Gram-Negative Enteric Bacilli (Enterobacteriaceae) – Part A

0.0(0)
studied byStudied by 0 people
learnLearn
examPractice Test
spaced repetitionSpaced Repetition
heart puzzleMatch
flashcardsFlashcards
Card Sorting

1/39

flashcard set

Earn XP

Description and Tags

Vocabulary flashcards covering classification, culture media, biochemical tests, antigenic markers, and virulence factors of Enterobacteriaceae as discussed in the lecture.

Study Analytics
Name
Mastery
Learn
Test
Matching
Spaced

No study sessions yet.

40 Terms

1
New cards

Enterobacteriaceae

A family of Gram-negative, facultative anaerobic rods that ferment glucose, reduce nitrate to nitrite, are oxidase-negative, and inhabit the intestinal tract.

2
New cards

Coliforms

Lactose-fermenting Enterobacteriaceae normally found in the colon; key genera include Escherichia, Klebsiella, and Enterobacter.

3
New cards

Non-lactose fermenters (NLF)

Enterobacteriaceae that do not ferment lactose; divided into invasive pathogens (e.g., Salmonella, Shigella, Yersinia) and opportunists (e.g., Proteus, Providencia, Morganella).

4
New cards

Seven tribes of Enterobacteriaceae

Escherichieae, Edwardsiellae, Salmonelleae, Citrobacteriaceae, Klebsielleae, Proteae, and Yersiniae.

5
New cards

Gram-negative bacilli (GNB)

Rod-shaped bacteria with a thin peptidoglycan layer and outer membrane, staining pink on Gram stain.

6
New cards

Facultative anaerobe

An organism that grows with or without oxygen, switching metabolic pathways accordingly.

7
New cards

Peritrichous flagella

Flagella distributed over the entire bacterial surface, providing motility to most Enterobacteriaceae.

8
New cards

SKY organisms

The three non-motile Enterobacteriaceae: Shigella, Klebsiella, Yersinia.

9
New cards

EK organisms

The two encapsulated Enterobacteriaceae: Enterobacter and Klebsiella.

10
New cards

EMB (Eosin Methylene Blue) agar

Primary isolation medium; Aeosin Y and methylene blue inhibit Gram-positives and indicate lactose fermentation (E. coli produces a green-metallic sheen).

11
New cards

MAC (MacConkey) agar

Primary isolation medium with crystal violet and bile salts; lactose fermenters appear pink/red, NLF are colorless.

12
New cards

DCA (Deoxycholate Citrate Agar)

Primary medium containing sodium deoxycholate/citrate; differentiates lactose fermenters (pink) from NLF (colorless).

13
New cards

HEA (Hektoen Enteric Agar)

Selective medium with bile salts; lactose/sucrose fermenters are yellow, NLF appear green or blue-green (black centers if H₂S+).

14
New cards

XLD (Xylose Lysine Deoxycholate) agar

Selective medium where lactose/sucrose fermenters are yellow, NLF are red; detects H₂S (black centers).

15
New cards

SSA (Salmonella-Shigella Agar)

Selective medium for Salmonella/Shigella; lactose fermenters are pink/red, NLF are colorless; H₂S producers show black centers.

16
New cards

TSIA (Triple Sugar Iron Agar)

Biochemical test containing glucose (0.1 %), lactose (1 %), sucrose (1 %); reports slant/butt reactions (A or K), gas, and H₂S production.

17
New cards

KIA (Kligler Iron Agar)

Carbohydrate test with glucose (0.1 %) and lactose (1 %); interpreted similarly to TSIA but lacks sucrose.

18
New cards

Oxidase test

Detects cytochrome c oxidase; Enterobacteriaceae are oxidase-negative (no color change).

19
New cards

Nitrate reduction test

Assesses ability to reduce nitrate to nitrite; almost all Enterobacteriaceae are positive except Pantoea agglomerans and some Erwinia spp.

20
New cards

IMViC reactions

Series of tests—Indole, Methyl Red, Voges-Proskauer, Citrate—used to differentiate Enterobacteriaceae.

21
New cards

Indole test

Detects tryptophanase converting tryptophan to indole; positive shows a red ring after adding Kovac’s or Ehrlich’s reagent.

22
New cards

Methyl Red test

Detects stable mixed-acid fermentation from glucose; red color after adding methyl red reagent indicates positivity.

23
New cards

Voges-Proskauer (VP) test

Detects butylene glycol pathway producing acetoin; red color after reagents (α-naphthol & KOH) indicates positivity.

24
New cards

Citrate utilization test

Determines ability to use citrate as sole carbon source on Simmons citrate agar; positive = growth with blue color.

25
New cards

Urease test

Detects hydrolysis of urea to ammonia using Christensen’s urea agar; positive turns medium pink/magenta.

26
New cards

Phenylalanine deaminase (PAD) test

Uses 10 % ferric chloride to detect phenylpyruvic acid; green color indicates Proteus, Providencia, Morganella group.

27
New cards

Lysine decarboxylase (LDC) test

Detects decarboxylation of lysine to cadaverine; positive tubes change from yellow to purple (bromcresol purple indicator).

28
New cards

LIA (Lysine Iron Agar)

Differentiates Enterobacteriaceae by lysine decarboxylation/deamination and H₂S production.

29
New cards

DNase test

Assesses DNA hydrolysis; Serratia spp. are uniquely DNase-positive among Enterobacteriaceae.

30
New cards

Type III secretion system

Needle-like apparatus that injects effector proteins into host cells; a major virulence factor of many enteric pathogens.

31
New cards

Endotoxin (Lipid A)

Heat-stable component of the outer membrane LPS of Gram-negative bacteria; induces fever and shock.

32
New cards

Enterotoxin

Exotoxin acting on the small intestine, causing fluid/electrolyte loss and diarrhea (e.g., ETEC heat-labile and heat-stable toxins).

33
New cards

Shiga toxin

Potent cytotoxin produced by Shigella dysenteriae and some E. coli (STEC); inhibits protein synthesis in host cells.

34
New cards

O antigen

Heat-stable somatic polysaccharide portion of LPS; used in serotyping of Enterobacteriaceae.

35
New cards

H antigen

Heat-labile antigen located on flagella; present only in motile Enterobacteriaceae.

36
New cards

K antigen

Capsular polysaccharide antigen; found in encapsulated species like Klebsiella, Salmonella, and some E. coli.

37
New cards

H₂S production

Black precipitate in media (TSIA, XLD, HEA) due to ferrous sulfide formation; characteristic of Salmonella, Proteus, Edwardsiella, etc.

38
New cards

Mixed-acid fermenter

Bacterium producing stable acidic end products (e.g., E. coli) yielding a positive Methyl Red test.

39
New cards

Butylene glycol fermenter

Organism converting glucose to neutral end products like acetoin, producing a positive VP test (e.g., Enterobacter, Klebsiella).

40
New cards

Proteus-Providencia-Morganella group

PAD-positive, urease-positive, often motile NLF opportunists; associated with UTIs and wound infections.