FSC-342 Quiz #2: Lecture 6 - Spores and Their Significance

What is hurdle technology in food safety?

A method that combines multiple mild environmental hurdles (like pH and water activity) to inhibit microbial growth, instead of pushing one factor to an extreme.

How does hurdle technology prevent microbial growth?

By "deoptimizing" several growth factors (e.g., pH, water activity), forcing bacteria to spend energy on survival rather than growth, which can lead to death.

What is the water activity (aW) threshold that prevents growth of pathogens?

aW < 0.85.

What pH level prevents growth of pathogens?

pH ≤ 4.6.

How can milder hurdles work together to inhibit pathogens?

Example: pH 5.2 with aW 0.92 can still inhibit growth when combined.

Why do federal canning rules integrate pH and aW?

Because low-acid foods (pH > 4.6 and aW > 0.85) require retort (pressure) processing to ensure safety.

How do bacterial cells respond to multiple hurdles?

They must pump protons to maintain internal pH, accumulate solutes for low aW, and maintain membrane fluidity with temperature changes—energy diversion limits growth.

What is the life cycle of a spore?

Sporulation → dormancy → activation → germination → outgrowth.

What is spore activation?

A priming step, e.g., heating spores at 80°C for 10 minutes.

What happens during spore germination?

Heat resistance is lost, and metabolism resumes during outgrowth.

Why are spores important in food safety?

They survive heat, drying, and chemicals; can cause illness/spoilage in low-acid foods; and psychrotrophic spore-formers spoil refrigerated foods.

What is required to control spores in food safety?

Targeting both spore inactivation and preventing germination/outgrowth.

Which sporeformers are most relevant to public health?

Clostridium botulinum, Clostridium perfringens, and Bacillus cereus.

Why is Clostridium botulinum a major hazard?

It is the principal microbial hazard in canned and minimally processed refrigerated foods; sets thermal processing targets.

What are the differences between C. botulinum types I and II?

Type I: proteolytic, produces heat-resistant spores. Type II: non-proteolytic, also produces heat-resistant spores.

Why are psychrotrophic clostridia a concern?

They can grow in chilled, vacuum-packed products.

How do C. perfringens spores vary in heat resistance?

Two classes: heat-resistant (D90°C = 15–145 min) and heat-sensitive (D90°C = 3–5 min).

How can C. perfringens spores survive cooking?

Both classes can survive heat and may be stimulated to germinate by heat shock during cooking.

What illness does C. perfringens cause?

Diarrheal foodborne illness.

Which two Bacillus species are pathogenic?

Bacillus anthracis and Bacillus cereus.

What toxins does Bacillus cereus produce?

Heat-labile enterotoxin (diarrhea) and heat-stable toxin (vomiting).

What concentration of B. cereus is typically needed to cause illness?

10^6 cells per gram of food.

At what temperatures can B. cereus spores germinate?

8°C–30°C.

Where are B. cereus spores usually located in the cell?

Central to subterminal region of the vegetative cell.

What is the heat resistance of B. cereus spores linked to food poisoning?

D95°C = 24 minutes.

Why is heat treatment of low-acid foods (pH > 4.6) critical?

They require processing to inactivate C. botulinum spores, though other spores may survive.

Why are spores not inactivated in acid foods (pH ≤ 4.6)?

Most spore-formers cannot grow under acidic conditions, so inactivation is unnecessary.

Which sporeformers cause spoilage in acid and low-acid canned foods?

Thermophilic organisms, thermophilic anaerobes, Bacillus mesophiles, heat-resistant molds, and yeasts.

What are the seven layers of a bacterial spore?

Exosporium → coats → outer membrane → cortex → germ cell wall → inner membrane → core.

Why is the spore core important?

It has low water content, high Ca-DPA, and SASP-bound DNA, making spores highly resistant.

What factors give spores resistance?

Low water content, Ca-DPA and SASP protection of DNA/proteins, low core pH, tight membranes, protective coats, and dehydrated cortex.

What makes spores dormant and extremely resistant?

No metabolism, dehydration, SASP protection, and long-term survival under stress.

What triggers spore germination?

Nutrient triggers (amino acids, sugars) and non-nutrient triggers (salts, dipicolinic acid).

What happens when spores germinate?

They lose extreme resistance and resume metabolic activity.

What is a D-value?

Time at a set temperature required for 1-log (90%) reduction in microbes.

What is a Z-value?

Temperature increase (°C) required to reduce the D-value by 10×.

What are the D- and Z-values of heat-resistant C. perfringens spores?

D90°C = 15–145 min; Z = 9–16°C.

What are the D- and Z-values of heat-sensitive C. perfringens spores?

D90°C = 3–5 min; Z = 6–8°C.

What is the target pathogen for low-acid canned foods?

Proteolytic Clostridium botulinum.

How is C. botulinum inactivated in food industry processing?

At 121°C for ≥2.4 minutes.

Why is rapid chilling after cooking essential for C. perfringens?

Because spores can germinate and double every 6–9 minutes at 43–45°C.

What spoilage organism affects acid juices after pasteurization?

Alicyclobacillus (causes off-flavors).

What is required for B. cereus illness?

High cell counts (>10^6 CFU/g) producing diarrheal and emetic toxins.

At what temperatures do B. cereus spores germinate?

8–30°C.

Do pasteurized foods like crabmeat (heated 85°C for 10 min) still require refrigeration for C. botulinum control?

Yes — refrigeration is still critical for controlling Group II C. botulinum.