Gram Positive Bacteria Flashcards
This non-hemolytic staph is sensitive to novobiocin.
S. epidermidis
Who is at greatest risk of disease from Listeria monocytogenes infection?
- Neonates
- Pregnant women
- Immunocompromised
What medically relevant Streptococcus spp. belongs to the Group B grouping?
S. agalactiae
What clinical diseases are associated with cutaneous exposure to B. anthracis?
- Papules → Ulcers → Eschar
- Lymphadenopathy
- Edema
- 20% mortality when untreated
What Enterococci spp. are clinically relevant?
- E. faecalis
- E. faecium
What types of infections does S. pyogenes cause?
- Respiratory tract infections
- Skin & soft tissue infections
- Toxin-mediated infections
- Immune-mediated infections
What risk factors are associated with Enterococci spp. infection?
- Urinary or intravascular catheters
- Hospitalization / nonsocomial infections
- Broad spectrum antibiotic use
What diseases are associated with B. cereus infection?
- Food poisoning (vomiting, diarrhea)
- Ocular infections
- Anthrax-like respiratory infection (rare)
What characteristics give Enterococci spp. their virulence?
- Antibiotic resistance
- Adherence & biofilms
What are the medically relevant gram-positive rods?
- Bacillus anthracis
- Bacillus cereus
- Corynebacterium diphtheriae
- Listeria monocytogenes
What term means pus-forming?
Pyogenic
What type of pathogen are Viridans streptococci?
Opportunistic pathogens - they are normal flora in the oropharynx, GI tract, and urinary tract
What gram-positive coccus is sensitive to optochin?
S. pneumoniae
What infections are associated with S. pyogenes?
- Pharyngitis
- Scarlet Fever (toxin-mediated following pharyngitis)
- Skin & soft tissue infections
- Bacteremia & sepsis
- Pneumonia (less common)
- Toxic shock syndrome
- Rheumatic fever (immune-mediated)
- Glomerulonephritis (immune-mediated)
What diseases are associated with C. diphtheria?
- Diphtheria (toxin-mediated, A+B exotoxin, inhibits protein synthesis)
- Exudative pharyngitis
- Cervical lymphadenopathy
- Psuedomembrane formation
- Myocarditis
- Neuropathy
What clinical diseases are associated with GI exposure to B. anthracis?
- Ulcers at site of invasion
- Lymphadenopathy
- Edema
- Sepsis
- Mortality (100%)
What pyogenic infections may result from S. aureus infection?
- Impetigo
- Folliculitis, furuncles (boils), carbuncles
- Cellulitis
- Bacteremia & Endocarditis
- Pneumonia & Empyema
- Osteomyelitis & Septic Arthritis
What are the three medically relevant staphylococcus species? What features differentiate the species?
S. aureus - Coagulase, B hemolytic
S. epidermidis - Non-hemolytic, Novobicin sensitive
S. saprophyticus - Non-hemolytic, Novobicin resistant
What toxins may be produced by some S. aureus?
- Cytolytic toxins (hemolysins)
- Leukocidin (Panton-Valentine Factor) - Forms pores in WBCs, contributes to MRSA
- Exfoliating toxins - cleve desmosomal protein in keratinocytes
- Superantigens - Enterotoxin A (food poisoning), Enterotoxin B (most potent, pseudomembrane colitis, toxic shock syndrome), Toxin shock syndrome toxin (associated with menstruation)
What infection is most commonly associated with S. saprophyticus?
Urinary tract infections in women
What characteristic gives S. epidermidis its virulence?
Ability to form biofilms
What enzyme differentiates Staphylococcus from Streptococcus?
Catalase
What test is important in diagnosing rheumatic fever following pharyangitis?
ASO TIters (Anti-Streoptolysin O Antibodies)
This catalase and coagulase negative, beta-hemolytic, gram-positive coccus is sensitive to bacitracin.
S. pyogenes
How do the B. cerreus toxins differ in their mechanism and disease presentation?
The heat-stable toxin has a short incubation and symptom duration period. Symptoms include vomiting, nausea, and cramps. Ingestion is of the actual toxin.
The heat-liable toxin has a longer incubation and symptom duration period. Symptoms include diarrhea, cramps, and nausea. In this case, the bacterial organism is ingested, which then produces and releases the toxin within the body.
What are the disease processed of S. aureus?
Pyogenic & Toxigenic (only by some S. aureus)
What toxin must S. pyogenes express in order to cause scarlet fever?
Spe toxin
What diseases are associated with S. agalactiae?
- Bacterimia & Pneumonia
- Meningitis
- Neonatl Sepsis
What virulence factors are associated with S. pyogenes?
- Capsule
- M protein (blocks complement to prevent phagocytosis)
- Lipoteichoic acid
- F protein
- Pyrogenic exotoxins (Spe toxins)
- Steptolysin S (B hemolysis)
- Steptokinase A & B (lyses blood clots)
What characteristics describe Corynebacterium spp.?
- Club-shaped
- Aerobic or facultative anaerobes
- Catalase positive
- No flagella
- Normal flora of skin, upper respiratory tract, GI tract, and urinary tract
What are the medically relevant gram-positive cocci?
Staphylococcus, Streptococcus, Enterococcus
What factors increase the virulence of S. aureus?
- Capsule & Biofilm
- Peptidoglycan - Edotoxin-like activity
- Teichoic Acids - adherence
- Staphylococcal protein A - binds IgG to inhibit opsonization
- Microbial Surface Components Recognizing Adhesive Matrix Molecules (MSCRAMM) - Adherence and clumping
- Toxins
- Enzymes
What diseases are associated with Listeria monocytogenes infection?
