Microbial Groups, Structures, and Pathogenic Strategies in Microbiology

Four main microbial groups

Prokaryotes in extreme environments that do not cause human disease; prokaryotes in diverse environments with some pathogens; eukaryotic organisms like fungi and protists; and noncellular infectious particles requiring a host.

Traits shared by bacteria

A protective multilayer envelope, a compact genome, and tightly synchronized internal processes enabling rapid growth.

Common bacterial shapes

Spherical forms, rod-shaped forms, and spiral forms.

Gram-positive envelope structure

A very thick multilayered peptidoglycan wall containing teichoic acids and often an external protein layer.

Gram-negative envelope structure

A thin peptidoglycan layer between two membranes, with an outer layer containing lipopolysaccharides.

Phototrophy

Use of light energy to build organic molecules from carbon dioxide and minerals.

Chemotrophy

Deriving energy from breaking chemical bonds in molecules.

Organotrophy

Using organic molecules such as sugars, lipids, or proteins as an energy source.

Lithotrophy

Using inorganic molecules as an electron source for energy and carbon fixation.

Lag phase characteristics

Adjustment period with no cell division while new components are synthesized.

Log phase characteristics

Period of maximum cell division and exponential population increase.

Stationary phase characteristics

Growth plateau when nutrients decline and waste builds up.

Death phase characteristics

Declining population as cells die from toxins and nutrient depletion.

Environmental factor limiting growth: low water activity

Insufficient moisture prevents nutrient processing and metabolic reactions.

Environmental factor: high temperature

Protein denaturation and membrane destruction can kill cells.

Environmental factor: low temperature

Reduced enzymatic activity and slowed division.

Environmental factor: high acidity

Disruption of membrane integrity and enzyme activity.

Environmental factor: high salt

Osmotic stress that dehydrates bacterial cells.

Environmental factor: high sugar

Water withdrawal from cells by osmotic pressure.

Environmental factor: lack of nutrients

Inability to sustain cellular processes and reproduction.

Horizontal gene transfer

Movement of DNA between unrelated cells in the same generation.

Vertical gene transfer

Transmission of DNA from a parent cell to daughter cells.

Contributors to bacterial diversity

Mutational changes, selective pressures, and loss of unnecessary genes.

Bacterial naming rules

Capitalized genus, lowercase species, italicized.

Definition of microbiome

Communities of microbes living on and in the body that influence digestion, immunity, and metabolism.

Digestive role of microbiome

Breakdown of complex polysaccharides and production of short-chain fatty acids.

Vitamin production by microbiome

Synthesis of essential vitamins such as B vitamins.

Microbial antagonism

Protection by preventing pathogen attachment, nutrient competition, and secretion of antimicrobial factors.

Dysbiosis

Imbalance of microbial composition that can contribute to disease.

Opportunistic infection

Disease caused when normally harmless microbes invade due to immune compromise or location changes.

Dairy fermentation outcome

Acid production that causes coagulation of milk proteins into curds.

Bread fermentation process

Yeast metabolism producing carbon dioxide to raise dough.

Difference in beer vs wine substrates

Grain-derived sugars versus fruit-derived sugars.

Pathogen entry step

Arrival through a specific portal such as respiratory, fecal-oral, or vector-borne routes.

Tissue attachment step

Binding to host cell surfaces using adhesion molecules.

Tissue damage step

Disruption of host tissues by toxins or invasive enzymes.

Immune avoidance step

Strategies that prevent detection or clearance by host defenses.

Pathogen exit step

Leaving the host through a route that allows transmission to new hosts.

Enteric pathogen definition

Microbe causing intestinal illness typically transmitted by fecal-oral routes.

Invasive enteric pathogen feature

Penetrates intestinal cells and causes inflammatory bloody diarrhea.

Enterotoxigenic enteric pathogen feature

Lives on intestinal surfaces and releases toxins that induce watery diarrhea.

Mucociliary escalator function

Removal of inhaled particles using mucus and rhythmic ciliary movement.

How Bordetella pertussis persists

Toxins disabling cilia and adhesins anchoring to airway tissues.

Pertussis toxin action

Interference with host signaling leading to fluid accumulation.

