chapter 6 food micro Flashcards
number and types of MO present in a product are influenced by:
a. The general environment from which the food was originally obtained
b. The microbiological quality of the food in its raw or unprocessed state
c. The sanitary conditions under which the product is handled and processed
d. The adequacy of subsequent packaging, handling and storage conditions in maintaining the flora @ low level
Why is it important to keep MO at a low level in foods?
Aesthetic
Public health
Product shelf life
Primary Sources of microorganisms found in food:
- Food Utensils
- Food Handlers
- Water, Soil, Air
- Plants and Plant Products
- Animal Feeds and Animal Hides
I-Intrinsic Parameters
- Composition, Nutrient content
- pH
- Presence and availability of water (moisture content)
- Oxidation-reduction potential
- Altered by cooking
- Biological & Physical structure
- Presence of antimicrobial substances
pH affects at least 2 aspects of a microbial cell:
functioning of its enzyme + transport of nutrients
Most MOs grow best @ pH around 7.0 (6.6-7.5),while few grow below 4.0
Bacteria tend to be more fastidious (picky) in their relationships to pH (especially pathogenic bacteria) than molds and yeasts.
pH (2)
- fruits, soft drinks, vinegar and wines fall below the point @ which bacteria normally grow and the excellent keeping quality of these products is due in great part to pH
- Fruits generally undergo mold and yeast spoilage and this is due to the capacity of these MO to grow at pH values below 3.5 which is a pH below the minimum for most food spoilage and all food poisoning bacteria
pH (3)
most of the meats and sea foods have a final ultimate pH of about 5.6 above which their products become susceptible to bacterial as well as to mold and yeast spoilage.
Most vegetables have higher pH values than fruits, consequently they should be subject to bacterial more than fungal spoilage.
Molds have a wider pH range. Therefore they can cause spoilage of soft drinks, fruits, etc.
Meat from fatigued animals spoils faster than that from rested animals and this is a direct consequenceof final pHattained upon completion of mortis
Why?
Upon the death of a well rested meat animal, the 1 % glycogen is converted into lactic acid that decreases the pH value from 7.4 to 5.6 depending on the type of animal.
Water activity (aw)
amount of water available for microbial (bacteria, yeast and mold) growth.
In general, lower water activity inhibits microbial growth
Water activity lowered by
Drying, Freezing
Addition of salt or sugar
The preservation of foods by drying or desiccation is a direct result of removal or binding of moisture without which MO do not grow.
The water requirements of MO is defined in terms of water activity aw
Water activity is based on a scale of 0 to 1.0 with pure water having a water activity of 1.00. Exp: Pure water has aw of 1.00 22 % NaCl solution-aw = 0.86 Saturated solution of NaCl –aw = 0.75 The aw of most fresh foods is above 0.99
moisture content (1)
Lowering the aw below the optimum of MO is to increase the length of the lag phase of growth and to decrease the growth rate and size of final population; this effect is a result of lowering available water for metabolic activities.
Shelf life is extended as more water is reduced
moisture content(2)
aw is also influenced by other environmental parameters such as pH, temperature of growth, and Eh (oxido-reduction potential)
*Most spoilage bacteria do not grow below aw 0.91 while spoilage molds can grow as low as 0.60-0.80. Molds play an important role in spoilage of bread and dried food.
Oxido-reduction potential (1)
It’s represented by Eh, it is a measure of potential difference in a food
In the oxidized range, the redox potential is + mV
In the reduced range, the redox potential is –mV
Among the substances in foods that help to maintain reducing conditions are
–SH groups in meats and ascorbic acid and reducing sugars in fruits and vegetables.
The O/R potential of food is influenced by:
The chemical composition of a food :Redox couple present, Ratio of oxidant to reductant
Specific processing treatment
Storage conditions (vacuum packed, liquid N2, CO2, etc..)
pH: if pH decreases the Eh increases
Availability of oxygen: if the food is stored in presence of air, high positive potential will result, thus increasing the access to air by mincing, cutting, chopping, grinding of food will increase the Eh
Aerobic MO require
positive Eh values (oxidized) for growth like Bacillus spp
Anaerobes require
negative Eh values (reduced) like Clostridium spp
microbial growth in the food reduces
the Eh due to oxygen depletion
Fresh Foods of plant and animal origin are in a reduced state due to
presence of reducing substances such as sugars, ascorbic acids and –SH groups
-Plant foods and especially plant juices tend to have Eh values from +300 mV to +400 mV that’s why these products are commonly spoiled by aerobic bacteria and molds
Processing food such as heating can also alter
the Eh. Food stored in air can have a wider Eh range than when stored under vacuum.
