MIC 401 Module 2

Bacterial Size

0.5-2 micrometers

Bacterial Morphology - Small Size

necessary because most nutrients obtained via diffusion (high surface area to volume ration favors efficient diffusion)

Bacterial Morphology - Shape

often typical for a genus/species and can be diagnostically useful; influences nutrient acquisition, attachment, movement, invasion; exist as single cells or in characteristic patterns

Strep

chain of bacteria

Staph

cluster of cocci

Palisades

cluster of bacilli

Monomorphic Bacteria

have one shape

Most Common Bacterial Shapes

cocci, bacilli, spirilli

Pleomorphic Bacteria

shape can be dependent on environment; enhances survival, infectivity, and/or transmission

Cytoplasm

gelatinous aqueous solution (80% water); site of all cellular functions and structures

Nucleoid

localized region of bacterial genome; single circular DNA chromosome (typically)

Ribosomes

protein synthesis factories; made of RNA and protein (70s); translate genetic code to amino acids; densely dispersed in cytoplasm; similar but smaller than eukaryotic version

Inclusion Bodies

dense particles of aggregates; surplus storage sites (excess nutrient, glycogen, fats); sites of viral reproduction; insoluble over-expressed recombinant proteins

Cytoskleleton

filamentous protein structures; give structure/support to cell shape and functions

Plasma Membrane - Boundary

cytoplasmic or cell membrane; surrounding the cell interior (intra vs extra cellular); detects and coordinates responses to environmental changes; flexible phospholipid bilayer containing membrane proteins (biosynthesis, energy, anchors, transporters, enzymes, receptors)

Plasma Membrane - Structure and Function

fluid mosaic lipid bilayer (proteins move around and relocate where most needed); allows cells to interact with and respond to the environment (maintain water balance, obtain nutrients, exchange gases, dispose of waste); selectively permeable; passive or active transport

Passive Transport

no energy required; movement in direction of concentration gradient (high → low) in attempt to equalize solute concentration on both sides; solute and water diffusion

Osmosis

water diffusion across a membrane from low to high solute (water follows salt)

Isotonic Environment

solute concentrations equal outside and inside the cell; no net water loss or gain

Hypertonic Environment

higher solute concentration outside cell than inside cell; water drawn out of the cell; results in plasmolysis (cytoplasm volume decreases and plasma membrane shrinks away from cell wall)

Hypotonic Environment

lower solute concentration outside cell than inside cell; water drawn into the cell (cytoplasm volume increases); results in cell swelling; can result in lysis/bursting if cell wall is damaged

Solute Diffusion

simples (move freely through a membrane); facilitated (move through transport protein)

Active Transport

substances are transported against their concentration gradient; requires cellular energy (ATP); needs a specific transmembrane character protein pump; faster than passive; used when the cell needs nutrients

Bacteria - External Structures

function in protection, adhesion, and movement

Cell Wall

outside the plasma membrane; rigid structural support and protection; peptidoglycan

Peptidoglycan

protein and sugar mesh made only by bacterial cells

Gram Stain

differential staining technique; classified bacteria into categories based on differences in chemical and physical CW properties; often initial step in prelim bacterial identification (performed on bodily fluids or biopsies when severe infection is suspected)

Gram Stain Pros

does not identify the exact type of bacteria, but allows for presumptive determination of organism; provides insight into cause of illness and information regarding initiation of relevant antibiotic therapy

Gram Stain Cons

not all bacteria can be definitively classified by this technique (spirochetes, mycoplasmas, mycobacteria)

Gram Stain Technique

stain (crystal violet) → mordant (iodine) → de stain (ethyl alcohol) → counter stain (safranin)

Gram Negative Bacteria

contains thin peptidoglycan layer, periplasmic space, outer membrane, porins; stains pink in gram stain

OM - Outer Membrane

protective, selective barrier in gram - bacteria; harder to kill (by enzymes, antibiotics, disinfectants); lipopolysaccharide/lipid A endotoxin; has its own proteins (OMPs)

Porins

pore forming protein channels in gram - bacteria; allow substances (amino acids, vitamins) to pass through OM; exclude large molecules and a variety of substances that may be harmful to the cell

Gram Positive Bacteria

lack an outer membrane; thick PG layer (highly sensitive to compounds that target PG - penicillins/lysozyme); retain moisture longer; provide protection from mechanical stress; presence of TAs; stain purple in gram stain

Teichoic Acids (TAs)

glycopolymers; attached to either PG or membrane; stabilize cell wall, help maintain shape and flexibility, aid cell division

Gram Intermediate Bacteria

cannot be determined as either gram+ or gram- due to CWs; mycoplasma and mycobacteria

