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114 Cards in this Set

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Bacteria vs Fungal cell structure

Bacteria- single-cell M/O, lack membrane-bound nucleus, lack other membrane bound organelles (no compartmentalization)

Fungi- Single, multi-cellular, or filamentous organisms, contain membrane-bound nucleus and organelles, Heterotrophic nutrition (saprophytes and parasites)- COMPARTMENTALIZATION

Two Phylums of bacteria?

Proteobacteria- gram-negatives

Firmicutes- gram-positives

G+ vs G- cell envelope structure

G+: cytoplasmic membrane, very thick peptidoglycan. Tend to be more heat resistant
G-: cytoplasmic membrane, very thin peptidoglycan envelope but complex with teichoic acid. Tend to be more acid resistant

G+: cytoplasmic membrane, very thick peptidoglycan. Tend to be more heat resistant

G-: cytoplasmic membrane, very thin peptidoglycan envelope but complex with teichoic acid. Tend to be more acid resistant

Nitrogeneous Bases of DNA and RNA

Enterobacteriaceae characteristics (general)

- Gram- negative, rod-shaped

-Motile by peritrichous flagella

-Meosphiles (optimum between 23-35C)

-Facultative anaerobes

-Both respiratory and fermentative metabolism of carbs.

-Reduce nitrate to nitrite (most species)

-Catalase-positive (helps overcome H2O2)

-Oxidase negative-alternative ETC

-Ecology and host range: soil, water, and vegetation, human, animal and plant pathogens, common inhabitants in the GI tract

TCA Cycle Steps/End-products (diagram)

Fermentation By-products? Diagram

By-products: Lactic acid, acetic acid and mixed acid (Esp. Enterobacteriaceae)

By-products: Lactic acid, acetic acid and mixed acid (Esp. Enterobacteriaceae)

Enterobacteriaceae genera significant to food?

- Citrobacter











-Indicators of fecal contamination water and food (according to the gov't)

-Fecal vs non-fecal origins

-Coliform genera: Citrobacter, Enterobacter, Escherichia, Klebsiella

Characteristics of Pseudomonas spp. Morphology

-Morphology: Gram-negative, rod shaped, motile by polar flagella (in liquid)

-may secrete pigments: Pyoverdin (fluorescein) produced by P. fluorescens and P. aeruginosa. Pyocyanin by P. aeruginosa (detect on agar, food spoilage determinant)

Pseudomonas spp. Biochemical and physiological characteristics

-Catalase positive- AEROBIC RESPIRATION

-Oxidase variable, usually positive

-Obligate aerobe

-Some strains can use nitrate as a final electron acceptor during respiration.

-Mesophilic to psychrotrophic.

-Utilize a wide range of organic substances

-No growth factors required

-Compete very efficiently for iron

-Absence of fermentation, photosynthesis, and nitrogen fixation.

-Not acidophiles

-Catabolically diverse


Steps in biofilm formation

1. Reversible attachment

2. Irreversible attachment-extracellular polysachharides

3. Maturation

4. Dispersion

Significance of biofilms for food?

1. Equipment contamination- when mechanical removal is difficult (pipes, drains etc..)

2. Continuous source of spoilage- one contaminated valve will continue to contaminate all products coming into contact

3. Difficult to remove by washing and sanitization- once film is formed cannot guarantee removal.

Most common species of Pseudomonas that spoil food?

P. fluorescens group (most common)

P. fragi

P. lundensis

P. putida

Meat and poultry spoilage! (odor, color, slime)

Dairy- produces heat stable lipases and proteases, spoil milk by causing bitterness, casein breakdown, and robiness due to production of slime and coagulation of proteins.

Butter- Putrid smells (P. putrefaciens), rancid (FFA) from P. fragi or P. fluorescens, Skunk-like smell- P. mephitica, BLACK- P. nigrifaciens

Vegetables- slime from pectin breakdown

Fish and ground meat- sulfidy off smell (H2S) from cysteine breakdown

Genera of lactic acid bacteria of importance in food?






