General microbiology
Meat most often spoils due to
1. chemical change (oxidative rancidity)
or
2.microbial growth
– fastest on fresh meat, may still be major spoilage
problem for processed depending on product
– 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
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
Factors important to spoilage control/shelf life
1. initial numbers
– most important for inactivation treatments
log.
survivors
heating time
Spoilage of Frankfurters
spoilage
level
108
107
6
number of 10
bacteria
105
per gram
104
103
102
2
4
6
time (days)
8
2. temperatures
– psychrophiles - can grow at 0oC (32oF)
– mesophiles - 25-40oC (77-103oF)
– thermophiles - 45-60oC (113-140oF)
Temperature Relationships of the Major
Groups of Bacteria
212oF
200
100oC
90
180
80
160
70 Obligate thermophiles
(optimum temp.)
60
Clostridium thermosaccharolyticum
50 Bacillus stearothermophilus
40 Mesophiles
(optimum temp.)
30
Escherichia coli
20 Bacillus subtilis
140
Facultative thermophiles
Streptococcus thermophilus
Clostridium perfringens
Psychrophiles
(optimum temp.)
Pseudomonas geniculuta
Achromobacter guttatus
10
0
-10
Ground Beef Spoilage
spoilage
level
108
number of
bacteria
per gram
15.5oC
10oC
4.5oC
0-2oC
106
24
36
time (hours)
60
96
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
5. pH
– reduced pH slows or inhibits growth
– very dependent on organism
6. specific inhibitors
–
–
–
–
–
–
–
nitrite
diacetate
lactate
sorbate
organic acids
lactoferrin
bacteriocins
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
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
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
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 foodborne 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
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 O157:H7
B. characteristics of outbreaks
– onset time
< 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
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)
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
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
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@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
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 160 F is more than adequate
o
– not a frequent problem (2,500 cases per year), but high fatalities
Prevention: appropriate cooking, prevent recontamination
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
7. Escherichia coli O157:H7
– 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
8. Campylobacter jejuni
–
–
–
–
infection
cramps, diarrhea, headache, muscle pain
common in animal G.I. tracts
most frequent cause of bacterial food-borne illness but hasn’t
received publicity ( ~ 2 million cases per year in food)
Prevention: appropriate cooking
9. Shigella spp
– intoxification (live ingestion and toxins)
– similar to E. coli O157:H7
– 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
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
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
(continued)
Characteristics of Some Pathogens of
Significance in Meat Products
Organism
Clostridium
botulinum
Staphylococcus
aureus
Salmonella spp.
Listeria
monocytogenes
Clostridium
perfringens
Escherichia coli
oxygen
temp.(oC) pH(min) salt(max.) water activity(Aw)
anaerobe
10-50
4.7
10-12
0.94
facultative
facultative
6.5-50
5-47
4.2
4.0
18-20
3
0.86/0.90
0.95
facultative
0-45
5.0
8
0.97
anaerobe
facultative
6.5-50
10-45
5.0
3.6
8
8
0.95
0.90
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
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
Prevention: avoid fish from areas with known marine
organisms
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
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