Common Bacterial Pathogens 1

Question 1

Which bacteria are gram + cocci?

Answer 1

Staphylococcus
S. aureus
SSNA (e.g. S. epidermidis)

Streptococcus
	S. pyogenes (Group A Strep)
	S. pneumoniae
	Enterococcus faecalis, E. faecium
	“Viridans” streptococci

Question 2

Where do people usually have S. aureus

Answer 2

Anterior nares and perineum

Asymptomatic carriage in 30% of healthy individuals

Question 3

Are cutaneous S. aureus infections usually systemic or local?

Answer 3

Local infections like boils, folliculitis, focal abscesses, often associated with foreign body

Question 4

What is the mechanism of S. aureus cutaneous infections? What are the major virulence factors?

Answer 4

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

Question 5

What are the three Staphylococcal toxinogenic diseases?

Answer 5

1. Staphylococcal Scalded Skin Syndrome (SSSS)
2. Toxic Shock Syndrome- TSST
3. Staphylococcal Food poisoning

Question 6

What happens in Staphylococcal Scalded Skin Syndrome?

Answer 6

epidermis falls off

Toxins are produced which attack desmosones

Question 7

What cells do superantigens target?

Answer 7

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

Question 8

What population is most common to get Toxic shock syndrome?

Answer 8

Menstruating women => tampons

1/3 of the cases are men

Question 9

What microbiological property is different with Staph. Epidermis than Staph. Aureus?

Answer 9

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)

Question 10

If Staph. epidermidis is normally on your skin flora, how can it be a pathogen?

Answer 10

Extracellular glycocalyx “slime” allows biofilm formation

=> adherence to foreign bodies, e.g., catheters, shunts, hip prostheses, artificial (or damaged) heart valves (*Endocarditis)

Question 11

Describe microbio properties of Strep. pyrogenes

Answer 11

Gram + cocci (all strep)
Catalase negative (like all strep)
B-hemolytic

Question 12

What causes streptococcal pharyngitis (strep throat)?

Answer 12

Strep. pyrogenes/ Group A strep

Question 13

Why is strep concerning?

Answer 13

Pharyngitis can result in rheumatic “Phever” and glomerulonePhritis

Question 14

What’s a key virulence factor in pharyngitis?

Answer 14

M protein

involved with adherence and has antiphagocytic properties (binds factor H and reduces C3b and C5a)

Question 15

How does strep lead to glomerulonephritis?

Answer 15

Type 3 immunopathology:
-immune complexes get stuck in kidney

*Coke colored urine

Question 16

Why can rheumatic fever follow Group A Strep pharyngitis?

Answer 16

You can produce antibodies → recognize bacterial antigens AND host antigens of myocardium and heart valves → progressive antibody mediated tissue damage

Question 17

How is endocarditis different from RF?

Answer 17

endocarditis is bacteria attacking tissue

RF is antibodies attacking tissue

Question 18

What are symptoms of rheumatic fever?

Answer 18

F J♥NES

i. Fever
ii. Joints - polyarthritis 
iii. ♥ - carditis
iv. Nodules (subcutaneous) 
v. Erythema marginatum 
    vi. Sydenham Chorea

Question 19

Microbio characteristics of S. pneumonia?

Answer 19

• Gram +
• Diplococci (pairs are also called pneumococcus)
• Catalase negative (all strep)
• Normal flora in UR tract of up to 40% of healthy people

Question 20

What are some invasive and non-invasive diseases caused by streptococcus pneumonia?

Answer 20

Non invasive:
       Pneumonia (~60% of bacterial pneumonia)
       Sinusitis
       otitis media
       bronchitis 

Invasive:
Meningitis
Bacteremia/septicemia

*BS MOPS

Question 21

What is the underlying cause of the pathogenesis of S. pneumonia?

Answer 21

=Ability to grow and evade host defenses

Question 22

How does S. pneumonia grow and evade host defenses?

Answer 22

ANTIPHAGOCYTIC POLYSACCHARIDE CAPSULE!
-MULTIPLE antigenic types of capsule (at least 91 distinct antigenic types)

Recovery/immunity due to development of anti capsular antibody

Question 23

What are predisposing factors to pneumococcal disease?

Answer 23

Young or old
Alcoholism (e.g., mucocillary defect)
Respiratory viral infection

Question 24

Who would you give the 23-valent pneumovax vaccine to?

Answer 24

=Adults (23 yr olds)

• IgM response
• protection against INVASIVE disease in elderly and immunocompromised adults. Ironically, does NOT provide protection against pneumonia.

Question 25

Who would you give the 7 and 13-valent Prevnar vaccine to?

Answer 25

=Kids

• Conjugate vaccines
• 7 valent is IgG response
• Confers herd immunity

Question 26

Where do you usually find enterococcus faecalis and faecium? (hint: entero)

Where do infections occur?

Answer 26

-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

Question 27

Why is it important to distinguish Enterococcus faceless from other “streptococci”?

Answer 27

• because of its intrinsic and emerging acquired antibiotic resistance including vancomycin!
• It is selected by therapy with cephalosporins (to kill streptococci and keep enterococci

Question 28

What bacteria causes cavities and can spread to bloodstream after dental extractions?

Answer 28

Viridans Streptococci
“you have Very Strapping teeth”

*Spreading into blood can lead to endocarditis!

Question 29

What is the major virulence trait of Viridians Streptococci?

Answer 29

Dextrans

-adherence to teeth, oral tissue, or to fibrin and platelets on damaged heart valves→ tissue damage/function