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Clin Micro 1 > Enterobacteriaceae Part 2 > Flashcards

Enterobacteriaceae Part 2 Flashcards

1
Q

Role of E. coli in intestinal NF

A

aids in digestion and competes w/ other bacteria via bacteriocins

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2
Q

Bacteriocins function

A
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3
Q

E. coli modes of transmission (3)

A
  1. Endogenous (opportunistic)
  2. Fecal-oral route
  3. Person to person
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4
Q

Enterotoxigenic (ETEC) key points (where, due to, resulting illness, symptoms, virulence factors)

A

Found in: tropics and subtropical climates
Due to: lack of sanitation; contaminated food and water
Causes: travelers diarrhea
Symptoms: watery diarrhea - self limiting in 1-5 days
Virulence factors: fimbriae, enterotoxins

*self limiting in 1-5 days

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5
Q

ETEC enterotoxins mechanism

A

Secreted by ETEC

Cause GI cells to undergo hypersecretion - fluids and electrolytes pumped out of GI cells

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6
Q

Enteroaggregative (EAEC) key points (characteristics, symptoms, virulence factors)

A

found packed in aggregates in between intestinal cells (appearance of stacked bricks)

Symptoms: watery diarrhea
Virulence factors: enterotoxins

Similar to ETEC but lasts longer; sometimes >2 weeks

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7
Q

Enteropathogenic (EPEC) key points (where, illness caused, virulence factors, symptoms)

A

Found in: underdeveloped countries
Causes: infantile diarrhea (esp severe in >1 year; mortality rate of 50% in prolonged cases)
Virulence factors: enterotoxins that may last 1-2 years, attachment and effacing
Symptoms: low grade fever, malaise, vomiting, diarrhea

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8
Q

Enteroinvasive (EIEC) key points (illness caused, virulence factors, symptoms)

A

Causes: dysentery
Virulence factors: invades enterocytes (cells that line the large intestine), enterotoxins; resembles shigella in pathogenic mechanisms
Symptoms: severe abdominal cramps, malaise, watery diarrhea, toxemia

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9
Q

Dysentery results in:

A

Necrosis, ulceration, inflammation of large intestine, results in destruction of intestinal mucosa

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10
Q

Enterohemorrhagic (EHEC) (shiga toxin producing E. coli (STEC) and verotoxigenic E. coli (VTEC))

A
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11
Q

Specific tests for O157:H7 and rxns

A

SMAC (negative/clear colonies)

MUG assay (~97% of O157:H7 MUG negative)

O157:H7 latex agglutination (positive - specific for O157:H7)

Chromagar mauve colonies (other E. coli blue, colorless, or inhibited)

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12
Q

MUG assay key points

A

Testing for beta glucouronidase

Observing for fluorescence

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13
Q

O157:H7 virulence factors:

Type III secretion system

A

Polypeptides assemble into a system that spans the 2 membranes/peptidoglycan of cell —> inserts proteins into host cell (like a needle)

Inhibits phagocytosis

rearranges cytoskeletons of eukaryotic cells

Induces apoptosis

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14
Q

O157:H7 virulence factors:

Shiga-like toxin

A

Inhibits host cells via:
attaching to neutrophils —> neuts spread toxin throughout body and cause widespread death of host cells and tissues

Avoid antimicrobials —> induce increased production of shiga-like toxin; exacerbates disease

Gene comes from ___??

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15
Q

O157:H7 virulence factors:

Enterotoxins

A

Bind to proteins on cells lining of intestinal tract —> portion of toxin enters cell —> triggers diarrhea, cramps, nausea, vomiting

Loss of electrolytes

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16
Q

O157:H7 virulence factors:

Hemolysin

A

Inserts into plasma membrane and causes cytoplasmic leakage

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17
Q

Key ID characteristics of E. coli

A

Indole (+)

Citrate (-)

Motility (+)

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18
Q

Key ID characteristics of Enterobacter

A

Moderate mucoid

Indole (-)

Ornithine (+)

Citrate (+)

Motility (+)

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19
Q

Key ID characteristics of C. freundii

A

Citrate (+)

Indole (-)

Ornithine (-)

H2S (+)

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20
Q

Key ID characteristics of C. koseri

A

Citrate (+)

Indole (+)

Ornithine (+)

H2S (-)

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21
Q

Key ID characteristics of K. pneumo

A

very mucoid

Indole (-)*

Citrate (+)

Ornithine (-)

Motility (-)

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22
Q

Key ID characteristics of K. oxytoca

A

very mucoid

Indole (+)*

Citrate (+)

Ornithine (-)

Motility (-)

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23
Q

Key ID characteristics of Serratia spp.

A

Delayed lactose (+)

DNase (+)

Indole (-)

Citrate (+)

Ornithine (+)

~20% produce red pigment

24
Q

LF trends (4)

A
  1. Most are indole (-) EXCEPT E. coli, K. oxytoca, C. koseri
  2. Most are ornithine (+) EXCEPT Klebsiella and C. freundii
  3. All citrate (+) EXCEPT E. coli
  4. All motility (-) EXCEPT E. coli and Enterobacter
25
Q

Media for stool/GI samples: BAP

A

can be useful to ID low NF counts

26
Q

Media for stool/GI samples: MAC

A

selective for GNRs; differential for LF/NLF

27
Q

Media for stool/GI samples: SMAC

A

rules out O157:H7

??more??

