Common Bacterial Pathogens 1 Flashcards
Which bacteria are gram + cocci?
Staphylococcus
S. aureus
SSNA (e.g. S. epidermidis)
Streptococcus S. pyogenes (Group A Strep) S. pneumoniae Enterococcus faecalis, E. faecium “Viridans” streptococci
Where do people usually have S. aureus
Anterior nares and perineum
Asymptomatic carriage in 30% of healthy individuals
Are cutaneous S. aureus infections usually systemic or local?
Local infections like boils, folliculitis, focal abscesses, often associated with foreign body
What is the mechanism of S. aureus cutaneous infections? What are the major virulence factors?
Localized abscess → formation of capsule → walls off infection → interferes with host defense
Coagulase:
-helps form fibrin capsule →interferes with phagocytosis
Alpha toxin:
-major cytotoxic agent → invasiveness and virulence
What are the three Staphylococcal toxinogenic diseases?
- Staphylococcal Scalded Skin Syndrome (SSSS)
- Toxic Shock Syndrome- TSST
- Staphylococcal Food poisoning
What happens in Staphylococcal Scalded Skin Syndrome?
epidermis falls off
Toxins are produced which attack desmosones
What cells do superantigens target?
Sags cause non-specific activation and proliferation of T-cells which release IL-2, INF-gamma, TNF-alpha
**Picture the little cofactor that grabs onto the side of MHC class II and forces APC to stay connected with T cell
What population is most common to get Toxic shock syndrome?
Menstruating women => tampons
1/3 of the cases are men
What microbiological property is different with Staph. Epidermis than Staph. Aureus?
Coagulase negative
- hence the nickname Coagulase Negative Staph (CNS)
- not to confused with catalase (all staph are positive)
Also called SSNA (staph species not aureus)
If Staph. epidermidis is normally on your skin flora, how can it be a pathogen?
Extracellular glycocalyx “slime” allows biofilm formation
=> adherence to foreign bodies, e.g., catheters, shunts, hip prostheses, artificial (or damaged) heart valves (*Endocarditis)
Describe microbio properties of Strep. pyrogenes
Gram + cocci (all strep)
Catalase negative (like all strep)
B-hemolytic
What causes streptococcal pharyngitis (strep throat)?
Strep. pyrogenes/ Group A strep
Why is strep concerning?
Pharyngitis can result in rheumatic “Phever” and glomerulonePhritis
What’s a key virulence factor in pharyngitis?
M protein
involved with adherence and has antiphagocytic properties (binds factor H and reduces C3b and C5a)
How does strep lead to glomerulonephritis?
Type 3 immunopathology:
-immune complexes get stuck in kidney
*Coke colored urine
Why can rheumatic fever follow Group A Strep pharyngitis?
You can produce antibodies → recognize bacterial antigens AND host antigens of myocardium and heart valves → progressive antibody mediated tissue damage
How is endocarditis different from RF?
endocarditis is bacteria attacking tissue
RF is antibodies attacking tissue
What are symptoms of rheumatic fever?
F J♥NES
i. Fever
ii. Joints - polyarthritis
iii. ♥ - carditis
iv. Nodules (subcutaneous)
v. Erythema marginatum
vi. Sydenham Chorea
Microbio characteristics of S. pneumonia?
- Gram +
- Diplococci (pairs are also called pneumococcus)
- Catalase negative (all strep)
- Normal flora in UR tract of up to 40% of healthy people
What are some invasive and non-invasive diseases caused by streptococcus pneumonia?
Non invasive:
Pneumonia (~60% of bacterial pneumonia)
Sinusitis
otitis media
bronchitis
Invasive:
Meningitis
Bacteremia/septicemia
*BS MOPS
What is the underlying cause of the pathogenesis of S. pneumonia?
=Ability to grow and evade host defenses
How does S. pneumonia grow and evade host defenses?
ANTIPHAGOCYTIC POLYSACCHARIDE CAPSULE!
-MULTIPLE antigenic types of capsule (at least 91 distinct antigenic types)
Recovery/immunity due to development of anti capsular antibody
What are predisposing factors to pneumococcal disease?
Young or old
Alcoholism (e.g., mucocillary defect)
Respiratory viral infection
Who would you give the 23-valent pneumovax vaccine to?
=Adults (23 yr olds)
- IgM response
- protection against INVASIVE disease in elderly and immunocompromised adults. Ironically, does NOT provide protection against pneumonia.
Who would you give the 7 and 13-valent Prevnar vaccine to?
=Kids
- Conjugate vaccines
- 7 valent is IgG response
- Confers herd immunity
Where do you usually find enterococcus faecalis and faecium? (hint: entero)
Where do infections occur?
-Normal flora in intestines
- infections: Urinary tract, surgical wounds, biliary tract, endocarditis
- Hospital acquired infection from patient to patient encounter on hands or medical devices
Why is it important to distinguish Enterococcus faceless from other “streptococci”?
- because of its intrinsic and emerging acquired antibiotic resistance including vancomycin!
- It is selected by therapy with cephalosporins (to kill streptococci and keep enterococci
What bacteria causes cavities and can spread to bloodstream after dental extractions?
Viridans Streptococci
“you have Very Strapping teeth”
*Spreading into blood can lead to endocarditis!
What is the major virulence trait of Viridians Streptococci?
Dextrans
-adherence to teeth, oral tissue, or to fibrin and platelets on damaged heart valves→ tissue damage/function
