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CLS 753 > Micro - Gram Negative Rods (Enterics) > Flashcards

Micro - Gram Negative Rods (Enterics) Flashcards

1
Q

CO2 loving organisms are called ___. Salt loving organisms are called ___

A

Capnophiles

Halophiles

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2
Q

Are Salmonella, Shigella and Yersinia considered normal flora?

A

Salmonella and Shigella are always pathogens

Yersinia sometimes normal flora, sometimes pathogen

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3
Q

Enterics look like this on a gram stain… Enterics have this unique appearance on the gram stain called ___, where the ends are more intensely stained than the middle

A

Short gram-negative rods or coccobacilli

  • plump
  • members indistinguishable

Bipolar staining

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4
Q

All enterics can ferment this sugar… All enterics have this metabolic oxygen requirement for growth…

A

Glucose

Facultative anaerobes

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5
Q

All enterics are catalase ___

A

Positive

-except Shigella dysenteriae

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6
Q

All enterics are oxidase ___

A

Negative

-except Plesiomonas shigelloides

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7
Q

Can enterics form spores? Can enterics reduce nitrate?

A

Never

Yes, into nitrites

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8
Q

Stool cultures routinely screen for these organisms (3)

A

Salmonella

Shigella

Campylobacter

  • most common cause of diarrhea in US
  • in meat
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9
Q

What is the most favored transport medium for stool?

A

Cary-Blair

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10
Q

Stool samples kept on ice must be processed within… Stool samples kept in transport medium must be delivered within…

A

2 hours

4 days

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11
Q

Primary culture media for enterics (4)

A

Blood agar

Chocolate agar

MacConkey agar

Phenylethyl alcohol agar (PEA)

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12
Q

What sugar does MacConkey agar contain? What color is a positive fermentation result?

A

Lactose

Pink colonies with or without pink agar

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13
Q

Motile enterics

A 
Proteus (vulgaris, mirabilis)
Providencia
Morganella morganii
E coli (O157:H7)
Serratia
Salmonella

-mnemonic = PP MESS

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14
Q

To definitively ID E coli, we can add this compound to culture media…

A

MUG = positive

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15
Q

E. coli - clinical findings (3)

A

UTI = most common cause

Septicemia

Nosocomial infections

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16
Q

E. coli - TSI and KIA results

A

TSI = A/A with or without gas

KIA = A/A with or without gas

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17
Q

E. coli - IMViC

A

+ + - -

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18
Q

EHEC is also known as this serotype… The strain produces this cytotoxin called…

A

O157:H7 and O157:nonmotile

Shiga-toxin or Verotoxin

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19
Q

O157:H7 infection can lead to these conditions (2)

A

HUS

Hemorrhagic colitis

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20
Q

O157:H7 - what does the O and H mean?

A

O = cell wall antigen

H = flagella antigen. May/may not be seen (O157:nonmotile)

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21
Q

What 2 tests should be used to differentiate O157:H7 from regular E. coli?

A

Sorbitol-MAC (SMAC)

MUG

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22
Q

O157:H7 - MUG result is…

A

Negative

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23
Q

O157:H7 - what do the colonies look like on a Sorbitol-MAC (SMAC) plate and why?

A

Colorless = does not ferment sorbitol

  • other E. coli strains can = pink
  • confirm non-fermenter with antisera and latex reagents
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24
Q

Klebsiella - what do colonies look like on a MAC plate?

A

Pink colonies = lactose-fermenter

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25
Q

Klebsiella - what special feature about them gives them a mucoid colony appearance?

A

Capsule

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26
Q

Klebsiella - IMViC results

A
      • +

- reverse reaction from E. coli

27
Q

Serratia - key feature

A

Red colonies

-prodigiosin pigment

28
Q

Proteus are highly motile, forming this type of pattern on plates called…

A

Swarming

-wave-like growth on plates

29
Q

Proteus, Morganella, and Providencia colonies have this color on MAC plates. Why?

A

Colorless

Cannot ferment lactose

30
Q

Proteus TSI and KIA results (2). Why is the slant that color?

A

Both tubes:
K/A with or without gas
H2S positive

Deaminase reaction (PAD = phenylalanine deaminase)

  • slant turns yellow, then red again due to deaminase
  • glucose fermentation only, no lactose fermentation
31
Q

How are Proteus vulgaris and Proteus mirabilis different?

A

P. vulgaris = indole positive

P. mirabilis = indole negative

32
Q

Proteus is similar to this other genus due to TSI and KIA results and H2S production… What test should we use to differentiate Proteus?

A

Salmonella
-both genera are K/A with H2S production

PAD (phenylalanine deaminase)
-rules out Salmonella/Shigella/Serratia

33
Q

Morganella morganii and Providencia are similar to Proteus, except for these two things

A

No swarming

H2S negative

34
Q

What are the 2 Salmonella species? Salmonella typhi is a serotype of this species

A

enterica and bongori, but thousands of serotypes

enterica

35
Q

S. typhi animal vector?

A

None

  • direct human to human transmission
  • contaminated poultry, dairy products, water
36
Q

Salmonella and Shigella are both very similar. Which genus has more biochemical reactions?