Characteristics (general) of LAB?



-Anaerobic (or microaerophilic- don't need it but can tolerate it)

-Catalase negative

-Nutritionally fastidious (needs nutrients from the environment)

-Cannot generate energy by respiration (incomplete TCA cycle and ETS)

-Generate ATP by fermentation with lactic acid as major end product

Homolactic vs Heterolactic fermentation?

Homolactic fermentation: EMP (Embden-Meyerhof-Parnas) pathway glycolysis + lactate dehydrogenase. End products: Lactic acid and ATP. Examples: Lactococcus, S. thermophilus, Pediococcus, some Lactobacillus

Heterolactic fermentation: Phosphoketalase pathway. Under anaerobic conditions: get CO2, lactic acid, ethanol, ATP. Under aerobic conditions: CO2, lactic acid, acetic acid and ATP. *Heterolactic fermentation not that efficient- will use up CHOs in environment quickly. Examples: Leuconostoc, Oenococcus, some Lactobacillus

Lactobacillus characteristics

Morphology: Rods or chains

CO2 from glucose: + or -

Cardinal temp: Can be psychrotrophic all the way to thermophilic

Species relevant to fermentation: L. bulgaricus

Species relevant to spoilage: L. fermentum

Species relevant to health: L. acidophilus, L. reuteri (probiotics)

Comments: Diverse genus

Lactococcus characteristics

Morphology: Cocci

CO2 from glucose: No

Cardinal temp: Likes milder temperatures (10C-37C) mostly psychrotrophic

Species relevant to fermentation: L. lactis

Species relevant to spoilage: none

Species relevant to health: none

Comments: Lancefield Group N

Streptococcus characteristics

Morphology: Cocci, chains (always)

CO2 from glucose: no

Cardinal temp: Thermophilic

Species relevant to fermentation: S. thermophilus

Species relevant to spoilage: none

Species relevant to health: S. pyogenes, S. pneumoniae, S. mutans **VERY BAD!

Comments: Lancefield Group A, B and others

Pediococcus characteristics

Morphology: Cocci and tetrads (always)

CO2 from glucose: No

Cardinal temp: Can be psychrotrophic or thermophilic

Species relevant to fermentation: P. acidilactici

Species relevant to spoilage: none

Species relevant to health: none

Comments: High salt tolerance- good in fermentated meats (pepperoni)

Leuconostoc characteristics

Morphology: Cocci

CO2 from glucose: YES

Cardinal temp: Milder temperatures 10-37C (psychrotrophic/mesophilic)

Species relevant to fermentation: L. mesenteroides

Species relevant to spoilage: L. carnosum (grows on carcasses)

Species relevant to health: None

Comments: Vegetable fermentation (sauerkraut)

Types of fermented foods and the LAB used

Dairy (yogurt, cheese, sour cream)- ex: S. thermophilus

Meat (fermented sausages)- ex: P. acidilactici

Vegetables (pickles, kimchi etc) ex: Leuconostoc, Pediococcus, LAB

Examples of LAB used as probiotics

Lactobacillus reuteri, Lactobacillus acidophilus

Antimicrobials made by LAB?

-Bacteriocins made by LAB: nisin!

-Also H2O2, acids (acetic, lactic) etc.. can be used as AMA in foods

Hemolytic Serology Categories

Alpha-hemolytic: green partial hydrolysis (Ex: Streptococcus pneumoniae, Streptococcus viridians)

Beta-hemolytic: clear, complete hydrolysis (ex: Streptococcus pyogenes- Type A bacitracin sensitive; Streptococcus agalactiae- Type B bacitracin resistant)

Gamma-hemolytic: No hemolysis- used in foods, non-pathogenic. Ex: Entococcus faecalis, E. faecium

Basic characteristics of bacterial spores

-Dormancy and Longevity

-Resistance to deleterious factors: resist factors that bacterial cells can not survive. Eg: heat (hot environment, boiling water), lack of water (arid environment), presence or absence of air (even aerobic spores don't need it), antimicrobial agents

Whats the name for spore formation?