-Cheeses have been reported to have negative Eh values
Solid meats have Eh values around -200 mV but in minced meats Eh values are around +200 mV
D-Nutrient content:
1-Water 2-Source of energy 3-Source of carbon 4-Source of nitrogen 5-Vitamins and related growth factors 6-Minerals
food microorganisms source of energy
- sugars, alcohols, amino acids
- Some microorganisms can use fats as source of energy, but their number is quite small
few MO use ………… as sources of energy
complex carbohydrates like starches and cellulose
All natural foods tend to have an abundant quantity of nutrients to MO
In general, molds have the
lowest requirements, followed by yeasts, gram negative bacteria, and gram positive bacteria
Essential oils in spices that have antimicrobial activity like:
- Eugenol in cloves (flower)
- Allicin in garlic
- Cinnamic aldehyde in cinnamon,
- Thymol in sage
Biological & Physical structures
Fruits and vegetables with damaged covering undergo spoilage much faster than those not damaged
The skin covering of fish and meats prevents the contamination and spoilage of these foods because it tends to dry out faster than freshly cut surfaces
Grinding and mixing increase surface area and distribute microbes which promotes microbial growth
Extrinsic parameters
They are the properties of the storage environment that affect both the food and their MO
Those of greatest importance to the welfare of food MO are:
Temperature of storage
Relative humidity of the environment
Presence and concentration of gases in the environment
Presence and activity of other microorganisms
Temperature of storage (psychotrophs)
-The psychrotrophs found most commonly on foods are those belonging to the genera of Pseudomonas and Enterococcus
These MO grow well @ refrigerator temperature (3-7 C) and cause spoilage of foods stored at this temperature in a certain time.
Temperature of storage(mesophiles)
Mesophilic bacteria are also found on foods held in refrigerator but these MO can not grow @ refrigerator temperature
Temperature of storage(thermophiles)
-Thermophilic bacteria of importance in food microbiology belong to the genera Bacillus & Clostridium that are very important in canning industry.
Molds are able to grow over wider ranges of pH, osmotic pressure, and nutrient content as well as over wider ranges of temperature than bacteria.
Relative Humidity of Environment
Relative humidity and water activity are interrelated.
When foods with low aware stored in environment of high humidity, water will transfer to the food and thus increasing the aw of the food leading to spoilage by the viable flora.
When the aw of a certain food is 0.60 , it’s important that this food is stored under conditions of R.H that do not allow the food to pick up moisture from the environment and to increase its aw.
There is a relationship between temperature and humidity. In general, the higher the temperature, lower is the relative humidity and vice-versa
Relative Humidity of Environment (2)
Foods that undergo surface spoilage from molds, yeasts, and some bacteria should be stored in conditions of low relative humidity to increase their shelf life.
This can also be done by proper wrapping of the food material also.
Variations in storage temperature should be minimal to avoid surface condensation in packed foods.
Ex: improperly wrapped meats tend to undergo surface spoilage in the refrigerator before deep spoilage occurs due the high RH and due to the meat spoilage flora.
Presence and Concentration of Gases in the Environment
O2influences the redox potential so the microbial growth
CO2: inhibitory effect on the growth of microorganisms
The storage of food in atmospheres containing 10% of CO2is referred to as “Controlled atmosphere” or “Modified atmosphere (MA)”.
Ex: Applied in case of fruits such as apples and pears
CO2retards fungal rotting of fruits
O3:added to food storage environments
It has a preservative effect on certain foods against spoilage of MO
It’s a strong oxidizing agent, so it should not be used on high lipid content foods,
It increases the rancidity effectiveness
Presence and Concentration of Gases in the Environment
Effects of CO2:
Its effect is usually bacteriostatic, although some microorganisms are killed by prolonged exposure
The inhibitory effect of CO2increases with decreasing temperature
Because @ lower temperatures the solubility of CO2increases, then the pH of certain food like meat for expwill decrease due to carbonic acid formation and thereby inhibiting the growth of microorganisms
Molds and Gram negative bacteria are the most sensitive, while Gram positive bacteria (lactobacilli) are more resistant
Spoiled food may be defined as food that has been damaged so as to make it undesirable for human consumption
A food is considered spoiled when it loses its acceptance qualities.
Detectable parameters associated with spoilage:
Changes in color, Odor, flavor (smell and taste), shape and texture
Formation of slime
Accumulation of gas (or foam)
Accumulation of liquid (exudate, purge
Food spoilage may be caused by:
Infestation with insects and rodents,
Physical injury of different kinds like bruising and freezing,
Growth of microorganisms or activity of enzymes
Types of Spoilage:
A-Physical spoilage: dehydration of fresh vegetables (wilting).
B-Chemical spoilage includes oxidation of fat, browning of fruits and vegetables, and autolytic degradation of some vegetables (by pectinases) and fishes (by proteinases).
C-Microbial spoilage results either as a consequence of microbial growth in a food or because of the action of some microbial enzymes present in a food.
CONDITIONS FOR SPOILAGE
- Water
- pH
- Physical structure
- Oxygen
- Temperature
Microorganisms causing most food contamination:
Bacteria, Parasitic worms, Fungi, and Viruses
Microbial food spoilage occurs as a consequence of:
Either microbial growth in a food
Or release of microbial extracellular and intracellular (following cell lysis) enzymes in the food environment
Toxins are sometimes produced
Algal toxins may contaminate shellfish
P.S. Spoilage by microbial growth occurs much faster than spoilage by microbial extra-or intracellular enzymes in the absence of viable microbial cells.
