycan Outer membrane with LPS, endotoxin lipid A Destroyed by hand sanitizer |
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Exotoxin |
Extracellular toxin Kills host or alters metabolism |
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Cytotoxin |
Exotoxin that is lethal to host |
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Enterotoxin |
Toxins that act in the intestines |
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Endotoxins |
Structural component of bacterial cells (i.e. Lipid A) Can effect intestine or entire body Causes fever, cramps |
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LPS |
Lipopolysaccharide Proteins found in the outer membrane of enteric pathogens Allow metabolites, sugars, etc. into cell Composed of O-antigen (carb chain) and lipid A (glycolipid, endotoxin, stimulates immune response) |
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Escheria coli (non-pathogenic) |
Found naturally in intestines Gastroenteritis if unfamiliar strain is consumed |
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ETEC Characteristics |
Enterotoxigenic E. coli High infective dose Watery gastroenteritis 1-2 day incubation, 1-2 day sickness Deadly mostly to children, elderly |
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ETEC - How it makes you sick |
Non-invasive Binds to small intestine with fimbriae Produces exotoxins: ST (heat-stable) and LT (heat-liable; less effective than cholera) |
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EPEC Characteristics |
Enteropathogenic E. coli High infective dose Watery gastroenteritis 1-2 day incubation, 1-2 day sickness Severe diarrhea in infants (may cause dehydration) |
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EPEC - How it makes you sick |
Moderately invasive Adheres to host cell with intimin Type III secretion, NOT exotoxins Attachment and effacement pathogen |
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EHEC Characteristics |
Enterohemorrhagic E. coli Low infective dose 3-4 day incubation, 3-7 day sickness - Hemorrhagic colitis (bloody stools) - Hemolytic uremic syndrome (HUS) |
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HUS |
Hemolytic uremic syndrome Kidneys blocked by damaged red blood cells Hemolytic anemia, acute renal failure |
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EHEC - How it makes you sick |
Type III secretion, contains LEE Attachment and effacement pathogen Makes shiga-like toxins that stop protein synthesis Asymptomatic in cows (no shiga toxin receptor) |
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EIEC
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Enteroinvasive E. coli
Low infective dose 1-2 days incubation, sick 1-2 days Watery gastroenteritis/ dysentery-like diarrhea Possible fever |
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EIEC – How it makes you sick
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Type III secretion
Intracellular pathogen Multiplies inside cells Highly related to Shigella Antibiotics bad: destroy pathogenic cells, which then release their shiga toxin |
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Shigellosis
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Most common cause of bacterial dysentery
Four species, all of which are human pathogens Low infective dose 3 or more days incubation, sickness for 2-7 days Watery gastroenteritis/ dysentery-like diarrhea Can cause fever Similar to EIEC |
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S. sonnei and S. dysenteriae
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Shigellosis sonnei is highly infectious, problem in day-care centers Shigellosis dysenteriae causes dysentery, fever, HUS and produces shiga toxin |
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Salmonellosis
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Most common intestinal salmonellosis are S. enterica Typhimurium, S. enterica Enteritidis, S. enterica Heidelberg
Variable number of cells to get sick 1-2 days before sickness, lasts 2-3 days (sometimes longer) Gastroenteritis More serious cases have bacteremia, infections, fever (because of endotoxin LPS) |
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Salmonellosis – How it gets you sick
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Invasive (grows inside enteric cells)
Attaches to small intestine with fimbriae Multiplies in other parts of body too, like lymph nodes Type III secretion – twice - Again after inside cell to create protective coating Transmission by undercooked meat, raw milk, raw eggs, fecal-oral route |
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Salmonella Typhi and Salmonella Paratyphi
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Both species only found in humans
Transmitted through fecal-oral route Low infective dose 1-2 weeks before sick, sick for long time Fever, diarrhea, headaches Colonizes liver Rare in US, common in developing countries Can be asymptomatic – typhoid Mary |
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Yersinia enterocolitica
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Common in undercooked pork
Invasive with type III secretion |
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Cholera
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Found in water and shellfish
Big problem in India/Africa Outbreak in Haiti – may present as asymptomatic |
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Vibrio
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Vibrionaceae family
Found in fin fish and shellfish |
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Vibrio cholera
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Very low infective dose
Between 1-4 days before sick, lasts 2-3 days Very severe watery diarrhea - Loss of water – one liter per hour - Need IV to prevent death, but only 25% of infected people show symptoms Cholera toxin binds to glycolipid receptor on intestinal cells |
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Vibrio parahaemolyticus
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Found in fish – especially sushi
High infective dose Get sick in 1 day, lasts for a week Diarrhea, abdominal cramps, nausea, vomiting, headache, fever, chills |
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Vibrio vulnificus
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Responsible for most seafood-related deaths
Sickness rare in healthy people In immunocompromised people - vomiting, diarrhea, abdominal pain 50% chance of death once in blood stream Lives in warm waters with low salt Transmission through under-cooked seafood, poorly sanitized water |
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Campylobacter jejuni
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Difficult to grow and study because it is a poor competitor Very low infective dose 2-9 days before sick, sick for a few days Severe abdominal cramping, diarrhea, nausea and vomiting, fever, headaches, dizziness 1 in 1000 cases causes GBS (Guillain Barré Syndrome) |
