chapter 6 food micro

Question 1

number and types of MO present in a product are influenced by:

Answer 1

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

Question 2

Why is it important to keep MO at a low level in foods?

Answer 2

Aesthetic
Public health
Product shelf life

Question 3

Primary Sources of microorganisms found in food:

Answer 3

1. Food Utensils
2. Food Handlers
3. Water, Soil, Air
4. Plants and Plant Products
5. Animal Feeds and Animal Hides

Question 4

I-Intrinsic Parameters

Answer 4

1. Composition, Nutrient content
2. pH
3. Presence and availability of water (moisture content)
4. Oxidation-reduction potential
5. Altered by cooking
6. Biological & Physical structure
7. Presence of antimicrobial substances

Question 5

pH affects at least 2 aspects of a microbial cell:

Answer 5

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.

Question 6

pH (2)

Answer 6

• 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

Question 7

pH (3)

Answer 7

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.

Question 8

Meat from fatigued animals spoils faster than that from rested animals and this is a direct consequenceof final pHattained upon completion of mortis
Why?

Answer 8

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.

Question 9

Water activity (aw)

Answer 9

amount of water available for microbial (bacteria, yeast and mold) growth.

Question 10

In general, lower water activity inhibits microbial growth

Water activity lowered by

Answer 10

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.

Question 11

The water requirements of MO is defined in terms of water activity aw

Answer 11

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

Question 12

moisture content (1)

Answer 12

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

Question 13

moisture content(2)

Answer 13

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.

Question 14

Oxido-reduction potential (1)

Answer 14

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

Question 15

Among the substances in foods that help to maintain reducing conditions are

Answer 15

–SH groups in meats and ascorbic acid and reducing sugars in fruits and vegetables.

Question 16

The O/R potential of food is influenced by:

Answer 16

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

Question 17

Aerobic MO require

Answer 17

positive Eh values (oxidized) for growth like Bacillus spp

Question 18

Anaerobes require

Answer 18

negative Eh values (reduced) like Clostridium spp

Question 19

microbial growth in the food reduces

Answer 19

the Eh due to oxygen depletion

Question 20

Fresh Foods of plant and animal origin are in a reduced state due to

Answer 20

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

Question 21

Processing food such as heating can also alter

Answer 21

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

Question 22

D-Nutrient content:

Answer 22

1-Water
2-Source of energy
3-Source of carbon
4-Source of nitrogen
5-Vitamins and related growth factors
6-Minerals

Question 23

food microorganisms source of energy

Answer 23

• sugars, alcohols, amino acids

- Some microorganisms can use fats as source of energy, but their number is quite small

Question 24

few MO use ………… as sources of energy

Answer 24

complex carbohydrates like starches and cellulose

Question 25

All natural foods tend to have an abundant quantity of nutrients to MO
In general, molds have the

Answer 25

lowest requirements, followed by yeasts, gram negative bacteria, and gram positive bacteria

Question 26

Essential oils in spices that have antimicrobial activity like:

Answer 26

• Eugenol in cloves (flower)
• Allicin in garlic
• Cinnamic aldehyde in cinnamon,
• Thymol in sage

Question 27

Biological & Physical structures

Answer 27

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

Question 28

Extrinsic parameters

Answer 28

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

Question 29

Temperature of storage (psychotrophs)

Answer 29

-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.

Question 30

Temperature of storage(mesophiles)

Answer 30

Mesophilic bacteria are also found on foods held in refrigerator but these MO can not grow @ refrigerator temperature

Question 31

Temperature of storage(thermophiles)

Answer 31

-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.

Question 32

Relative Humidity of Environment

Answer 32

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

Question 33

Relative Humidity of Environment (2)

Answer 33

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.

Question 34

Presence and Concentration of Gases in the Environment

Answer 34

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

Question 35

O3:added to food storage environments

Answer 35

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

Question 36

Presence and Concentration of Gases in the Environment

Effects of CO2:

Answer 36

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

Question 37

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:

Answer 37

Changes in color, Odor, flavor (smell and taste), shape and texture
Formation of slime
Accumulation of gas (or foam)
Accumulation of liquid (exudate, purge

Question 38

Food spoilage may be caused by:

Answer 38

Infestation with insects and rodents,
Physical injury of different kinds like bruising and freezing,
Growth of microorganisms or activity of enzymes

Question 39

Types of Spoilage:

Answer 39

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.

