Bacteriology Flashcards
(36 cards)
Respiration and Fermentation
Fermentation: glucose/organic molecules are electron donors/acceptors
Energy generated by substrate level phosphorylation
End products: acids that may accumulate in growth medium
Inefficient energy generators but do not require oxygen
Respiration: electron receptor is O2 or NO3- (inorganic compound when anaerobic)
Electrons transported through chain of carriers in plasma membrane
Causes protons to be pumped from cytosol to external side of PM
Proton-motive force potential energy harvested by ATP Synthase
P-M Force also powers flagellar motor and uptake of small molecules into cell
Very efficient energy generator, allows microorganisms to grow quickly
Ribosomes
70S ribonucleoprotein structures composed of 50S & 30S subunits
50S: 2 RNA molecules – 23S and 5S + 34 proteins
30S: 1 RNA molecule – 16S + 21 proteins
Use PCR to identify nonculturable bacteria with conserved/varied regions of 16S
Target for Abx due to differences from human ribosomes – Abx inhibit protein synthesis
Capsules
Organic polysaccharides layers attached to exterior of bacteria (B. anthracis poly-D-glu)
Highly hydrated & prevent desiccation in environment
Pathogen virulence: prevent phagocytosis and complement activation on cell surface
Common encapsulated bacteria: S. pneumoniae, N. meningitidis, H. influenzae
Serologic typing via K antigens; develop vaccines against the capsule K antigens
Catalase
Degrades hydrogen peroxide to water and oxygen,
Allows bacteria to grow in oxygen (with Superoxide dismutase!)
Oxidase
Measures ability of bacteria to oxidase – bacteria with unique cytochrome c are positive
P. aeruginosa, Neisseria spp,
Superoxide Dismutase
Enzyme degrades superoxide anion into hydrogen peroxide,
Allows bacteria to grow in oxygen (with catalase!)
TSST-1
Superantigen, activates multiple subsets of T cells, cytokine release and overactivation
Leads to fever, hypotension shock multisystem organ failure
Pili
Long, filamentous structures distributed over surface of cell
Pilin: monomeric protein that assembles into pilus polymer
Mediates adherence by binding host cell receptors (accounts for tissue specificity)
Useful in biofilm formation
Phase Variation: turn on/off pili production
Antigenic Variation: change type of pilin produced (N. gonorrhoeae)
Transferrin
Human protein that binds iron extracellularly, targeted by bacteria via siderophores
N. meningitidis & N. gonorrhoeae have transferring surface receptors to steal iron
Siderophores
Low molecular weight molecules which remove iron from transferrin & allow it to be taken up by bacterial cells
Cytochrome
P. aeruginosa and Neisseria spp. have ETC with unique cytochrome c
Detect these bacteria with oxidase test – can oxidize/change color of phenylenediamine
Gram-Positive vs. Gram-Negative
Gram-Positive: thick cells walls; cell walls have teichoic acids – may function as adhesins;
Retain crystal violet staining,
Gram-Negative: Thin cell wall, loses crystal violet stain and picks up RED color
Two lipid bilayer membranes – cytoplasmic and outer layer (periplasm space)
Porins, outer leaflet has LPS, not phospholipids (Lipid A, Core polysaccharide, O antigen)
Peptidoglycan
Makes up cell wall, external to plasma membrane, protects cell from lysis & gives shape
Polymers of 2-alternating sugars (NAG/NAM) build pentapeptide side chains of L/D AAs
5th peptide leaved and 3rd peptide cross-links with other 4th peptide via Glycine residues
Penicillin Binding Proteins (PBPs) facilitate chain cross-linking
Toxin Mechanism: Pertussis
Pertussis Toxin: S1-S5, AB Toxin,
S2-S4: B – toxin adherence to host
S1: A – enzymatic activity – ADP-ribosylates Gs causing increase in cAMP
S5: scaffold to position other subunits
Toxin Mechanism: Toxic Shock Syndrome
TSST-1 – superantigen, occurs without bacteremia, activates many T cell subsets
Cytokine overactivation fever, hypotension shock organ failure
Enterotoxins A-E, G-I - superantigens
SPE-A/C – superantigens
How to Identify Strep
Gram Positive Cocci, grows in chains, catalase-negative, coagulase-negative,
beta-hemolytic, rapid strep test, ASO antibody titers diagnose recent infection