Sporulation! It is a stage in the life-cycle of a spore-forming bacterium

Spore Structure (diagram)

Stages of sporulation in bacteria

Spore transformation to Vegetative Cell (Germination)

Activation: a treatment to facilitate the germination process, reversible- can be activated by sublethal heat, low pH, chemicals etc. *Must remove outer coats
Germination: degradation events triggered by germinants (nutrients L-alanine, ribosides;...

Activation: a treatment to facilitate the germination process, reversible- can be activated by sublethal heat, low pH, chemicals etc. *Must remove outer coats

Germination: degradation events triggered by germinants (nutrients L-alanine, ribosides; non-nutrients: Ca-dipicolinic acid; enzymes: lysozymes; physical process; high hydrostatic pressure), irreversible, loss of heat resistance, release of dipicolinic acid, cortex hydrolysis, core hydration (loss of refractility- phase-bright to phase-dark); decrease in optical density

Outgrowth- development of vegetative cell from a germinated spore- emergence from the spore coat, elongation of the emergent cell

Factors in spore resistance

1. Vegetative cell makeup and characteristics- optimum growth temperature of cell will yield same resistance in spore- thermophilic spores>spores of mesophiles>spores of psychtrophiles. More heat exposure increases resistance.

2. Spore structure

Spore structure- Core SASP resistance

Resistant to Dry heat, UV radiation, Desiccation and freezing

Spore structure- Core dehydration resistance

Resistant to Wet heat and hydrogen peroxide

Spore structure- Core minerals resistance

Resistant to dry heat, wet heat and hydrogen peroxide

Spore structure- Spore Cortex resistance

Resistant to wet heat, lytic enzymes, hydrogen peroxide. NOT resistant to UV radiation.

Spore structure- Spore coats resistance

Resistant to Lytic enzymes, and hydrogen peroxide. Not resistant to wet heat or UV radiation.

Heat resistance in spores is a measure of what compared to the vegetative cell?

Refers to the temperature at which the decimal reduction (killing by 90%) time of a heated suspension is 10 minutes.

Control of spores- Ways to inactivate (sporicidal)

1. Severe heat (retort)

2. Gamma radiation- heavy; spices use gamma radiation

3. Hydrogen peroxide (high concentration and heat): vapor (used with sterile packaging)

4. Ethylene oxide- in non-foods (disposable pipettes)

5. Chlorine

6. Ozone

7. Combination "hurdle process"

Control of spores- Inhibition of germination and/or outgrowth (sporostatic)

1. Bacteriocin: Nisin

2. Nitrite

Bacillus cereus

Mesophilic aerobe, facultative anaerobe. Importance in foods: food intoxication, cooked rice, pasta, meats, soups, salads, puddings.

Bacillus subtilis

Mesophilic aerobe, obligate aerobe. Spoilage: "ropy" bakery product; softening of pickles

Alicyclobacillus spp.

Thermophilic aerobe. Acidophile: growth at pH 2.5-5.5 (opt: 3.5-4). Optimum temp: 46-50C. In foods: flat sour spoilage, spoilage of fruit juices and iced teas

Bacillus coagulans

Thermophilic aerobe. Facultative anaerobe. Growth opt >50C. Aciduric: opt pH 6. In foods: flat sour spoilage, spoilage of canned tomato juice and other acid foods.

Bacillus stearothermophilus

Thermophilic aerobe. Facultative anaerobe. Growth at 40-70C (opt >60C). In foods: flat sour spoilage; spoilage of low acid canned vegetables.

Clostridium sporogenes

Mesophilic anaerobe. Putrefactive anaerobe. In foods: spoilage of canned vegetables (swelling and putrid odor).

Proteolytic Clostridium botulinum

Mesophilic anaerobe. Produce toxin types: A, B, F. Digests gelatin, milk and meat. In foods: Food intoxication, home-canned foods; foods subjected to faulty processing or temperature abuse.

