streptococcus, pneumococci, listeria, anthrax Flashcards
What is the meaning of beta, alpha and gamma hemolysis?
Beta hemolysis: complete hemolysis
alpha hemolysis: partial hemolysis
gamma hemolysis: no hemolysis
What is another name for group A strep? (GAS)
streptococcus pyogenes
How would you distinguish between group A and group b strep?
Group A strep is sensitive to bacitracin while group B strep is not.
What does the CAMP test identify? How does it work?
Identifies group B strep. Camp factor damages the RBC, which when combined with the enzyme secreted by S. aureus, creates a zone of hemolysis.
What is another test to differentiate GBS?
Hippurate hydrolysis.
What kind of hemolysis would you see with group A/B strep?
Group A and B strep both show alpha hemolysis. However, the field of clearance is larger with group A strep
If strep tests positive for hydrolysis of esculin in bile salts, what species would you suspect?
Group D strep: Enterococcus faecalis will hydrolyze and turn the tube brown.
Name all the species within Groups A, B, and D streptococci
Group A strep: streptococcus pyogenes
Group B strep: streptococcus agalactiae
Group D strep: 1. Enterococcus: E faecalis
2. Non-enterococcus: streptococcus bovis
What are the main differences between enterococcus and non-enterococcus strep?
Enterococcus: Growth in high salt medium Resistant to antibiotics Causes UTI, bacteremia, and endocarditis Non-enterococcus: Lack of growth in high salt medium Sensitive to penicillin Causes endocarditis
What are the nontypeable streptococci species?
Strep pneumoniae
Strep viridans
What is unique about the morphology of S. pneumoniae?
lancet-shaped diplococci
What are two methods of distinguishing S. pneumoniae from S. viridans?
- Strep pneumoniae is sensitive to optochin
2. Strep pneumoniae is lysed by bile
Where is each species of strep localized to, normally?
group A strep: oral flora (less common) group B strep: vaginal flora (less common) group D strep: colonic flora S. pneumoniae: oral flora (less common) S. viridans: oral flora
What is the morphology of most strep species?
Gram + cocci in chains (exception is strep pneumoniae)
Are most streptococci catalase positive or negative?
Catalase negative
What kind of hemolysis will you observe with group A strep?
beta hemolysis
What is the significance of the M protein for S pygenes?
Antiphagocytic molecule. Specific types cause rheumatic fever/glomerulonephritis
Does Group A strep have a capsule? a pilus?
Yes, has a capsule composed of hyluronic acid
Also has a pilus for adhesion to pharyngeal cells
What are the three types of diseases caused by GAS?
- Pyogenic diseases
- Toxigenic diseases
- immunologic diseases
Give an example of pyogenic diseases caused by GAS
pharyngitis
impetigo and cellulitis
necrotizing fasciitis
pneumonia,meningitis
Give examples of toxigenic diseases caused by GAS
scarlet fever
toxic shock syndrome
Which proteins in GAS help with adhesion to host cells?
M protein
Protein F
lipoteichoic acid
Which proteins help with evasion of host defenses?
capsule, M protein
Which toxins released by GAS are related to pyogenic inflammation?
hyaluronidase streptokinase streptodornase streptolysin O streptolysin S exotoxin B
Which toxins released by GAS are related to toxigenic disease?
erythrogenic toxin (scarlet fever) pyrogenic exotoxin (TSS) These are both superantigens
Does isolation of group A strep in a nontoxic individual indicate infection?
No
What does scarlet fever look like?
sandpaper like rash all over
Pastia’s lines (red lines at the axillary and inguinal regions)
How soon after a GAS pharyngeal infection would you see rheumatic fever?
2 weeks
What is the cause of Rheumatic fever?
streptococcal M proteins react with antigens in the joint, heart, and brain tissues
How can you prevent rheumatic fever?
By treating GAS within 8 days of onset.
How soon after a GAS skin infection would you expect to see acute glomerulonephritis?
2-3 weeks
What is the point of the ASO titer?
Confirmat previous/recent streptococcal infection
What are the symptoms of acute glomerulonephritis?
hypertension, edema, smoky urine
What are the four ways in which you could diagnose GAS?
- culture skin/pharynx, grow, check for beta hemolysis and inhibition by bacitracin
- rapid strep test
- culture invasive tissue
- elevated ASO titer
How do you treat group A strep?
penicillin G or erythromycin
What are the symptoms of GBS?