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GBS
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Guillain Barré Syndrome
Paralysis of legs, arms, lungs, face Autoimmune – body begins attacking itself |
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Campylobacter jejuni – How it makes you sick
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Produces CDT exotoxin (cytolethal distending toxin)
Stops cells from reproducing – breaks DNA Found naturally in chickens, wild birds Sometimes cows, dogs, cats, rodents |
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Gram-positive food microbes
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Clostridium perfringens*
Clostridium botulinum* Bacillus anthracis* Bacillus cereus* Listeria monocytogenes; Staphylococcus *Form spores* |
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Spores
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Dormant bacteria only found in gram positive bacteria Do not have nutritional requirements Resistant to harsh environments, impermeable to many chemicals Can survive for a very long time (40 million years) |
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Spore Germination
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Germinate when they receive signals that conditions are good for growth
Cooking causes them to germinate Bad competitors, so only proliferate when other competitors can’t (i.e. cooking) |
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Spores – How they make you sick
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Most cause foodborne intoxication through extracellular digestive enzymes
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Bacillus cereus
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Soil microbe
Does not grow in humans Grows in high-starch and high-protein foods Causes two types of intoxication - gastroenteritis (watery) or emetic disease (vomiting) Starchy foods usually cause vomiting High-protein foods usually cause gastroenteritis |
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Bacillus cereus – How it makes you sick
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Toxin is heat-stable, pH stable and protease-stable
To control, prevent soil contamination Do not hold foods at warm temperatures for long |
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Bacillus anthracis
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Pathogen in animals and humans
Can get from cutaneous (through a cut/wound), inhalation or foodborne - Ingestion of poorly cooked meat from infected animals Most likely results from infection, not intoxication Symptoms are nausea, loss of appetite, bloody diarrhea, fever, bad stomach pain Very rare but has a high mortality rate |
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Clostridium perfringens
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Found in soil and animal intestines
Causes gas gangrene High infective dose Sick in less than one day, lasts less than one day Watery gastroenteritis, similar to B. cereus |
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Clostridium perfringens – How it makes you sick
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Not infection or intoxication…toxicoinfection!
Colonization doesn’t occur but toxins are made inside humans Heat stable enterotoxin made during sporulation in intestine Thermophile – grows well in very hot temperatures Spores survive boiling |
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Clostridium botulinum
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About 25 cases per year
Causes botulism and reduces wrinkles Anaeorobic, spore-forming soil microbe Blurred vision, dizziness, difficulty speaking, gradual paralysis |
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Clostridium botulinum – How it makes you sick
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Vegetative cells sensitive to oxygen, heat, low pH and high salt
Foodborne intoxication caused by a neurotoxin - Stops muscles from contracting, blocks release of acetylcholine |
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Staphylococcus aureus
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Colonizes skin and nasal passages
Causes skin infections, toxic shock syndrome, scalded skin syndrome (newborns), gastroenteritis Needs to grow in foods to cause illness 100,000 cells needed 2-6 hours until sick, lasts 1 day |
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Staphylococcus aureus – How it makes you sick
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Does not form spores
Non-pathogenic inhabitant of human body Causes foodborne intoxication after ingesting its enterotoxins First enterotoxin discovered - Pyrogenic exotoxins (PT) Superantigens – extremely strong immunostimulatory properties Causes activation of T-cells, resulting in inflammation Salt tolerant, grows well in fatty and salty foods Tolerant to low amounts of available water and very heat-stable, but acid sensitive |
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Listeria monocytogenes
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Does not create spores but is a foodborne infection
Widespread in vegetation and domestic animals Carried asymptomatically by a small percent of the human population Low infective dose, takes up to four weeks for symptoms Healthy people might experience acute febrile gastroenteritis but, in most cases, no disease Immunocompromised and elderly contract sepsis, encephalitis and meningitis |
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Listeria monocytogenes – How it makes you sick
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Cell-to-cell transmission
Spreads to organs and eventually to brain or fetus Salt tolerant Psychrotroph Anaerobe |
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Food and water-borne viral disease
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Causes gastroenteritis, systemic infections
Viruses are not cells, nor are they living Foodborne viral pathogens are naked (are not enveloped in a membrane) Much more difficult to culture - Require living cells, i.e. chick embryos Difficult to detect in food - Need electron microscope, antibodies, PCR (a nucleic acid) |
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Viral disease – How is makes you sick
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Cause foodborne infections – only replicate inside host cells
Viruses are host specific If they infect humans, they can only replicate in humans Transmitted by fecal-oral route Viruses survive in food longer than bacteria (weeks to months) Survive freezing and acidic conditions |
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Viral foodborne illnesses
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Gastroenteritis – human rotavirus, norovirus
Extra-intestinal infections – polio virus, hepatitis A virus |
