Bailey Flashcards
Oligotrophs
Can grow with limited nutrients
Microaerophiles
Require lower levels of oxygen
Mesophiles
Grow well in mild temps (15-45 Celsius/59-113 F)
Gram + bacteria membrane
Murein/Peptidoglycan cell wall outside of the cell membrane
Gram - bacteria membrane
Thin Murein layer between 2 layers of cell membrane
Structure of Murein
Nam & Nag backbone
Nams are connected by cross-linked peptides
Difference in peptide chain bonding in Murein between gram + and -
In gram + lysine binds to alanine via pentameric glycine
In gram - DAP binds to alanine
What is a common target for antibiotics?
Biosynthesis of Murein
Surface structure of gram + bacteria
Teichoic acid
Surface structure of gram - bacteria
LPS (Lipopolysaccharide)
Structure of LPS
Lipid A
Polysaccharide core
O-antigen (highly variable - defines type of bacteria)
Function of LPS
Induces TNF-alpha which leads to septic shock at high levels (shock/organ failure/low bp)
What are PAMPs?
Pathogen associated molecular patterns
LPS and Teichoic acid are PAMPs
How do cells of the immune system recognize PAMPs?
Using PRRs (pattern recognition receptors)
TLR 4 recognizes what
LPS (Gm -)
TLR 2 recognizes what
Peptidoglycan (Gm +)
TLR 2+6 recognize what
Teichoic acids (Gm +)
TLR 5 recognizes what
Flagella
3 additional extracellular structures on bacteria
Pili (fimbriae)
Flagella
Glycocalyx
Pili function
Attach bacteria to cells & other surfaces
Adhesins definition & function
Specialized proteins on tip of fimbriae specifically developed for adherence (major cause of virulence)
Monotrichous bacteria
1 flagella
Lophotrichous bacteria
A few flagella
Petritrichous bacteria
Has flagella everywhere
Which direction of flagella turning results in a run & which makes it tumble?
CCW = run (pushes forward) CW = tumble (goes backward/tangled)
Taxis definition
Movement of bacteria that is directed (either toward something good or away from bad)
Glycocalyx definition/types/structure
D - Substance that surrounds a cell
T - 1. Capsule- Well organized,firmly attached layer
2. Slime layer- Not well organized or firmly
attached
S - Usually made of polysaccharides, but can include monosaccharides & glycoproteins
Function of capsule
Masks LPS/Teichoic acids
Can the immune system ever recognize and encapsulated bacteria?
Yes via TLR 5 recognizing flagella or sometimes the capsular polysaccharide
What does the O antigen in a serological designation represent?
Presence of LPS
What does the H antigen represent?
Flagella
What does the K antigen represent?
Capsules
2 broad classes of bacterial pathogens
- Opportunistic
2. Primary
What are the virulence determinants that make a bacterial pathogen a primary class?
- Adhere
- Colonize
- Invade
- Induce damage
Methods of adherence
-Nonspecific
-Specific
~Irreversible
~Anchoring
Via adhesins (often found on fimbriae)
Can also occur by binding to fibronectin in plasma
and associated with mucosal surfaces
What is a limiting factor of colonization?
Nutrient availibility
How do bacteria take up nutrients?
- Carrier-mediated diffusion (facilitated)
- Phosphorylation-linked transport (group translocation)
- Active transport (energy dependent)
What is the action of hyaluronidase?
Degrades hyaluronic acid (which is a common component of the ECM)
What is the action of collagenase?
Degrades collagen (which is an important component of connective tissue)
What does Type I exotoxin do?
Membrane acting
Toxins bind surface receptors and stimulate transmembrane signals
What does Type II exotoxin do?
Membrane damaging
Toxins directly affect host cell membranes (ex. create pores)
What does Type III exotoxin do?
Intracellular effectors
Get into the host cell and induce enzymatic activity
What is the ideal therapeutic index for an antibiotic?
A high number
What does a therapeutic index of 1 indicate?
You need a toxic does in order to eradicate the miccrobe
What is therapeutic index?
Ratio of toxic dose:effective dose
What are the 5 ways that antibiotics inhibit bacteria?
- Inhibition of cell wall synthesis
- Disruption of cell membrane function
- Inhibition of protein synthesis
- Inhibition of nucleic acid synthesis
- Action as antimetabolites (needed for bacterial replication)
How does penicillin disrupt cell wall synthesis?