Ergotism
Toxic condition caused by growth of a fungus in grains
Aflatoxins
Carcinogens produced in fungus-infected grains and nut products (ex: sesame in tahini)
Fumonisins
Carcinogens produced in fungus-infected corn
FOOD PRESERVATION-EARLY METHODS
Smoking Drying/Desiccation/Dehydration Salting Jams to preserve fruits Yogurt and Cheese Making to Preserve Milk Cooling
FOOD PRESERVATION
1
Filtration
commonly used for water, beer, wine, juices, soft drinks, and other liquids
Refrigeration
refrigeration at 5°C retards but does not stop microbial growth
Reducing water availability
Drying
Freeze-drying (lyophilization)
Addition of high concentrations of solutes such as sugar or salt
FOOD PRESERVATION
2
-Pasteurization
Kills pathogens and substantially reduces number of spoilage organisms
Chemical-Based Preservation
GRAS:chemicalagents “generally recognized as safe”
Radiation
Non-Ionizing Radiation (ultraviolet (UV) radiation): used for surfaces of food-handling equipment, does not penetrate foods
Ionizing radiation (gamma radiation) to extend shelf life or sterilize meat, seafood, fruits, and vegetables
Microbial Product-Based Inhibition
Bacteriocins: bactericidal proteins active against related species
Some form pores in plasma membranes
Some inhibit protein or RNA synthesis
Ex: nisinused in low-acid foods to inactivate Clostridium botulinum during canning process
food preservation - aseptic packaging
Pre-sterilized materials are assembled into packages and aseptically filled with heat-sterilized liquid foods.
canning
-Canning provides a useful extension to the cooking process
Cooked foods are hermetically sealed in metal cans or in bottles
Food heated in special containers (retorts) to 115°C for 25 to 100 minutes
kills spoilage microbes, but not necessarily all microbes in food
In commercial canning the cooking process is designed
to reduce an absolute minimum the risk of Clostridium botulinumspores surviving
Other more heat resistant spores may survive the canning process and subsequently cause spoilage of the canned foods
Spoilage may also occur if the seal of the can is faulty, permitting the entry of microbes:
oContamination of the food doesn’t produce a detectable change in its appearance
oIn others gases evolve during the microbial contamination and growth which cause swelling of the can giving it a “blown” appearance.
ex: this typically happens when a yeast contaminate canned fruit
However, Blown cans may also result from the chemical reaction between the acids in food and the metal of the can by the production of hydrogen: lacquer applied to the inner surface of cans overcomes this problem.
The foodborne Illness is caused by
1-the infection with microorganisms, 2-ingestion of toxins produced, and 3-chemical poisoning.
Foodborne pathogens:
Foodborne pathogens include: enteric viruses, protozoan parasites, Yersinia enterocolitica, Vibriospp., Staphylococcus aureus, CampylobacterInfections, Listeria monocytogenes, Salmonellaspp., Shigellaspp., Escherichia coli, Clostridium botulinum, Clostridium perfringensand Bacillus cereus.
Foodborne Infection
Ingestion of microbes, followed by growth, tissue invasion, and/or release of toxins, ex: Salmonella
1. Food doesn’t support growth of the pathogens but merely carries them
Ex. Pathogens causing typhoid, tuberculosis etc…
2. Food can serve as a culture medium for the growth of the pathogens to numbers –likelihood of infection
Ex. Salmonella spp., Escherichia coli
Foodborne Intoxications or food poisoning
Ingestion of toxins in foods in which microbes have grown (organism may or may not be growing)
Include staphylococcal food poisoning, botulism, Clostridium perfringensfood poisoning, and Bacillus cereusfood poisoning
The main factors responsible for the foodborne illness include:
a) Improper holding temperature during processing.
b) Inadequate cooling during storage.
c) Contaminated equipments and utensils.
d) Food from unsafe source.
e) Poor personal hygiene.
f) Adding contaminated ingredients to cooked foods.