Question 40

CONDITIONS FOR SPOILAGE

Answer 40

• Water
• pH
• Physical structure
• Oxygen
• Temperature

Question 41

Microorganisms causing most food contamination:

Answer 41

Bacteria, Parasitic worms, Fungi, and Viruses

Question 42

Microbial food spoilage occurs as a consequence of:

Answer 42

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.

Question 43

Ergotism

Answer 43

Toxic condition caused by growth of a fungus in grains

Question 44

Aflatoxins

Answer 44

Carcinogens produced in fungus-infected grains and nut products (ex: sesame in tahini)

Question 45

Fumonisins

Answer 45

Carcinogens produced in fungus-infected corn

Question 46

FOOD PRESERVATION-EARLY METHODS

Answer 46

Smoking
Drying/Desiccation/Dehydration
Salting
Jams to preserve fruits
Yogurt and Cheese Making to Preserve Milk
Cooling

Question 47

FOOD PRESERVATION

1

Answer 47

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

Question 48

FOOD PRESERVATION

2

Answer 48

-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

Question 49

Microbial Product-Based Inhibition

Answer 49

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

Question 50

food preservation - aseptic packaging

Answer 50

Pre-sterilized materials are assembled into packages and aseptically filled with heat-sterilized liquid foods.

Question 51

canning

Answer 51

-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

Question 52

In commercial canning the cooking process is designed

Answer 52

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

Question 53

Spoilage may also occur if the seal of the can is faulty, permitting the entry of microbes:

Answer 53

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.

Question 54

The foodborne Illness is caused by

Answer 54

1-the infection with microorganisms, 2-ingestion of toxins produced, and 3-chemical poisoning.

Question 55

Foodborne pathogens:

Answer 55

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.

Question 56

Foodborne Infection

Answer 56

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

Question 57

Foodborne Intoxications or food poisoning

Answer 57

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

Question 58

The main factors responsible for the foodborne illness include:

Answer 58

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.

Question 59

WHO RULES FOR SAFE FOOD PREPARATION

Answer 59

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

Question 60

ENTEROBACTERIACAE

Answer 60

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

Question 61

Escherichia coli

Answer 61

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

Question 62

E. coli food sources and symptoms:

Answer 62

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

Question 63

Escherichia coli

Major groups:

Answer 63

Enterotoxigenic(ETEC)
Enteropathogenic(EPEC)
Enteroinvasive(EIEC)
Enterohemorrhagic(EHEC)
Enteroaggregative(EAEC)

Question 64

Enterotoxigenic(ETEC)

Answer 64

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

Question 65

Enterotoxigenic reservoir, transmission and prevention:

Answer 65

Reservoir: man
Transmission:
Contaminated food, less frequently water and milk
Direct contact (rare): fecal contamination→handPrevention:
Proper hygienic procedures
Disposal of human feces
Provide safe water supplies
Encourage breast feeding
Milk pasteurization

Question 66

Enteropathogenic(EPEC)

Answer 66

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

Question 67

Enteropathogenic(EPEC) transmission and prevention:

Answer 67

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

Question 68

Enteroinvasive(EIEC)

Answer 68

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

Question 69

Enterohemorrhagic(EHEC) (O157: H7)

Answer 69

Watery diarrhea with blood, hemorrhagic colitis

Question 70

Enteroaggreagative(EAEC)(not well understood but believed to act similarly as ETEC)

Answer 70

Transmission: fecal-oral

Symptoms: watery, non-inflammatory diarrhea, blood and pus unusual, fever is occasional

Question 71

Salmonella spp.

Answer 71

Most species are gram (-ve), rod shaped and motile

Non spore-formers, can grow aerobically and anaerobically

Question 72

Disease Salmonellosis

Answer 72

acute enterocolitis, with sudden onset of headache, abdominal pain, diarrhea, nausea, fever, chills, and sometimes vomiting, Dehydration, prostration

Question 73

Three different syndromes in humans by different types of Salmonella

Answer 73

S. typhi: Typhoid fever, S. paratyphiA, B&C: enteric fever, S. enteriditis: Gastroenteritis

Question 74

salmonellosis: Incubation Time

Answer 74

5 to 72 hours; usually 12 to 48 hours

Question 75

Salmonella spp. (Cont’d)

Answer 75

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

Question 76

Control of Salmonellosis:

Answer 76

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

Question 77

Shigella

Answer 77

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

Question 78

shigella onset, mode of transmission, treatment, prevention:

Answer 78

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

Question 79

Campylobacter jejuni

Answer 79

 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)

Question 80

Yersinia enterocolitica

Answer 80

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

Question 81

Yersinia enterocolitica

Answer 81

 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

Question 82

Yersinia enterocolitia(con’d)
Mode of transmission and prevention;

Answer 82

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

Question 83

VIBRIOS

Answer 83

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.

