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USMLE Step 1 > Microbiology - Gram Negative & Spirochetes > Flashcards

Microbiology - Gram Negative & Spirochetes Flashcards

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1
Q

Penicillin and gram negative bugs

A
  • Most are resistant to Penicillin G
  • but can be susceptible to penicillin derivatives (e.g. amoxicillin and ampicillin)
  • Gram negative outer membrane layer inhibits entry of penicillin G
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2
Q

Neisseria

A

Gram - diplocci
Both ferment glucose
Produce IgA proteases

N. MeningoCocci - ferments Maltose and Glucose

N. Gonorrohae - ferments only Glucose

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3
Q

N. Gonorroeae

A
  • no polysaccharide capsule
  • no maltose fermentation
  • no vaccine (due to rapid antigenic variation of pilus proteins)
  • sexually transmitted
  • causes gonorrhoae, septic arthritis, neo natal conjunctivis, PD, and Fitz-Hugh-Curtis syndrome (infecting liver capsule_
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4
Q

Treatment of N. Gonorrhoeae

A
  • Ceftriaxone + (Azithromycin or Doxycycline) for possible chlamydiae coinfection
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5
Q

N. Meningiditis

A
  • Polysaccharide capsule
  • Maltose and Glucose fermentation
  • Vaccine (none for type B)
  • Transmitted via respiratory and oral secretions
  • Causes meningococcemia, meningitis, and Waterhouse-Friedrichsen syndrome
  • Associated with dorms or military
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6
Q

Treatment for Meningiditis

A
  • Ceftriazone or Peniillin G

Prophylaxis: Rifampin, Ciprofloxacin, or Ceftriaxone in close contacts

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7
Q

H. influenzae

A

Gram - bacilli

  • causes Epiglottis (“cherry red” in children)
  • MOPS (Menigitis, Otitis Media, Pneumonia)
  • Aerosol transmission
  • produces IgA protease
  • most invasive disease caused by capsular type B
  • DOES NOT CAUSE FLU
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8
Q

Vaccine for H. influenzae

A
  • contains type B capsular polysaccharide (polyribosylribitol phosphate) conjugated to diptheria toxoid or protein
  • Given between 2 and 18 months of age
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9
Q

Treatment for H. influenzae

A

Ceftriaxone, Rifampin prophylaxis in close contacts

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10
Q

Most common cause of septic arthritis in sexually active young people

A

N. gonorrhoeae

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11
Q

Routes of infection: H. influenzae

A

Pharynx –> lymphatics –> Meninges

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12
Q

Culture for H. influenzae

A

Chocolate with factors V (NAD+) and X (hematin)

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13
Q

Legionella pneumophila

A

Aerobic gram - rod
- poor Gram stain, use silver stain
intracellular pathogen that grows in macrophages
-requres charcoal yeast extract with iron and cysteine
- common cause of pneumonaie in elderly

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14
Q

Legionnaire’s disease

A
  • caused by Legionella pneumoniae

- severe ATYPICAL pneumoniae, fever, GI, and CNS symptoms

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15
Q

Pontiac fever

A
  • caused by Legionella pneumoniae

- mild - flu like sunrome

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16
Q

Labs for Legionella pneumoniae

A
  • Detected clinically by presence of antigen in urine

- Patients present with HYPOnatremia

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17
Q

Pseudomonas aeruginosa

A

Aerobic gram - rod
associated with wound and burn infections
Non-lactose fermenting, oxidase positive
Produces pyocyanin (blue green) pigment
has grape-like odor
Produces endotoxin (fever, shock) and exotoxin A (inactivates EF-2)

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18
Q

Transmission of L. pneumoniae

A

Aerosol transmission
Usually from environmental water source habitat (e.g. air conditioning)
NO PERSON to PERSON TRANSMISSION

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19
Q

Clinical findings of P. aeruginosa

A 
PSEUDOS
Pneumonia (esp. in cystic fibrosis)
Sepsis (black lesions in skin)
External otitis media
UTI
Drug Use and Diabetic Osteomyelitis
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20
Q

Treatment of P. aeriuginiosa

A

Aminoglycoside plus

extended-spectrum penicillin (e.g. piperacillin, ticarcillin)

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21
Q

E. coli

A 
Gram - Bacilli, Lactose fermenter
Virulence factors:
Fimbriae - cystitis and pyelonephritis
K capsule - pneumonia, neonatal meningitis
LPS endotoxin - septic shock
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22
Q

EIEC: Mechanism

A

Microbe invades intestinal mucosa and causes necrosis and inflammation.

Clinical manifestations: similar to Shigella

23
Q

EIEC: Presentation

A

INVASIVE; dystentary

24
Q

ETEC

A

Mechanism: Labile toxin/stabile toxin.
No inflammation or invasion

Presentation: Traveler’s diarrhea (watery)

25
Q

EPEC

A

Mechanism: No toxin produced. Adheres to apical surface, flattens villi absorption

Presentation: Diarrhea usually in children (Pediatrics)

26
Q

EHEC: Mechanism:

A

O157:H7 is most common serotype. Produces Shiga-like toxin and Hemolytic-uremic syndrome (triad of anemia, thrombocyteopenia, and ARF)

Endothelium swells and narrows lumen, leading to mechanical hemolysis and reduced renal blood flow; damaged endothelium consumes platelets

27
Q

EHEC: Presentation

A

Dysentery (toxin alone causes necrosis and inflammation)

Does not ferment sorbitol (distinguishes it from other E. coli)

28
Q

Klebsiella

A

Gram - bacilli
Lactose fermenter
Intestinal flora causing lobar pneumonia in alcoholics and diabetics when aspirated
Very mucoid colonies caused by abundant polysaccharide capsule.
Red “currant jelly” sputum
- Causes nosocomial UTIs