WHO RULES FOR SAFE FOOD PREPARATION
Choose food processed for safety
Cook food thoroughly
Eat cooked food immediately
Store cooked food carefully
Reheat cooked foods thoroughly
Avoid contact between raw foods and cooked foods
Wash hands repeatedly
Keep all kitchen surfaces meticulously clean
Protect foods from insects, rodents, and other animals
Use pure water
ENTEROBACTERIACAE
Largest, most heterogeneous collection of medically important gram-negative bacilli
Ubiquitous organisms
Found worldwide in soil, water, and vegetation, and are part of the normal intestinal flora of most animals including humans
Cause a variety of human diseases: septicemia, urinary tract infection, intestinal infection
Can cause opportunistic infections
Include: Escherichia coli, Salmonella, Shigella, Yersinia
Others: Klebsiella, Proteus, Serratia, Citrobacter, Morganella, Enterobacter
Virulence factors:Endotoxin (Lipopolysaccharide), Capsule, Antigenic phase variation, Adherence and persistence (colonization), antimicrobial resistance
Escherichia coli
Lactose and glucose fermenters Gram (-ve) rods Some motile and others are not Responsible for diseases such as UTIs and gastroenteritis Common cause of nosocomial infections
E. coli food sources and symptoms:
Food Sources: Any food exposed to sewage-contaminated water
Symptoms: abdominal pain, diarrhea, fever, Chills, blood in feces, nausea, dehydration, prostration
Incubation Time: about 11 hours
Control measures: Chill and heat foods rapidly, Enforce good personal hygiene rules
Control flies, Prepare foods safely
Escherichia coli
Major groups:
Enterotoxigenic(ETEC) Enteropathogenic(EPEC) Enteroinvasive(EIEC) Enterohemorrhagic(EHEC) Enteroaggregative(EAEC)
Enterotoxigenic(ETEC)
Occurrence: -in developing countries: major cause of dehydration in infants and children
-in children under 3 years
-Travelers visiting developing countries
Travelers’ diarrhea (duration 3-5 days)
Symptoms: vomiting, abdominal pain, cramps and low grade fever
Heat stable and heat labile enterotoxins
Enterotoxigenic reservoir, transmission and prevention:
Reservoir: man Transmission: Contaminated food, less frequently water and milk Direct contact (rare): fecal contamination→handPrevention: Proper hygienic procedures Disposal of human feces Provide safe water supplies Encourage breast feeding Milk pasteurization
Enteropathogenic(EPEC)
Occurrence: -most cases in developing countries and in infants
Causes infant summer diarrhea (< 1 year)
Symptoms: watery diarrhea-mucous, fever, dehydration
Diarrhea can become severe, chronic and leads to death
Enteropathogenic(EPEC) transmission and prevention:
Transmission:
Contaminated infant formula
Weaning foods
Prevention:
Adequate sanitary habits in infant nurseries
Use clean , sterilized bottles, water and food
Isolate babies with diarrhea from normal babies
Encourage breast feeding
Enteroinvasive(EIEC)
Occurrence: -more common in developing countries
-occasional infections and outbreaks in developed countries
Causes: Bloody diarrhea and inflammatory disease of gut mucosa
Reservoir: man and few cases with food due to large infectious dose
Transmission:
Little evidence suggests contaminated food
Prevention:
Same as ETEC
Enterohemorrhagic(EHEC) (O157: H7)
Watery diarrhea with blood, hemorrhagic colitis
Enteroaggreagative(EAEC)(not well understood but believed to act similarly as ETEC)
Transmission: fecal-oral
Symptoms: watery, non-inflammatory diarrhea, blood and pus unusual, fever is occasional
Salmonella spp.
Most species are gram (-ve), rod shaped and motile
Non spore-formers, can grow aerobically and anaerobically
Disease Salmonellosis
acute enterocolitis, with sudden onset of headache, abdominal pain, diarrhea, nausea, fever, chills, and sometimes vomiting, Dehydration, prostration
Three different syndromes in humans by different types of Salmonella
S. typhi: Typhoid fever, S. paratyphiA, B&C: enteric fever, S. enteriditis: Gastroenteritis
salmonellosis: Incubation Time
5 to 72 hours; usually 12 to 48 hours
Salmonella spp. (Cont’d)
Occurrence: worldwide
Food sources: meat, poultry, egg products, or via humans carriers
Mode of transmission:
Fecal oral transmission from person to person
Raw and undercooked food: eggs, milk, milk products, food derived from infected animals
Control of Salmonellosis:
Carriers: food handlers and in families
Prevent post processing contamination: proper hygiene and food handling
Proper cleaning of utensils avoid cross contamination
Cook thoroughly
Chill rapidly
Shigella
Shigellais a gram negative bacteria
Non-motile, rod shaped, non spore former.
Non lactose fermenter, produce acid from carbohydrates fermentation, do not produce H2S
Foods include:salads (potato, chicken, seafood, vegetable), raw vegetables, milk and other dairy products, and meat products especially poultry.These foods usually are contaminated through cross-contamination from fecal matter
Disease: Shigellosis
Symptoms:abdominal pain, cramps, diarrhea, fever, vomiting, blood, pus, or mucus in stool
shigella onset, mode of transmission, treatment, prevention:
Onset: in 12-50 hours
Some strains produce theenterotoxin shigatoxin, which is similar to thetoxin ofE.coliO157:H7
Mode of transmission: fecal-oral route (infectious dose 10-100 cells), flies, pets, food handling
Shigellainfection is typically via ingestion (fecal–oral contamination); depending on age and condition of the host, fewer than 100 bacterial cells can be enough to cause an infection
Treatment: antibiotics, fluids
Prevention: sanitary control of water, food, and milk, sewage disposal,
hygiene of breast feeding
Campylobacter jejuni
Curved s-shaped gram (-) rods, motile with a single polar flagellum at one or both ends.