Non-proteolytic Clostridium botulinum

Mesophilic anaerobe. Produce toxin types: B, E, F. Saccharolytic. Psychrotrophic. In foods: Food intoxication. Food implicated: fermented marine products, dried fish, vacuum packed fish.

Clostridium perfringens

Mesophilic anaerobe. Air-tolerant. Rapid growth. Stormy fermentation of lactose in milk. In foods: foodborne non-invasive infection. Food implicated: meat and poultry products.

Clostridium tyrobutyricum

Mesophilic anaerobe. Some strain produce toxin type E. In foods: gas formation ("late blowing") of cheeses.

Clostridium thermosaccharolyticum

Thermophilic anaerobe. Opt. growth 55-62C. In foods: spoiled canned vegetables

Desulfotomaculum nigrificans

Thermophilic anaerobe. Obligate thermophile: min growth temp at 43C or greater. In foods: Hydrogen sulfide spoilage of acid canned vegetables (blackened appearance and rotten egg odor). No swelling of can.

General characteristics of Fungi

-Eukaryotic, heterotrophic (saprophytes- dead matter or hypotrophic- parasites).

-Strictly aerobic--> facultative anaerobic (can metabolize without it ex: yeasts). Relevance to foods: growth on surface, probably fungi.

Cell wall contains chitin (like insects) and cellulose (like plants) or both.

Morphology of Fungi

Single-celled (eg yeast): generally larger than bacteria.

Dimorphic (ex: Candida): unicellular or pseudohyphae

Multicellular (eg: mold): thread-like strands called hyphae (collectively- mycelium). Septate or non-septate.

Mushrooms- complex

Mushroom structure

Morphology of foodborne fungi

Propagation of fungi

Binary fission: rare

Budding: common in unicellular (eg: Saccharomyces cerevisiae).

Elongation of hyphae (at tip): propagation

Fragmentation of hyphae: each piece becomes a new colony

Formation of spores: Asexual or sexual

Characteristics of Chytridiomycota

Septate hyphae: None

Asexual sporulation: motile zoospores

Sexual sporulation: oospores

Comments: lower fungi

Characteristics of Zygomycota

Septate hyphae: Yes

Asexual sporulation: Non-motile sporangiospores

Sexual sporulation: Zygospores

Comments: lower fungi, not xerophilic, not resistant to heat and chemicals, rare mycotoxin production

Characteristics of Ascomycota

Septate hyphae: Yes

Asexual sporulation: Condiospores

Sexual sporulation: Ascospore

Comments: Higher fungi, mostly xerophilic, often resistant to heat and chemicals

Characteristics of Basidiomycota

Septate hyphae: Yes

Asexual sporulation: Rare

Sexual sporulation: Basidiospores

Comments: Higher fungi, mushrooms, puffballs, rusts, jelly fungi. No significance to food spoilage

Characteristics of Deuteromycota

Septate hyphae: Yes

Asexual sporulation: Conidiospores

Sexual sporulation: None

Comments: Higher fungi. Some are xerophilic, not resistant to heat, some resistant to chemicals, production of mycotoxin is common

Asexual fungal spore types

Conidia or conidiospores- Penicillum spp, Aspergillus spp. 
Sporangiospores: Rhizopus spp.

Conidia or conidiospores- Penicillum spp, Aspergillus spp.

Sporangiospores: Rhizopus spp.

Sexual Fungal Spores

Zygospores: spore resulting from the fusion of haploid mating hyphae to produce a diploid zygospore. Eg: Rhizopus spp.

Ascospores: Spores of different mating types in an ascus (pod). Eg: Saccharomyces spp.

Basidiospores: Haploid spores formed on a fungal structure called a basidium. Eg: mushrooms.

