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Infectious Agents > Gram-Negative Rods: Enterobacteriaceae > Flashcards

Gram-Negative Rods: Enterobacteriaceae Flashcards

1
Q

Proteobacteria are _______ or ______

A

Gram negative rods; cocci

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2
Q

Enterobacteriaceae

A

Gram neg rods, free living (saphrophytes)

  • part of indigenous flora of people and animals
  • metabolically active
  • fast growing under aerobic and anaerobic conditions
  • motile
  • acid-fast (spore forming)
  • opportunistic pathogens
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3
Q

Enterobacteriaceae are primarily inhabitants of the ________

A

Lower GIT

- main facultative anaerobic portion of bacterial content of the cecum and colon

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4
Q

Other locations of enterobacteriaceae

A
  • female genital tract
  • transient colonizers of skin and oral cavity
  • respiratory tract (small numbers) –> increase in hospitalized patients
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5
Q

What is the most common species among the indigenous flora of mammals and some birds?

A

E. coli

- followed by: Klebsiella, proteus, and enterobacter

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6
Q

What species are primarily pathogenic and not part of the normal flora?

A
  • salmonella
  • shigella
  • certain strains of E. coli
  • yersinia
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7
Q

Length may vary from ____ to ________

A

Large coccobacilli; elongated, filamentous rods

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8
Q

Sides are _____, ends are _____

A

Parallel; round

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9
Q

Morphological features

A
  • motile strains have peritrichous flagella
  • fimbriae
  • capsules and/or slime layers
  • typical features of GN bacteria (cell wall, cell membrane, etc)
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10
Q

Growth

A

Readily grow on simple media (facultative anaerobes)

  • resistance to bile salts and many bacteriostatic dyes
  • grow under almost any conditions –> interferes with isolation of fastidious bacteria when looking at clinical specimens
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11
Q

What 3 morphological features are used for identifying and subtyping?

A
  • LPS
  • capsule/slime layer
  • flagellar antigens
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12
Q

H, K, and O antigens

A

H antigens: flagella (protein)
K antigens: capsule/slime layer (polysaccharides)
O antigens: LPS (polysaccharide)

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13
Q

What do all enterobacteriaceae have in common?

A

All are:

  • facultative anaerobes
  • ferment glucose (with gas produced)
  • reduce nitrates to nitritie
  • cytochrome oxidase negative!!
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14
Q

Rapid fermentation of lactose is a useful characteristic for ________

A

Initial differentiation

  • most common members of intestinal flora ferment lactose promptly in more than 90% of isolates
  • most (esp intestinal pathogens) are rarely positive
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15
Q

What are common toxins produced by all enterobacteriaceae?

A

All possess:

  • LPS (endotoxin)
  • –> leads to: fever, leukopenia, activation of blood coag factors)
  • some produce exotoxins
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16
Q

Most enterobacteriaceae only infect a host under _______

A

Predisposing circumstances

- stress, lack of colostrum, change in diet, infections, antibiotics, etc

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17
Q

Members of normal flora act as opportunistic pathogens when ______

A

They are displaced from their normal site or if local/systemic defense mechanisms are damaged

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18
Q

What are the most common sites of opportunistic infections?

A

Wound and urogenital tract infections

- may occur at any body site, especially in septicemia

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19
Q

What contributes to the antimicrobial susceptibility of enterobacteriaceae?

A

Combo of chromosomal and plasmid-mediated resistance make them the most variable

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20
Q

What antibiotics are these bacteria usually resistant to?

A
  • penicillin G (except in the urinary tract)
  • erythromycin
  • clindamycin
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21
Q

What is the major facultative anaerobic species of bacteria in the intestine of warm-blooded animals throughout their life?

A

E. coli

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22
Q

Aerobic culture of feces or intestinal contents yields ____

A

E. coli

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23
Q

What are the major diseases caused by E. coli?

A
  • enteric infections
  • septicemia
  • urinary tract infections
  • mastitis
24
Q

How do you identify E. coli?

A
  • biotyping
  • serotyping
  • phage-typing
  • colicin-typing
  • virulence factor expression
25
Q

Fimbrial antigens are referred to as _____ when serotyping

A

F antigen

26
Q

What are the 6 classes of E. coli that cause diarrheal diseases?