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Human rotavirus
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Major cause of gastroenteritis in babies
By age 4, most children are immune Low infection dose (10-100 viral particles) 1-3 days to get sick, lasts up to a week Diarrhea and vomiting |
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Norovirus
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Stomach flu – diarrhea and vomiting
About 10-100 particles needed Sick in 1-2 days, lasts 1-3 days Food and surfaces are easily contaminated Inactivated by heat or chlorine |
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Enterovirus
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a virus that infects the body through the gastrointestinal tract
Does not cause gastroenteritis, but causes damage to other organs In the Picornavirus family |
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Polio virus
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Infective dose unknown
Takes several days for symptoms to start Three phases - First phase is asymptomatic but for mild diarrhea where the virus is excreted - Second phase is viremia, when the virus is in the blood - Third phase results in CNS infection and, ultimately, paralysis 95% do not make it past phase one Older victims more likely to get to other stages Infants who contract it have life-long immunity Immunization only way to control it |
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Hepatitis A virus
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Inflammation of the liver
Transmitted by fecal-oral route Symptoms begin 15-50 days after contracting it - First phase results in diarrhea and lasts one week - Second phase results in extensive liver damage, Jaundice and severe weakness Infants get life-long immunity Very bad for adults |
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TSE
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Transmissible Spongiform Encephalopathy – Mad Cow Disease (BSE)
Progressive and fatal neurodegenerative disease Brain dysfunction, coma and death Signs – personality changes, loss of coordination, involuntary jerking, insomnia, confusion |
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TSE – How it makes you sick
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Caused by prions
Infectious protein directs the formation of more proteins like itself Normal animal tissues miss-fold and become infectious Prions are highly resistant to heat and chemical treatments |
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Yeasts
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Important for food fermentations and spoilage, but do not cause foodborne diseases
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Molds
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Fungi that form mycelia (a mat-like or branched colony)
Spores are made in large quantities and are somewhat stress tolerant Some are edible, although some are poisonous too Food fermentations, spoilage through extracellular digestive enzymes All cause foodborne intoxication |
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Hypha
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One branch of the mycelia
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Mycotoxins
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Toxic secondary metabolites produced by molds
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Claviceps purpurea
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Plant pathogen particularly prevalent in rye
Grows inside rye/wheat kernels when damp Favored by a cool, wet winter followed by a warm, moist spring Contain ergot toxins (Heat-stable, mold toxin that affects neurons) |
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Claviceps purpruea – How it makes you sick
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Causes two forms of symptoms
- Hallucinations, delusion, confusion, convulsions, paralysis - Gangrene in extremities - burning of skin = blisters and dry rot – extremities fall off Maybe caused Salem witch trials |
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Aspergillus flavus
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Mold that grows on grains, nuts, cereals in warm and damp conditions
Produces aflatoxin |
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Aflatoxin
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Causes disease only with very high concentrations
Heat-stable Metabolized in liver Causes liver damage and tumors Natural carcinogen - Low doses over many years |
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Protozoa and parasitic worms
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Eukaryotic pathogens that cause infections
Protozoa are unicellular Worms are multicellular Transmitted by fecal-oral route of animal to human |
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Trophozoites
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Vegetative (growing) cells of parasites and worms
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Cysts
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For parasites and worms: Dormant stage, Initiates disease
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Oocysts
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Worms and parasites: sexual reproduction, contains sporozoites, initiates disease
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Entamoeba histolytica
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Only infects humans – through fecal-oral route
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Toxoplasma gondii
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Causes toxoplasmosis
Mainly asymptomatic in healthy people, serious gastroenteritis in immunocompromised people May cause neurological birth defects Transmitted from mice to cats to humans, or contaminated food / undercooked meat |
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Giardia lamblia
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Low infective dose
Sick after 1-2 weeks, for 5 days or longer Diarrhea, gas and weight loss |
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Giardia lamblia – How it makes you sick
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Cysts consumed in food or water
Asymptomatic in some people and most animals Associated with untreated drinking water Cysts are resistant to chlorination, but can be removed through filtering |
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Cryptosporidium parvum
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Low infective dose (10 oocysts)
Sick after 2-10 days, for 1-2 weeks or longer Diarrhea, abdominal pain, vomiting Epidemics traced to water supplies in water purification plant (Milwaukee) Resistant to chlorination, small oocysts difficult to filter |
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Parasitic worm infections - When are they infectious?