Mycoplasma

lack a cell wall; contain a sterol-enriched plasma membrane; pleomorphic; naturally resistant to many commonly used antibiotics

Mycobacteria

have a thick, myocolic acid rich cell wall (thick waxy lipid); grow slowly because nutrients and gases do not readily cross; dyes, chemicals, antibiotics do not penetrate well; acid fast stain (appear red/pink)

Glycocalyx

capsule and slime layer external to cell wall; sticky, carbohydrate enriched mucoid layer, helps bacteria adhere; protects from desiccation, immune response, antibiotics, disinfection

Glycocalyx Slime Layer

irregular, diffuse, loosely associated, unorganized layer of polysaccharides, glycoproteins, glycolipids

Glycocalyx Capsule Layer

organized, dense, well-defined, attached layer of polysaccharides or proteins; primary virulence factor

Polysaccharide Capsule

protective carbohydrate layer anchored to the external surface of some bacterial cells; if produced, often are the single most important determinant of virulence; protects against phagocytosis, antibiotics, desiccation, environmental stressors; used to group species into serogroups; may be immunogenic and elicit protective antibodies, used for some vaccines

Serogroups

antigenic variety of capsule produces

Filamentous Appendages

protein subunit appendages that extend outward and interact with environment; function in attachment, DNA uptake, transfer, motility; fimbria/pili and flagella

Pilli

short, hair like surface structures of repeating pilin subunits with tip adhesion; either evenly around the surface of the cell or localized to one or both of the poles; typical of gram - but with some gram +; exchange of genetic material by conjugation; movement by twitching motility; adherence is the key virulence characteristic

Flagella

helical, long, motility structures spin like a rotary propellor (produced by 50% of bacteria, majority of bacilli; penetrate viscous environments → infect and invade; taxis

Taxis

motile response towards or away from an environmental stimulus (chemicals, light, osmotic pressure, oxygen, temperature)

Extracellular Flagella Types

monotrichous, amphitrichous, lophotrichous, peritrichous

Intracellular Flagella Types

endoflagella (axial filaments); located in periplasmic space of spriochetes, allow for corkscrew like movement

Endospores

bacteria typically vegetative; some gram positive baccili make them to survive harsh condition; metabolically inactive structures that allow cells to enter a dormant state (highly resistant to environmental stressors); when conditions improve they germinate into vegetative cells

Process of Sporulation

DNA replicates → membranes form around the DNA → forespore forms additional membranes → protective cortex forms around the spore → protein coat forms around the cortex → spore is released

Endospores - Importance

produced by clinically relevant species of bacillus, clostridium and clostridioides; survive for extended periods in soil and on surfaces (including food prep and healthcare facilities)

Bacterial Virulence Mechanisms - Toxins

substances produced by or derived from microbes that have adverse host effects

Bacterial Virulence Mechanisms - Immune System Evasion

avoidance and/or inhibition of the host’s immune response

Bacterial Virulence Mechanisms - Persistence

biofilms, endospores, latency

Bacterial Virulence Mechanisms - Invasion

entry into and exit out of host cells and/or tissues

Bacterial Virulence Mechanisms - Nutrient Acquisition

obtained from the host for viability and multiplication

Bacterial Virulence Mechanisms - Adhesion

attachment to host cells; includes colonization of host

Colonization

after entering a host, the pathogen must adhere to host tissues to persist and multiply in order to establish an infection

Factors that Determine Attachment Between Pathogen and Host

adhesions that bind to certain surface receptors on certain host cells; many adhesions are assembled into pili that extend out from the bacterial surface, other adhesions are directly associated with microbial surface; specificity for adhesion attachment due to tropism

Tropism

preference of a pathogen for a specific host and/or specific cell or tissue within the host; pathogenic microbes require specific host/microbial features to interact with host and establish infection (can change and evolve over time); host factors impact whether infection and/or disease develops; if adhesions and/or receptors can be altered to interfere with attachment, infection and disease can be prevented or controlled

Bacterial Life Phases

unicellular (planktonic, free floating) and multicellular (biofilm, attached sessile cells)

Biofilms

cooperatively functioning microbial communities (single or diverse species) encased in a self secreted sticky substance (EPS) that forms a protective surrounding matrix (multiple layers); periodically free cells are released to spread to new areas

EPS

comprised of biopolymers of microbial origin in which biofilm microorganisms are embedded (contain a wide variety of polysaccharides, proteins, glycoproteins and lipids, extracellular DNS produced by embedded archaeal, bacterial, and eukaryotic microbes)

Quorum Sensing

cell to cell chemical communication system allowing microbes within the biofilm to coordinate activities/alter gene expression to benefit the community

Biofilms and Disease

80% of human infections originate from them; their microbes are >100-1000X more resistant to antibiotics and disinfectants; infections are protected from the immune system