Question 84

Vibrio cholera

Answer 84

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

Question 85

Vibrio parahemolyticus:

Answer 85

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

Question 86

Listeria monocytogenes

Answer 86

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

Question 87

Listeria monocytogenes(cont’d) 2

Answer 87

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

Question 88

Brucellaspp.

Answer 88

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

Question 89

Staphylococcal Food Poisoning

Identification:

Answer 89

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

Question 90

Staphylococcal Food Poisoning Infectious agent:

Answer 90

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

Question 91

Staphylococcal Food Poisoning Occurrence,Reservoir

Answer 91

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

Question 92

Staphylococcal Food Poisoning Mode of transmission

Answer 92

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

Question 93

Staphylococcal Food Poisoning prevention

Answer 93

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

Question 94

Other illnesses:

Answer 94

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

Question 95

Clostridium botulinum

Answer 95

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

Question 96

Clostridium botulinum(cont’d)
Reservoir:
Transmission Symptoms:

Answer 96

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.

Question 97

Clostridium botulinum(cont’d)
Prevention:
treatment:

Answer 97

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

Question 98

Clostridium perfringens

Answer 98

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

Question 99

Bacillus cereus

Answer 99

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

Question 100

FOODBORNE VIRUSESHEPATITIS A VIRUS

Answer 100

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

Question 101

HEPATITIS A VIRUS (CONT’D)

Mode of Transmission Signs & SymptomsIncubation period

Answer 101

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

Question 102

HEPATITIS A VIRUS (CONT’D)

Prevention

Answer 102

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

Question 103

Microorganisms play a major role in the production of food and beverages:

Answer 103

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

Question 104

I-Dairy Products

Answer 104

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

Question 105

cheese

Answer 105

1. The milk protein casein curdles because of the action by lactic acid bacteria or the enzyme rennin or chymosin.
2. Cheese is the curd separated from the liquid portion of milk, called whey.
3. The growth of microorganisms in cheeses is called ripening.
4. Hard cheeses are produced by lactic acid bacteria growing in the interior of the curd.
5. A Propionibactertiumspp. Produces CO2 which forms the holes in Swiss cheese
6. Semisoft cheeses are ripened by bacteria growing on the surface
7. Soft cheeses (Roquefort, Blue cheese) are ripened by Penicilliuminoculated into the cheese.

Question 106

yoghurt

Answer 106

1. Yoghurt is made from milk
2. 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.
3. Acid produced from the fermentation causes the protein in the milk (casein) to coagulate into a semisolid curd

Question 107

C- Other Dairy Products

Answer 107

1. Old-fashioned buttermilk was produced by lactic acid bacteria growing during the butter-making process.
2. Commercial buttermilk is made by letting lactic acid bacteria grow in skim milk for 12 hours.
3. Sour cream are produced by Lactobacilli, Streptococci, or yeasts growing in low-fat milk.

Question 108

II-Nondairy Fermentations

Answer 108

1. Sugars in bread dough are fermented by yeast to ethanol and C02; C02causes the bread to rise.
2. Sauerkraut, pickles, olives, and soy sauce are the products of microbial fermentations.
3. The beans of cocoa and coffee undergo a fermentation step

Question 109

bread

Answer 109

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.

Question 110

III-Alcoholic Beverages and Vinegar

Answer 110

1. Carbohydrates obtained from grains, potatoes, or molasses are fermented by yeasts to produce ethanol in the production of beer, and distilled spirits.
2. The sugars in fruits such as grapes are fermented by yeasts to produce wines.
3. In wine-making, lactic acid bacteria convert malic acid into lactic acid in malolacticfermentation in fruits with high acidity.
4. Acetobacterand Gluconobacteroxidize ethanol in wine to acetic acid (vinegar).

Question 111

Beer brewing

Answer 111

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

Question 112

Wine

Answer 112

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.

Question 113

Wine Processing:

Answer 113

Grape must -->
Fermentation -->
Post fermentation-->
Bottling –packaging
(+/-maturation in bottle)

Question 114

wine fermentation

Answer 114

-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

Question 115

Wine Fermentation:

Answer 115

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

Question 116

Distilled Spirits

Answer 116

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

Question 117

B-VINEGAR PRODUCTION

Answer 117

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