Microaerophilic. Grow with 10% CO2 / 5% O2 . Some species / strains require additional H2 in the
atmosphere
C. jejuni will grow at 42o C and this is used as a selection criterion.
The organism is unusually thin (0.2 - 0.9 )
Reservoirs:
Poultry
Pets - especially young puppies
Water supply
Raw milk
Most cases occur in the summer months, late spring to early autumn
Disease Characteristics
Low infectious dose
Two disease entities:
Diarrhea
Dysentery
Associated with Guillain-Barre syndrome (Ascending muscle weakness or paralysis,
rapidly progressing, 40% of GBS patients have evidence of Campylobacter infection)
Yersinia enterocolitica
Disease: acute enteric illness: inflammation and ulceration of intestine, acute diarrhea, fever,
headache, vomiting, anorexia, rarely septicemia
Symptoms:
Children and adolescents: digestive upset, severe abdominal pain resembling acute
appendicitis
Adults: acute abdominal disorders, diarrhea, fever, arthritis
Both groups: skin and eye infections
Incubation Time: 3 to 7 days
Occurrence: worldwide, most cases among children
Reservoir: wide variety of animals without signs of disease: swine-pigs
Food Sources: Contaminated raw pork or beef, Drinking water, milk products, tofu
Yersinia enterocolitica
Disease: acute enteric illness: inflammation and ulceration of intestine, acute diarrhea, fever,
headache, vomiting, anorexia, rarely septicemia
Symptoms:
Children and adolescents: digestive upset, severe abdominal pain resembling acute
appendicitis
Adults: acute abdominal disorders, diarrhea, fever, arthritis
Both groups: skin and eye infections
Incubation Time: 3 to 7 days
Occurrence: worldwide, most cases among children
Reservoir: wide variety of animals without signs of disease: swine-pigs
Food Sources: Contaminated raw pork or beef, Drinking water, milk products, tofu
Yersinia enterocolitia(con’d) Mode of transmission and prevention;
Fecal-oral (food, water)
Contact with infected animals and persons
Nosocomial transmission (transfusion)
High inoculum needed for production of illness
Prevention:
proper hygienic procedure, enforce good personal hygiene rules
Pasteurize or heat-process foods
Sanitize equipment and utensils
Always purchase foods from approved sources
VIBRIOS
Vibrios: gram negative, straight or curved rods, mobile species.
They can have a respiratory metabolism or a fermentative one.
They can grow on almost any type of sugar but need at least 2-3% NaCl to survive because most are found in salt water habitats
Most commonly found in surface waters.
In most cases people become infected with this bacteria when eating raw or undercooked seafood and the bacteria are most commonly found in clams, oysters, and scallops.
Vibrio cholera
Fairly common as a foodborne disease.
Can be transmitted by water or food.
Disease: Cholera that has caused many outbreaks all over the world.The disease is caused by a enterotoxin that acts on the mucosal epithelium.
The onset is within one hour and can cause fatality within three hours if untreated.
Symptoms: diarrhea, dehydration, acidosis, shock
Treatment:-IV fluids -Plenty of sugars whether IV or by mouth
Reservoir: man
Prevention: vaccine (1992), education, sanitation, improvement on sewage and water systems
Vibrio parahemolyticus:
Vibrio parahemolyticusfood poisoning:
Watery diarrhea and abdominal cramps in the majority of cases
Sometimes nausea, vomiting, fever, chills and headache
Systemic infection and death rarely occur
Food Sources: Raw seafood, sushi, saltwater fish, shellfish, Fish products, salty foods, cucumbers
Mode of transmission: ingestion of raw or inadequately cooked seafood or any food cross-contaminated by handling raw seafood or by rinsing with contaminated seawater
Incubation Time: Usually 10 to 20 hours
Preventive measures:
Educate consumers of the risks associated with eating raw seafood
Educate seafood handlers and processors on the following preventive measures
Cook seafood at adequate temperatures to kill the organism
Keep all seafood adequately refrigerated before eating
Separate raw from cooked foods
Avoid use of seawater in food handling areas or to rinse food
Listeria monocytogenes
Listeria monocytogenesis a gram positive rod, facultative anaerobe, catalase +ve, oxidase +ve, motile, non spore former
It is highly resistant to freezing, drying, and heat which makes it unusually difficult to kill.
Disease: Listeriosisand is contracted when food is not washed properly.Contamination is usually by the cross-contamination from fecal matter.
