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Microbiology Part 1 > Lec15 Anaerobes and Gram + Bacilli > Flashcards

Lec15 Anaerobes and Gram + Bacilli Flashcards

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1
Q

What are some general characteristics of anaerobes?

A
  • often normal human commensals
  • cause disease when in high levels or introduced to sterile site
  • form abscesses
  • their toxins can cause tissue destruction
  • metabolism leads to gas production
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2
Q

How do you treat anaerobic infections?

A
  • penicillin [amoxi, ampi, piper, ticar]
  • combo of penicillin and beta lactamase inhibitor [for serious intestinal infection]
  • 2nd gen cephalosporins
  • carbapenems [imi, erta, mero]

not as highlighted:
metronidazole
clindamycin
oral vancomycin

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3
Q

What is metronidazole? mech of action?

A
  • interrupts electron transport chain in bacteria

- generates toxic metabolites that cause DNA fragmentation

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4
Q

Where does clindamycin act on bacteria?

A

protein synthesis inhibitor at translocation step

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5
Q

What are micro characteristics of clostridium difficile?

A
  • gram positive
  • anaerobic
  • spore forming
  • bacillus
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6
Q

What is pathogenesis of c. difficile?

A
  • can colonize colon of asymptomatic patients at low levels

- pathogenic when normal flora of colon destroyed by systemic antibitiocs

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7
Q

What drugs is c. diff usually resistant to?

A
  • many!

- beta lactams, clindamycin, cephalosporins, fluoroquinolones

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8
Q

How is C. difficile diagnosed?

A
  • by pseudomembranous colitis
  • by EIA toxin assay [enzyme immunoassay] = most often
  • by cytotoxicity assay
  • by PCR
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9
Q

What are the two c diff toxins? functions?

A

toxin A = enterotoxin
- chemotactic for neutrophils

toxin B = cytotoxin

  • disrupts tight cell junctions
  • increases permeability of intestinal wall and causes diarrhea
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10
Q

What is worst case complication associated with C diff?

A
  • toxic megacolon –> massive dilation of colon and septic shock
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11
Q

How is toxic megacolon treated?

A
  • by bowel resection

- if bowel not removed may cause death

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12
Q

What are standard treatments for c difficile?

A
  • metronidazole

- oral vancomycin

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13
Q

What is cause of c difficile relapses? how can you avoid?

A
  • due to spore formation

- avoid by: probiotics, intravenous immune globulin, fecal transplant

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14
Q

What makes strains of c diff hypervirulent?

A

mutation in regulatory gene leads to loss of regulation of toxin production

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15
Q

What are micro properties of clostridium perfringens?

A
  • gram positive rectangular rod [but often decolorizes]
  • double zones of hemolysis on blood culture plate
    = zone of complete hemolysis by theta toxin, wider zone of partial hemolysis by alpha toxin
  • india ink prep to highlight capsule
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16
Q

What makes up the double zone of hemolysis with c. perfringens?

A

zone of complete hemolysis by theta toxin

wider zone of partial hemolysis by alpha toxin

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17
Q

What is function of c. perfringens alpha toxin?

A
  • mediates hemolysis, vascular permiability, tissue destruction
18
Q

What diseases are caused by clostridium perfringens?

A
  • soft tissue infections: cellulitis, fasciitis, suppurative myositis, gas gangrene [myonecrosis]
  • food poisoning
  • necrotizing enteritis
  • bacteremia/septicemia
19
Q

In what circumstance does c. perfringens infect gall bladder?

A
  • often in conjunction with other GI organisms like E coli or klebsiella
20
Q

What is mech of food poisoning from c. perfringens?

A
  • short incubation period [8-24 hrs]
  • abdominal cramps and watery diarrhea
  • usually lasts 24-48 hrs
  • enterotoxin is heat labile but spores can survive at low temp
21
Q

How do you treat c. perfringens?

A

penicillin

22
Q

What is effect of clostridium tetani = tetanus? how is it transmitted?

A
  • produces toxin tetanospasmin that upregulates excitatory synaptic activity, decreases inhibitory
  • -> spastic paralysis
  • classic finding: risus sardonicus = sardonic grin from face muscles being permanently flexed
  • organism can survive in soil as terminal spores, get from rusty nail in soil
23
Q

What is effect of clostridium botulinum?

A
  • has AB toxin that prevents release of acetylcholine at synapse –> flaccid paralysis
  • botulism
24
Q

What causes botulism from clostridium botulinum

A
  • foodborne botulism associated with improperly canned foods
  • infant botulism associated with spore contamination of honey, infant powder milk
  • rarely, wound botulism
  • inhalational botulism [potential bioterrism]
25
Q

What is stridor?

A

high pitched sound made when patient with airway compression inhales

26
Q

What is ludwig’s angina?

A
  • consequence of severe mixed anaerobic infections of pharyngeal space
27
Q

What are micro properties of bacteroides fragilis?

A
  • pleomorphic gram negative rod
  • has polysaccharide capsule
  • has catalase and superoxide dismutase so oxygen tolerance
28
Q

What is the most common anaerobic gram negative to cause disease?

A

bacteroides fragilis

29
Q

What are actinomyces? micro properties?

A
  • gram positive
  • branching filamentous rod
  • molar teeth colonies on agar
  • sulfur granules = colonies of actinomyes
30
Q

Where can you get actinomyces infection?

A

spreads from sterile site like mouth to cerebral, cervicofacial, thoracic, abdominal, pelvic

31
Q

who is at risk for nocardia infection?

A

happens a lot in patients who are immunocompromised

32
Q

mirco properties of nocardia?

A
  • beaded, branching, filament structure
  • gram positive bacili
  • stain with modified acid fast stain
  • stain weakly positive with regular acid fast stain
  • dry colonies
33
Q

Where do you get nocardia infection?

A

lungs

brain

34
Q

How do you treat nocardia?

A

high dose trimethoprim-sulfamethoxazole for months

35
Q

How do you treat actinomyces?

A

treat with penicillin

36
Q

How do actinomyces and nocardia differ?

A

both gram pos branching bacillus

actinomyces: anaerobic only
nocardia: aerobic and anaerobic

actinomyces: does not stain acid fast
nocardia: will stain acid fast

treat:

actinomyces: penicillin
nocardia: trimethoprim-sulfamethoxazole

37
Q

What are properties of myobacterium fortuitum? treat?

A
  • faster growth than myobacterium tuberculosis
  • gram positive beaded bacilli [like nocardia]
  • environmental organism that can contaminate surgical sites
  • treat with surgical debridement, macrolides, and beta lactams
  • usually very resistant to antibiotics
38
Q

What are properties of corynebacterium diphtheriae? diseases?

A
  • gram positive bacillus
  • organisms do not invade
  • produce exotoxin
  • cause tough pharyngeal membrane –> lead to airway constriction and death
  • cardiac and neurotoxicity
39
Q

How do you treat corynebacterium diphtheriae? prevent?

A
  • treat with antitoxin

- prevent with vaccine

40
Q

What is DTaP?

A

toxin based vaccine for:
diphtheria: diphtheria toxin
tetanus: tetanus toxoid
acellular pertussis: pertussis toxin

Microbiology Part 1 (24 decks)

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