Microbiology - Gram Negative & Spirochetes Flashcards Preview

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

Flashcards in Microbiology - Gram Negative & Spirochetes Deck (54):
1

Penicillin and gram negative bugs

- 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

2

Neisseria

Gram - diplocci
Both ferment glucose
Produce IgA proteases

N. MeningoCocci - ferments Maltose and Glucose

N. Gonorrohae - ferments only Glucose

3

N. Gonorroeae

- 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_

4

Treatment of N. Gonorrhoeae

- Ceftriaxone + (Azithromycin or Doxycycline) for possible chlamydiae coinfection

5

N. Meningiditis

- 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

6

Treatment for Meningiditis

- Ceftriazone or Peniillin G

Prophylaxis: Rifampin, Ciprofloxacin, or Ceftriaxone in close contacts

7

H. influenzae

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

8

Vaccine for H. influenzae

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

9

Treatment for H. influenzae

Ceftriaxone, Rifampin prophylaxis in close contacts

10

Most common cause of septic arthritis in sexually active young people

N. gonorrhoeae

11

Routes of infection: H. influenzae

Pharynx --> lymphatics --> Meninges

12

Culture for H. influenzae

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

13

Legionella pneumophila

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

14

Legionnaire's disease

- caused by Legionella pneumoniae
- severe ATYPICAL pneumoniae, fever, GI, and CNS symptoms

15

Pontiac fever

- caused by Legionella pneumoniae
- mild - flu like sunrome

16

Labs for Legionella pneumoniae

- Detected clinically by presence of antigen in urine
- Patients present with HYPOnatremia

17

Pseudomonas aeruginosa

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)

18

Transmission of L. pneumoniae

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

19

Clinical findings of P. aeruginosa

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

20

Treatment of P. aeriuginiosa

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

21

E. coli

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

22

EIEC: Mechanism

Microbe invades intestinal mucosa and causes necrosis and inflammation.

Clinical manifestations: similar to Shigella

23

EIEC: Presentation

INVASIVE; dystentary

24

ETEC

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

Presentation: Traveler's diarrhea (watery)

25

EPEC

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

Presentation: Diarrhea usually in children (Pediatrics)

26

EHEC: Mechanism:

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

EHEC: Presentation

Dysentery (toxin alone causes necrosis and inflammation)
Does not ferment sorbitol (distinguishes it from other E. coli)

28

Klebsiella

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

Klebsiella (4 A's)

Aspiration pneumonia
Abscess in lungs and liver
Alcoholics
di-Abetics

30

Salmonella

- 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

Shigella

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

Salmonella typhi

- 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

Campylobacter jejuni

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

Vibrio cholerae

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

Yersinia enterocolitica

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

H. pylori

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

Treatment for H. pylori

TRIPLE THERAPY
PPI. Clarithromycin, Amoxicillin, and/04 Metronidazole

38

Spirochetes

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

39

Visualizing Borellae

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

40

Visualizing Treponema

Visualized by dark field microscopy

41

Leptospira interrogans

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

Weil's disease

ictohemorrhagic leptospirosis
-severe form with jaundice and azotemia from liver and kidney dysfunction
- fever, hemorrhage, and anemia

43

Lyme disease

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

44

Treatment of Lyme disease

Doxycycline, Ceftriaxone

45

3 stages of Lyme disease

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

Syphillis

- caused by Treponema pallidum (spirochete)

47

Primary Syphillis

Localized disease presenting with painless chancre
- Screen with VDRL and confirm diagnosis with FTA-ABS

48

Secondary syphillis

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

Tertiary syphillis

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

50

Signs of Tertiary syphillis

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

51

Congenital syphillis

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

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

52

VDRL false positive

VRDL detects nonspecific antibody that react with beef cardiolipin

- False positives seen in mononucleosis, hepatitis, some drugs, rheumatic fever, SLE, and leprosy

53

Jarisch-Herxheimer reaction

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

54

VDRL false positive mneumonic

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