Cleaves ala bond (cleaves the cross-linking peptides of Murein)
Methods of antibacterial inhibition of protein synthesis
Prevent 30S or 50S subunits from forming
Prevent ribosomes from recognizing RNA
What is one inhibitor of DNA replication that isn’t toxic to human cells
Metronidazole
It is inert, but can be converted to an active form by anaerobic microbes
Used for abscesses & periodontitis
What are the methods of inhibiting nucleic acid synthesis
- Inhibiting DNA replication (most too toxic though)
- Affecting DNA gyrase (gyrase relieves strain while DNA is unwound by helicase)
- Inhibit RNA polymerase
Steps in the action of antibiotics
- Drug penetrates the envelope
- Transport into the cell
- Drug binds to target
Mechanisms of drug resistance
- Synthesis of enzymes that inactivate the drug
- Prevention of access to the target site
a. Inhibiting uptake
b. Increasing secretion of the drug - Modification of the target site
Example of enzymes that inactivate antibiotics
B-lactamases inactivate b-lactin antibiotics like penicillin
Example of preventing access of antibiotics to their target site
Some bacteria develop efflux pumps to pump antibiotics out of them
Example of modification of target site
Alteration of metabolic pathway
Modify enzyme affinity
How does antibiotic resistance spread?
- Chromosome associated resistance
- Plasmid mediated resistance (most common)
- Rapid spread of resistance
How do you combat an antibiotic resistant pathogen?
Synergism
Antagonism
Indifference (many antibiotics are indifferent)?
Are antibiotics effective against all microbes?
NO
not against viruses
Identifying factors of streptococci
Gm + Chains or diplococci Non-spore forming Facultative anaerobes Catalase negative Infect humans & animals
Methods of classifying streptococci
- Hemolysis pattern (alpha, beta, gamma)
- Lancefield group (Displays A-U antigen on cell wall/+ or - agglutination)
- Species
Alpha hemolysis in blood agar
Partial hemolysis and green discoloration of hemoglobin
Beta hemolysis in blood agar
Clear zone of complete hemolysis
Gamma hemolysis in blood agar
No zone of clearing
Group A streptococcal diseases
Beta-hemolytic
- Acute pharyngitis (strep throat)
- Scarlet fever (strep throat + rash)
- Pyoderma (skin infections)
- Group A streptococcal pneumonia
- Necrotizing fasciitis & myositis (hospital gangrene & flesh-eating bacteria)
- Childbed fever
- Foodborne outbreaks
What is the cause of Group A streptococcal (GAS) infections?
S. pyogenes
What are the sites of infection for ARF?
Acute Rheumatic Fever -
Pharynx is the only site of infection that is followed by ARF
How to prevent ARF
Acute Rheumatic Fever -
Treating strep throat with full course of penicillin will prevent ARF (cannot treat it with penicillin after it has started)
APSGN
Acute Post-Streptococcal Glomerulonephritis
Inflammation of glomeruli of kidneys causes smoky urine
Can follow pharyngitis or impetigo infections
Where are group A infections encountered?
- Live on skin & mucous membranes (20% of school-aged children carry w/o symptoms)
- Infected respiratory droplets
- Hand-to-hand-to-mouth
- Food
- Skin/wound infections
- Towels
- Shed skin
Methods of entry of group A infections
Cannot penetrate intact skin
Bacteria bind to epithelial cells via adhesins
-Lipoteichoic acid (LTA) binds fibronectin
-Protein F binds fibronectin
-M protein binds keratinocytes
Methods of spread of group A infections
Remains localized on skin or mucous membranes
Spreads rapidly in deeper tissue infections
Group A bacteria avoid phagocytosis via
M protein - binds host serum proteins/inhibits formation of opsonins
Hyaluronic acid capsule - mucoid capsule that makes it slippery, interfering with phagocyte attachment
C5a peptidase - inactivates phagocyte chemotaxin
Superantigens
Mimic the effects of endotoxins (activated T cells release of cytokines)
Cause toxic shock syndrome
GBS
What is it? Where is it? What does it cause?
Group B Streptococci Beta-hemolytic Has a different polysaccharide capsule Inhabit lower GI & female genital tracts Cause cellulitis, arthritis, and meningitis
GDS
Group D Streptococci
Alpha or Gamma hemolytic
Enterococci and nonenterococci
Normal flora of GI & genitourinary tracts
-Low virulence, usually accompany other bacterial infections
Enterococci
Worlds toughest pathogenic bacteria
Antibiotic synergism required (penicillin & an aminoglycoside)
VRE
Low virulence but untreatable
Can transfer vancomycin resistance to staphylococci
Nonenterococcal group D streptococci
S. bovis - most common for human disease
Subacute bacterial endocarditis - abnormal heart valves (most commonly caused by viridians streptococci)
Bacteremia - colonic lesions
Most strains are killed by penicillin, do not grow in high salt
Viridans streptococci
Alpha hemolytic (greening) 30-60% of orophayngeal flora Low virulence Most common cause of subacute bacterial endocarditis Responsible for dental caries