- neonatal sepsis/meningitis
2. postpartum endometritis/wound infection in adults
How do you treat GBS?
penicillin or ampicillin
What kind of hemolysis do you see with group D strep?
alpha or gamma hemolysis
Where are Group D streptococci found? What unique property do they have that allows them to grow there?
Colonic bacterial flora
Has the ability to grow in bile
How do you treat group D strep?
If enterococci: use vancomycin + aminoglycoside
If S. bovis, use penicillin
You observe strep species that is lysed by bile and inhibited by optochin. What do you suspect? What kind of hemolysis would you expect?
Strep pneumoniae. Alpha hemolytic colonies.
What kind of hemolysis does strep pneumoniae have?
alpha hemolysis
What is the quellung reaction?
Rxn where antibody binds to bacterial capsule and allows the capsule to be visualized.
Basis for typing reaction. If there is no quellung rxn, means bacteria has no capsule
What are the pathogenic factors of S. pneumoniae?
lipoteichoic acid
pneumolysin (alpha hemolysis)
IgA protease (cleaves mucosal igA for better colonization)
How do you treat S. pneumoniae?
Otitis media: amoxicillin
pneumonia: fluoroquinolone and amox
Meningitis: vancomycin + ceftriaxone
What are the two pneumococcal vaccines? Which is more effective for whom?
Pneumococcal polyvalent: (T cell independent) better for elderly
Pneumococcal conjugate: (T cell dependent): better for children under 2
What kind of hemolysis does strep viridans produce?
alpha hemolysis
What is the response of strep viridans to bile/optochin?
Not lysed by bile. Resistant to optochin
What are the important species within strep viridans?
S. sanguis
S. mutans
S. mitis
We know that strep viridans is an important part of the oral flora. What is it clinically relevant?
It can enter the blood stream after dental surgery to cause endocarditis
Can also cause oral abscess that can lead to sinus/brain abscess after dental surgery
How do you treat strep viridans?
Penicillin for abscess. Penicillin/vancomycin for endocarditis.
What is the morphology of Bacillis anthracis?
Large gram positive rods, spore-forming, aerobic
What would happen if the anthrax colonies were plated on blood agar?
no hemolysis
What is unique about the anthrax capsule?
Made up of poly-glutamic acid
What is a risk factor for developing anthrax?
Exposure to grazing animals or their products: hides
What is unique about anthrax spores?
They are centrally located
What are the important factors in the pathogenesis of anthrax?
- Protective antigen: Forms pores in macrophages
- Edema factor: Causes edema in association with PA adenylate cyclase
- Lethal factor: Lethal in association with PA phosphokinase of MAPK pathway
What are the clinical syndromes of anthrax?
- cutaneous anthrax
- inhalation anthrax
- gastrointestinal anthrax
How would you treat and prevent anthrax?
- Cipro/doxycycline
2. There is also a vaccine, which is not commonly used
What are the properties of listeria monocytogenes?
Small aerobic gram + rod. Non spore forming
Where is listeria monocytogenes commonly found?
animals, plants, unpasteurized milk and cheese. Commonly found in refridgerated foods because it grows well at low temperature.
Is listeria motile?
Yes. tumbles!
What happens if you plate listeria on a blood agar plate?
narrow zone of beta hemolysis
Describe the pathogenesis of listeria
Invades mononuclear phagocytic cells (macrophage)
- Grows intracellularly
- Evades endosomes through listeriolysin O
What are the clinical symptoms of listeria?
Neonatal sepsis and meningitis
or in immunocompromised host
How do you treat listeria?
Ampicillin
trimethoprim-sulfamethoxazole
What is the most important virulence factor of group A strep?
M protein. It determines whether the pt will later have rheumatic fever vs glomerulonephritis because it is an important antigen.
What does steptolysin O do?
hemolysin it is oxygen-labile and an important antigen
What is streptolysin S?
Oxygen stable hemolysin. NOT antigenic
pyrogenic exotoxin A
Toxin responsible for streptococcal toxic shock syndrome. Similar to staphylococcal TSST. Also a superantigen
Exotoxin B
Responsible for Strep A’s “flesh eating behavior”
What is the most common cause of bacterial pharyngitis?
Streptococcus pyogenes
What bacteria can form impetigo–honey colored crusted lesions of the skin?
Either Staph aureus or GAS
What is the most common cause of endocarditis?
Viridans strep. Common after dental surgery
A patient has endocarditis. What are the possible organisms that could be responsible?
- Strep viridans (think oral surgery)
- Staphylococcus aureus
- Staphylococcus epidermidis
- Enterococcus
- Group A strep
Evidence of endocarditis=splinter hemorrhage and enlarged spleen
