General microbiology

1
General microbiology

• Meat most often spoils due to
• 1. chemical change (oxidative rancidity)
• or2.microbial growth
• fastest on fresh meat, may still be major
  spoilage problem for processed depending on
  product

2
when an animal is slaughtered, it becomes a race
to see who will get it first

• microbial growth is likely because most meat cuts
  and products have a high water content (Aw
  0.99) and are highly nutritious
• contamination occurs as soon as the animal is
  slaughtered so constant intervention and addition
  of barriers is important to shelf life and safety

3
Contamination will include

• 1. mold
• 2. yeast
• 3. bacteria
• Bacteria are the primary problem because
  they grow fastest - but yeast and molds also
  cause problems in specific cases where bacteria
  are inhibited

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Factors important to spoilage control/shelf life

• 1. initial numbers
• most important for inactivation treatments

log.survivors
heating time
5
Spoilage of Frankfurters
15.5oC (1 day)
10oC (2 days)
4.5oC (5 days)
spoilage level
108
107
0oC (16 days)
106
number of bacteria per gram
105
15.5oC (3 days)
10oC (6 days)
4.5oC (14 days)
104
103
0oC (45 days)
102
2
4
6
8
time (days)
6
2. temperatures

• psychrophiles - can grow at 0oC (32oF)
• mesophiles - 25-40oC (77-103oF)
• thermophiles - 45-60oC (113-140oF)

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Temperature Relationships of the Major Groups of
Bacteria
100oC
212oF
200
90
180
80
160
Obligate thermophiles (optimum
temp.) Clostridium thermosaccharolyticumBacillus
stearothermophilus
70
60
140
Facultative thermophiles Streptococcus
thermophilusClostridium perfringens
50
Mesophiles (optimum temp.) Escherichia
coliBacillus subtilis
40
Psychrophiles(optimum temp.) Pseudomonas
geniculutaAchromobacter guttatus
30
20
10
0
-10
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Ground Beef Spoilage
spoilage level
108
number of bacteria per gram
15.5oC
10oC
4.5oC
0-2oC
106
24
36
60
96
time (hours)
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3. oxygen

• aerobes
• Pseudomonas - fresh meat
• facultative anaerobes
• lactic acid organisms
• salted product
• strict anaerobes
• 4. Aw
• available water
• bacteria grow at about 0.91 or more
• molds above 0.75
• major role of salt

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5. pH

• reduced pH slows or inhibits growth
• very dependent on organism
• 6. specific inhibitors
• nitrite
• diacetate
• lactate
• sorbate
• organic acids
• lactoferrin
• bacteriocins

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For control, processors combine or stack as
many barriers together as possible to maximize
inhibitory effects---Barrier concept

• most are additive, a few are synergistic

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Fresh meat spoilage is typically by
psychrophilic, gram negative aerobes
(Pseudomonas)

• or
• pychrophilic, gram positive, facultative
  anaerobes (lactics) - (vacuum-packaged fresh
  meat)
• processed products spoilage is most often by the
  lactics

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Shelf life is an important issue and needs to be
measured and understood for every product.

• accelerated shelf life testing is the
  utilization of higher than normal temperature for
  relative comparisons of shelf life

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Microbial pathogens/safety issues

• Centers for Disease Control and Prevention - CDC
  (Atlanta)
• often quoted for food-borne illness causes 76
  million cases per year of GI tract illnesses,
  325,000 hospitalizations and 5,000 deaths per
  year.
• national investigative and monitoring
  organization
• in 1996, CDC, USDA-APHIS and FDA established the
  food-borne Disease Active Surveillance Network
  (FoodNet) - internet site to collect food-borne
  disease information
• over 90 of food-related illness cases are caused
  by bacteria
• about 60 of food related cases are from meat,
  poultry and fish
• 82 of cases are due to unknown causes

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To help identify likely organisms

• A. Categories of causes for illnesses
• 1. infection
• live organisms ingested
• salmonella
• 2. intoxication (poisoning)
• toxin ingested
• Staphylococcus aureus, Clostridium botulinum
• 3. intoxification
• live organisms which produce toxin after
  ingestion
• E. coli O157H7