A

Salmonella - positive for more biochemical reactions than Shigella
-Shigella mostly biochemically inert

37
Q

Salmonella vs Shigella - which has the higher infective dose? Which infection can result in a carrier state?

A

Salmonella = 10^6 cells
-Shigella low infective dose (10-200 cells)

Salmonella

38
Q

S. typhi - before 3 weeks, we should try to recover the organism from ___ samples. After 3 weeks, collect specimen from ___ samples

A

Blood

Stool

  • organism hides in gall bladder, sheds in stool
  • untreated leads to perforated GI tract
  • high fever that doesn’t go away, enlarged lymphs
  • vaccine available
39
Q

Salmonella possess this structure to allow them to attach to intestinal epithelial cells

A

Pili

-epithelial cells engulf organism, resist killing

40
Q

Salmonella possess this cell wall structure that is responsible for septic shock and death. S. typhi resist phagocytosis and complement via this structure

A

LPS O antigen (endotoxin)

Capsular Vi antigen

  • Vi antigen often blocks O antigen
  • Vi inactivated by boiling 30 mins
41
Q

Salmonella - IMViC reactions

A
      • citrate variable
42
Q

Salmonella colonies have this color on MAC plates. Why?

A

Colorless

Does not ferment lactose

43
Q

Enterics that can make H2S

A

Proteus

Salmonella

44
Q

Salmonella has this color on Hektoen Enteric agar and this on XLD

A

HE = green-black, or green with black center

  • from sulfur reduction
  • Salmonella = H2S positive

XLD = red with black center

45
Q

Salmonella antisera slide agglutination - can Salmonella be positive for Vi and negative for O? Why or why not?

A

No

O antigen (LPS) must always be present. Vi antigen (capsule) is masking O antigen. Heat suspension to inactivate Vi antigen and retest

46
Q

How many serotypes of Shigella are there? Which one is the most virulent and name the species

A

4 = serogroups A, B, C, D

Shigella dysenteriae = serogroup A

47
Q

Does Shigella have an animal reservoir?

A

No

  • only human to human transmission
  • contaminated food, water
  • similar to Salmonella
48
Q

What does it mean when an organism requires close contact for transmission?

A

Organism is sensitive and fragile (ie Shigella)

49
Q

S. dysenteriae produces a cytotoxin called… Which can lead to this condition

A

Shiga toxin
-also produces several enterotoxin

HUS

  • severe infection
  • similar to O157:H7 infection
50
Q

Shigella colonies have this color on MAC plates. Why?

A

Colorless

Does not ferment lactose

51
Q

Shigella has this color on Hektoen Enteric agar and this on XLD

A

HE = green

XLD = red/colorless

52
Q

How many Yersinia species are pathogenic and what are they? Which one is the bioterror agent?

A

Y. pestis = bioterror

Y. enterocolitica = most common

Y. pseudotuberculosis

53
Q

Yersinia pestis causes this disease

A

Plague (black death)

  • transmitted by fleas on rats
  • 3 forms: bubonic, pneumonic, septicemic
  • endotoxin deposited in capillaries, blocks blood flow = blackening of bodies
54
Q

Yersinia pestis - what is unique about the temperatures it can grow at?

A

Better growth at room temp than 37C

55
Q

Yersinia pestis has this unique type of bipolar staining that looks like…

A

Safety pin

56
Q

Yersinia pestis - what do colonies look like at 24 hrs on a blood agar plate? What do colonies look like at 72 hrs?

A

Pinpoint colonies too small to be seen with the eye
-very slow growth

White colonies with fried egg appearance

57
Q

Yersinia pestis colonies look like this on a MAC plate…

A

Colorless = non-lactose fermenter

58
Q

This species of Yersinia mimics appendicitis. Can refrigeration kill it or prevent its growth?

A

Yersinia enterocolitica

No, survives in the cold

59
Q

Yersinia spp selective media is called… What does Yersinia look like on this media?

A

CIN (Cefsulodin-igrasan-novobiocin)

Transparent with red center (bull’s eye)

60
Q

This species of Yersinia is a common animal pathogen and rarely causes disease in humans

A

Yersinia pseudotuberculosis

-seen in people working with animals

61
Q

These 3 enterics are lactose fermenters, the rest are not

A

Serratia
E. coli
Klebsiella

62
Q

These 2 enterics can produce capsules

A

Klebsiella

Salmonella typhi

63
Q

Which is the only enteric that is catalase negative?

A

Shigella dysenteriae

64
Q

No members of Enterobacteriaceae have this type of hemolysis…

A

Alpha

CLS 753 (12 decks)

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