Healthcare-Acquired Biofilm Infections

implanted or indwelling medical devices are common sources (PICC lines, catheters, chemotherapy ports, prosthetic joints, teeth implants)

Biofilm Formation

linked to persistent, recurrent, and often treatment-refractory/chronic infections

Tissue/Mucosal-Associated Biofilms

biofilm develops within mucus, tissue, or on host surfaces (CF lung infection, chronic wounds, osteomyelitis, chronic rhinosinusitis, otitis media, periodontitis)

Device-Associated Biofilms

biofilm develops on a foreign material, making physical removal particularly important (urinary catheters, entral venous catheters, prosthetic joints, prosthetic valves, implanted devices)

Invasins

membrane associated or secreted virulence factors that function to assist microbial invasion; act locally to damage host cells and/or have immediate effect of facilitating the growth and spread of the pathogen

Iron

essential for survival; freely circulated in host tissues/blood; to acquire and remove it from host transport proteins (transferrin, lactoferrin, heme, etc), bacteria produce membrane bound proteins and/or secreted binding siderophores

Exoenzymes

extracellular enzymes that break down nutrients to facilitate spread; allow pathogens to scavenge nutrients and damage host tissues

Normal Host Cell Functions are Disrupted When Pathogens:

invade/release from host cells, exploit host nutrients, secrete exoenzymes to facilitate spread, release toxins

Toxins

major virulence factors; promote infection and disease by directly damaging host tissues or disabling the immune system

Exotoxins

soluble proteins produced and actively secreted or released by both gram+ and gram - bacteria with adverse host effects → toxic and active in low concentrations (destroy host cells, alter immune response, disrupt cellular metabolism, aid in bacterial growth or spread); named indicated organism that makes and type of cell it targets)

Endotoxin

lipid A portion of LPS within the gram - bacterial outer membrane; released upon cell lysis; inflammatory; endotoxemia may result in systemic inflammatory response; many treatment issues

Septic Shock

can be caused by endotoxins; characterized by fever, hills, fatigue, malaise, tachycardia, and hypotension; life-threatening hypotension can trigger multiorgan failure

Key Mechanisms of Immune Evasion - Hide From Host Defenses

antigen masking, mimicry, and variation; intracellular lifestyle; latency

Key Mechanisms of Immune Evasion - Undermine

suppress immune function (break down antibodies, infect immune system cells, block immune system signals, inhibit production of immune system factors); avoid phagocytosis (make a capsule, block phagosome-lysosome fusion, neutralize hydrolytic enzymes in phagocytes, toxin damage to phagocytic cells, evolve to thrive inside the phagolysosome)

Antigen Masking

pathogen covered in host factors to avoid immune detection

Antigen Mimicry

pathogen’s antigens resemble host molecules, helping it evade immune detection

Antigen Variation

pathogen switches its antigens, thwarting the mounting immune response

Intracellular Pathogens

include viruses, some cellular pathogens; reside, multiply, and survive inside host cells (pirates)

Latency/Persistence

ability of a pathogen to remain dormant; “stay under the radar”; usually causes persistent or recurrent disease (strike and retreat); can confer protection from drug therapies

Infectious Dose (ID⁵⁰)

number of pathogens needed to establish an infection in 50% of exposed host; more infectious have a lower value; does not always mean dangerous (common cold)

Lethal Dose (LD⁵⁰)

amount of pathogen/toxin needed to kill 50% of affected host that are not treated; lower value = higher virulence

Factors that Effect ID⁵⁰ and LD⁵⁰

species affected, host’s immune fitness, route of exposure

Bacterial Reproduction

asexual by binary fission; offspring arise from a single organism and inherit the genes of that parent cell only; no exchange or recombination of genetic information

Binary Fission

when nutritional requirements are met, cell enlarges in size → replicates all cellular components → divides to produce a new “daughter” cell; wide range in time frame for doubling; rate impacted by environmental conditions

Generation Time

the time it takes for the population to double through one round of binary fission; bacteria can grow rapidly or remain dormant for thousands of years; dependent on environmental conditions and type of organism

Growth Curve

bacterial growth pattern in a closed culture system plotted as a function of time; 4 distinct phases

Culture Density

the number of cells per unit volume

Lag Phase

no increase in number of living bacterial cells

Log Phase

exponential increase in number if living bacterial cells

Stationary Phase

plateau in number of living bacterial cells; rate of cell division and death roughly equal; endospores made

Death or Decline Phase

exponential decrease in number of living bacterial cells; endospores released

Conditions that Microbes Will Adapt To

temperature, pH, salinity, oxygen levels, nutrient availability

Minimum Temperature

lowest that supports growth

Optimal Temperature

cellular growth the highest