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Worms are only infectious in their dormant stage, eggs and cysts
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Trichinella spiralis
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Larvae encysts in muscles
Disease contracted by eating a meat-eating animals (pigs, bear) - First symptoms are pain and mild diarrhea - Weeks later, there’s fever, weakness, swelling, muscle pain Prevent by cooking pork to 145° F, prevent animal infection |
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Taenia saginata, Taenia solium
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Saginata is found in beef, solium is found in pork
Human infection generally limited to intestines Worms can grow 10 meters long Subtle symptoms - weakness, nutritional deficiencies, higher disease susceptibility - T. solium can result in brain infections |
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Diphyllobothrium latum
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Fish tapeworm – ingestion of raw or undercooked fish Humans are unsuitable hosts Fish must be cooked, brined or frozen for 24-48 hours
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Why manipulate microbes in food? |
Food safety Avoid spoilage Proper food fermentation |
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Thermophile |
Grows at warm temperatures |
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Mesophile |
Grows at ambient/body temperature |
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Psychrophile |
Only grows in cold temperature |
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Psychotrophs |
Grows in cold and room temperature |
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Q10 = [growth rate (T + 10 c) / growth rate (T)] |
Effect of temperature on growth rate Equals about 2 between Tmin and Topt Increased temp = decreased Q (survival) |
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Changes in temperature and membrane structure |
Increase in temp = increased lipid viscosity, can't maintain structure, enzymes denatured Fatty acid saturation of membrane increases with temp Decrease in temp = hibernation, low metabolic activity |
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Chaperones |
Produced in high temps to increase thermal tolerance Produced in low pH to protect against low internal pH Provide favorable conditions for protein folding/unfolding |
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Proteases |
Produced in high temps to increase thermal tolerance Produced in low pH to protect against low internal pH Catalyze hydrolytic cleavage of peptide bonds |
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Temperature and survival |
Decrease in temp = increased survival Increase in temp = proteases and chaperones, ultimately decreased survival *Heat-stable toxins can still be present and pose a risk after cell death* |
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Least to most heat resistance in foodborne pathogens |
Bacterial endospores > naked viruses > mold spores > gram + cells, yeasts > gram - cells > enveloped viruses |
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Target of food preservation |
Focuses on destruction of mesophiles |
(thermophiles, mesophiles, psychorphiles, or psychrotrophs) |
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Microbial growth: lag phase |
Cells are adapting to new growth conditions |
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Microbial growth: exponential phase |
Cell doubling occurs over specific time intervals |
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Microbial growth: stationary phase |
No net increase/decrease Occurs when nutrients are limited Cells hardest to kill during this phase Cells shrink, induce stress responses, lower metabolic rate, produce secondary metabolites |
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Difficulties of microbial detection |
Not evenly distributed in food Present in low amounts Food interferes with microbial isolation Cells are dead but toxins are still present |
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CFU |
Colony-forming units Grow on agar to determine number of live colonies |
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Spectrophotometer |
Measures indirectly More microbes = higher absorbance |
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Microscopy |
Direct total counting Works well with liquid cultures composed of one organism |
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Flow cytometry |
Direct total counting Counts individual bacteria as they flow past a laser |
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Molecular methods of microbial analysis |
PCR using DNA Reverse PCR using RNA |
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Immunology-based microbial analysis |
Antibodies are used to target a specific organism |
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Indicator microorganisms |
Use specific bacteria to make generalizations - i.e. search for a spoilage microbe to see if food will spoil |
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D-value |
Decimal reduction time Equals change in time for a 1-log reduction of a population |
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Z-value |