Perinatal and adult listeriosis: disseminated infection often with CNS involvement
Symptoms: nausea, diarrhea, in pregnant women: prenatal septicemia, meningitis, encephalitis, or intrauterine or cervical infections leading to spontaneous abortion and possible death
Reservoir: humans, fowls, and animals, water, soil, sewage, milk,
Asymptomatic carriers among humans exist
Listeria monocytogenes(cont’d) 2
Onset
Gastrointestinal 1-12 hours
More serious symptoms: 2 days-3 weeks
Food Sources:
Vegetables fertilized with contaminated manure
Milk contaminated after pasteurization
Contaminated cheeses and meat
Foods marketed as refrigerated and ready to eathave been associated with most of the outbreaks
Prevention Controls
Pasteurize or heat-process foods
Avoid re-contaminating foods
Refrigerate or freeze all dairy products
Use proper equipment cleaning and food safety procedures
Risk groups: Newborns, elderly, immuno-compromised, pregnant women
Brucellaspp.
Aerobic gram –vecoccobacilli, Catalase +ve, non-spore forming, non-motile, non fermentative
B. abortus(goats and cattle), B.suis(swine), B.melitensis(goats and sheep), B. canis(dogs): all infect humans
Disease: Brucellosis
Occurrence: worldwide
Mode of transmission: Ingestion of contaminated food, especially milk and dairy products from contaminated animals, occupational contact: veterinarians, butchers, meat packers, and farmers, airborne route occasionally
No person to person exposure
Prevention:
Educate public about risks of drinking untreated milk
Pasteurize milk and dairy products
Educate farmers and workers in slaughter houses
Examination of cattle
Staphylococcal Food Poisoning
Identification:
Staphylococcal food poisoning is an intoxication and not an infection
Characterized by an abrupt and sometimes violent onset
Causes severe nausea, cramps, vomiting and diarrhea, low blood pressure, and fever
Duration of the illness is 1-2 days
Staphylococcal Food Poisoning Infectious agent:
Staphylococcus aureus
Gram (+ve) coccioccuringin grape like clusters
Aerobic or facultative anaerobes
Non-motile, non-spore forming
Mesophiles
Coagulase positive, catalase positive
Produce heat-stable enterotoxin: stimulates the vomiting center in the brain and causes vomiting and nausea
Staphylococcal Food Poisoning Occurrence,Reservoir
Occurrence Widespread and relatively frequent Incubation period 2-4 hours Reservoir Man usually 40-50% of healthy individuals are carriers Occasionally cows, dogs and fowl
Staphylococcal Food Poisoning Mode of transmission
Mode of transmission
Ingestion of food held at room temperature
Human origin (from food handlers): purulent discharges of infected fingers, infected eyes, abscesses, facial acne, nasopharyngeal secretions
Foods involved: raw milk, ice cream, hard cheeses, meat and poultry products, rice balls or sushi (food handlers)
Others: chocolate, bakery products, beef, turkey, chicken and eggs
Staphylococcal Food Poisoning prevention
Proper cooking of food
Cold storage
Proper personal and food hygiene for food handlers
Temporarily exclude food handlers with lesions of face, hands or nose
Other illnesses:
Skin infection
Can reach blood leading to bacteremia and sometimes endocarditis
Conjunctivitis especially in newborn, elderly and few adults
Toxic shock syndrome: fever, vomiting nausea, diarrhea and hypertension
Clostridium botulinum
Gram +velarge rods, motile by flagella, anaerobic, spore former (heat resistant spores 100ºC 3 hrs)
Natural habitat: soil, GI tract in humans and animals
Disease: Botulism
Occurrence: worldwide
An intoxication that is caused by the ingestion of a virulent nerve toxin
Classical botulism: strict intoxication (ingestion of toxin)
Infant botulism: most common form, colonization of intestinal tract
wound botulism: rare, present among cocaine sniffers
Food Sources: Inadequately processed home-canned foods –major causes of botulism
String beans, sweet corn, beets, asparagus, fruits –peaches and pears
Preserved fish and meats
Clostridium botulinum(cont’d)
Reservoir:
Transmission Symptoms:
Reservoir: spores in soil, vegetables, spices and potatoes
Transmission: ingestion of food containing toxin: canned food, vacuum packed food, smoked salmon, sausages, sea food
Symptoms: (within 12-36 hours, sometimes earlier, sometimes weeks later)
Earliest: digestive disturbance, Nausea +vomiting, diarrhea + fatigue, loss of coordination, dizziness and headache; double vision
Fever could occur
Later: abdominal pain and either diarrhea or constipation, difficulty in swallowing and speaking; visual difficulty (blurred, ptosis, dilated pupils), dryness of mouth and constriction of throat, Involuntary muscle paralyzes (loss of mouth and throat function), respiratory impairment paralysis spread to respiratory and heart
Death usually occur due to respiratory failure (usually within 3 –6 days but period varies).
Infant Botulism: constipation (days to week after onset), generalized weakness and a weak cry, poor feeding and sucking reflex, lack of facial expression, floppiness, respiratory arrest may occur although death is rare.
