Food Microbiology Flashcards
Describe microbial interaction and food
Food is rarely, if ever sterile
Microbial associations - most times no discernible effect
However, some instances m
Can cause spoilage, food-borne disease (food poisoning) and be beneficial
What is the economic problem of food spoilage?
- not of quality expected by consumer (quality, NOT spoilage)
- undesirable growth of microbes
- production of volatile compounds (metabolism)
What are possible causes of food spoilage?
- insect damage
- physical injury (bruising, pressure, freezing, drying and radiation )
- activity of indigenous enzymes
- naturally occurring chemical changes
- Activity of bacteria, yeasts and moulds
What is the shelf life of food?
The time during which it remains stable and retains its desired qualities
What are the classifications of food spoilage?
Perishable- fresh fruits, fish, meats
Semi-perishable- eggs, onions, potatoes, carrots, beans
Non-perishable - flour, cereal
What factors influence microbial growth ?
Intrinsic- inherent to the food:
- pH
- moisture content(water activity)
- Redox potential
- nutrient content
- antimicrobial constituent
- biological structures
Extrinsic- environmental factors
-Temperature of storage
-Composition of gases and relative humidity in the atmosphere surrounding the food
What are the basic principles of food preservation?
- to slow down activity: spoilage/disease-causing microbes
- to kill all microbes
What processes are used in food preservation?
- Drying
- smoking
- freezing
- Vacuum packing
- salt
- sugar
- pickling
- Cranning and bottling
- irradiation
- modified atmosphere
- biological processes
Think of these as methods of preventing or eliminating microbial growth
What is food fermentation?
This is the process of converting carbs to alcohol or organic acids using microorganisms-yeasts or bacteria - under anaerobic conditions
Positive interaction: microbes+food
- anaerobic catabolism of organic compounds
- lactic acid Bacteria
- acetic acid Bacteria
- yeast (Saccharonyces cerevisiae)
- Mold (aspergillus)
What cultures are used for dairy products?
Starter cultures:
-lactic acidosis Bacteria (lactobacillus, leuconostoc, lactococcus, pediococcus, streptococcus)
Second inoculum:
-Propionibacterium (Swiss cheese), peniccillium roqueforti(blue cheese)
What is the function of microbes in meat products?
Nitrate converted to nitrite: Micrococcus, staph, xylosus, staph. carnosus
- improve flavor: micrococcus
- increase acidity. (Lowering pH): pediococcus and lactobacillus
- mound growth: penicillium nalgiovense (desired in some Italian salamis)
Give examples of meat products. How are they process differently ?
Sausage: pork/beef+salt+ seasonings
- salami, pepperoni, bolognas
- process different in North America and Europe
- America: rapid, high temps(sour tasting)
- Europe: slow, lower temps(no sour taste)
Why is food safety a major source of concern, according to CDC?
CDC estimates in the US:
- 1 in 6 Americans get sick from contaminated foods or beverages each year
- 128,000 hospitalized
- 3,000 die (children/ elderly/immunocompromised)
Why is food safety a major source of concern, according to the USDA?
The United States department of agricultural estimates that foodborne illnesses cost more than 15.6 billion dollars each year
Why is food safety(food Borne diseases) a major source of concern?
- changes in demographics
- changes in food preferences
- changes in food processing/production
- changes in food distribution
- microbial adaptation
Give the general epidemiology of food borne diseases
Sex- equally affects both men and women
Age- all at risk, highest incidence: infants/pre-school, elderly, immunocompromised
Seasonal incidence:
- outbreak in warmer months.
- salmonella:summer/early autumn
- campylobacter spp. : late spring/ early summer.
What are the 2 major categories of food borne diseases ?
- Food poisoning
2. Food-borne infection
Explain food poisoning as a category of food borne diseases
AKA: food-borne intoxication, food toxemia
Consumption of food containing preformed toxins
-enterotoxins, neurotoxins
Usually bacterial: S. aureus, B. cereus, C. botulinum
Occasional fungi: mushroom-amantia
Occasional algae: -ciguatera
Not an infection
Usually rapid onset(mins hrs)
-exception C. botulinum (hrs-days)
Short duration(24. Hrs)
May be fatal
Explain food-borne infections as a category of food-borne infection
Consumption of food containing microbe
-(food acts as vehicle for entry)
- bacterial: C. Jejuni, salmonella, shigella, E. coli, V. parahaemolyticus
- Viral: norovirus
- protozoan: C. Parvum, C. cayetanenisis
Longer incubation:
- 1st colonization
- damage: toxin production, invasion
- longer duration
- may be fatal
What is the mode of transmission of staphylococcus aureus?
