Enterobacteriaceae Part 2 Flashcards by Maddie Wilson

Role of E. coli in intestinal NF

aids in digestion and competes w/ other bacteria via bacteriocins

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Bacteriocins function

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E. coli modes of transmission (3)

Endogenous (opportunistic)
Fecal-oral route
Person to person

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

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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ETEC enterotoxins mechanism

Secreted by ETEC

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

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

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

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

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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Dysentery results in:

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

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

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Specific tests for O157:H7 and rxns

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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MUG assay key points

Testing for beta glucouronidase

Observing for fluorescence

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O157:H7 virulence factors:

Type III secretion system

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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O157:H7 virulence factors:

Shiga-like toxin

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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O157:H7 virulence factors:

Enterotoxins

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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O157:H7 virulence factors:

Hemolysin

Inserts into plasma membrane and causes cytoplasmic leakage

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Key ID characteristics of E. coli

Indole (+)

Citrate (-)

Motility (+)

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Key ID characteristics of Enterobacter

Moderate mucoid

Indole (-)

Ornithine (+)

Citrate (+)

Motility (+)

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Key ID characteristics of C. freundii

Citrate (+)

Indole (-)

Ornithine (-)

H2S (+)

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Key ID characteristics of C. koseri

Citrate (+)

Indole (+)

Ornithine (+)

H2S (-)

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Key ID characteristics of K. pneumo

very mucoid

Indole (-)*

Citrate (+)

Ornithine (-)

Motility (-)

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Key ID characteristics of K. oxytoca

very mucoid

Indole (+)*

Citrate (+)

Ornithine (-)

Motility (-)

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Key ID characteristics of Serratia spp.

Delayed lactose (+)

DNase (+)

Indole (-)

Citrate (+)

Ornithine (+)

~20% produce red pigment

LF trends (4)

Most are indole (-) EXCEPT E. coli, K. oxytoca, C. koseri
Most are ornithine (+) EXCEPT Klebsiella and C. freundii
All citrate (+) EXCEPT E. coli
All motility (-) EXCEPT E. coli and Enterobacter

Media for stool/GI samples: BAP

can be useful to ID low NF counts

Media for stool/GI samples: MAC

selective for GNRs; differential for LF/NLF

Media for stool/GI samples: SMAC

rules out O157:H7 | ??more??

Media for stool/GI samples: HEA

ID of Salmonella/Shigella

Media for stool/GI samples: CAMPY

ID of C. jejuni

Media for stool/GI samples: EMB

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

3 colony types on EMB

Coli-type Aerogenes type NLF

Features of Coli-type colonies on EMB

- 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

Features of Aerogenes type colonies on EMB

- less dark than coli-type colonies | - dark center surrounded by wide, light-colored mucoid rim —> FISH EYE

NLF colonies on EMB

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

Media for stool/GI samples: chromagar O157:H7

What orgs form coli-type colonies on EMB?

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

What orgs form Aerogenes type colonies on EMB?

MR NEGATIVE LFs including most strains of Klebsiella and Enterobacter

Key ID characteristics of Proteus

fishy odor PAD (+) H2S (+) Urease (+) Motility (+) (strong pos) P. vulgaris indole (+) ornithine (-) P. mirabilis indole (-) ornithine (+)

Key ID characteristics of Morganella

PAD (+) Urease (+) Ornithine (+) Citrate (-)

Key ID characteristics of Providencia

PAD (+) Ornithine (-) Citrate (+)

Key ID characteristics of Salmonella

H2S (+) Citrate (+) (most of the time) Ornithine (+) Motility (+) Urease (-)

Key ID characteristics of Shigella

EVERYTHING NEGATIVE EXCEPT: S. sonnei —> ONPG (+) and Ornithine (+) For the most part biochemically inert

Key ID characteristics of Yersinia

Motile (+) at 25C; nonmotile at 36C CIN agar (+) Urease (+) GS: safety pin; strong bipolar staining

Confluent vs. swarming growth

Confluent —> growth across entire plate; completely covered Swarming —> moving; can see edges

Two types of infection caused by Salmonella enterica

1. Gastroenteritis | 2. Typhoid fever

Gastroenteritis (symptoms, acquired from, sources)

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

Typhoid fever (symptoms, acquired from)

SYMPTOMS: septicemia, prolonged fever, gastroenteritis —> often fatal via intestinal hemorrhage or perforation, kidney failure, peritonitis ACQUIRED FROM: humans are ONLY source

Mary Mallon

Early 1900s Private cook; asymptomatic carrier of typhoid —> TYPHOID MARY Caused outbreaks in at least 7 fams Quarantined for a long time

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

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)

S. sonnei

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

S. dysenteriae

AKA group A Most severe form of dysentery Severe ulceration of bowel *EXOTOXIN: shiga-toxin —> results in destruction of epithelial cells

Y. enterocolitica causes ______

Y. pestis causes ______

Selenite broth use/purpose

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

Selenite broth: Ingredients

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

Selenite broth: Procedure

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

CIN agar stands for

Cefsulodin-Irgasan-Novobiocin