(EXAM 3) VBS 2032: Food safety and antibiotic resistance Lab 1

For foods to be of good quality...

they must be shown to be free of pathogenic microorganisms, or within specified safe low levels.

coliform bacteria - what are they?

- inhabit the intestinal tract of many animals including humans and the environment (water, soil, plants)

- Gram-negative, rod-shaped bacterium that can ferment lactose with the production of acid and gas when incubated at 35-37C

- Species of Escherichia, Klebsiella and Enterobacter are common coliform bacteria

how are coliform bacteria used in food safety?

- used as "indicator" organisms to determine the quality of foods.

- presence of coliforms suggests that food is contaminated with fecal matter and may contain pathogens that are transmitted through the fecal-oral route

fecal coliform

- naturally found in digestive tract

- gram neg rods that ferment lactose

-marker for fecal contamination

- Food safety labs regularly test for levels of total and fecal coliforms.

- ex: E. Coli

non-coliforms

non-lactose fermenters

- salmonella, shigella

what media encourages the growth of coliforms?

MacConkey media

• Selects for gram-negative enterics

• Differentiates based on lactose fermentation (pink colonies)

how is food safety measured in labs?

- stomacher

- enrichment technique

stomacher process + disadvantages

- stomacher = machine that homogenizes or disperses food particles present in a sterile plastic bag.

- Samples of the food suspension (homogenate) are then plated on various types of selective and differential media. (direct plating technique)

disadvantages:

- bacteria present in small numbers may be missed.

- some bacteria like Salmonella sp. are present in a physiological state called "viable but not culturable" (VBNC) that does not allow for growth directly on standard solid media.

enrichment culture

• Medium that favors the growth of a particular microorganism while

inhibiting the growth of others

• Used to increase the small number of desired microbe to a level that can be detected

• MAC broth selects for Gram-negative enterics

• High temp (44oC) helps select for E. coli

enrichment technique

- a small amount of homogenate is first cultured in a semi-selective liquid media that permits growth of the desired organism.

- After 24-48 hours of growth, small samples are plated.

- The number of observed colonies CANNOT be used to directly to calculate CFU/ml, however, statistical methods are used to make estimations of bacterial numbers originally present in the food.

what is a potential source of antibiotic-resistant bacteria? what is the FDA doing about it?

use of medically-important antibiotics in animal agriculture

- subtherapeutic levels of abx have routinely been used to promote growth and prevent disease in animal production

- FDA is moving to eliminate their use for these purposes + working to bring remaining therapeutic uses of antibiotics under the supervision of licensed veterinarians

dilution =

culture / total vol (diluent+culture)

safety tips for handling + preparing common foods

meat + poultry: avoid raw/undercooked, cook to internal temp 165ºF

seafood: avoid raw/undercooked, cook it to 145º, refrigerate, canned might be a safer choice

dairy: avoid unpasteurized

eggs: avoid raw/undercooked, use pasteurized eggs w recipes where eggs are raw/undercooked

sprouts: avoid raw/undercooked

vegetables: wash them, cook them

cheese: avoid cheeses made from unpasteurized milk, use pasteurized, safer = processed cheeses, cream cheese, hard cheese

common foodborne microbes

• Norovirus

• Salmonella

• Clostridium perfringens and botulinum

• Campylobacter

• Staphylococcus aureus

• Listeria

• E. coli

• Vibrio

chicken + food poisoning

- Americans eat more chicken than any other meat.

- Chicken can be a nutritious choice, but raw chicken is often contaminated with Campylobacter ands ometimes with Salmonella and Clostridium perfringens.

how to prevent getting food poisoning from chicken

- use food thermometer to make sure internal temp >165º F

- keep raw chicken + its juices away from ready to eat foods like salads or food that's already cooked

- don't wash raw chicken: juices can spread around kitchen + contaminate foods, utensils, ccountertops

What type of selective and differential liquid media was used in the enrichment technique with the chicken drumsticks? What does this media select for?

MacConkey broth

- selects: gram neg enterics

- differentiates: lactose fermentation

- used to increase the small number of desired microbe to a level that can be detected

What appearance do you predict each bag will have after incubation?

if gram negative enterics are present that can ferment lactose (ex: E. Coli), the broth will turn pink

What temperature was used for incubation? Why?

44º (a slightly higher temp than other coliforms) bc this temp selects for E. Coli