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B. characteristics of outbreaks

• onset time
• lt 1 hr. - probably chemical
• chemical causes can include ciguatoxin and
  scombrotoxin, both from fish as well as any
  environmental toxins
• onset time may be dose related
• 1-7 hrs. - Staphylococcus aureus
• 8-14 hrs. - Clostridium perfringens
• over 14 hrs. - other organisms
• intensity
• Staph.
• specific symptoms
• paralysis - Cl. botulinum

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Specific organisms of concern in meat products

• 1. Staphyloccus aureus
• poisoning (toxin)
• nausea, vomiting, stomach cramps, diarrhea 3 - 6
  hrs onset --- severe!
• usually cooked, prepared foods
• does not compete well in raw foods (not
  refrigerated appropriately)
• lowest growth 45oF 60oF for
  toxin
• killed by 145oF cook, inhibited by acid
• tolerate 17 salt
• toxin is heat-stable
• humans are most common source (at least 50 are
  carriers)
• Prevention thorough cooking, rapid chilling,
  rapid acidification (fermentation)

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2. Salmonella sp. (2000 types)

• infection
• G.I. upset - diarrhea, cramps, fever, vomiting,
  diarrhea included (flu-like)
• usually cooked, recontaminated foods (eggs,
  chicken) or undercooked products
• present on much fresh meat
• separate fresh and finished (packaging) areas
• needs 45oF to grow
• killed by 140oF
• very susceptible to salt
• sources poultry 60 pork,
  beef 20
• second most common food pathogen 1.4 million
  cases
• Prevention cook appropriately, avoid
  recontamination

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3. Clostridium botulinum - poisoning (toxin)

• very potent neurotoxin blocks neuromuscular
  motor end plate
• 1 tablespoon would kill 1/2 of U.S. population
• impaired swallowing, dizziness, poor
  coordination, muscle paralysis
• botox cosmetic treatments to reduce skin wrinkles
• recoveries improved by using respirators, etc.
  until effects wear off, still 10-20 mortality
• low acid, vacuum cans/packages
• need 250oF for destruction
• toxin is more heat-susceptible (80oC -10 minutes)
• susceptible to acids (below pH 5.0)
• inhibited by nitrite
• contamination level is low but widespread
  (outbreaks are rare)
• honey suspected in some cases of infant botulism
• Prevention appropriate cooking (retort),
  refrigeration, use of nitrite

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4. Cl. perfringens

• intoxification (live ingestion ? toxin)
• G.I. upset - diarrhea, cramps - seldom nausea
• usually cooked products held at warm temperatures
• needs at least 50oF - best_at_115oF
• most common in foods held on steam tables for
  extended time
• need 212oF for inactivation
• also susceptible to acid (5.0) and salt
• Prevention appropriate cooking, rapid chilling

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5. Listeria monocytogenes

• infection
• survives and grows at 32oF very
  significant

• often found in meat though dairy products are
  most common problem
• concern is absorption and transport to other
  vital organs
• causing abortions, meningitis, etc.
• flu-like symptoms in normal individuals
• refrigeration is not a safeguard
• but needs oxygen for best growth
• commonly found in processing plant environments,
  widespread in environment
• salt tolerant (to 25)

• heat sensitive, cooking to 160oF is more than
  adequate
• not a frequent problem (2,500 cases per year)
• Prevention appropriate cooking, prevent
  recontamination

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6. Yersinia enterocolitica

• infection
• tolerates refrigeration temperature well (to
  33oF) survives freezing
• G.I. upset, diarrhea, fever, vomiting ---
  resembles appendicitis
• ?from all livestock including dogs and cats
• but pork is most common source
• acid (pH 4.6), salt and cold tolerant --- also
  survives vacuum
• does not compete well with other organisms
• will survive in fermented sausage but nitrite is
  quite effective for control
• Prevention cook appropriately

