Food Quiz Questions + Characteristics of Cocci

Blood agar

Trypticase soy agar with 5% sheeps blood. The nutrient in the media is enriched by the blood, which is required by the most fastidious organisms. Blood also serves as the indicator for hemolysis.

Mannitol salts agar

Selective and differential growth media for the growth of staphylococci. The high salt concentrations of this media inhibits the growth of most bacteria, but allows staph to grow uninhibited. As mannitol is fermented, the pH drops, and the medium turns yellow.

Differential media

The medium allows one to distinguish specific characteristics of different organisms by changes such as color.

Subculture

To cultivate again, on a new medium.

Alpha hemolysis of on blood agar

Colonies turn media green - hemoglobin is altered; S. pneumonia or S. mitis.

Beta hemolysis on blood agar

Clear zones in the media appear around the colonies (halos) - pyogenic; S. pyogenes or S. aureus.

Gamma hemolysis on blood agar

Light green/no color - non-pathogenic.

Why high salt is differential for staph?

The high salt concentrations inhibit the growth of other bacteria.

S. aureus

Staphylococci; gram+; hemolytic-beta or gamma; MSA-beta or gamma

S. epidermidis

Cocci; gram+; hemolytic-beta or gamma; MSA-gamma

S. pyogenes

Streptococci; gram+; hemo-beta; MSA-beta

S. mitis

Cocci; gram+; hemo-alpha; MSA-alpha

S. pneumonia

Diplococci; gram+; hemo- alpha; MSA-alpha

T/F- the heterotrophic plate count examines a very narrow selection of bacteria in a sample in order to determine spoilage an microbial combination

True

T/F - Most bacteria found in plant based foods and many bacteria in animal based food are harmless saprophytes from the environment

True

T/F food products are the primary vector of microbial diseases of the GI system

True

T/F- a common test for coliform bacteria in milk samples is he methylene blue reductase test (MBRT)

True

T/F- Pasteurization is a means of processing raw milk to assure that it is relatively free of bacteria and is safe for human consumption

True

T/F- Processed meats and cheeses are less likely to cause food borne illness becasue they are carefully processed with the latest modern techniques

False

T/F- The MBRT ends when the milk sample has lost 80% of its blue color, and the time is recorded

True

T/F- the heterotrophic medium in a HPC will allow many bacteria in the sample to grow, but despite being a complete medium, does not allow many or most bacteria to grow

True

T/F solid food is often diluted one gram food to 9 grams sterile water and then homogenized, resulting in solid samples, unlike liquid samples, start testing at a 1:10 dilution

True

T/F Recent innovations like flash freezing, IQF, and new types of pasteurization have improved the microbial safety of many types of food while creating opportunities for other types of problems

True

Human diseases that might become milkborne via contaminated milk handlers include:

A- streptococcal infection

B- shigellosis

C- Salmonellosis

A & B

A, B, & C

A, B & C