Humans are the main reservoirs
What are the microbial characteristics of staphylococcus aureus ?
- encapsulated gram positive, catalase positive cocci
- coagulase positive
- B-hemolytic on blood agar plate
What is the epidemiology of staphylococcus aureus ?
- typically infected food handler
- about 50% humans carry staphylococci
What is the pathogenicity of staphylococcus aureus?
- enterotoxins
- heat stable, acid stable
-incubation: under 6 hours of ingestion caused by pre-formed toxin
- Nausea, vomitting, watery diarrhoea, dehydration
- duration: less than 48 hours
-implicated foods: bakery products, cooked meats, fruit and vegetables
What are the microbiological characteristics of bacillus cereus?
-obligate aerobe, spore forming gram positive rods, arranged singularly or in pairs
- produces toxins: neurotoxins
- heat stable, acid stable
What is the mode of transmission of bacillus cereus?
-ubiquitous organism of the soil: commonly found in low levels in raw, dried, and processed foods
- ingestion of foods kept at ambient conditions after cooking
- incubation: under 4 hours of ingestion
- nausea, vomitting
- duration: under 24 hrs
- incubation: under 4 hours of ingestion
- easy cross-contamination
- air, soil, water and dust
Describe bacillus cereus food poisoning pathogenicity
Pathogenicity:
- opportunistic pathogen
- Intoxication characterized by two forms:
- An emetic form with severe nausea and vomiting- linked primarily to fried rice, milk and pasta
Implicated foods: cooked rice and pulses (beans, lentils, etc.)
What are the microbial characteristics of C. botulinum?
Gram positive (at least in early stage of growth), anaerobic, spore-forming bacillus
Explain the mode of transmission of C. botulinum food poisoning
- adult botulism, caused by ingestion of preformed toxin in food
- infant botulism, in which the organism replicates and secretes toxin in the intestinal tract
Give the epidemiology of C. botulinum food poisoning
Sporadic
Explain the pathogenicity of C. botulinum food poisoning
Pathogenicity :
- neurotoxins: Heat labile
- incubation: 18-36 hours of ingestion
- initial: nausea, vomiting, abdominal pain, diarrhoea
- Characteristics: symmetrical descending flaccid paralysis
- fatal: within 24 hours
- mortality rate : 10-20%
- typically: home canning practices
- easy cross-contamination
- air, soil, water and dust
Explain ciguatera as a marine associated food poisoning
Ciguatera: Gambierdiscus toxicus (Algae)
-Baracuda, grouper, amberjacks
-neurotoxin: ciguatoxin
- incubation: 3-6 hours
- nausea, abdominal pain, watery diarrhea
Explain Scombroid as a marine associated food poisonings
Scombroid: Non-allergic histamine
- bacteria: Stenotrophomonas maltophilia, M. morganii
- histidine —> histamine (scombrotoxin)
- incubation : mins- 3 hrs
- watery diarrhoea, nausea, metallic taste
Explain the pathogenicity of Algae
Neurotoxic: Karelia brevis (Brevitoxins )
Paralytic: Alexandria spp., Gymnodinium catenatum, Pyrodinium bahamense, Gonyaulax spp. (Saxitoxins)
-short incubation: under 1-3 hours
- mouth numbness, tingling in extremities, GI upset(Brevetoxins)
- duration
Explain the epidemiology of Campylobacter spp.
Worldwide importance because of djarrheal disease
C. jejuni- 90% of cases
C. coli- most of the 10%
What is the most of transmission of campylobacter spp.?
Mode of transmission:
Ingestion of organisms in undercooked food, contaminated water, and raw milk
What are the microbial characteristics of campylobacter Sp.?
Gram negative spiral and S -shaped bacteria; darting motility; microaerophilic; will grow only under reduced oxygen tension; optimal growth temperature is at 42 C
Examples: C. jejuni, C. fetus (sterility/ spontaneous abortion- sheep/cattle)
Explain the pathogenicity of campylobacter spp.?
- acute enteric disease of variable severity;diarrhea, abdominal pain, malaise, fever, nausea and vomiting; prolonged illness in up to 20% of patients
- incubation: 3-5 days
Watery-bloody diarrhoea, abdominal pain, fever(invasive)
-duration: 1 week
- intestinal tract of wide variety of wild and domestic animals (zoonotic)
- commercially raised poultry
- normal commensal of cows
- long-term commensal of sheep
- Pigs( carriers of C. coli)
- C. jejuni intestinal commensal cats and dogs
What is the number 1 bacterial cause of food-borne disease US?
Campylobacter spp.
What are the microbial characteristics of salmonellosis?