Temperature change that causes a 1 log reduction in D-value - i.e. Temp that causes D-value to reduce from 30 min to 3 min |
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F-value |
Time needed to destroy a specific number of organisms at a specific temp |
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Pasteurization |
Time and temp to destroy most heat-resistant pathogen in a food |
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Commercial sterilization |
Time and temp required to destroy C. botulinum |
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Canning |
Commercial sterilization of foods in airtight containers |
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Water activity |
Refers to available water in a food Helps determine microbial growth, but not death No growth below 0.60 Most organisms grow best at 0.97 to 0.99 |
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Compatible solutes at low aW |
Used to decrease/increase water in a cell Results in higher pathogenic resistance |
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How to lower aW |
Dry or freeze-dry food Add in intermediate-moisture foods Add salt Blend in ingredients with low water activity |
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Humectants |
Bind water and lower water activity without making food taste dry |
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Affects of changing pH |
Lower pH prevents microbial growth pH outside of optimal range affects growth and survival Yeasts and molds have greater pH tolerances Most bacteria don't grow at pH < 4.5 |
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Acid-tolerant bacteria at low pH |
Capable of fermentation (except acetobacter) Use proteases and chaperones to protect against low pH Some perform enzymatic reactions that pump H+ out of the cell, consume H+, or produce CO2/NH3 |
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Acetobacter |
Turns ethanol into acetic acid |
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Yeasts, molds, and acid |
Yeasts and molds don't grow with organic acids or weak acids (i.e. acetic acid) These don't dissociate, meaning they can enter the cell Once in cell, they dissociate and lower internal pH |
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Sulfiting agents for Preservation |
Protect wine, dried fruits from bacteria, yeasts and mold Protect fruits and veggies from browning by obstructing an enzyme Most effective agent is SO2 |
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Reduction of O2 toxicity |
Addition of NADH oxidase avoids production of ROS (reactive oxygen species)
Catalase and peroxidase transform H2O2 into H2O Superoxide dismutase and high manganese concentrations get rid of ROS |
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Anaerobic respiration and energy |
Uses nitrate, sulfite, or trimethylamine-oxide (TMAO) as e- acceptor Uses ETS for e- transport (Electron Transport System) Releases 2-4 mol ATP for every mol of glucose |
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Aerobic respiration and energy |
Oxygen acts as a metabolite and accepts e- Uses ETS for e- transport Oxidation of sugars to CO2, NAD, H2O Releases 38 mol ATP for every mol of glucose |
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Energy through fermentation |
No ETS; instead, substrate-level phosphorylation Restore NAD with amino acids Lactate or EtOH are e- acceptors Releases 2 mol ATP for every mol of glucose |
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Aerobe |
Requires oxygen (final e- acceptor) |
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Microaerophile |
Needs oxygen in lower concentrations High concentration of oxygen is toxic |
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Strict anaerobe |
Doesn't need oxygen, which can be toxic |
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Facultative anaerobe |
Switches between aerobic and anaerobic respiration Fermentation |
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Aerotolerant anaerobe |
Exclusively anaerobic metabolism Doesn't mind oxygen Fermentation |
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Eh (redox potential) |
High Eh signifies more oxygen and aerobic respiration Low Eh signifies less oxygen and anaerobic respiration/fermentation Depends on concentration of compounds, affinity to e- |
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Vacuum packaging |
Uses oxygen-impermeable material Decreases Eh to microaerophile levels May encourage anaerobes |
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Modified atmosphere |
Gas-impermeable container Similar to vacuum packaging, but combined with refrigeration |
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Sulfur dioxide and sulfite |
Treat food with SO2, HSO3- Lowers Eh Inhibits aerobes |
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Ozone treatment |
Eh > air Microbes killed, very effective Organic matter oxidized as well (rancidity) Organic matter may shield microbes from O3 |
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Food preservatives |
Chemical agents added to food to extend shelf-life i.e. antibiotics (non-therapeutic only, like nisin or natamycin), saltpeter (prevents lipid oxidation, limits anaerobes) |