Formation of zygospores

Formation of ascospores (formed in single cell fungi)

Formation of basidiospores

Beneficial fungi examples

Yeast- fermentation

Edible fungi- mushrooms, morels, truffles

Cheese production (surface ripened)

Decomposition in the biosphere- wood-rotting fungi

Symbiosis between fungus and plant

Produce antiobiotics- penicillin produced by Penicillum spps

Detrimental/Pathogenic Fungi Examples

Detrimental- spoilage

Pathogenic- plant pathogens (eg: Irish potato famine; loss of chestnut trees); Human pathogens: A. Invasive: athletes foot, ringworm, Candidiasis. B. Toxigenic: mycotoxins

Mucor characteristics

Identifying characteristics: nonseptate hyphae, smooth non-striated sporangiospores, produce no rhizoids.

Important properties in food spoilage: Grow on refrigerated meat ("whiskers"). Black spots on frozen mutton, Very common on bread.

Rhizopus characteristics

Identifying characteristics: Nonseptate hyphae, umbrella-shaped columellae, large sporangiospore with striated wall. Dark sporangia containing dark to pale spores.

Important properties in food spoilage: Bread mold, watery soft rot of fruits, black spot on beed, bacon, frozen mutton.

Aspergillus characteristics

Identifying characteristics: Black, brownish black, purple brown conidiospores. Yellow to green conidia. Dark sclerotia.

Important properties in food spoilage: A. niger: black rot on fruits and vegetables. Yellow, green to black on large number of foods.

Penicillium characteristics

Identifying characteristics: P. digitarum: yellow green conidia, P. italicum & P. expansum: blue-green conidia, P. camemberti: gray conidia.

Important properties in food spoilage: Blue/green rots of citrus fruits. Soft rots of apple, pear, peaches.

Geotrichum characteristics

Identifying characteristics: Arthroconidia formation, White colonies- colorless conidia.

Important properties in food spoilage: Machinery mold, soft rot of citrus fruits, peaches. Common in dairy products. Some have strong odors.

Fusarium characteristics

Identifying characteristics: Cottony, pink, red, purple, brown colonies. Sickle shaped conidia. Extensive mycelium, colorless conidia.

Important properties in food spoilage: Soft rot of rigs, brown rot of citrus fruits/pineapples, bacon and refrigerated meat spoilage and pickle softening.

Saccharomyces characteristics

Identifying characteristics: Multilateral budding, spherical spores, white or cream colonies, typical yeasty odor

Important properties in food spoilage: S. cerevisiae: ubiquitous contaminant, sometimes fermentative spoilage of soft drinks, some strains are preservative resistant.

Zygosaccharomyces characteristics

Identifying characteristics: multilateral budding, "dumbbell" shaped asci, 1-4 ascospores/ascus, Bean-shaped ascospores, strong fermenter of sugars!

Important properties in food spoilage: Z. bailii: highly resistant to preservatives, xerophile, capable of growth at aw: 0.8, pH 1.8, heat resistant, ascospores, spoil tomato sauce, mayonnaise, salad dressing, soft drinks, fruit juices etc. Z. rouxii: grow at aw: 0.62

Candida characteristics

Identifying characteristics: Cells are spherical, cylindrical, ovoid, or elongate. Pseudomycelium formation.

Important properties in food spoilage: Common yeasts in fresh ground beef and poultry. C. krusei: preservative resistant, form films on pickles, olives sauces. C. parapsilosis: spoil cheese, margarine, dairy and fruit products

Most problemative species of fruit concentrates (etc), ketchup, salad dressings, relishes.. etc.

Zygosaccharomyces bailii and Zygosaccharomyces rouxii.

Why?? Can grow at low water activity, grows over wide range of solute contents. Resistance to preservatives!

Behavior of M/O refers to what?

Their growth, survival and death in foods

Their growth, survival and death in foods

Microbial Growth Requirements


-Nutritional needs: carbon source, nitrogen source, growth factors/vitamins/minerals

-Environment: temperature, oxygen presence or absence, pH


A. Strict Aerobe- Ex: Pseudomonas

B. Facultative Anaerobe- Ex: Escherichia coli

C. Micro-aeorphilic or Aerotolerant Anaerobes- Ex: Lactic acid bacteria; Leuconostoc

D. Strict Anaerobe- Ex: Clostridium botulinum

Facultative anaerobes will grow better under which oxygen condition?

