General and Food Microbiology Study Materials Flashcards

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Gram stain

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A differential staining technique that classifies bacteria into **Gram-positive** or **Gram-negative** based on cell wall structure. It helps guide identification and antibiotic choices.

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Autoclaving

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A sterilization method using **pressurized steam** (typically 121°C at 15 psi) to kill all forms of microbial life, including spores. It is widely used for media, instruments, and some heat-stable materials.

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Water activity ($a_w$)

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A measure of free water available for microbial growth, ranging from 0 to 1. Lowering $a_w$ (e.g., drying, adding solutes) inhibits many microbes and is a key food preservation strategy.

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Generation time

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The time required for a microbial population to double during exponential growth. It varies widely by species and conditions and is used in growth rate calculations.

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Pasteurization

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A heat treatment that reduces microbial load and inactivates pathogens without sterilizing the product. Common regimes include **HTST** and **LTLT** for milk and liquid foods.

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Selective media

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Culture media formulated to favor the growth of certain organisms while inhibiting others using specific nutrients or inhibitory compounds. Useful for isolating pathogens from mixed samples.

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Fermentation

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A metabolic process in which organisms convert carbohydrates to acids, gases, or alcohol under anaerobic conditions. It is exploited in food production (yogurt, bread, beer) and preservation.

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Spoilage organism

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A microbe that causes undesirable changes in food (odor, texture, discoloration) but not necessarily illness. Spoilage reduces product acceptability and shelf life.

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Exponential phase

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The growth phase where cells divide at a constant and maximal rate, resulting in logarithmic increase in population. It is the phase most representative for studying growth kinetics.

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Horizontal gene transfer

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Transfer of genetic material between organisms by mechanisms like **conjugation**, **transformation**, and **transduction**. It accelerates adaptation, such as spread of antibiotic resistance.

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Psychrophile

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An organism adapted to cold environments, with optimal growth below ~15°C. These organisms are relevant to refrigerated food spoilage.

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Colony forming unit (CFU)

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A unit used to estimate the number of viable bacteria or fungal cells in a sample, based on the number of colonies formed on agar. CFU counts are standard in food and environmental testing.

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Antiseptic

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A chemical agent applied to living tissues to reduce the possibility of infection, sepsis, or putrefaction. Antiseptics differ from disinfectants, which are used on inanimate surfaces.

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Selective pressure

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An environmental factor (e.g., antibiotic exposure) that favors survival of organisms with advantageous traits. Selective pressure drives evolution and resistance development.

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Lactic acid bacteria

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A group of Gram-positive bacteria (e.g., Lactobacillus) that ferment sugars to lactic acid and are widely used in food fermentations. They also contribute to preservation by lowering pH.

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Sterility assurance level (SAL)

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A quantitative measure of the probability of a single viable microorganism surviving a sterilization process. SAL informs risk-based decisions for sterile medical devices and critical processes.

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Enrichment culture

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A technique that promotes growth of a target organism by providing selective nutrients or conditions, increasing the chance of detection from mixed samples. Commonly used in pathogen detection from food.