Overview
This lecture discusses how temperature affects the growth of microorganisms, focusing on the five main temperature-based categories and their significance to human health and food spoilage.
Temperature Categories of Microorganisms
- Microorganisms are grouped by preferred temperature: psychrophiles, psychrotrophs, mesophiles, thermophiles, and hyperthermophiles.
- Psychrophiles thrive in cold environments, often found in freezer temperatures.
- Psychrotrophs grow well in refrigerator temperatures and are major contributors to food spoilage.
- Mesophiles prefer moderate temperatures (optimal at 37°C/98.6°F), matching human body temperature.
- Thermophiles grow in hot environments, above 45°C, such as compost piles and sunlit soils.
- Hyperthermophiles live in extremely hot environments, like hot springs or deep-sea vents, with growth possible up to 121°C.
Growth Curves & Enzyme Activity
- Each microbial group has a growth range (about 30°C), with minimal, optimal, and maximal growth temperatures.
- Growth increases gradually to the optimal temperature, then drops rapidly after maximum due to enzyme inactivation or denaturation.
- High temperatures destroy protein-based enzymes, limiting microbial survival.
Health Relevance & Food Safety
- Mesophiles include most human pathogens, causing disease and room-temperature food spoilage.
- Psychrotrophs are the main culprits of refrigerated food spoilage, but not major human pathogens.
- Thermophiles and hyperthermophiles are not health concerns as they do not grow at body or room temperature but can cause food spoilage without illness.
- Many lab incubators are set to 37°C to culture important mesophilic pathogens like E. coli, Staph, and Strep.
Key Terms & Definitions
- Psychrophile — Microorganisms that grow best at very cold temperatures, even in freezers.
- Psychrotroph — Microorganisms that grow at refrigerator temperatures and cause food spoilage.
- Mesophile — Microorganisms with optimal growth at moderate temperatures (around 37°C), includes most human pathogens.
- Thermophile — Microorganisms that thrive at high temperatures above 45°C; not associated with human disease.
- Hyperthermophile — Microorganisms growing at extremely high temperatures, up to 121°C, found in volcanic or deep-sea environments.
- Optimal growth temperature — Temperature at which a microorganism grows best.
- Enzyme denaturation — Loss of enzyme function due to high temperatures causing protein structure breakdown.
Action Items / Next Steps
- Review the categories and characteristics of temperature-based microbial groups.
- Memorize which groups are linked to human disease versus food spoilage.
- Understand the importance of optimal growth temperature for lab culture conditions.