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Dangers of saltpeter |
Turns into nitrites in the body - Nitrites can form nitrosamines, which are carcinogens - Vitamin C inhibits this reaction |
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Microbial resistance to radiation |
Viruses > bacterial spores > yeasts and mold > gram (+) bacteria > gram (-) bacteria > insects > humans |
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How can mold growth help bacterial growth? |
Metaboliza acids to increase pH Break down high MW barriers like proteins |
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Molds |
Habitat: soil, plants, spores in air Oxygen: strict aerobes that grow on food surfaces Never thermophiles Tolerance: low pH, low water activity Growth: slow Medium: fruits, fermented foods, breads, preservatives |
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Yeasts |
Habitat: plant microbiota Oxygen: aerobes or facultative anaerobes (latter can grow throughout food) Tolerance: low pH, low water activity Never thermophiles Growth: slow, faster than molds Medium: fruit juices, jams, fermented foods; most require >1% sugar |
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Lactic Acid Bacteria |
Habitat: plant/animal microbiota Oxygen: facultative anaerobes, aerotolerant anaerobes Tolerance: low pH, moderate water activity Growth: slower than other bacteria, faster than molds/yeasts Medium: milk, meats, juices, cut fruit and veggies; important in fermentation (use soluble sugars to produce lactic acid) Require heme (and sometimes vitamin K) for respiration |
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Endospore-forming bacteria |
Habitat: mainly soil Oxygen: facultative/strict anaerobes Tolerance: moderate pH, moderate water activity Growth: slower than other bacteria Medium: cooked/canned foods, herbs/spices, moist baked foods, foods high in carbs and protein |
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Enterics |
Habitat: human/animal intestine (except erwinia) Oxygen: facultative anaerobes Tolerance: pH 4.5, water activity 0.94 Never thermophiles Growth: moderate/high Medium: all foods handled without good sanitation; prefer sugars but can consume proteins (exception: erwinia on veggies) |
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Pseudomonas |
Habitat: soil, water, plants Oxygen: facultative anaerobe Tolerance: pH 5.5, water activity 0.97 Growth: very fast (aerobic conditions) Medium: low-sugar, non-acidic cold foods, refrigerated meat, non-fermented dairy/vegetables |
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Staphylococcus aureus |
Habitat: human/animal skin Oxygen: facultative anaerobe Tolerance: pH 4.5, low water activity, growth at 7-48 Celsius |
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Homofermentation |
Glycolysis EMP pathway 2 ATP consumed 4 ATP produced 2 NADH produced Lactic acid end product |
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Heterofermentation |
Phosphoketolase pathway 1 ATP consumed 2 ATP produced Lactic acid end product Ethanol end product CO2 end product |
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Lactic acid in LAB metabolism |
Synthesis provides NAD+ for the cell Lowers pH and prevents competition Allows growth at different temperatures Changes taste to more sour flavor |
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Alteration of fermentation end products |
Pentoses and hexoses Oxygen, citric acid, and amino acids pH and temperature |
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Swiss cheese |
Milk innoculated with thermophilic cultures - Steptococcus thermophilus, Lactobacillus helveticus, Propionibacterium species CO2 gas produced - this it what creates the holes |
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Camembert and Roquefort cheese |
Inoculated with Lactococcus lactis and Leuconostoc cremoris Camembert has Penicillium camemberti Roquefort has Penicillium roqueforti In these, mold increases flavor and pH |
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Sauerkraut fermentation |
Two phases: heterofermentation (Leuconostoc mesenteroides) followed by homofermentation (Lactobacillus plantarum) |
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Regeneration of NAD+ |
Lactate synthesis Respiration Oxygen metabolism Reduction of other cell components (i.e. pyruvate) |
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Yogurt fermentation |
Done by streptococcus thermophilus and Lactobacillus delbrueckii |
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Butter, sour cream, buttermilk fermentation |
Lactococcus lactis Leuconostoc mesenteroides |
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Guidelines for LAB fermentation |
Require high amount of soluble sugars Require low oxygen Require (and produce) low pH |
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Single step LAB fermentations (examples) |
Tempeh (soybeans + Rhizophus) Natto (soybeans + B. subtilus) |
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Multistep LAB fermentations (examples) |
Soy sauce Step 1: koji Soy + Aspergillus oryzae = sugar, peptides, amino acids Step 2: moromi sugars, peptides, amino acids + S. rouxii/L. delbrueckii/P. soyae = peptides, salt, low pH |
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