Salmonella enteritica subspecies enteric serotype xxx
Characteristics:
Gram-negative, flagellated facultatively anaerobic bacilli characterized by O, H an Vi antigens.
-there are over 1800 known serovars which current classification considers to be separate species
Explain the pathogenicity of salmonellosis
Gastrienterritis: S. Typhimurium, S. Enteritidis, S. Newport
- incubation: 8-48 hours - duration: 2-3 days - nausea, vomitting, watery/bloody diarrhea
- Septicemia/Bacteremia(focal infection): rare, S. Cholerasuis
- Enteric fever (typhoid and paratyphoid fever): S. Typhi, S. Paratyphi
- most severe
Discuss the mode of transmission of salmonellosis
The fecal-oral route and can be transmitted by food and water, by direct animal contact, and rarely from person-to-person
High risk groups- infants and immunocompromised individuals
What are possible sources of salmonellosis infection?
- Food(poultry, eggs, meat)
- water
- contact with animals
- vegetables with human or animal waste fertilizer
What are the microbial characteristics of E. coli?
Gram-negative, facultative anaerobic, Rod-shaved, coliforms bacterium of the genus Escherichia that is commonly found in the lower intestine of warm-blood organisms
Catalase positive, oxidase negative
-lactose fermenter
What is the mode of transmission of E. coli?
-cattle and other ruminant animals are the main carriers
Explain the complex pathogenicity of E. coli
Strain: EHEC- E. coli O 157:H7
- non-invasive, verotoxin: similar time shiga toxin (shig. Dysenteriae)
- Inhibits protein synthesis in host cell
- SMAC -sorbitol MacConkey Agar- recommenced for the detection of E. coli O157: H7 which ferments lactose but doesn’t ferment sorbitol, produces colorless to pale yellow colonies in the presence of neutral pH indicator
Incubation: 3-7 days
Symptoms:
- watery-bloody diarrhoea,
- haemolytic uremic syndrome (HUS)
- thrombic thrombocytopenia purapura(TTP)
Duration: 1 week
Implicated foods: raw meat and salad greens
What are the OTHER types of E. coli?
ETEC: enterotoxic E. Coli
EPEC: enteropathogenic E. Coli
EIEC: Enteroinvasive E. Coli
EAEC: Enteroadherent E. coli
What is ETEC: enterotoxic E. Coli?
ETEC: enterotoxic E. Coli
- noninvasive, enterotoxin
- causes: traveller’s diarrhoea: profuse watery diarrhea
What is EPEC: enteropathogenic E. Coli?
EPEC: enteropathogenic E. Coli
-Non-invasive, no toxin production, effaced microvilli
-causes: watery diahrrea in children in developing countries
What is EIEC: Enteroinvasive E. Coli?
EIEC: Enteroinvasive E. Coli
- invasive, no toxin production
- causes: bloody diarrhoea similar to shigellosis
What is EAEC: Enteroadherent E. coli?
EAEC: Enteroadherent E. coli
- possible toxin production, no invasion
- causes: bloody diahrrea
Discuss the microbial characteristics of listeria monocytogenes
- gram-positive, non-spore forming, and catalase positive bacilli
- narrow ring of B- hemolytic
- cold growth
- aerobic/facultative anaerobic
What is the mode of transmission of listeria monicytogenes?
-Consumption of contaminated food
Discuss the pathogenicity of listeria monocytogenes
Pathogenicity:
-pathogenic bacterium which causes a group of diseases collectively known as listeriosis
- mild form of gastrointestinal illness in healthy adults
- May be serious for the very young, elderly, immunocompromised individuals and pregnant women
What are the sources of 8 fiction of listeria monocytogenes?
- Raw meat
- deli meats
- ready to eat meat products
- soft cheeses
- unpasteurized
- raw sprouts
- chilled smoked seafood
Why is listeria monocytogenes a major concern?
- it’s ubiquitous nature
- its ability to survive and grow at low temperatures, I.e. typical refrigeration temperature
- the severity
- the high case fatality rate
What are the high risk groups of listeria monocytogenes?
- extremely young
- old
- pregnant
- immunocompromised
- pregnant women 20X more likely to get listeriosis than any other population
- spontaneous abortion , neonatal meningitis/sepsis
These high risk groups
- have high mortality rate of 25-50%
- and neurological sequelae as a result of bacterial meningitis.
Which foods are susceptible to Ayers India enterocolytica? What can this cause?
Pork, lettuce
Invasive, causes watery/bloody diarrhea
What foods are susceptible to vibrio parahaemolyticus? What can this cause?
