Environmental and Physiological Influences on Oral Microbes

Vocabulary flashcards covering microbial growth measurement, cellular metabolic pathways (glycolysis, respiration, fermentation), nutrient sources, and oral environmental influences (temperature, redox potential, pH) based on Lecture 3 of DBS1 Infection and Defence.

Viable Count

A method to measure living bacterial populations based on colony-forming units (CFU), calculated as: $\text{Number of colonies on plate} \times \text{reciprocal of sample dilution} = \text{number of bacteria/ml}$.

Counting Chamber Method

A direct microscopic total cell count technique where a bacterial suspension fills a shallow volume over a slide grid of 25 large squares by capillary action to count and average cell numbers.

Turbidity

An indirect method used to estimate bacterial growth and population density by measuring the cloudiness of a liquid culture broth.

Lag Phase

The initial period in a bacterial growth curve following inoculation where cells adapt to new conditions and synthesize necessary enzymes with little to no increase in cell number.

Log (Exponential Growth) Phase

The period of a bacterial growth curve characterized by maximal, constant cell division where the population doubles at a regular rate.

Stationary Phase

The phase in a bacterial growth curve where the rate of cell division equals the rate of cell death due to nutrient depletion and toxin accumulation.

Death (Logarithmic Decline) Phase

The final stage of the bacterial growth curve where the rate of cell death significantly exceeds the formation of new cells.

Cytopathic Effect (CPE)

Observable morphological changes in host cell cultures induced by viral infection, including cell rounding, syncytia formation, and inclusion bodies.

Plaque Assay

A quantitative viral enumeration method that measures visible clear zones (plaques) where viruses have lysed host cell monolayers to determine plaque-forming units (PFU).

Hemagglutination

A diagnostic method used to detect viral growth based on the ability of certain viruses to bind to surface receptors on red blood cells and cause clumping.

Chemotaxis

The directed movement of microbial cells toward attractants such as nutrients or away from repellents in the oral environment.

Induction (Metabolic Control)

The activation of specific microbial genes required to metabolize a nutrient when that nutrient (such as sugar) becomes present in the environment.

Repression (Metabolic Control)

The downregulation or switching off of nonessential microbial metabolic genes when nutrients are limited or preferred resources are available.

Endogenous Nutrients

Primary nutrient sources supplied internally by the host, including saliva (providing amino acids, proteins, glycoproteins, vitamins, and gases) and gingival crevicular fluid (GCF, providing albumin, proteins, glycoproteins, and haem).

Exogenous Nutrients

Dietary nutrient sources introduced from outside the host, such as fermentable carbohydrates (sucrose), dairy products (casein), and leafy greens (nitrate).

Extracellular Polymers (EPS)

Polymers synthesized outside the bacterial cell from dietary sugars, including glucan and mutan produced by glucosyltransferases, as well as labile fructan produced by fructosyltransferase.

Intracellular Polymers (IPS)

Glycogen-like storage polysaccharides accumulated inside bacterial cells that can be catabolized for energy and acid production when exogenous carbohydrates are absent.

Saccharolytic Pathway

The metabolic pathway involving the breakdown of dietary starches and complex sugars into monosaccharides by salivary/bacterial amylase, maltase, and sucrase.

Asaccharolytic Pathway

The metabolic breakdown of host and dietary proteins and peptides into amino acids by bacterial proteases, yielding short-chain fatty acids, ammonia, and sulphur compounds.

Glycolysis

A 10-step enzymatic process converting one glucose molecule into two pyruvate molecules; it consists of an investment phase (consuming $2\,\text{ATP}$), a cleavage phase, and a payoff phase (yielding $4\,\text{ATP}$ and $2\,\text{NADH}$, with a net gain of $2\,\text{ATP}$).

Aerobic Respiration

A catabolic process where glucose is completely oxidized using $O_2$ as the final electron acceptor, yielding $H_2O$, $CO_2$, and up to $38\,\text{ATP}$.

Anaerobic Respiration

Respiration utilizing an inorganic terminal electron acceptor other than oxygen (e.g., $NO_3^-$, $SO_4^{2-}$, or $CO_2$), producing less ATP than aerobic respiration but more than fermentation.

