BIO 2010- Module 16: Food Microbiology- How Safe is Your Food?

What role do microorganisms play in fermented foods?

They help prepare the food by producing flavors, preserving it, or altering texture.

what are some fermented food products microorganisms make?

soy sauce, cheeses, yogurt, alcoholic beverages, and even bread.

what is spoilage?

when bacteria grow in food

How does bacteria grow?

They increase in the number of bacterial cells, not the size of individual cells.

What does bacterial indicator mean?

It's a microorganism whose presence signals contamination or a potential health risk, even if the organism itself is not harmful.

What are coliforms?

Bacterial indicator of sanitary quality of food and water. Lactose-fermenting, gram-negative bacilli.

What are fecal coliforms/indicators?

Fecal coliforms are bacteria from the intestines of warm-blooded animals; their presence in food or water indicates fecal contamination.

What does it mean if we find fecal coliforms in our food?

The presence of fecal coliforms on our food or in our water is an indicator of fecal contamination and potential disease that may range from mild gastroenteritis to blood-borne infections and death.

What type of microbes can cause foodborne diseases?

Bacteria, virus, protozoan and parasites

When may contamination from fecal coliforms most likely happen? (may not need to know this)

-may occur during production (for example: from fertilizer added to grow vegetables)

-during transportation, during slaughter of livestock animals

-during processing and packaging, or during handling

-preparation for consumption at home or in restaurants.

What are the two categories of foodborne diseases?

food infections and food intoxications

What is food infection?

Illness caused by live pathogens that multiply in the gastrointestinal tract.

What is food intoxication?

Illness caused by preformed toxins produced by microbes in food.

Symptoms appear quickly after consuming the toxin.

What are preformed toxins?

toxins produced by bacteria in food before consumption

What is the difference between food infection and food intoxication?

Food infection is caused by live pathogens multiplying in the GI tract (slower onset, fever common, killed by cooking), whereas food intoxication is caused by preformed toxins in food (rapid onset, fever rare, some toxins heat-stable).

How long does it typically take for symptoms to appear in a food infection?

48-72 hours (delayed onset)

How long does it typically take for symptoms to appear in a food intoxication?

4-6 hours (sudden onset)

Is fever more common in food infection or food intoxication?

More common in food infection; rare in food intoxication

Can cooking kill the pathogen in a food infection?

Yes

Are all toxins destroyed by heat in food intoxication?

No, some toxins are heat-stable

What are the common symptoms shared by both food infections and intoxications?

Gastroenteritis: diarrhea (may be bloody), nausea, vomiting, abdominal cramps

What are 3 bacteria commonly associated with food infections?

Campylobacter - found in raw milk; #1 cause of foodborne infection.

Escherichia coli (E. coli) - found in raw meat, dairy, and vegetables.

Salmonella - commonly found in poultry and eggs.

What are 3 bacteria commonly associated with food intoxications?

Staphylococcus aureus - normal skin/nasal flora

Clostridium perfringens - cooked meats

Clostridium botulinum - canned foods or honey; toxin affects the nervous system.

What are the most common causes of foodborne diseases?

-Campylobacter - #1 food infection

-Staphylococcus aureus - #1 food intoxication

-Noroviruses - #1 foodborne disease

-Salmonellosis - #1 hospitalizations, deaths -food infections

-Listeria - multiplies at 4oC- frequent food recalls

What are common sources of contamination?

-Feces may get onto meats and poultry during slaughtering

-Raw eggs can be contaminated with Salmonella from infected chickens

-Fruits and vegetable can be contaminated with contaminated water

What is the first step in preventing foodborne illness before handling food?

Wash hands properly.

How can you prevent cross-contamination between fruits/vegetables and meat?

Wash fruits and vegetables thoroughly and keep them separate from raw meat.

What should you do with leftovers to prevent foodborne illness?

Refrigerate leftovers promptly and reheat them properly before eating.

What selective/differential agar is used for the detection of fecal coliforms?

Deoxycholate Agar (Selective & Differential for coliforms).

What is serial dilution?

A step-by-step process of diluting a sample multiple times in a sequence to reduce the concentration of bacteria so they can be accurately counted.

What is a dilution?

The process of reducing the concentration of a sample

What is Aliquot?

The stock solution to be diluted

What is diluent?

liquid to dilute the stock solution

What is the formula serial dilution?

Total dilution = (Dilution of tube 1) × (Dilution of tube 2)

Example: If Tube 1 = 1/10 and Tube 2 = 1/10

Total dilution = 1/10 × 1/10 = 1/100

What is the formula for dilution?

Dilution = Volume of aliquot ÷ (Volume of aliquot + Volume of diluent)

What is a dilution factor?

Dilution factor = 1 ÷ dilution (Example: A 1/10 dilution has a dilution factor of 10.)

What is the formula for calculating the concentration of the original stock?

Original concentration = (CFU/mL) × dilution factor

Example: If you obtain 50 colonies on plate from a 0.2 ml sample after 1:100 dilution:

50 cfu/0.2 ml x 100 = 2. 5 x104cfu/ml total or for the solid food: the unit will be cfu/g