CFS CFS Food Microbiology 2

Question 1

At what minimum water activity (a_w) can most bacteria grow and pose a food safety risk?

Accepted Answer

0.91

Answer

Most bacteria require a minimum water activity of approximately 0.91 to grow, which is why intermediate-moisture foods formulated below this threshold can suppress bacterial proliferation.

Question 2

Escherichia coli O157:H7 is classified as an enterohemorrhagic pathogen (EHEC). What toxin does it produce that causes severe illness?

Accepted Answer

Shiga toxin (Stx1 and Stx2)

Answer

E. coli O157:H7 produces Shiga toxins (Stx1 and Stx2) that damage intestinal cells and can cause hemolytic uremic syndrome (HUS), a potentially fatal kidney complication.

Question 3

HTST (High-Temperature Short-Time) pasteurization of fluid milk in the US is conducted at approximately which conditions?

Accepted Answer

72°C (161°F) for 15 seconds

Answer

US HTST pasteurization heats milk to a minimum of 72°C (161°F) for at least 15 seconds, providing a 5-log reduction of Coxiella burnetii, the most heat-resistant non-spore-forming pathogen of concern.

Question 4

Salmonella is most commonly associated with which type of food vehicle in the United States?

Accepted Answer

Poultry, eggs, and egg products

Answer

Poultry and eggs are the most common vehicles for Salmonella in the US, with the CDC attributing the majority of salmonellosis outbreaks to these animal-derived foods.

Question 5

Staphylococcus aureus food poisoning differs from most other bacterial foodborne illnesses because:

Accepted Answer

Illness is caused by a pre-formed heat-stable enterotoxin, not live bacteria

Answer

S. aureus illness is intoxication, not infection — the bacteria produce heat-stable enterotoxins in food that remain active even after the bacteria are killed by cooking, with symptoms appearing within 1–6 hours.

CFS - Certified Food Scientist Practice Test

CFS - Certified Food Scientist Practice Test

CFS CFS Food Microbiology 2