Comprehensive Bacterial Structure, Staining, and Antibiotic Resistance Guide

Coccus

sphere/round

Bacillus

rod

Coccobacillus

short rod

Vibrio

comma

Spirochete

flexible, thin, spiral-shaped rod

Spirillum

rigid, spiral-shaped rod

Pleomorphic

no defined shape

Gram negative

Thin peptidoglycan layer, LPS, Outer membrane, Trimeric Porins, Periplasm

Gram positive

Thick peptidoglycan layer, Teichoic Acid, Lipoteichoic acid, Can initiate endotoxin-like activities

Acid-fast

Mycolic acid layer (outer layer), Waxy coat, Tetrameric porins

Peptidoglycan

repeating disaccharide (NAG/NAM) crosslinked by tetrapeptides, Found in most bacterial cell walls, Rigid support, cell shape, protection from osmotic damage, Confers gram reaction, target of cell wall inhibitors and lysozyme, can induce endotoxin-like shock

Lipoproteins

Component of bacterial cell walls, Stability

Outer membrane proteins

LPS, Component of gram-negative cell walls, part of outer membrane, Lipid A = toxic moiety, induces toxic shock, O antigen = attachment, highly immunogenic

Endotoxin

Component of gram-negative cell walls, part of outer membrane

Trimeric Porins

Component of gram-negative cell walls, Transport, Channel passing through outer membrane

Teichoic acid

Anchored to peptidoglycan, Component of gram-positive cell walls, Attachment, Can induce endotoxin-like shock

Lipoteichoic acid

Anchored to cell membrane, Component of gram-positive cell walls, Attachment, Can induce endotoxin-like shock

Mycolic acid layer

Component of acid-fast cell walls, Resistance to desiccation and chemicals, Confers acid-fast reaction

Tetrameric Porins

Component of acid-fast cell walls, Transport, Channel passing through mycolic acid layer

Gram staining

Fixation → Crystal Violet (purple) → Iodine → Decolorization → Safranin (red); + = purple, - = red

Acid-fast staining

identifies mycolic acids = Primary Carbolfuchsin (red) → acid-alcohol wash → methylene blue; + = red, - = blue

Mycobacterium

Clinically-relevant genera that are acid-fast

Nocardia

Clinically-relevant genera that are acid-fast

Flagella

Filamentous appendages that move the bacteria towards nutrients and other attractants; 3 components: Filament, Hook, Basal body

Pili/fimbriae

Rigid, hair like proteinaceous structures; Composed of pilins; 2 classes of pili: Ordinary/common and Sex pilus/conjugation pilus/F pilus

Glycocalyx

Polysaccharides and glycoproteins; Function: Promote adherence of bacteria to surfaces for biofilm formation, Barrier to toxic hydrophobic molecules (antibiotics), Inhibits phagocytosis, Virulence factor?

Slime layer

Easily removed, diffuse, unorganized layer that protects from antibiotics/desiccation and allows adherence to smooth surfaces.

Capsule

Well organized, uniform, rigid layer consisting of polysaccharides, serving as a virulence factor.

Quellung Reaction

Swelling of capsule.

Genome

Includes the chromosome which is a single, circular DNA molecule with no introns and no histones.

Chromosome

A single, circular, double-stranded DNA molecule that is haploid.

Plasmid

Extra-chromosomal DNA found in some bacteria that encodes for ancillary, non-essential information, such as roles in conjugation, drug resistance, and toxin production.

Ribosomes

Consist of rRNA and protein, involved in protein synthesis; bacterial ribosomes are 70s, made up of 50s and 30s subunits.

Inclusion Bodies

Granules, vesicles, or vacuoles within the cytoplasm, most bound by a thin 'non-unit' membrane, serving as a storage depot for energy or structural building blocks.

Endospores

Resting stage allowing an organism to survive harsh environmental conditions, containing 1 chromosome, low amounts of protein/ribosome, high concentrations of calcium bound to dipicolinic acid, and a keratin spore coat.

Clostridium

A clinically relevant genus of bacteria that produces endospores.

Aminoglycosides

Antibiotics that bind to the 30s ribosomal subunit, causing misreading of the genetic code.

Tetracyclines

Antibiotics that bind reversibly to the 30s ribosomal subunit, preventing the addition of amino acids to the elongating peptide chain.

Lincosamides and Chloramphenicol

Antibiotics that bind to the 50s ribosomal subunit and inhibit peptidyl transferases.

Corynebacterium diphtheria

Detection of inclusion bodies can aid in the identification of this bacterium.

Psychrophiles

Bacteria that thrive at low temperatures.

Mesophiles

Most pathogenic bacteria that grow optimally at moderate temperatures.

Obligate Aerobe

Requires oxygen and has enzymes for reactive oxygen species (ROS).

