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FOOD BACTERIOLOGY

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Natalie Bums

on 18 September 2014

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Transcript of FOOD BACTERIOLOGY

smaller than bacteria
not true living organisms
composed of genetic material enclosed in a protein coat
invades a host in order to replicate

FOOD BACTERIOLOGY
CONTROL & PREVENTION
MODIFIED APC METHOD
What is Food Bacteriology?
- is the study of the microorganisms that inhabit, create, or contaminate food
BACTERIAL GROWTH
4 PHASES:
-Lag Phase
-Log Phase
-Stationary Phase
-Death Phase
FOOD MICROBIOLOGY
- concerned with the desirable and undesirable effects microbes can have on the quality and safety of food products
- presence of bacteria, viruses, and fungi in food and food products.
PROCEDURES:
DISCUSSION OF RESULTS:
OBJECTIVES:
-describe basic mechanisms and indications of microbial food spoilage;
-describe how certain microbes are used in food preservation;
-list important pathogens of concern in meat and poultry products;
-describe sources of microbes in meat and poultry products;

-explain fundamental methods of controlling microbial contamination of meat and poultry;
-discuss how these organisms are brought to food supplies;
-discuss how they cause gastrointestinal infection in man


-help identify the microbes present in food
-help in controlling microbes in food
-help in food preservation & food safety

What is its importance?
TYPES OF MICROBES
BACTERIA

small, single-celled organisms that occur in almost any natural environment
can multiply to form groups or colonies on a food source

FUNGI


MOLDS
- branching filamentous structure
colonies: colorful, furry or downy coating on food/surfaces

YEAST
- egg-shaped, smaller than molds
reproduce by process of budding
colonies: creamy white



VIRUSES

smaller than bacteria
not true living organisms
composed of genetic material enclosed in a protein coat
invades a host in order to replicate

PARASITES

derive nourishment from hosts
cause foodborne & water illness

FACTORS THAT AFFECT BACTERIAL GROWTH IN FOOD
-ACIDITY
-TEMPERATURE
-TIME
-OXYGEN
-MOISTURE

Spoilage
is caused by physical & chemical changes in food products that result in undesirable odors, flavors, textures, or colors.

3 primary mechanisms:
autolytic enzymatic spoilage
lipid oxidation
microbial spoilage

MICROBES AND FOOD SPOILAGE
FOOD SAFETY
Pathogens:

Salmonella, Campylobacter, Listeria monocytogenes, Clostridium botulinum, Bacillus cereus, Staphlococcus aureus, E. coli (O157:H7).

SOURCES OF MICROBES IN FOOD
Animals
People
Equipment
Water supplies
Food ingredients
Air currents

RESTRICTION OF GROWTH
Sanitation
Temperature
Acidity
Salting and Drying
Vacuum packaging

A.)Surface Sampling
(Swabbing, Contact Plates, Excision method )

ADVANTAGE:
1. provides valuable insight into the relative cleanliness of that area.
DISADVANTAGE:
2. Recovery of all microorganisms from a surface may not always be possible.


Several methods available to determine total cell numbers in the food.
Many of these methods allow for the enumeration of important groups of bacteria, such as coliforms.
Few can allow you to count the number of microbes from a specific genus like Salmonella. 

DISADVANTAGES:
Some methods are expensive.
Some methods require longer preparation.
Some methods are complicated.

B. METHODS TO DETERMINE TOTAL MICROBIAL NUMBERS (SPC, Spiral Plate Counter, Dry Petrifilms, Most Probable Numbers, Membrane filters, Dye Reduction, Impedance)

ADVANTAGES:
C. MOLECULAR METHODS TO DETECT BACTERIA METABOLITES
(Oligonucleotide DNA Probes, Polymerase Chain Reaction,  Immunoprecipitation, ELISA)

ADVANTAGES:
Predict product shelf life and prevent spoilage.
Detect  specific genera or species of foodborne pathogens or other metabolites.
DISADVANTAGES:
Reagents are expensive.
Use is generally more on diagnostic than preventive due to its cost.

D. HOMOGENATION
(Blender, Colwell Stomacher)


ADVANTAGE:
simpler compared to other methods
DISADVANTAGE:
poor method for solid muscle parts

MATERIALS
• Alcohol lamp
• Blender or sterile bags
• Erlenmeyer flask or beaker (500ml or higher)
• Mannitol Salt Agar
• MacConkey Agar
• Nutrient Agar or Blood Agar Plate
• Sterile forceps
• 4 pieces of 9.9ml of sterile water in test tubes
• Sterile serological pipettes

Baird Parker Agar (7112)

– is used for the detection and enumeration Staphyloccocus aureus in foods.

Plate Count Agar (Standard Methods Agar) M091
- is recommended for the determination of plate counts of microorganisms in food, water, waste water, and also from clinical samples.

Violet Red Bile Agar (7165) -
is used for the enumeration of coliforms in food and dairy product conforms to American Public Health Association (APHA).

OPTIONAL MEDIUMS:
COLONY COUNT:

1) If <1, get average and dilution
ex. <1 x 100^2 CFU/ ml food

2) If >250, get average count and dilution, use actual count
ex. 290 CFU x 10^2 CFU/ml food

3) If within 25 – 250, use formula

CFU/ml FOOD = TOTAL COLONIES COUNTED x DF x VCF (if using 0.1 ml)
A.) MSA (Mannitol Salt Agar)
Possible bacteria:
- Staphylococcus aureus:
- golden yellow colonies
- medium sized


Work up:
- Gram Positive cocci in clusters
- Catalase (+)
- Coagulase (+)
- O/F test (Oxidase – (+) Fermentative – (+)

B.) NA (Nutrient Agar) or
BAP (Blood Agar Plate)
Possible bacteria:
-
Bacillus cereus
:
- Beta – hemolytic
- large sized
- frosted glass appearance


Work – up:
- Gram Positive rods
- check for spore formation
(FREEZE - THAWING METHOD)
*Lactobacillus - non sporeformer
*Bacillus spp. – sporeformer

C.) MacConkey agar
Possible bacteria:

Non- enteric:
- Non – fermenter (Pseudomonas spp.)
- colorless (K/K)
- oxidase (+) = non –eneteric
- oxidase (-) = Salmonella/Shigella
- BAP – green colonies

- Enterics:
- Lactose fermenter (
Escherichia coli
)
- Non- lactose fermenter (
Shigella/Salmonella
)
Work up:
- Gram Negative rods
- dark pink slightly elevated colonies
- TSI (A/A or A/AG) –
E. coli
-TSI (K/A with H2s in stab line) –
Salmonella
-TSI (K/A) -
Shigella
- do Battery Test (IMViC)

REPORTING OF RESULTS:
Example:

E. coli (380 x 105 CFU/ml) isolated after 48 hours.

**If in case of multiple colonies, report one by one.**

- Incorrect sample preparation and dilution
- Inaccurate pipetting
- Delays during inoculation
- Agar is mishanded
- Poor mixing technique in petri dishes
- Incorrect incubation conditions
- Bacterial colonies vs. Food Particles

FACTORS AFFECTING RESULTS:
A. Reducing opportunities for bacteria to enter processing environments (e.g. kitchen) and come into contact with products


B. Making the environment for bacteria as inhospitable as possible to reduce their numbers and minimize their growth.
- Serve hot foods immediately or keep them heated above 60 degrees Celsius.
- Heat canned foods thoroughly before tasting.
- Wash hands, food preparation surfaces and utensils thoroughly before and after handling raw foods to prevent recontamination of cooked foods.

SUMMARY
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