Gram Positive Bacteria

Question 1

leading pathogens in humans that cause ~1/3 of bacterial infections

Answer 1

cocci

Question 2

staphylococcus characteristics

Answer 2

• 40+ species
• gram-positive cocci
• catalase-positive*
• non-spore forming
• non-motile
• most are encapsulated*

Question 3

staphylococcus aureus

Answer 3

• normal flora of skin and mucous membrane
• coagulase-positive
• most infections are mild: impetigo, folliculitis, furuncle (boil)
• severe infections: deep trauma, surgical wounds, medical devices
• produce a variety of enzymes and toxins (exfoliation toxin, enterotoxins- super antigen)
• associated ocular conditions: bacterial keratitis, hordeolum, preseptal cellulitis

Question 4

most common cause of bacterial keratitis in North America

Answer 4

staphylococcus aureus

Question 5

methicillin-resistant staphylococcus aureus

Answer 5

• resistant to beta-lactam antibiotics
• community-acquired and hospital-acquired strains
• risk groups: immunocompromised, hospitalized, nursing homes, high-density living
• treatment with vancomycin

Question 6

coagulase-negative staphylococci

Answer 6

• staphylococcus epidermidis

- staphylococcus saprophyticus

Question 7

staphylococcus epidermidis

Answer 7

• normal flora of skin (including eyelid margin and conjunctiva)
• associated with infections of medical devices (biofilm)
• associated with several ocular infections, including hordeolum

Question 8

staphylococcus saprophyticus

Answer 8

• normal flora of GI tract
• associated with 20% of urinary tract infections
• tissue tropism

Question 9

hordeolum

Answer 9

• infected gland: internal or external
• causative organisms: staph aureus, staph epidermidis
• treat with oral antibiotics

Question 10

streptococcus

Answer 10

• gram-positive cocci
• catalase-negative*
• non-spore forming
• non-motile
• alpha- and beta-hemolytic groups
• most are non-pathogenic

Question 11

streptococcus pneumoniae

Answer 11

• alpha-hemolytic (partial breakdown of RBCs)
• commensal organism in the oropharynx*
• preceding insult
• causes pyogenic infections* (pneumonia, otitis media, sinusitis, meningitis)
• associated with endophthalmitis (rare)

Question 12

streptococcus pyogenes

Answer 12

• group A streptococcus (GAS)
• > 120 serotypes
• beta-hemolytic (produces enzyme that completely breaks down RBCs)
• frequent human pathogen (not commensal)
• streptococcal pharyngitis, impetigo

Question 13

scarlet fever

Answer 13

• specific strain of strep pyogenes
• erythrogenic toxin
• punctate red rash
• pharyngitis
• uveitis

Question 14

rheumatic fever

Answer 14

• 2-3 weeks post-strep infection (usually after multiple infections)
• molecular mimicry
• targets: joints (polyarthritis), heart (carditis), skin (subcutaneous nodules)
• treated with oral antibiotics

Question 15

poststreptococcal glomerulonephritis

Answer 15

• strep throat, scarlet fever, or impetigo initially
• immune complexes
• proteinuria
• hematuria

Question 16

Viridians group streptococci

Answer 16

• non-pyogenic strep
• alpha-hemolytic
• normal oral flora
• associated diseases: dental carries, endocarditis

Question 17

preseptal cellulitis

Answer 17

• in front of orbital septum
• swollen eyelid
• may be painful to touch
• afebrile (not feverish)
• normal VA and EOMs*
• causative organisms: staph aureus, strep pneumoniae, strep pyogenes
• treat with oral antibiotics

Question 18

Enterococcus faecalis and faecium

Answer 18

• gram-postive
• catalase-negative
• GI commensals
• gamma-hemolytic (non-hemolytic)
• associated illnesses: UTI (catheters), bacteremia, bacterial endocarditis, meningitis
• very resistant to antibiotics

Question 19

bacillus

Answer 19

• spore-forming rods*
• catalase-positive
• soil dwelling

Question 20

Bacillus cereus

Answer 20

• food poisoning (enterotoxin)

- “fried rice” syndrome (cereulide toxin)

Question 21

Bacillus anthracis

Answer 21

• common in sheep, cows, etc.
• anthrax toxin: protective antigen, lethal factor, edema factor
• diseases: cutaneous (95% of cases), gastrointestinal (50% fatal w/o tx), pulmonary (90% fatal w/o tx)

Question 22

Corynebacterium diphtheriae

Answer 22

• pleomorphic
• spread through respiratory droplets and oral secretions
• diphtheria toxin
• diphtheria: fever, lymphadenopathy, respiratory distress, pseudomembrane
• vaccine available

Question 23

Actinomyces israelli

Answer 23

• filamentous bacteria*
• part of normal oral cavity flora
• actinomycosis (rare): most commonly inoculated through dental procedures, forms large abscesses w/ granulomas
• most common cause of canaliculitis
• very treatable with antibiotics

Question 24

Mycobacterium tuberculosis

Answer 24

• acid-fast bacilli
• lipid-dense cell wall (mycolic acid)
• transmitted via respiratory droplets
• slow doubling time- intracellular reproduction
• predisposing factors: poverty, HIV infection, immunosuppression

Question 25

Tuberculosis

Answer 25

• cell-mediated immunity
• granulomas and caseation
• classic symptoms: chronic cough, fever, night sweats, weight loss, hemoptysis
• treatment with antibiotics

Question 26

Mycobacterium leprae

Answer 26

• obligate intracellular bacillus*
• acid fast
• lipid-dense cell wall
• transmission is unclear
• leprosy: affects skin and nerves in the hands and feet; diffuse thickening, loss of sensation, muscle weakness, loss of blinking reflex
• treated with antibiotics