Staphylococcus Aureus (General, Pathogenicity, CM, Dx, Treatment)
General: Gram Positive cocci, grows in masses, normal skin inhabitant, coagulase-positive, catalase-positive, facultative anaerobe
Pathogenicity:
Alpha-toxin: Beta-hemolytic, pore-forming toxin
A Protein: binds Fc of IgG to prevent phagocytosis
TSST-1: Superantigen, causes toxic shock
Exfoliatin: exotoxin, causes scalded skin syndrome, splitting of stratum spinosum
And stratum granulosum
Enterotoxins A-E, G-I: superantigen, causes toxic shock and staph food poisoning
Resistant to 30min boiling
Coagulase: activates fibrinogen to fibrin – protect abscesses from neutrophils
PVL: Panton-Valentine Leukocidin: pore-forming toxin common in MRSA,
Carried by bacteriophage
Clinical Manifestations:
SSTI: Abscesses (Furuncle, Carbuncle), Cellulitis,
Scalded Skin Syndrome
Pneumonia (viral superinfection)
Staphylococcal food poisoning (2-5 hrs after eating enterotoxins)
Toxic Shock Syndrome (tampon use, rash, hypotension organ failure)
Skin desquamation upon recovery
Osteomyelitis and Septic Arthritis if disseminates
Endocarditis – tricuspid valve biofilm (Osler’s nodes, Janeway Lesions,
conjunctival hemorrhages, heart murmurs)
Diagnosis:
Gram Positive Staining, coagulase-positive, cocci, catalase-positive
Treatment:
No PCN – all staph have evolved penicillinase; drain any pus
Oxacillin, Nafcillin – Anti-staph Abx
Vancomycin/Linezolid/Daptomycin – for MRSA (altered PBP-2’)
Staphylococcus saphrophyticus
Common cause of UTIs in young women (G+ cocci, coagulase-negative, catalase+)
Streptococcus pneumoniae
G+ Diplococci, encapsulated, optochin-sensitive, causes meningitis, otitis media, pneumonia, sinusitis, bile-sensitive, alpha-hemolytic (pneumolysin - partial clearing)
Streptococcus pyogenes
General: Gram+ cocci, grows in chains, catalase-negative, bacitracin-sensitive, metabolically facultative, beta-hemolytic, aka: Group A strep, encapsulated
Pathogenicity:
Streptolysin S/O: pore-forming toxin, beta-hemolytic, ASO titers
Streptokinase: cleaves fibrin to enable dissemination
Protein M: molecular mimicry to myosin, on cell wall – prevent phagocytosis
SPEs: SPE-A, SPE-C: Superantigens (STSS/SF) – carried by phage
SPE-B: protease (NF)
C5a peptidase: prevents neutrophil chemotaxis to infection site
DNAase
Clinical Manifestations:
Pharyngitis: Gray exudate on tonsils, fever, sore throat
Rheumatic Fever: previous strep throat, JONES
PSGN: facial edema, cola-colored urine, Abx don’t prevent, HT
Scarlet Fever: strawberry tongue, rash avoids mouth
Strep TSS: due to wound infection dissemination, no rash, no tampon use
SSTI: impetigo, erysipelas/cellulitis, necrotizing fasciitis, myositis
Diagnosis: G+ cocci, ASO titers, throat culture, beta-hemolytic
Treatment: PCN, Amoxicillin, or Ampicillin, Clindamycin affects SPE production,
IVIG for STSS
Streptococcus agalactiae
G+ cocci, beta-hemolytic, grows in chains, bacitracin-resistant, Group B strep
Natural inhabitant of vagina - Cause of neonate sepsis and meningitis,
Need to test mother prior to delivery - prophylactic PCN/Vancomycin
Viridans Streptococci
G+ cocci, bile-resistant, group of many strep, causes dental caries (normal mouth resident) or endocarditis or deep tissue abscesses, alpha-hemolytic
Streptococcus gallolyticus
Group D strep, gamma-hemolytic (no clearance), often associated with colon cancer
Usually perform colonoscopy after strep gallolyticus diagnosis (AKA: S. bovis)
Bacillus anthracis
General: Gram+ rod, strict aerobe, grow in bamboo-like chains, spore-forming,
found in animal meet/hides, bioterrorism concern
Pathogenicity:
Anthrax Toxin: AB Toxin: EF (adenylate cyclase toxin - increases cAMP - swelling)
LF (cleaves MAP kinase – black eschar),
Protective Antigen – forms pore, binds cell membranes
Poly-D-glutamic acid capsule
Clinical Manifestations:
GI Anthrax: N/V/D, ulcers form at site of infection (mouth, esophagus, intestine
Inhalation Anthrax: Woolsorter’s disease, widened mediastinum due to
Large necrotic mediastinal LNs, fever, SOB, hypotension
Cutaneous Anthrax: Painless black eschar with surrounding edema
Diagnosis: Gram stain, serologic tests