Clostridium botulinum(cont’d)
Prevention:
treatment:
Education
Effective control of processing and preparation of processed and canned food (Use of approved heat processes )
Rejection of all gassy (swollen)/ spoiled canned foods
Refusal even to taste a doubtful food
Boiling of suspected food at least 15min
Avoid raw or precooked foods that have been frozen, thawed, and held at room temperature
Treatment: Only known successful treatment –administration of antitoxin
Clostridium perfringens
Gram positive rod, spore forming, anaerobic but tolerant of some exposure to air, under optimal conditions, is capable of doubling every 10 minutes
Causes gas gangrene and food poisoning
Characterized by intestinal disorder with sudden onset of colic, followed by diarrhea, nausea is common , but vomiting and fever are usually absent
In general, it is a mild disease of short duration (1 day or less) and rarely fatal in healthy persons: disease is produced by toxins elaborated by the organisms
Occurrence: widespread
Reservoir: soil, also the GI tract of healthy persons and animals (cattle, pigs, poultry and fish)
Mode of transmission:
Ingestion of food contaminated by soil or feces
Prevention:
Education of food handlers
Eat meats as soon as they are cooked, and properly refrigerate and reheat
Bacillus cereus
Gram +verods (large rods tend to grow in chains) involved in food poisoning,
Grows aerobically and non aerobically, motile & spore former
Two enterotoxins:
Heat stable: vomiting
Heat labile: diarrhea
Bacillus cereus food poisoning:
Two forms: 1-diarrheal (Incubation period:8-16 hours):Abdominal pain, watery diarrhea, some nausea
2-emetic: malaise, vomiting and nausea (Incubation period: 30 min-5 hours)
Occurrence: Europe: mostly diarrheal form
USA: 2 forms rarely reported
Reservoir: soil, milk, dairy products, cereals, spices, herbs, meat, vegetables, sauces, soups; the outbreaks include rice and other foods as macaroni
Transmission:
Ingestion of food left at room temperature after cooking
Mishandled food
Prevention: refrigeration, proper storage, reheating
FOODBORNE VIRUSESHEPATITIS A VIRUS
It is an enterovirus of the Picornaviridaefamily
Resistant to denaturation by acid (pH=3), drying, and temperatures as high as 56˚Cand as low as -20˚C
It causes Hepatitis A
Occurrence
It occurs sporadically and epidemically worldwide (especially in developing countries where sanitation is poor)
Reservoir
Mainly man
Rarely chimpanzees and other primates
HEPATITIS A VIRUS (CONT’D)
Mode of Transmission Signs & SymptomsIncubation period
Mode of Transmission
Person to person via the fecal-oral route
Ingestion of contaminated food:
Through infected handlers
Raw or undercooked mollusks harvested from contaminated water
Ingestion of contaminated water
Signs & Symptoms
Usually a mild illness characterized by sudden onset of: fever, malaise, nausea, anorexia, and abdominal discomfort, followed in several days by jaundice
Varies in clinical severity from a mild illness lasting 1-2 weeks to a severe disabling disease lasting several months
Prolonged relapsing hepatitis for up to 1 year occurs in ~15% of the cases
Incubation period
Range 15-50 days (average: 28-30 days)
Maximum infectivity occurs during the second half of incubation and continues after onset of jaundice
Asymptomatic carriers
HEPATITIS A VIRUS (CONT’D)
Prevention
Education of food handlers
Proper sanitation
When traveling to endemic areas:
oDo not eat raw or undercooked seafood
oDo not drink untreated water or beverages with ice
oDo not eat fruits and vegetables unless cooked or peeled
Vaccine: recommended for children, for travelers to areas where HAV is endemic, and for people at high risk
Microorganisms play a major role in the production of food and beverages:
Alcoholic beverages (beer, wine,…)
Dairy products (yogurt, cheeses, butter, ..)
Fish and meat products (fish sauce and some sausages)
Plant products (dough, pickles, cocoa and coffee beans)
Bread
I-Dairy Products
Milk from cows, sheep, goat, buffalo, camel may be used to produce fermented dairy products like cheese, yogurt and butter.
This production has been traditionally a means of food preservation by lowering the aw , increasing acidity and bacteriocinformation.
The MO used in the production of fermented dairy products are primarily lactic acid bacteria that are naturally present in milk
Other MO may be involved in later maturation of processes of some cheeses like Camembert, blue cheese…
Fermentation generates lactic acid that modifies milk proteins and forms flavor and aroma compounds notably diacetylwhich imparts buttery flavor.
More recently popularized dairy products include fermented “health” drinks and foods referred to probiotics.
These products contain Lactobacillus acidophilusand Bifidobacterium bifidumwhich improve the functioning of the digestive system and stabilize its microflora
cheese
- The milk protein casein curdles because of the action by lactic acid bacteria or the enzyme rennin or chymosin.
- Cheese is the curd separated from the liquid portion of milk, called whey.
- The growth of microorganisms in cheeses is called ripening.
- Hard cheeses are produced by lactic acid bacteria growing in the interior of the curd.
