Exam 1

Question 1

What are the three most common causes of bacterial menigitis?

Answer 1

PIN Strep Pnuem, Heamophplis influensa, Niesseria meningitis

Question 2

What are the most common causes of bacterial meningitis in neonates?

Answer 2

E. coli, group B strep, Listeria

Question 3

What are the most common causes of bacterial meningitis in children over one year of age?

Answer 3

Pneumonoccocus, Meningococcus and group B streptococci,

Question 4

What are the most common causes of bacterial meningitis in adults?

Answer 4

Pneumonoccocus, Meningococcus, S. Aureus, occacionaly H. influenza (non-typable)

Question 5

What is the most common cause of bacterial meningitis in Elderly and pregnant woman?

Answer 5

Listeria monocytogenes

Question 6

What is the culture characteristics of S. pneumonae

Answer 6

G+ diplococci, Bile soluble, alpha hemolysis on blood agar plate, Requires catalase, grows best in 5% Co2

Question 7

What is the culture characteristics of N. meningitidis?

Answer 7

G- diplococcus, facultative anaerob, has lipopolysacharide

Question 8

What is the culture characteristics of H. influenza?

Answer 8

Small pleomorphic gram negative rod. Oxidase positive, facultative anaerobes. Requires hemin (factor x) and NAD (factor y) for growth. Use chocolate (hemoylsed blood) agar to grow. Capsulated and non capsulated (nontypable). May have beta lactamase that inactivates ampicillin

Question 9

What is the culture characteristics of Listeria meningitidis?

Answer 9

Beta hemolytic gram positive rod. Aerobic and facultatively anaerobic. Motile. May be gram variable and can be confused with S. pneumoniae, H. influenzae and diphtheroids.

Question 10

What is th most common cause for Streptococcal Pharyngitis?

Answer 10

Predominant species for streptococcal pharyngitis is
S. pyogenes (Group A streptococcus or GAS) Group
C and Group G strep may also be causes.

Question 11

What are the most common causes of Pharyngitis?

Answer 11

Beta hemolytic strep 15% of causes

Viruses 50% of causes (Rhinovirus, Adenovirus, influenza
A and B, Epstein Barr virus, Cytomegalovirus, HIV, Coxsackievirus, RSV, Metapneumovirus, Coronavirus)

30% no diagnosis

Question 12

What are the virulence factors for Group A strep?

Answer 12

•Capsule in some strains (decreased phagocytosis)
-Lipoteichoic acid in peptidoglycan cell wall (adhesion)
•M-protein (inhibits antibody binding and compliment
related opsinization)
•Fibronectin binding protein (adhesion)
•Vimectin (muscle adhesion)
•Streptolysin O (hemolysis on blood agar. Titers high and
help with diagnosis of PSGN and rheumatic fever)
•Hyaluronidase (skin, deep tissue spread)
•Streptokinase (binds plasminogen → plasmin → fibrin →
fibrin degradation products)
•Streptococcal pyrogenic exotoxins (SPE) A,B and C toxins.
(fever, rash of scarlet fever, streptococcal toxic shock
syndrome toxin. May also function as superantigens and
induce cytokine production.)

Question 13

What are some of the complications of Group A strep infection?

