Enterobacterales - glucose fermenters

Question 1

Name the clinically significant Enterobacterales (7)

Answer 1

Most common

LF
E. coli
Klebsiella
Citrobacter
Enterobacter

NLF
Proteus
Morganella*
Providencia*
Serratia

Question 2

Name the Enterobacterales that are less common (8)

Answer 2

Citrobacter

Salmonella

Shigella

Yersenia

Cronobacter

Plesiomonas

Providencia rustigianii

Edwardsiella

Question 3

What biochemical test is used to verify MALDI results for Gram negatives?

Answer 3

Oxidase

Enterobacterales are oxidase negative

Question 4

What are 4 characteristics of Enterobacterales?

Answer 4

1. reduce nitrate to nitrate (UTI test-urinalysis)
2. Glucose fermenters (lower the pH)
3. Oxidase negative
4. Grow on MAC
5. Exception of oxidase positve: Plesiomonas shigelloides, Franconibacter, and Siccibacter

Question 5

pH indicator of MAC plate?

Answer 5

Neutral red

pH 4 = red

pH 9 = yellow

Question 6

pH indicator of glucose slant?

Answer 6

Phenol red

pH 4 = yellow

pH 9 = red

Question 7

Name 3 Enterobacterales that ferment lactose

Answer 7

E. coli
Klebsiell pneumoniae
Citrobacter freundii

Question 8

Name 4 Enterobacterales that DO NOT ferment lactose

Answer 8

Salmonella
Shigella
Proteus
Serratia

Question 9

E. coli

Answer 9

Oxidase negative

Strong lactose fermentation

motile

Indole +

Question 10

Can MALDI distinguish E. coli from Shigella?

Answer 10

NOPE

Can perform indole and motility tests

E. coli positive for both

Shigella negative for both

Question 11

Name 7 diseases associated with E. coli

Answer 11

1) Urinary tract infection
2) Gastrointestinal disease - Shiga toxin may have complications (HUS)
3) Skin and surgical site infections
4) Ventilator associated Pneumonia - #3 organism
5) Line infections
6) Sepsis (dysregulation of host response)
7) Neonatal meningitis (#2, first is GBS) transmitted vertically

Question 12

Uncomplicated cystitis

Answer 12

bladder infection only

pain during urination, pelvic discomfort, blood may be present

Question 13

Complicated cystitis

Answer 13

Bladder infection with concern for disseminated infection

Fever, chills, flank pain, plus cystitis symptoms

Question 14

pyelonephritis

Answer 14

Infections of the kidneys

Nausea, vomiting, Fever, chills, flank pain, plus cystitis symptoms

Question 15

How are UTIs diagnosed?

Answer 15

1) dipstick (nitrate reduced to nitrites) (false negatives become some UTI organisms don’t reduce nitrate)
name them

2) WBC in urine observed under microscope

3) Quantitative culture on MAC (loop used depends on specimen source)

1uL loop = 1 colony = 1000 CFU
10uL loop = 1 colony = 100 CFU

Question 16

How are GI diseases caused by E. coli transmitted and treated?

Answer 16

Contaminated food or water

Diarrhea, vomiting, fatigue, loss of appetite

Antibiotics are NOT administered to prevent toxin release
(this can lead to Hemolytic Uremic Syndrome)

Question 17

It’s important to identify which E. coli strain to prevent Hemolytic Uremic Syndrome?

And how it is detected?

Answer 17

EHEC because it produces Shiga toxin

Identification can be done based on lack of sorbitol fermentation on MAC plates

Detected Shiga toxin in stool by Enzyme immunoassays (EIA) after bacteria is grown in Vero cells (THIS IS NOT DONE IN THE LAB)

Question 18

Key characteristics of Klebsiella pneumoniae

Answer 18

Large mucoid colinies

Lactose fermenter

Indole negative

Oxidase negative

Intrinsically resistant to ampicillin

Question 19

Klebsiella oxytoca

Answer 19

indole positive

Question 20

Klebsiella aerogenes

Answer 20

Lactose fermenter
Indole negative
Oxidase negative

Intrinsic resistance to:
ampicillin + sulbactam
1st gen cephalosporin (cefazolin)
and 3rd gen cephalosporins
AmpC beta Lactamase

Question 21

Rare Klebsiella species (2)

Answer 21

K. rhinoscleromatis - granulomatous (phagocytes don’t function properly) disease of the respiratory tract. Found in tropical regions. Only diagnosed by pathology

K. granulomatis (sexually transmitted genital ulcers) found in tropical regions