Enterobacteriaceae

Question 1

What are 4 major characteristics of all bacteria in the family Enterobacteriaceae?

Answer 1

1. negative Gram stain (thin peptidoglycan, hide their cell wall by outer membrane with LPS)
2. rods
3. catalase positive
4. oxidase negative

Question 2

What are the major 2 groups of Enterobacteriaceae? What bacteria are found in each group?

Answer 2

1. LACTOSE FERMENTERS (coliform)
   - Citrobacter
   - E. coli
   - Enterobacter
   - Klebsiella
2. LACTOSE NON-FERMENTERS (pathogenic)
   - Salmonella
   - Proteus
   - Yersinia
   - SHigella

Question 3

How do the members of the CEEK and SPY-Sh compare in lactose fermentation, gas production, and urease tests?

Answer 3

LACTOSE FERMENTATION
- positive = pink on MacConkey = CEEK
- negative = yellow on MacConkey = SPY-Sh

GAS
- CO2 = yellow on TSI = EK
- H2S = black on TSI = CPS
- no gas = red = Y

UREASE
- positive = pink = CKPY
- negative = yellow = ES

Question 4

What respiration do all Enterobacteriaceae undergo? How do they grow?

Answer 4

facultative anaerobe

non-fastidious and non-spore-forming on bile containing media - MacConkey agar

Question 5

Almost all Enterobacteriaceae are motile. What are 2 exceptions?

Answer 5

1. Klebsiella
2. Shigella

lack flagella

Question 6

What is the primary habitat for Enterobacteriaceae? Where else can they be found?

Answer 6

small and large intestine (commensal of digestive tract)

• GI tract
• mammary glands
• urogenital tract
• respiratory tract
• environment

Question 7

How are Enterobacteriaceae transmitted? How do they enter and leave hosts? What is one exception?

Answer 7

oral-fecal transmission

ENTRY: oral route by ingestion of contaminated food/feed and water
EXIt: feces, urine, milk, nasal discharge

Y. pestis enters host via flea bites

Question 8

What are the 5 main opportunistic diseases caused by Enterobacteriaceae?

Answer 8

1. diarrhea
2. urinary tract infection
3. septicemia
4. pneumonia
5. meningitis

Question 9

What are the 6 main impacts of Enterobacteriaceae?

Answer 9

1. major cause of GI infection (diarrhea, dehydration)
2. major cause of liver abscesses
3. cause 70% of UTIs
4. cause 33% of bacteremia and septicemia
5. major cause of meningitis
6. major cause of mastitis originating from the environment (Proteus and coliforms)

Question 10

What is the main way that hosts die due to Enterobacteriaceae?

Answer 10

diarrhea and dehydration—> acid-base and electrolyte disturbance

Question 11

What are the 3 main surface structures used as virulence factors in Enterobaceriaceae?

Answer 11

1. capsule
2. flagella, fimbriae, adhesins, invesins
3. LPS endotoxin

Question 12

What 5 things does the lipopolysaccharide on the membrane of Enterobacteriacea cause?

Answer 12

1. intestinal adhesion
2. colonization
3. inflammation
4. fever (pyrogenic)
5. blood vessel damage —> ischemic necrosis

Question 13

What are the 2 enzymes used as virulence factors in Enterobacteriaceae? What do they do?

Answer 13

1. catalase
2. superoxide dismutase

detoxify free radicals

Question 14

What 3 toxins and secreted substances act as virulence factors in Enterobacteriaceae?

Answer 14

1. hemolysins - kill host RBC to make iron available for bacteria
2. siderophores/enterobactin - rob iron from host cell
3. pathogenic island that codes for type three secretion systems (T3SS)

Question 15

What are type three secretion systems (T3SS)? In what bacteria are they characteristic?

Answer 15

syringe-like apparatus on the cell wall that can inject bacterial enzymes, toxins, and cytokine inhibitors into host cells

G- ; G+ bacteria lack these

Question 16

What 3 parts of Enterobacteriaceae contribute to their antigenic diversity?

Answer 16

• somatic LPS (O) antigens
• flagella (H) antigens
• capsular (K) antigens

Question 17

What part of LPS acts as an endotoxin? What does it do? Which part of LPS is variable?

Answer 17

lipid A
- destroy blood vessels
- induce fever (pyrogen)

O antigen

Question 18

What 4 culture media can be used for isolation, differentiation, and growth of Enterobacteriaceae?

Answer 18

1. blood agar
2. MacConkey agar - most G+ bacteria cannot grow on this media since it has bile salt and crystal violet on it, except Enterococcus)
3. eosin-methylene blue (EMB) agar
4. triple sugar iron (TSI) agar

Question 19

Why is Enterobacteriaceae such a global threat?

Answer 19

contributes 3 genera to AMR (ESKAPE)
- carbapenem resistant