Gram Negative Rods

Question 1

McConkeys agar**

Answer 1

• good for enteric organisms***

- also for nonenterics like Yersinia and Pseudomonas

Question 2

lactose fermenters vs. nonfermenters**

Answer 2

Fermenters

• turn purple on McConkeys
  1. Fast –> klebsiella, enterobacter, E. coli
  2. slow –> citrobacter, serratia

Non-fermenters

• turn clear on McConkeys
  1. oxidase + –> pseudomonas*
  2. oxidase - –> salmonella, proteus, shigella, yersinia

Question 3

gram negative rods

Answer 3

• thin peptidoglycan wall surrounded by LPS –> Lipid A endotoxin
• enterobacteriacea family

Question 4

Klebsiella pneumoniae

Answer 4

-pneumonia in alcoholics and diabetics*

• red “jelly” sputum in lungs
• HEMORRHAGIC lungs***

Question 5

E. coli

Answer 5

• fibrimbiae attach to mucosa and can climb mucociliary tract
• most don’t have a capsule
• capsule (K antigen) seen in meningeal strains*** (ex. meningitis in newborns)

Question 6

types of E. coli***

Answer 6

1. enterohemorrhagic (EHEC) –> hemorrhagic/bloody diarrhea
2. enterinvasive (EIEC) –> shigella like dysentery
3. enteropathogenic (EPEC) –> childrens diarrhea
4. enterotoxigenic (ETEC) –> travelers diarrhea (clear)
   - due to inc cAMP/GMP –> inc water secretion

• EHEC and EIEC more invasive –> bloody diarrhea***
• EPEC and ETEC less invasive –> clear diarrhea***

Question 7

EHEC

Answer 7

-E. coli 0157:H7**

• only the toxin causes the illness***
• no invasion of host

-HUS in children***** (hemolytic anemia, thrombocytopenia, renal failure)

Question 8

EIEC

Answer 8

-only the organism kills it with invasion, not the toxin***

Question 9

enterobacter

Answer 9

• nosocomial UTIs

- resistant to antibiotics

Question 10

citrobacter and serratia

Answer 10

citrobacter
-normal gut flora

serratia**

• red colonies (red pigment)**
• nosocomial
• cause osteomyelittis in IV drug users

Question 11

MacConkey lactose fermenters***

Answer 11

1. citrobacter (slow)
2. serratia (slow)
3. klebsiella (rapid)
4. enterobacter (rapid)
5. E. coli (rapid)

Question 12

Pseudomonas aeruginosa

Answer 12

-resistant attitude –> use antipseudomonal drugs

• BE PSEUDO**
• external otitis “swimmers eare”**

-loves water*

• blue-green pigment (pyocyanin)
• flourescent green colonies on culture**
• grape-like odor**

Question 13

salmonella

Answer 13

• flagellated (motile)
• spread bloodstream
• 2 types: typhoid fever and diarrhea
• bloody diarrhea + fecal leukocyte (monocytic response)
• osteomyelitis in sickle cell patients***

Question 14

salmonella typhi (typhoid fever)

Answer 14

-fever, constipation, diarrhea

• Rose spots** (macules on trunk/abdomen)
• Pulse-temp dissociation** (high fever, slow pulse)

Question 15

Shigella

Answer 15

• no flagella (non-motile)
• spread cell to cell
• invades mucosal cells (Peyer’s patch M cells) inducing apoptosis
• very few bacteria can cause disease*
• PMN (neutrophil) response

Question 16

Proteus

Answer 16

• swarming phenotype** –> bulls eye on blood agar
• no individual colonies**

-produces urease** –> alkaline pH with ammonia (protects stomach) –> massive kidney stone (staghorn) from high pH**

Question 17

Helicobacter Pylori

Answer 17

• primary cause of gastritis and peptic ulcers**
• urease +
• urea breath test POS*** - diagnostic

Question 18

Legionella

Answer 18

• flu like pneumonia (rapid progression to severe)
• silver stain (hard to gram stain)
• require special cultures –> Buffered charcoal yeast extract (BCYE)**
• cough/diarrhea/confusion*(low Na)/G. stain neg.

Question 19

Bacteroides fragilis

Answer 19

• obligate anaerobe (GNR) - can’t breath air

- part of polymicrobial GI infections