Denitrification

A form of anaerobic respiration where nitrate ($NO_3^-$) serves as the terminal electron acceptor and is reduced to nitrite ($NO_2^-$).

Sulphate Reduction

An anaerobic respiratory pathway in which sulphate serves as the electron acceptor and is reduced to hydrogen sulphide ($H_2S$).

Fermentation

An anaerobic biochemical pathway that breaks down organic molecules (such as pyruvate) into acids or alcohols without an electron transport chain or the citric acid cycle.

Homofermentation

A fermentation pathway favoured during carbohydrate excess where pyruvate is converted exclusively or predominantly into lactic acid.

Heterofermentation

A fermentation pathway favoured during carbohydrate limitation where glucose metabolism yields a mixture of acetate, formate, and ethanol.

Arginine Deiminase System (ADS)

A three-gene system in certain streptococci that hydrolyzes L-arginine into L-citrulline, carbamoyl phosphate, and L-ornithine, generating ATP and ammonia ($NH_3$), which protonates to $NH_4^+$ and elevates plaque pH.

Urease

A bacterial enzyme that hydrolyzes urea into ammonia ($NH_3$) and carbon dioxide ($CO_2$), resulting in an increased local pH.

Enterosalivary Nitrate-Nitrite-Nitric Oxide Pathway

The pathway where dietary nitrate ($NO_3^-$) is concentrated in saliva and reduced by oral bacteria (via nitrate reductase) to nitrite ($NO_2^-$), which is subsequently converted systemically to nitric oxide ($NO$) to regulate vascular tone and blood pressure.

Metabolic Cross-Feeding

A cooperative interspecies interaction where the metabolic waste of one bacterium serves as a primary substrate for another, such as Veillonella metabolizing lactic acid produced by Streptococcus into weaker acetate and propionate.

Redox Potential ($E_h$)

A measure of the electrical potential indicating the affinity of a medium to gain (oxidizing) or donate (reducing) electrons, critically determining the ecological niche of oral microbes.

High Redox Potential ($+200\,\text{mV}$)

An oxidizing environment characteristic of oxygenated saliva that promotes the growth of aerobic and facultatively anaerobic bacteria.

Low Redox Potential ($-100\,\text{mV}$ to $-200\,\text{mV}$)

A reducing, oxygen-depleted environment characteristic of deep periodontal pockets ($-200\,\text{mV}$) and mature plaque ($-141\,\text{mV}$ at 7 days) that permits the survival of obligate anaerobes.

Superoxide Dismutase

A detoxifying enzyme that protects organisms from oxidative damage by catalyzing the dismutation of superoxide radicals ($O_2^{\bullet-}$) into hydrogen peroxide ($H_2O_2$) and oxygen ($O_2$).

Catalase

An antioxidant enzyme that decomposes harmful hydrogen peroxide ($2H_2O_2$) into water ($2H_2O$) and elemental oxygen ($O_2$).

Peroxidase

An enzyme that reduces hydrogen peroxide ($H_2O_2$) to water ($2H_2O$) using NADH and a proton ($H^+$) as reducing agents.

Aciduric Bacteria

Microorganisms, such as Streptococcus mutans and Lactobacillus species, that possess the physiological mechanisms to survive and actively multiply in low-pH environments ($< 5.0$).

Neutrophiles

Bacteria that exhibit optimum growth near neutral pH ($6.5\text{--}7.5$), including health-associated oral taxa such as Streptococcus sanguinis, Actinomyces naeslundii, and Neisseria species.

Alkaliphiles

Bacteria that thrive in alkaline pH conditions ($8.0\text{--}9.0$), such as the periodontopathogen Porphyromonas gingivalis, typically enriched in the presence of inflammatory gingival crevicular fluid.

Microaerophiles

Organisms that require oxygen for survival and growth but only at lower partial pressures than present in the ambient atmosphere (such as Aggregatibacter actinomycetemcomitans).

Aerotolerant Anaerobes

Microbes that do not utilize oxygen for energy production via respiration but can tolerate its presence without incurring lethal oxidative damage (e.g., Streptococcus sanguinis).