Answer 13

PSGN:
•Risk greatest children 5 to 12 and adults > 60
•Can occur following pharyngitis or skin infection (5 to
10% attack rate from pharyngitis and 25% from skin
infection in one epidemic). Can also be sporadic
•Related to circulating strain virulence factors (SPEB)
•Results in immune complex disease in glomerulus
•Edema, hematuria, hypertension
•Therapy supportive and prognosis usually good.
(Patients recover renal function)
SCARLET FEVER:
-Rash starts in head and neck, spreads to torso and limbs.
-Rash desquamates
ACUTE RHUEMATIC FEVER
•Occurs after streptococcal pharyngitis (2 to 3 weeks
later)
•Arthritis, carditis, subcutaneous nodules, chorea
(movement disorder), erythema marginatum (rash)
•May have fever, increased ESR and CRP
•Usually children age 5 to 15.
•More common in developing world
•Late sequelae include rheumatic heart disease with
mitral stenosis and increased risk for endocarditis
PANDAS
PERITONSILAR ABSCESS
–Can extend into deep spaces of neck
–Other organisms can become involved (Fusobacterium
necrophorum) Anaerobe resistant to azithromycin. Leads to septic thrombosis of jugular vein and septic pulmonary emboli to lungs causing lung abscess
–Require surgical drainage of neck abscess
NECROTISING FASCIiTIS
–Bacteremic spread to site of blunt trauma. Infection spreads along fascial planes killing tissue above fascia. Skin becomes necrotic with large bullae (blisters). May also be complication of chickenpox (varicella zoster virus infection with vesicular (small fluid blisters) skin rash)
–High mortality rate. Requires surgical debridement

Question 14

Cat Bites?

Answer 14

Pasturella multicida

Question 15

Dog bites?

Answer 15

Capnocytophaga canimorsis

Question 16

Salt water?

Answer 16

Vibrio vulnificus

Question 17

Fresh water?

Answer 17

Aeromonas hydrophila

Question 18

Hot tubs, nuetropenic pts, burns, wet/chronic ulcers?

Answer 18

Pseudomonas aeruginosa

Question 19

Workers with domestic animals?

Answer 19

Erysipelothrix rhusiopathiae

Question 20

Immuniocompromised?

Answer 20

Cryptococcus neoformans

Question 21

What are the morpholgical features of S. Aureus?

Answer 21

–Gram positive coccus that grows in clusters in liquid
media
–Yellow colored (aureus) colonies
–Catalase positive
–Coagulase positive
-Variety of toxins giving rise to other clinical syndromes
•Heat stabile toxin causing food poisoning
•Toxic shock syndrome toxin-1 (TSST-1) causing toxic shock
syndrome
•Exfoliating toxin causing scalded skin syndrome in neonates

Question 22

What can we use to treat MRSA?

Answer 22

No beta lactams, must use Vancomycin, but not great at treating S. aureus, Linozolid has use that is being evaluated, expensive and causes thrombocytopenia

Question 23

What is Diarrhea?

Answer 23

– Excretion of more than 200 grams of stool / 24 hours with increased loss of water and electrolytes.
– 3 or more loose or watery stools per day.
– Either due to increased water excretion or decreased
water absorption.
– Acute diarrhea lasts less than 14 days and includes most infectious causes.
– Chronic diarrhea lasts more than 14 days and includes infectious and non infectious causes.

Question 24

Which serotypes of Vibrio cholera are the infectious ones, what makes them infectious?

Answer 24

– Caused by serotypes O1 and O139
– Curved gram negative rod grown on selective media in the lab
– Infectious dose 104 to 1011 depending on stomach acidity, presence of food bolus.
– Attachment and colonization of small bowel epithelium
• Cholera enterotoxin produces persistent activation of adenylate cyclase.
• Increased cAMP levels results in increased chloride excretion and decreased sodium absorption and massive fluid loss.

Question 25

What is the most common cause of travelers diahrrea?

Answer 25

Enterotoxigenic E. coli

Question 26

Finegoldia magna (formerly Peptostreptococcus )

Answer 26

– Important gram positive anaerobic coccus in respiratory and intra-abdominal and pelvic infection, complicated skin and soft tissue infection

Question 27

How do you explain C. perfiringes pathogenesis

Answer 27

• Alpha toxin has sphyngomyelinase and phospholipase C activity. (a cytolysin)
• Introduction of spores into deep tissue at time of injury
• If devitalized, anaerobic environment promotes growth of organism and myonecrosis or gas gangrene occurs within 24 to 36 hours
• White cells are absent from infected tissue
• Shock is secondary to effects of alpha and theta toxins – Decreased cardiac output- alpha toxin
– Decreased systemic vascular resistance- theta toxin