A
  • ETEC: enterotoxigenic
  • EIEC: enteroinvasive
  • EHEC: enterohemorrhagic
  • EPEC: enteropathogenic
  • EAEC: enteroaggregative
  • AIEC: adherent-invasive
27
Q

ETEC commonly infects:

A

Travelers and infants

28
Q

Clinical signs of ETEC

A

Diarrhea, without fever!!

- mild discomfort to severe cholera-like syndrome

29
Q

Colonization of ETEC

A

Requires fimbriae mediated colonization and elaboration of one or more enterotoxins (ST or LT)

30
Q

EPEC clinical signs

A

Similar to ETEC:

  • watery diarrhea
  • no fever
  • no blood
31
Q

Adherence of EPEC

A

Due to rearrangements of actin in the vicinity of adherent bacteria to form “attaching and effacing” lesions

  • results in loss of microvilli and absorptive surfaces
  • do not produce ST or LT toxins –> use type 3 secretion system
32
Q

EHEC clinical signs

A

Copious bloody discharge

  • no fever!
  • well known serotype is O157:H7
33
Q

What does EHEC infect that is life-threatening?

A

Kidneys

- causes hemolytic uremia

34
Q

EHEC has similar attachement mechanisms as _____

A

EPEC

35
Q

ETEC, EPEC, EHEC are all ______

A

Non-invasive!!

- just result in localized infection

36
Q

EIEC clinical signs

A

Dysentery-like diarrhea

  • fever!!
  • bloody diarrhea
  • painful
  • requires higher hospitalization
  • commonly infects humans and primates
37
Q

EIEC attachment mechanism

A

Penetrates and multiplies within epithelial cells (invasive!!) of the colon
= widespread cell destruction
- lack fimbrial adhesins, LT or ST toxin, and shiga toxin

38
Q

Distinguishing feature of EAEC strains

A

Ability to attach to tissue culture cells in an aggregative manner
- “stacks of bricks”

39
Q

EAEC is associated with _________

A

Persistent diarrhea in young children

  • also associated with disease in livestock
  • do not invade
40
Q

AIEC diseases:

A
  • Crohn’s disease in humans
  • histiocytic ulcerative colitis in dogs
  • chronic bloody mucoid diarrhea and weight loss
41
Q

Flagella

A
  • uropathogenic E. coli: contributes to UTI colonization

- enterotoxigenic E. coli: contributes to adhesion

42
Q

Capsule

A

Most septicemias in people are caused by strains with K1 capsular polysaccharide
- some strains that cause diarrhea in calves and pigs have capsules that contribute to adhesion to gut mucosa or serum resistance

43
Q

K1

A

Enhances invasiveness and increases resistance to phagocytosis and serum killing (complement)

44
Q

LPS

A

Contributes to septicemic disease as with all GN bacteria

45
Q

Fimbriae

A

Essential virulence factors in E. coli for adherence to host cell surfaces

46
Q

Enterotoxigenic E. coli fimbriae

A

Mediate adherence to glycoproteins on the surface of intestinal epithelial cells

47
Q

Cattle and swine fimbrial types

A

F4, F5, F6, F18, F41

48
Q

Human ETEC, plasma encoded fimbriae

A

F2 (CFA 1), and F3 (CFA 2)

49
Q

Receptors for fimbriae are more highly expressed in _____

A

Neonates

50
Q

Avian pathogenic E. coli (APEC) virulence factors

A 
Type 1 (F1)
- also expressed by other pathogenic E. coli and other enterobacteriaceae
51
Q

ExPEC-F17c

A

Mediates intestinal adherence to initiate infection

52
Q

Uropathogenic E. coli (UPEC)

A

P fimbriae

53
Q

What are the 2 primary types of enterotoxins?

A

LT and ST

- one or both are essential virulence factors (besides fimbriae) for enterotoxigneic E. coli (ETEC)

54
Q

Shiga toxin

A

STx

  • aka: verotoxin, Shia-like toxin, edema disease principle
  • heat-labile high MW toxin similar to Shiga toxin produced by Shigella dysenteriae
55
Q

Alpha-hemolysin

A

RTX toxin

  • produced by certain porcine E. coli
  • damages cell membranes
56
Q

Iron uptake system

A

Important in septicemic strains from calves, lambs, and people
- plasmid genes code for siderophores, specific high-affinity iron uptake systems

57
Q

Type 3 secretion system

A

Used by EPEC

  • encoded in their chromosome (in a pathogenicity island)
  • injects bacterial effector proteins into host cells to affect host cell function

Infectious Agents (44 decks)

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