- Gastroenteritis
- Meningitis
- Neonatal disease - Abortion, stillbirth, granulomatous infantispectic, meningitis, meningoencephalitis, septicemia
This bacteria is catalase-positive, non-hemolytic, and resistant to novobiocin.
S. saprophyticus
What skin infections are associated with S. pyogenes?
- Impetigo
- Erysipelas
- Cellulitis
- Necrotizing Fasciitis (“flesh-eating”)
What characteristics describe Listeria monocytogenes?
- Coccobacillus (short rods), in pairs or short chains
- Intracellular pathogen
- Can grow at low temperature
- Halophilic
- Normal flora of animals
What is the most medically relevant Corynebacterium spp.?
C. diphtheriae - Humans are the only reservoir. Possible asymptomatic carriage on skin or oropharynx
What are the virulence factors of B. anthracis?
- Spore-forming
- Polypeptide capsule (unusual as most capsules are made of polysaccharides)
- Toxins (protective antigen, edema factor, lethal factor → exhibit A+B toxin structure)
What diseases are associated with Viridans streptococci?
- Cavities
- Bacteremia
- Abscesses in the brain, oropharynx, or peritoneal cavity
What diseases are associated with S. pneumoniae infection?
- Pneumonia
- Otitis media (mostly children)
- Sinusitis
- Meningitis
- Bacteremia
What virulence factors are associated with S. pneumoniae?
- Capsules (can exhibit recombination or point mutations to change surface antigens)
- IgA protease at mucosal surfaces to escape mucus
- Pneumolysin (lysis of Hb, cholesterol, epithelial cells, phagocytes)
- Peptidoglycan & Teichoic Acid
What clinical diseases are associated with inhaled exposure to B. anthracis?
- Long incubation period if spread by spore
- Initial nonspecific symptoms - fever, myalgia, cough, malaise
- Progressive symptoms - worsening couch, fever, edema, enlargement of lymph nodes, respiratory failure, sepsis, shock
- Death within 3 days of symptom onset when untreated
Describe the mechanism of action for the diphtheria toxin.
A+B exotoxin. B subunit binds heparin-binding receptor. The A unit enters the cell and inactivates EF-2 to stop protein synthesis.
This bacteria is resistant to optochin.
Enterococcus spp.
What diseases/infections are associated with Enterococci spp.?
- Urinary tract infections
- Peritonitis
- Bacteremia
- Endocarditis
What disease are associated with S. epidermidis infection?
- Endocarditis
- Infections of shunts and catheters
- Infections of prosthetic joints
Describe the mechanism of action for all three B. anthracis toxins.
Protective antigen - B subunit, binds to host cells for entry
Edema factor - A subunit, adenylate cyclase increases cAMP and causes tissue edema
Lethal factor - A subunit, zinc-dependent protease stimulates cytokine release by macrophages and macrophage lysis
What population is especially at risk for S. agalactiae infection and why?
Neonates are especially at risk for S. agalactiae. Bacteria colonize the GI tract and urinary tract of mothers, which may be exposed to the neonate during childbirth. S. agalactiae is an important cause of neonatal sepsis.
What is the staphylococcal chromosome cassette?
A mobile genetic element that houses the Mec gene, giving S. aureus methicillin resistance
What are the medically relevant Streptoccus spp.?
- S. pneumoniaw
- S. pyogenes
- S. agalctiae
- Viridans streptococci
What characteristic defines S. agalactiae serotypes?
Capsular polysaccharides, which provide protection against phagocytosis
What types of infections are associated with B. anthracis?
Skin, lung, and GI infections
What toxin-mediated infections are associated with S. aureus infection?
- Bullous impetigo
- Scaled skin syndrome (Ritter’s disease)
- Food poisoning
- Toxic shock syndrome
What enzymes are associated with S. aureus virulence?
- Coagulase - converts fibrinogen to fibrin (forms protective barrier around organism)
- Catalase - prevents H2O2 toxicity
- Hyaluronidase - Hydrolyzes hyaluronic acid in CT
- Staphylokinase (Fibrinoylsin) - dissolves fibrin clots (promotes spread)
- Lipase, Phospholipase, Nuclease, Protease (provides essential components for organism)
- B-lactamase - penicillin resistance
What are the general characteristics of Staphylococcus spp.?
Facultative aerobes, halophilic
Exposure through human-to-human contact or fomites
Normal flora on the skin and mucosal surfaces
S. aureus - Nasopharnyx
S. epidermidis - Skin
S. saprophyticus - GI Tract
What are the virulence factors of Listeria monocytogenes?
- Beta hemolytic
- Listeriolysin O (cytolysin)
- Internals (attachment proteins)
- ActA (actin-enabled motility)
What type of organism are Streptococci spp. and in what environment do they prefer to grow?
Aerotolerant anaerobes that prefer high CO2 (capnophilic)
What is the mechanism for methicillin resistance in S. aureus?
The mecA/C gene encodes a penicillin binding protein (PBP2a) with lower affinity for methicillin. Because of this, the antibiotic is unable to bind with transpeptidase to disrupt cell wall structure.
What virulence factors are associated with B. cereus?
- Heat-stable enterotoxin
- Heat-liable enterotoxin
- Cytotoxic enzymes
What genes encode in Methicillin resistance in S. aureus?
mecA (more common) & mecC
What hemolysis mechanisms do each Steptococcus spp. exhibit?
S. pyogenes - beta hemolytic
S. agalactiae - beta hemolytic
S. pneumoniae - alpha hemolytic
Viridans streptococci - alpha or gamma hemolytic
How is B. anthracis generally spread to humans?
The bacteria naturally exists in soil and commonly infects herbivores. Humans are then exposed through contaminated animal products. B. anthracis is also known to be a bioterrorism agent.
To which grouping does S. pyogenes belong?
Group A