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7. Escherichia coli O157H7

• first found in 1982 - originally McDonalds (not
  publicized)
• later Jack-in-the-Box case - 475 people -
  3 deaths
• - lots of
  publicity
• intoxification (live ingestion ? toxins)
• G.I. upset - bloody diarrhea and kidney failure
  in children
• survives freezing and refrigeration very well but
  will not grow until about 38-40oF
• heat sensitive
• 140oF for less than 1 minute will kill 90
• now recommend cooking to 155oF-160oF internal
  temperature rather than 140oF internal for cooked
  hamburgers
• can survive in fermented sausage
• primarily dairy cattle source (?)
• Prevention appropriate cooking

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8. Campylobacter jejuni

• infection
• cramps, diarrhea, headache, muscle pain
• common in animal G.I. tracts
• most frequent cause of bacterial food-borne
  illness but hasnt received publicity ( 2
  million cases per year in food)
• Prevention appropriate cooking

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9. Shigella spp

• intoxification (live ingestion and toxins)
• similar to E. coli O157H7
• believed to be source of genetic pathogenicity of
  E. coli
• bloody diarrhea, cramps, fever
• typically derived form fecal contamination (water
  sources) and under cooking - often sea foods
• third most common food-caused illness organisms
  according to FoodNet
• Prevention avoid contamination, appropriate
  cooking

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10. Bacillus cereus

• toxin ( 2 forms - short onset, - long onset
• sporeforming organism like clostridia that
  prefers warm temperatures
• relatively quick onset - 1-5 hours ( may be 15-30
  min) - vomiting - 8-16 hours - diarrhea
• generally need high numbers of organism
• common soil organism, sources are usually dirt or
  dust
• usually occurs in food held warm below 140oF
• long recognized but not one of the majors
• Prevention appropriate cooking (thermophile) and
  appropriate chilling

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11. Vibrio spp

• intoxification (live ingestion ? toxins)
• V. cholera - toxin causing water-borne cholera
• frequent world wide but not in U.S.
• V. parahaemolyticus
• diarrhea, cramps, fever sometimes nausea and
  vomiting
• typical source is fish and seafood
• Prevention appropriate cooking

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Characteristics of Some Pathogens of
Significance in Meat Products

• Organism oxygen temp.(oC)
  pH(min) salt(max.) water activity(Aw)
• Clostridiumbotulinum anaerobe
  10-50 4.7 10-12 0.94
• Staphylococcusaureus facultative
  6.5-50 4.2 18-20 0.86/0.90
• Salmonella spp. facultative 5-47 4.0
  3 0.95
• Listeria monocytogenes facultative
  0-45 5.0 8 0.97
• Clostridiumperfringens anaerobe
  6.5-50 5.0 8 0.95
• Escherichia coli facultative 10-45 3.6
  8 0.90

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Additional sources of food-borne illness

• 1. Viruses
• more common than bacteria as causes of food-borne
  illness (31 million cases per year)
• Norwalk virus - flu-like symptoms
• 23 million cases per year ( 9 million
  food-borne)
• 2. Non bacterial toxins
• a. scombroid poisoning
• partially spoiled fish particularly mackerel and
  tuna
• reason for icing fish ASAP
• bacteria convert histidine (amino acid) to
  histamine and produce severe allergy-like
  reactions
• nausea, vomiting, headache, hives, itching,
  breathing difficulties
• onset may be 10 minutes
• Prevention avoid aged fish

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b. ciguatera poisoning

• caused by a neurotoxin accumulated in fish
  (mackerel, snappers, etc.)
• toxin comes from small marine food
  organisms/algae
• symptoms can include numbness, tingling lips,
  temperature switching sensations, blurred
  vision, potential respiratory paralysis
• usually resolved but can be fatal (40)
• Prevention avoid fish from areas with known
  marine organisms

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c. shellfish poisoning

• shellfish (mussels, clams, etc.) accumulate
  toxins form food organisms (algae/plankton) as
  well as high levels of bacteria and viruses from
  environment (collectors)
• nausea, vomiting, tingling, paralysis
• Prevention appropriate cooking for
  bacteria/viruses
• avoid harvest during times when plankton/algae
  levels are high

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d. tetrodo toxin

• found in organs of puffer fish (blowfish)
• rapid paralysis (neurotoxin) and likely death
  (4-6 hours)
• requires skilled preparation of fish to avoid
  toxin contamination