29
Q

Klebsiella (4 A’s)

A

Aspiration pneumonia
Abscess in lungs and liver
Alcoholics
di-Abetics

30
Q

Salmonella

A
  • Gram negative bacilli, Lactose non-fermenter
  • Large inoculum
  • Have flagella
  • Can disseminate hematogenously
  • Produces H2S
  • Abx may prolong symptoms
    Invades intestinal mucosa and causes MONOCYTIC response
  • Cause bloody diarrhea
31
Q

Shigella

A

Gram - bacilli, Lactose non-fermenter
Cell to cell transmission; no hematogenous
Only reservoirs are humans and primates
Doesn’t produce hydrogen sulfide
Abx shorten excretion of organism in feces
Invades intestinal mucosa and causes PMN infiltration

32
Q

Salmonella typhi

A
  • caues typhoid fever
  • found only in humans
  • characterized by rose spots on the abdomen, fever, diarrhea, headache
  • Can remain in remain gall bladder and cause a carrier

Tx: ceftriaxone

33
Q

Campylobacter jejuni

A

Gram - bacillil, S or comma shaped
major cause of bloody diarrhea, especially in children.
Fecal-oral transmission in poultry, meat, unpasteurized milk
- common antecedent of Guillain-Barre syndrome and reactive arthritis

34
Q

Vibrio cholerae

A 
Gram - bacilli, Oxidase +
Comma shaped, oxidase positive
Grows in alkaline media
Ferments glucose
Produces produce rice-water diarrhea via toxin that permanently activates Gs thus increases cGMP
Tx: Prompt oral rehydration
35
Q

Yersinia enterocolitica

A

Gram negative bacilli (Anaerobe)
- usually transmitted through pet feces (e.g. puppies), contaminated milk or pork
Causes mesenteric adenitis that can mimic Crohn’s or appendicits

36
Q

H. pylori

A

Curved gram negative rod, Urease +
causes gastritis and up to 90% of duodenal ulcers

  • Increases risk of peptic ulcer, gastric adenocarcinoma, and lymphoma.
  • Creates alkaline environment.
  • Most common initial treatment is “triple therapy” (PPI, clarithromycin, amoxicillin)
37
Q

Treatment for H. pylori

A

TRIPLE THERAPY

PPI. Clarithromycin, Amoxicillin, and/04 Metronidazole

38
Q

Spirochetes

A

spiral shaped bacteria with axial filaments and include BLT (Boriella, Leptospira, Treponemia)

39
Q

Visualizing Borellae

A

Use aniline dyes (Wright’s or Giemsa) stain in light microscopy

40
Q

Visualizing Treponema

A

Visualized by dark field microscopy

41
Q

Leptospira interrogans

A

found in waer contaminated with animal urine

  • causes leptospirosis: flu-like symptoms, jaundice, photophobia with conjunctiviis
  • common among surfers and in tropics (e.g. Hawaii)
42
Q

Weil’s disease

A

ictohemorrhagic leptospirosis

  • severe form with jaundice and azotemia from liver and kidney dysfunction
  • fever, hemorrhage, and anemia
43
Q

Lyme disease

A
  • caused by Borrelia burgdoferi, transmitted by tick Ixodes .(also vector for Babesia)
  • natural reservoir is mouse
  • common in Northeastern United States
44
Q

Treatment of Lyme disease

A

Doxycycline, Ceftriaxone

45
Q

3 stages of Lyme disease

A

Stage1 - erythema chornicum migrans (expanding “bulls-eye” red rash with central clearing, flu-like symptoms

Stage 2 - neurological (facial nerve palsy) and cardiac (AV nodal block) manifestations

Stage 3 - musculoskeletal (chronic monoarthritis and migratory polyarthritis), neurological (encephalopathy and polyneuropathy), and cutaneous manifestations

46
Q

Syphillis

A
  • caused by Treponema pallidum (spirochete)
47
Q

Primary Syphillis

A

Localized disease presenting with painless chancre

- Screen with VDRL and confirm diagnosis with FTA-ABS

48
Q

Secondary syphillis

A

Disseminated disease with constitutional symptoms, maculopapular rash (palms and soles), condylomata lata

Treponema present in chancres of primary and condylomata of secondary syphillis and may be visualized by dark field microscopy

49
Q

Tertiary syphillis

A

Gummas (chronic granulomas, painless indurated lesion)
Aortitis (vasa vasorum destruction)
Neurosyphillis (tabes dorsalis) - may find pleocytosis (WBC) in lumbar puncture
Argyll Robertson pupil

50
Q

Signs of Tertiary syphillis

A 
Broad-based ataxia
Positive Romberg test
Charcot joint (loss of sensation in joint)
Stroke without hypertension
**Test spinal fluid with VDRL**
51
Q

Congenital syphillis

A

Saber shins
Saddle nose
CN VIII deafness
Hutchinson’s teeth, mulberry molars

Early prevention is key, as placental transmission typically occurs after trimester

52
Q

VDRL false positive

A

VRDL detects nonspecific antibody that react with beef cardiolipin

  • False positives seen in mononucleosis, hepatitis, some drugs, rheumatic fever, SLE, and leprosy
53
Q

Jarisch-Herxheimer reaction

A

Flu-like symptoms immediately after antibiotics are started - due to killed bacteria release pyrogens

54
Q

VDRL false positive mneumonic

A 
("VDRL")
V-iruses (mono, hepatitis)
D-rugs
R-heumatic fever
L-upus and leprosy

USMLE Step 1 (34 decks)

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