Invasive
Causes watery/bloody diahrrea
What foods susceptible to Bacillus cereus ? What can this cause?
Any foods
Nom-invasive, enterotoxin
Causes watery/bloody diahrrea(similar to C. Perfringens)
What foods are susceptible of Clostridium perfringens? What does this lead to?
Various meats, gravy
Non-invasive, enterotoxin
Causes: watery diahrrea
What are the foods that are susceptible to Shigella spp.? What can this lead to?
Any foods
Invasive, (shiga toxin for dysentry)
Causes watery-bloody diarrhea
What is the norovirus?
Estimated 50% outbreaks of acute, non-bacterial gastroenteritis (USA)
- Small (27 nm dia)
- Non-enveloped, ss +ve sense RNA
- Amorohous surface: feathery, ragged outline
Discuss the pathogenicity of the norovirus
- Older children and adults (Children under 5 yrs comeback in lecture )
- incubation: 24-48 hrs, Duration: 24-60 hrs
- Vomitting, abdominal cramps, myalgias, malaise, headache, nausea, low grade fever and 1-2 days diahrrea
How can the norovirus be trans,otter?
Norovirus spreads when a person gets. Poop or vomit from an infected person in their mouth possibly Via
Providing care
Shaking hands
Changing diapers
Touching contaminated surfaces
Touching your mouth
What are the microbial characteristics if vibrio cholerae?
Microbial characteristics:
- gram-negative, highly motile curved rods with a single polar flagellum
- Non lactose fermenter
- Only two serogroups, O1 and O139, are responsible for all epidemic and endemic cholera
What are the mode of transmission of vibrio cholerae?
Ingestion of water or food prepared with water containing V. cholerae
Fecal-oral transmission
- water borne
- poor hygiene
Explain the pathogenicity 9f cholera
Is an extremely virulent disease that can cause severe acute watery diahrrea
Symptoms- 12 hours and 5 days for a person to show symptoms after ingesting contaminated food or water
Result: Profuse watery duahrrhea occurs (20-30 L/day)
“RICE WATER STOOL”
What are the 5 key steps in prevention of food borne disease ?
- Keep clean
- Separate raw and cooked
- Cook thoroughly.
- Keep food at safe temperatures
- Use safe water and raw materials
How to best keep a place and yourself clean?
- wash your hands before handling food and often during food preparation
- wash your hands after going to the toilet
- wash and sanitize all surfaces and equipment used for food preparation
- Protect kitchen areas and food from insects, pests and other animals
- rats and mice
- flies
- cockroaches
-pests may carry pathogens and may also cause physical contamination of food with their droppings, eggs, fur and dead bodies
What are behaviors that may contaminate foods?
- Scratching the scalp
- Running fingers through hair
- Wiping or touching the nose
- Rubbing an ear
- Touching a pimple or open sore
- Wearing a dirty uniform
- Coughing or sneezing into the hand
- Spitting in the establishment
- Not washing after visiting the bathroom
How can raw and cooked foods be separated?
- food contaminated with pathogens from another source.
- Separate raw meat, poultry and seafood from other foods
- Use separate equipment and utensils such as knives and cutting boards for handling raw foods
- Store food in containers to avoid contact between raw and prepared
How can we ensure food is cooked thoroughly?
- Cook food thoroughly, especially meat, poultry, eggs and seafood
- bring foods like soups and stews to boiling to make sure
- for meat and poultry, make sure that juices are clear, not pink. Ideally, use a thermometer
- reheat cooked food thoroughly
- Under ideal conditions, bacteria multiply rapidly between 5 degrees Celsius (41F) and 60 degreees Celsius (140F)
The danger zone for food
- under 5C bacteria multiply slower
- freezing does not kill bacteria
- over 60C, most bacteria are killed (not endospore)
What are the appropriate cooking temperatures?
- Poultry, stuffed meats, and stuffed pasta: 73.9C(165F)
- Ground beef and ground pork: 68.3C(155F)
- Eggs, fish, and pork products: 62.7C (147F)
- Reheat ALL foods (leftovers) to 73.9C(165F)
How can foods be kelt at safe temperatures?
- Do not leave cooked food at room temperature for more than 2 hours
- Refrigerate promptly all cooked and perishable food (preferably below 5 degrees Celsius)
- keep cooked food piping hot ( more than 60C) prior to serving
- do not store food too long even in the refrigerator
- Do not thaw frozen food at room temperature
How to properly use safe water and raw materials ?
- use safe water or treat it to make it safe
- select fresh and wholesome foods
- choose foods processed for safety, such as pasteurized milk
- wash fruits and vegetables, especially if eaten raw
- Do not use food beyond its expiry date