28
Q

Media for stool/GI samples: HEA

A

ID of Salmonella/Shigella

29
Q

Media for stool/GI samples: CAMPY

A

ID of C. jejuni

30
Q

Media for stool/GI samples: EMB

A

selective/differential for GNR; diff LF/NLF

esp. for coliforms from food/water samples

lactose as carb source = acidic = darker colonies

peptones = basic = lighter colonies

Eosin Y + Methylene blue

31
Q

3 colony types on EMB

A

Coli-type

Aerogenes type

NLF

32
Q

Features of Coli-type colonies on EMB

A
  • very dark, almost black when observed directly against light
  • green metallic sheen due to methylene blue ppt —> from high amt of acid prod from LF
33
Q

Features of Aerogenes type colonies on EMB

A
  • less dark than coli-type colonies

- dark center surrounded by wide, light-colored mucoid rim —> FISH EYE

34
Q

NLF colonies on EMB

A

-prod no acids from fermentation —> colorless alkaline rxn (breakdown of peptones)

35
Q

Media for stool/GI samples: chromagar O157:H7

A

-

36
Q

What orgs form coli-type colonies on EMB?

A

MR POSITIVE LFs such as E. coli and some strains of Citrobacter

37
Q

What orgs form Aerogenes type colonies on EMB?

A

MR NEGATIVE LFs including most strains of Klebsiella and Enterobacter

38
Q

Key ID characteristics of Proteus

A

fishy odor

PAD (+)

H2S (+)

Urease (+)

Motility (+) (strong pos)

P. vulgaris indole (+) ornithine (-)

P. mirabilis indole (-) ornithine (+)

39
Q

Key ID characteristics of Morganella

A

PAD (+)

Urease (+)

Ornithine (+)

Citrate (-)

40
Q

Key ID characteristics of Providencia

A

PAD (+)

Ornithine (-)

Citrate (+)

41
Q

Key ID characteristics of Salmonella

A

H2S (+)

Citrate (+) (most of the time)

Ornithine (+)

Motility (+)

Urease (-)

42
Q

Key ID characteristics of Shigella

A

EVERYTHING NEGATIVE EXCEPT:

S. sonnei —> ONPG (+) and Ornithine (+)

For the most part biochemically inert

43
Q

Key ID characteristics of Yersinia

A

Motile (+) at 25C; nonmotile at 36C

CIN agar (+)

Urease (+)

GS: safety pin; strong bipolar staining

44
Q

Confluent vs. swarming growth

A

Confluent —> growth across entire plate; completely covered

Swarming —> moving; can see edges

45
Q

Two types of infection caused by Salmonella enterica

A
  1. Gastroenteritis

2. Typhoid fever

46
Q

Gastroenteritis (symptoms, acquired from, sources)

A

SYMPTOMS: vomiting, fever, diarrhea, abdominal pain
—> spontaneous recovery 2 days to 1 week

ACQUIRED FROM: contaminated food; 8-36 hrs after ingestion

SOURCES: reptiles; feces of chickens, turkeys, cattle

47
Q

Typhoid fever (symptoms, acquired from)

A

SYMPTOMS: septicemia, prolonged fever, gastroenteritis
—> often fatal via intestinal hemorrhage or perforation, kidney failure, peritonitis

ACQUIRED FROM: humans are ONLY source

48
Q

Mary Mallon

A

Early 1900s

Private cook; asymptomatic carrier of typhoid —> TYPHOID MARY

Caused outbreaks in at least 7 fams

Quarantined for a long time

49
Q

Bacillary dysentery (AKA, symptoms, transmission, causative agents)

A

AKA Shigellosis

SYMPTOMS: mild-moderate diarrhea and fever; self-limiting; blood, mucus, pus in stool
—> many leukocytes due to invasion if colon tissues —> causes inflammatory response

TRANSMISSION: fecal-oral

CAUSATIVE AGENTS: S. sonnei (group D) and S. dysenteriae (group A)

50
Q

S. sonnei

A

AKA group D

Most common spp in US

Low infectious dose

Incubation period ~1-3 days

Self limiting 2-3 days with fluid and electrolyte replacement

51
Q

S. dysenteriae

A

AKA group A

Most severe form of dysentery

Severe ulceration of bowel

*EXOTOXIN: shiga-toxin —> results in destruction of epithelial cells

52
Q

Y. enterocolitica causes ______

A
53
Q

Y. pestis causes ______

A
54
Q

Selenite broth use/purpose

A

Enrichment broth used for recovery of low numbers of Salmonella/some strains of Shigella from stool and other specimens containing large amts of mixed bacteria

55
Q

Selenite broth: Ingredients

A

Sodium selenite —> inhibits growth of many GNRs and enterococcus

Lactose/phosphate buffers —> maintain neutral pH (selenite most effective at neutral pH)

*variation: can add cystine to increase recovery of Salmonella

56
Q

Selenite broth: Procedure

A

1-2g of stool inoculated into broth

Incubated at 35-37C

Subcultures to enteric media after 12-18 hrs incubation

*Beyond 12-18 hrs overgrowth of NF is likely bc inhibitory effect of selenite wears off

57
Q

CIN agar stands for

A

Cefsulodin-Irgasan-Novobiocin

Clin Micro 1 (3 decks)

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