- A Propionibactertiumspp. Produces CO2 which forms the holes in Swiss cheese
- Semisoft cheeses are ripened by bacteria growing on the surface
- Soft cheeses (Roquefort, Blue cheese) are ripened by Penicilliuminoculated into the cheese.
yoghurt
- Yoghurt is made from milk
- The thickened milk is fermented by a mixture of Streptococcus salivarius ssp thermophilus for acid production
and Lactobacillus bulgaricus (official name Lactobacillus delbrueckii ssp. bulgaricus) for flavor and aroma.
Often these two are co-cultured with other lactic acid bacteria for taste or health effects (probiotics). These
include L. acidophilus, L. casei and Bifidobacterium species. - Acid produced from the fermentation causes the protein in the milk (casein) to coagulate into a semisolid curd
C- Other Dairy Products
- Old-fashioned buttermilk was produced by lactic acid bacteria growing during the butter-making process.
- Commercial buttermilk is made by letting lactic acid bacteria grow in skim milk for 12 hours.
- Sour cream are produced by Lactobacilli, Streptococci, or yeasts growing in low-fat milk.
II-Nondairy Fermentations
- Sugars in bread dough are fermented by yeast to ethanol and C02; C02causes the bread to rise.
- Sauerkraut, pickles, olives, and soy sauce are the products of microbial fermentations.
- The beans of cocoa and coffee undergo a fermentation step
bread
It’s made by mixing Saccharomyces cerevisiae (baker’s yeast) under aerobic conditions with flour and water in the process known as kneading
This distributes the yeast through the dough.
The mixture is allowed to prove during which the yeast grows to produce large quantities of CO2.
This becomes trapped as bubbles within the dough and these cause the dough to rise.
Then the bread mixture is kneaded for a second time to distribute the carbonic acid produced by the yeast.
Once the dough has risen again bread is baked.
Sour dough is made by another yeast Sacharomycesexiguusused with lactobacilli together to produce an acid product that gives the bread its sour taste.
III-Alcoholic Beverages and Vinegar
- Carbohydrates obtained from grains, potatoes, or molasses are fermented by yeasts to produce ethanol in the production of beer, and distilled spirits.
- The sugars in fruits such as grapes are fermented by yeasts to produce wines.
- In wine-making, lactic acid bacteria convert malic acid into lactic acid in malolacticfermentation in fruits with high acidity.
- Acetobacterand Gluconobacteroxidize ethanol in wine to acetic acid (vinegar).
Beer brewing
beer production process: 1. malting 2. mashing and wort preparation 3. yeast fermentation 4. post fermentation
-Two kinds of drinks (beer) are the result of fermentation by Saccharomyces cerevisiae according to different temperatures of fermentation: one can occur at 14-23 C & the other one can occur at 6-12 ºC.
Most Beers are filtered to remove yeasts before packaging.
The beer may be disinfected either by cold filtration through 0.45μm filter or by pasteurization
Wine
Much of the world’s commercial wine is made of grapes, but other fruits can be used as well .
Grape juice is particularly successful for wine production because it contains high levels of fermentable sugars (mainly glucose and fructose) and other nutrients that are necessary for the fermentation and the growth of the yeasts
Most wines are table wines and contain 12-14 % ethanol some regions produce fortified wines with 22 % ethanol.
Wine Processing:
Grape must --> Fermentation --> Post fermentation--> Bottling –packaging (+/-maturation in bottle)
wine fermentation
-Alcoholic fermentation of wine is carried out by indigenous yeast or added starter yeast
The yeasts responsible for the fermentation are Sacharomycescerevisiaeand S. ellipsoideus
Fermentation is carried out without O2so the yeasts produce alcohol
The primary fermentation that generates different quantities of ethanol, CO2, higher alcohols, esters, aldehydes and ketones.
The secondary fermentation to produce wine carbonation or to reduce acidity where malic acid is converted to lactic acid
If starter is added, it’s better to pasteurize the must (starter material)to kill the MO that are present in the skin of grapes
Wine Fermentation:
White wine fermentation is often between 16-20 ºC for 1-4 weeks
Red wine fermentation is normally maintained at 24-29 ºC so the fermentation is shorter than the white wine, it lasts only for 3-days.
Normally yeast fermentation stops when all available sugar has been metabolized, in general the concentration of alcohol builds up to a point where it kills the yeast preventing further fermentation
Distilled Spirits
Produced by the fermentation of grain mash (similar to beer), followed by distillation to increase the alcohol content
Different types of grains are used to produce different types of spirits
Ex. Whisky, vodka, and rum
B-VINEGAR PRODUCTION
Natural solutions of fermentable sugars (fruit juice or other plant extracts) are exposed to alcoholic fermentation by yeasts 1st.
Then, they are exposed to bacterial oxidation of the ethanol to acetic acid (acetification)
It’s a highly aerobic fermentation, it’s a biotransformation by acetic acid bacteria : Acetobacterspp. which oxidize the ethanol to acetic acid:
Ethanol Acetaldehyde Acetaldehydehydrate acetic acid
104
NB: sometimes vinegar is contaminated by certain lactic acid bacteria that cause over oxidation of the acetic acid that’s transformed to CO2+ H2O