Tracheal cytotoxin action

Damage to ciliated epithelium that halts clearance.

How Mycobacterium tuberculosis persists

Survival and replication inside macrophages.

How Bacillus anthracis persists

Durable spores and toxins that disrupt immune signaling and cause edema.

Anthrax protective antigen role

Formation of a pore allowing other toxin components into the cell.

Edema factor role

Induction of electrolyte and water secretion into tissues.

Lethal factor role

Destruction of signaling proteins that coordinate immune responses.

Staphylococcus characteristics

Gram-positive clusters, halotolerant, and facultative anaerobic metabolism.

Coagulase test significance

Ability to clot plasma distinguishing pathogenic species.

Streptococcus characteristics

Gram-positive chains using fermentation and often inhabiting the throat.

Lancefield grouping basis

Classification by surface polysaccharides.

Group A Streptococcus importance

Highly pathogenic species causing multiple diseases.

Spiral-shaped STI pathogen

Microbe that can cross the placenta, causing congenital abnormalities.

Intracellular STI pathogen

Microbe causing eye infection preventable by newborn prophylaxis.

Vector definition

Arthropod transferring pathogens between hosts by feeding.

Six-legged vectors

Mosquitoes, lice, fleas, botflies, and bedbugs.

Eight-legged vectors

Mites and ticks.

Difference between prokaryotes and eukaryotes: nucleus

Presence of a membrane-enclosed compartment for genetic material.

Difference: organelles

Specialized membrane-bound structures enabling compartmentalization.

Difference: separation of transcription and translation

Genetic processes occur in separate locations in eukaryotes.

General fungal nutrition

Absorption of externally digested nutrients.

Fungal motility

Lack of self-directed movement.

Primary risk group for fungal disease

Individuals with compromised immune defenses.

Algal characteristics

Photosynthetic eukaryotes producing oxygen and often using paired flagella.

Protozoan characteristics

Motile, heterotrophic unicellular eukaryotic predators.

Adhesion and invasion by protozoa

Binding to host receptors and enzyme-mediated tissue penetration.

Antigenic variation by protozoa

Rapid changes to surface proteins to evade adaptive immunity.

Protozoan immune manipulation

Alteration of cytokine responses to promote parasite survival.

Protozoan-induced cell lysis

Destruction of host cells during replication cycles.

Virus classification as living or nonliving

Lack of independent metabolism and reliance on host replication.

Attachment step of viral replication

Binding to specific host cell receptors.

Penetration step

Entry via fusion or endocytosis.

Uncoating step

Release of viral genome into the host.

Genome replication step

Use of host or viral enzymes to duplicate nucleic acids.

Assembly step

Formation of new viral particles from components.

Release step

Exit via cell burst or membrane budding.

Cytopathic effect: lysis

Cell bursting due to viral overload.

Cytopathic effect: syncytia formation

Fusion of multiple cells into giant nonfunctional structures.

Cytopathic effect: apoptosis induction

Triggering programmed cell death.

Immunopathology

Host immune response causing collateral tissue damage.

Organism component of infection chain

Characteristics of the microbe including virulence.

Reservoir component

Habitat such as animals, humans, or environment.

Transmission component

Route such as air, surfaces, vectors, or person-to-person spread.

Susceptible host component

Individual with appropriate portal of entry and immune status.

Epidemic definition

Increased number of cases in a limited region.

Endemic definition

Constant baseline level of disease in an area.

Pandemic definition

Widespread disease across continents.

Prevalence definition

Total active cases in a population.

Incidence definition

Number of new cases over a time frame.

Nosocomial infection definition

Infection acquired in a hospital or health-care setting.

Factors increasing emerging diseases

Population growth, urban expansion, travel, warming climate, wildlife markets, and microbial evolution.

High-temperature control method

Use of sustained heat to destroy microbes.

High-pressure control method

Pressure increase allowing high heat without boiling.

Refrigeration control method

Cold temperatures slowing microbial metabolism.

Filtration control method

Physical removal of microbes using pore-sized barriers.

Irradiation control method

DNA-damaging radiation such as UV or gamma.

Antiseptic purpose

Reduction of microbes on living tissue.