Bacterial Growth & Physiology

Comprehensive vocabulary flashcards covering bacterial growth definitions, colony calculation, doubling times, binary fission steps, culture media types, hemolysis, the in vitro growth curve, and oxygen/pH growth requirements.

Bacterial Growth

An increase in both the size and the number of bacterial organisms.

Broth

A liquid nutrient culture medium in which bacterial growth is indicated by turbidity (cloudiness), whereas a clear solution indicates an absence of bacterial growth.

Bacterial Colony

A macroscopic cluster of approximately $1\text{ million}$ bacteria visible to the naked eye on solid media, formed from a single parent bacterium after $20\text{--}30$ generations of binary fission.

Generation Time (Doubling Time)

The time required for a bacterium to divide and produce $2$ daughter cells, ranging from very fast ($13\,\text{min}$ in Vibrio cholerae) to very slow ($24\,\text{hrs}$ in Mycobacterium tuberculosis).

Binary Fission

An asexual reproduction process in which a single parent cell divides to produce two identical daughter cells.

Septum Formation (Step 3 of Binary Fission)

The stage of binary fission in which a division septum begins to form in the cell center and the FtsZ Z-ring constricts between the segregated circular DNA copies.

Antibiotic Susceptibility Testing (AST)

A laboratory procedure (such as the Kirby-Bauer test) performed on cultured bacteria to determine whether a pathogen is resistant or susceptible to specific antibiotics like methicillin.

Simple Media

A basic culture medium that provides the minimum requirements necessary for the growth of most non-fastidious bacteria.

Peptone Water

A simple liquid medium consisting of peptone (amino acids and small proteins) and $0.5\%\,\text{NaCl}$, used to support bacterial growth and serve as a base for sugar fermentation media.

Nutrient Broth

A simple liquid culture medium composed of peptone and meat extract that enhances bacterial growth.

Nutrient Agar

A solid simple medium prepared by adding $2\%$ agar (derived from marine algae/seaweed) to nutrient broth, solidifying into a jelly-like matrix upon cooling.

Enriched Media

A nutrient medium supplemented with rich biological components such as blood or serum to support the growth of fastidious bacteria.

Fastidious Bacteria

Organisms that have complex nutritional demands and require specific nutrient proteins, blood, or serum to grow.

Blood Agar

An enriched medium made of nutrient agar cooled to $45\text{--}50\,^\circ\text{C}$ and supplemented with $5\text{--}10\%$ sheep blood, used to cultivate Streptococcus spp. and observe hemolysis patterns.

Hemolysis Patterns on Blood Agar

The breakdown of red blood cells by bacterial enzymes, categorized as complete (beta; clear zone; e.g., Staphylococcus aureus, Streptococcus pyogenes), partial (alpha; greenish zone; e.g., Streptococcus viridans, pneumococci), or absent (gamma; no zone; e.g., Enterococci).

Chocolate Agar

An enriched medium prepared by heating blood in nutrient agar to $80\,^\circ\text{C}$, which lyses RBCs to release hematin ($X$ and $V$ factors) and gives a chocolate-brown color; required for Haemophilus spp. and Neisseria spp.

Selective Media

A culture medium containing specific chemicals, dyes, or antibiotics that inhibit the growth of unwanted organisms while allowing target bacteria to grow.

Lowenstein-Jensen Medium

A selective medium containing malachite green, used specifically for the isolation and growth of Mycobacterium tuberculosis.

Blood Tellurite Agar

A selective medium containing potassium tellurite that is toxic to most Gram-negative and some Gram-positive bacteria, selectively allowing Corynebacterium diphtheriae to grow and form characteristic black colonies.

Differential Media

A medium containing indicators (such as sugars or pH dyes) that produce visible colony or medium changes to distinguish between look-alike microorganisms.

MacConkey's Agar

A selective and differential medium containing bile salts and crystal violet (inhibiting Gram-positive bacteria), lactose, and neutral red; lactose fermenters produce pink colonies, while non-lactose fermenters produce pale colonies.

Mannitol Salt Agar (MSA)

A selective and differential medium with $7.5\%\,\text{NaCl}$ (inhibits non-staphylococci), mannitol, and phenol red; Staphylococcus aureus ferments mannitol forming yellow colonies/medium, while Staphylococcus epidermidis yields pink colonies/medium.

Thiosulfate-Citrate-Bile-Sucrose Agar (TCBS)

A selective and differential medium for Vibrio species (e.g., Vibrio cholerae); selective agents (thiosulfate, citrate, bile salts) inhibit Gram-positives and Enterobacteriaceae, while sucrose fermentation turns the bromothymol blue indicator yellow.

Bacterial Growth Curve

The standard four-stage pattern of in vitro bacterial growth in a closed liquid culture, comprising the lag phase, log phase, stationary phase, and decline phase.

Lag Phase

The initial growth phase where bacterial cell count remains constant while cells enlarge and metabolically adapt to the new medium.

Log Phase (Exponential Phase)

The active division phase where bacteria multiply exponentially by binary fission; clinically referred to as the golden phase when infection symptoms emerge.

Stationary Phase

The plateau phase where the rate of bacterial cell division equals the rate of cell death due to nutrient depletion and toxic waste accumulation.

Decline Phase

The terminal phase of the growth curve where bacterial death outpaces division due to profound nutrient exhaustion and waste toxicity.

Autotrophic Bacteria

Bacteria capable of synthesizing their own organic food from inorganic substances to support life processes autonomously.

Heterotrophic Bacteria

Bacteria that cannot synthesize their own food and rely on external sources or living hosts to obtain necessary organic nutrients, salts, and vitamins.

Obligate Aerobes

Bacteria strictly dependent on oxygen for survival; they carry out aerobic respiration generating $38\,\text{ATP}$ per glucose molecule ($2\,\text{ATP}$ from glycolysis, $2\,\text{ATP}$ from the Krebs cycle, and $34\,\text{ATP}$ from oxidative phosphorylation with $O_2$ as the final electron acceptor).

Superoxide Dismutase and Catalase

Protective enzymes in aerobic bacteria that detoxify harmful metabolic byproducts by decomposing superoxide and hydrogen peroxide ($H_2O_2$) into water.

Obligate Anaerobes

Bacteria that cannot grow in the presence of $O_2$ (e.g., Bacteroides fragilis); lacking catalase and superoxide dismutase, they yield $17\,\text{ATP}$ per glucose using inorganic electron acceptors such as nitrate, sulfate, or $CO_2$.

Facultative Anaerobes

Bacteria that utilize aerobic respiration in the presence of oxygen, but adapt to oxygen absence by undergoing fermentation to produce acid and alcohol without the Krebs cycle.

Micro-aerophiles

Bacteria that require a low oxygen concentration of $2\text{--}10\%\,O_2$ and cannot tolerate ambient air ($21\%\,O_2$) due to low intracellular levels of superoxide dismutase and catalase (e.g., Campylobacter, Helicobacter).

Aero-tolerant Anaerobes

Anaerobic bacteria that do not use oxygen for energy metabolism but possess cellular mechanisms that allow them to tolerate its presence.

Capnophiles

Specialized bacteria that require carbon dioxide concentrations significantly higher than the ambient atmospheric level of $0.03\%\,CO_2$.

Neutrophiles

Bacteria that grow optimally in a neutral pH range of $7.2\text{--}7.4$, representing the standard requirement for most bacterial species.