Grow faster in the presence of oxygen!

Categories Based on Optimum Growth Temp

Psychrophiles- love low temperatures (0-20C), grow in the fridge

Psychrotrophs- huge range of temperatures: 5-40C

Mesophiles- 20-40C, mostly 35-37C

Thermophiles- 45-75C

Microbial categories based on acid environment

Acidophiles- fungi: Zygosaccharomyces

Acid-tolerant: LAB; grow better without acidic environment though

Acid sensitive: Pseudomonas, Clostridium

**Fungi tend to tolerate acid better than bacteria in general

You leave two foods out on the counter- one gains weight and the other loses weight. In regards to water activity- which had a lower initial aw? Which is more susceptible to M/O growth? Why?

The food that gained weight had a lower water activity because its absorbing water vapor from the air; whereas the one that was losing weight had a relatively higher aw- was losing water to the environment (more susceptible to M/O growth- more free water)

What are intermediate moisture foods?

A food product that has a water activity below that which is required for the growth of m/o; or a food containing unavailable water. Characterized as an aw: 0.65-0.90 and general soft texture.

Minimum aw for M/O growth

Bacteria: minimum 0.9 (eg: Clostridium botulinum min is 0.94) Exception: Staphylococcus aureus- 0.85

Most spoilage molds: minimum: 0.8

Most spoilage yeasts: minimum: 0.85. Exception some Zygosaccharomyces spp.

In regards to food components- bloating of solid foods or container swelling is implicating what type of breakdown?

Degradation of CHOs with CO2 production/other gas

In regards to food components- slime is implicating what type of breakdown?

Breakdown of complex CHOs (polymerization)- pectin is example.

In regards to food components- texture loss is often implicating what type of breakdown? What about rancidity?

Proteolysis (by proteinases and peptidases). Rancidity= lipolysis by lipases.

Parmesan cheese owes its sharp flavor to what

Lipolysis by M/O

Types of food packaging techniques for M/O control

Air and spoilage- if it needs O2, make anaerobic environment.

Surface vs Bulk- air in headspace; differential spoilage

Food packaging: Headspace (remove oxygen), Canning and Vacuum packaging (no air in headspace or no headspace); Modified Atmospheric Pressure (if you can't get rid of O2- then modify amounts)

Low-acid foods were categorized by the gov't in regards to what M/O? What pH were they based on?

Clostridium botulinum- pH 4.6.

Low-acid foods are at a pH between 4.6-5.3 (cheeses) and greater than 5.3- bread, fish, meat, beans, milk, vegetables, egg whites; pH 7.6-9.5: lots of problems!

What does incidence refer to?

How M/O got into food.

Unintentional (contamination): What is the source and point of entry into food? What is the level of contamination?

Intentional: intentional inoculation of microbiota into foods (starter cultures or probiotics)

What are the points of entry of contaminant along the food chain?

Consequences of M/O contamination depend on what?

-Types of contaminating M/O

-Size of contaminant (eg: cfu/g or ml)

-Metabolic activity

-Types of contaminating M/O

-Size of contaminant (eg: cfu/g or ml)

-Metabolic activity

What does thermoduric mean?

Tolerates pasteurization temperatures, may find in pasteurized foods. Ex: Some Bacillus spores (B. coagulans); some Clostridium spores (C. putrefaciens); Lactobacillus viridescens; some fungal spores

Food spoilage during growth of small inocula (effect of cfu/g on likelihood of spoilage)

Caveats: in conjunction with numbers (population count), spoilage depends on type of M/O and their metabolic activity.  Signs of spoilage in milk may appear sooner than they do in other foods. 

10^5 cfu/g- start worrying, can hit spoilage po...

Caveats: in conjunction with numbers (population count), spoilage depends on type of M/O and their metabolic activity. Signs of spoilage in milk may appear sooner than they do in other foods.

10^5 cfu/g- start worrying, can hit spoilage population very quickly

Dairy cattle breeds? Which produce dairy products/milk?