Microaerophile

Requires oxygen at lower levels and has enzymes for ROS.

Facultative Anaerobe

Does not require oxygen but will use it if available and has enzymes for ROS.

Obligate Anaerobe

Cannot survive in the presence of oxygen and has no enzymes for ROS.

Capnophiles

Bacteria that require 5-10% carbon dioxide.

Halotolerant Bacteria

Do not require NaCl but can grow under saline conditions.

Chemoheterotrophs

Use organic compounds as source of energy/carbon.

Fastidious

Require ADDITIONAL organic compounds (vitamins) in their culture media.

Growth factors

Essential for growth (vitamins, AA, purines, pyrimidines); organism CANNOT synthesize.

Liquid Media (broth)

Used for growing large numbers of bacteria.

Solid Media (agars)

Used for isolation of PURE CULTURES and estimating the number of viable bacteria in a sample.

Agar

A solidifying agent NOT a nutrient.

Semi-solid agars

Used for determining motility, growing microaerophiles, and some transport media.

Basal Media

Sustain growth of less fastidious bacteria; examples include nutrient agar/broth and tryptic soy agar.

Enriched Media

Basal media + additional nutrients (blood/egg yolk) to cultivate fastidious organisms.

Selective Media

Reagents (dyes, NaCl) added that inhibit growth of unwanted bacteria and allow growth of others.

Differential (indicator) Media

Contain components (dyes, pH indicators) that allow differentiation of closely related taxa based on appearance.

Transport Media

Used for transport of specimens to lab, preserving microbial viability, and maintaining the original ratio of microbes.

Pure culture

Contains only 1 species of microbe.

Subculture

Growing cells from a pure culture.

Snap-Freeze

Cells in broth with cryopreservative.

Freeze-dry (lyophilize)

Cells suspended in lyophilization medium.

Binary Fission

Most COMMON mode of bacterial growth.

Budding

Unequal division of cellular material.

Fragmentation

Mode of growth in filamentous bacteria.

Conidiospores

Mode of growth in some filamentous bacteria.

Generation Time

Time required for population to double.

Growth Curve

Describes the phases of bacterial growth in a closed system.

Lag Phase

No cell division; cells preparing for growth.

Log (exponential) Phase

Exponential growth, primary metabolites produced, highly vulnerable to antibiotics and environment.

Stationary Phase

Zero population growth due to nutrient depletion and waste product toxicity; secondary metabolites produced.

Death/decline Phase

Exponential death of bacteria.

Batch Culture

Growth in a closed system; exponential growth cannot be maintained.

Continuous Culture

Growth in a chemostat; fresh medium added, effluent removed, exponential growth can be maintained.

Mutualism

Benefits both microbe and host.

Commensalism

Benefits microbe, nothing to host.

Parasitism

Benefits microbe, HARMS the host.

Normal microbiota

Stable polymicrobial communities found in skin, conjunctiva, respiratory, urogenital, and GI tracts.

Pathogenicity

Ability of a microbe to damage a host (produce disease).

Virulence

Relative capacity of a microbe to cause damage in a host.

Transmissibility

Relative ease with which an infectious agent spreads between hosts.

Infectivity

Capacity of a microbe to become established in a host.

Adhesions

Macromolecules that bind bacteria to host cells/tissues.

Attachment specificity

The ability of bacteria to bind to specific receptors on host cells.

Tissue tropism

The preference of a pathogen to infect specific tissues, exemplified by enteropathogenic E. coli K88 binding to receptors on pig enterocytes.

Host specificity

The restriction of a pathogen to infect only certain hosts, such as E. coli K88 which infects ONLY PIGS.

Capsules

Structures that impair phagocytosis, mediate adherence & biofilm formation, and prevent dessication.

Toxins

Substances that damage host cell/tissue.

Exotoxins

Proteins (enzymes) that usually cause highly specific effects and can be categorized into four major types.

Endotoxins

Components of the LPS of the outer membrane, with the Lipid A portion being a toxin released when bacteria are lysed.

Lipid A

A component of endotoxins that triggers systemic inflammatory responses such as fever and shock.

Biofilms

Communities of bacteria that enable high cell densities and facilitate quorum sensing.

Colonization

The establishment of a pathogen at the appropriate portal of entry, involving adherence to host cells and/or ECM.

Invasion

The process by which pathogens breach epithelial barriers and cause local damage to host cells.

Damage

The ways pathogens can harm the host, including using nutrients, causing direct damage, and producing toxins.

Transmission

The process by which pathogens exit the host and spread to new hosts or reservoirs.

Subclinical disease

A condition that does NOT cause any noticeable illness, exemplified by Leptospira.

Acute disease

A disease that develops rapidly but has a short duration, such as campylobacteriosis.