Holstein-Friesian: main type for milk

Brown Swiss



Jersey: golden milk color; fat contains carotene; cheddar cheese use to come from them

Milking shorthorn

Definition of milk

A fluid secreted by the mammary glands of females for the nourishment of their young; cow's milk used as a food source for humans.

What pre-harvest factors affect milk microbiota?

Production practices- is milk collected indoors? Increased chance of contaminants from environment.

Animals activities: diet/exercise..

Animals health

Harvesting Raw milk

Preparing cow for milk- clean the udder prior to milking in milking parlor.

Milking- hand milking increases risk of contaminants vs milking machines

Storage on the farm- very important; MUST be refrigerated! Pick up frequency- daily (ideal); otherwise increased M/O growth

Entry point of contamination in milk (of the udder)

Contamination outside the udder can contaminate once in contact with milk from teat cistern.

Teat cistern can get contaminated too.

** VERY LITTLE contaminants in raw milk of healthy cows

Raw Milk Microbiota Sources

Cows Udder: Foremilk vs final milk: Micrococcus spp. and Staphylococcus albus- Washing and disinfection.

Cow's health status: particularly mastitis- Streptococcus agalactiae, Staphylococus aureus, Escherichia coli, Corynebacterium, Pseudomonas aeruginosa, Klebsiella. Impacts milk biota. Impacts yogurt and cheese industry.

Utensils/Milking machine: general cleanliness and sanitation. Milk stones made, porous, harbors bacteria.

Environment in milking parlor: proximity to maure piles, silos etc. Airborne bacteria of soil sources.

Trucks- ex: ice-cream mix outbreak

Raw Milk Microbiota Profile

Total counts:

Aseptically draw milk- 5x10^2-1x10^3 (mostly micrococci)

Milking machine- 1x10^3-1x10^4

Bulk-milk tank- 1x10^4-1x10^5 (mostly psychrotrophs)

Genera that may be present in raw milk






Additional biota:







Milk as a spoilage medium

Milk compositions and M/o requirements- supports the most fastidious microorganisms (eg: LAB).

Milk is 87% water, 4.9% lactose, 3.9% fat, 3.5% protein (casein mainly), 0.7% ash (salt). Has water and fat soluble vitamins. pH ~6.5 and a titratable acid level of 0.17.

Spoilage before processing of milk causes

-Heavily contaminated environment (equipment etc)

-Temperature abuse

-Lengthy refrigerated storage

Main spoilage M/O in milk


Bacilli and Pseudomonas

Proteolytic and lipolytic bacteria: products yield, flavor defects (cardboard taste, oxidized)

Alcaligenes spp: gram negative, psychrotroph, produces capsules- causes ropiness defect: milk tastes sweet and appears ropy (stringy) in texture.

Animal Source Pathogens in milk

Mycobacterium bovis (tuberculosis in children)

M. tuberculosis (tuberculosis)

M. paratuberculosis (Johne's disease in ruminants; Crohn's disease in humans)

Brucella spp- Infectious abortion in animals and brucellosis or undulant fever in humans

Coxiella burnetti- Q fever in humans

LIsteria monocytogenes: listeriosis

Escherichia coli O157:H7: gastroenteritis; hemolytic uremic syndrome

Salmonella spp: gastroenteritis; typhoid fever

Staphylococcus aureus: Intoxication

Human Source Pathogens in milk

Streptococcus pyogenes: scarlet fever/sore throat

Salmonella enterica serovar Typhi: Typhoid fever

Shigella spp: Shigellosis

Corynebacterium spp: Diphtheria

Environment Source Pathogens in milk

Bacillus cereus: intoxication

Bacillus anthracis: anthrax

Clostridium pefringens: Gastroenteritis

Clostridium botulinum: Botulism

Listeria monocytogenes: Listerosis

Post-harvest Processing and MO Quality in Milk

Raw milk- unprocessed

Pasteurized milk- mildly processed

UHT milk- highly processed

Yogurt, buttermilk, sour-cream, cheese- mild processed and fermented

Concentrated, condensed, powdered- milk to high processing