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MLSCI 340 > LAB 8 - Enterobacteriaceae > Flashcards

LAB 8 - Enterobacteriaceae Flashcards

1
Q

aerogenic vs anaerogenic

A

organisms that ferment glucose producing acid and gas vs acid only

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2
Q

these organisms cause GI distress due to toxins

A

B. cereus
S. aureus
C. perfringens

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3
Q

Wilson Blair agar

A

inhibits GPOS

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4
Q

what is the general rule for inoculation of media and biochemical tests?

A

least selective (most enriched) to most selective
liquid to semi solid to solid

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5
Q

E. coli on SMAC

A

white

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6
Q

Yersinia on HEK

A

tgn/yel

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7
Q

E. coli O157:H7 on STEC chromagar

A

mauve

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8
Q

Yersinia on CIN

A

bulls eye

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9
Q

spot indole

A

p-dimethylamino-cinnanaldehyde
highly sensitive but will not work on pigmented organisms

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10
Q

Kovac’s indole vs spot indole

A

Kovac’s = paradimethylaminobenzaldehyde; cherry red pr pink
spot indole = blue/green

tests for tryptophanase

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11
Q

what is the purpose of aerosporin media?

A

has polymyxin B (antibiotic for GNBs)
inhibits GNB; selective for GPS

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12
Q

phenylethyl alcohol agar (PEA)

A
  • The active ingredient, phenylethyl alcohol, inhibits or markedly reduces the growth of Gram-negative organisms by interfering with DNA synthesis
  • supports growth of GPCs and anaerobes
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13
Q

colistin nalidixic acid

A

Colistin, a polypeptide antibiotic of the polymyxin group, and nalidixic acid, a first-generation quinolone, are primarily active against gram-negative bacteria thereby making Columbia CNA Agar a good medium for the selective isolation of gram-positive cocci.

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14
Q

decarboxylase test

A
  • after the fermentation of glucose in the medium, acids are produced which lower the pH = purple to yellow
  • if the organism produces decarboxylase, decarboxylation, or hydrolysis of the amino acid occurs in response to the acid pH = alkaline end products (amies) = purple
  • Decarboxylation is an anaerobic reaction
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15
Q

pH indicators of decarboxylase test

A

bromcresol purple and cresol red

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16
Q

indicator for TSI

A

phenol red

17
Q

when is susceptibility testing performed on enteric pathogens?

A

self-limiting so usually don’t
- unless immunocompromised, hospitalized pts, prolonged infections
- Shigella and Vibrio = automatic testing due to severity

18
Q

serological methods for ID of Shigella, Salmonella, and E. coli O157:H7

A
  • O (somatic antigen) - heat-stabile antigen located in cell wall, resistant to alcohol
  • H (flagellar) - heat-labile; resists formalin
  • K (capsular) - heat-labile polysaccharide; K1 of E. coli, Vi of S. Typhi; may mask O antigen
19
Q

Serologic grouping of Shigella sp. is based on the ____ antigen

A

O antigen
- if agg fails = suspension is heated to remove capsular antigen and is retested with O antisera

20
Q

Shigella serotypes

A

A = S. dysenteriae
B = S. flexneri
C = S. boydii
D = S. sonnei

21
Q

primary intestinal pathogens

A
  • Salmonella, Shigella, Yersinia enterocolitica, E. coli O157:H7 = true pathogens
  • NOT commensal flora of GIq
22
Q

oxidase test principle

A
  • tetramethyl-p-phenylenediamine (TMPD) interacts with the ETC at level of cytochrome c
  • produces dark purple indophenol
  • found only in bacteria whose electron transport systems contain cytochrome c oxidase
23
Q

what can inhibit oxidase activity?

A

carb fermentation or components of selective media

24
Q

why must TSI reactions be read within the 18-24 hr inc period?

A

acid reactions may revert to alkaline due to oxidative decarboxylation; glucose fermenters may falsely appear to be non-fermenters

25
Q

detection of hydrogen sulfide in TSI

A

due to sodium thiosulfate and ferrous ammonium sulfate

26
Q

TSI ingredients

A

pH-sensitive dye (phenol red), 1% lactose, 1% sucrose, 0.1% glucose, as well as sodium thiosulfate and ferrous sulfate or ferrous ammonium sulfate

27
Q

citrate utilization

A
  • certain organisms can use citrate as their sole source of carbon
  • pos = growth -> blue due to alkaline end products produced (bromothymol blue)
  • useful for differentiation of lactose fermenters
  • Kleb and Enterobacter utilize citrate but E. coli does not
28
Q

Malonate utilization

A
  • utilize malonate as a source of carbon?
  • end products = acetate and CO2
  • alkaline pH so bromthymol blue changes from green to blue (alkaline) in a positive test
29
Q

Phenylalanine deaminase test

A
  • test for ability to deaminate phenylalanine to phenyl pyruvic acid by adding ferric chloride as an indicator
  • Proteus-Providence (+); rest of colifs (-)
  • green is pos
30
Q

urease

A
  • splits urea into CO2 and ammonia
  • phenol red turns deep cerise due to alkalinity
31
Q

Orthonitrophenyl-beta-galactopyranoside (ONPG) test

A
  • orthonitrophenyl-beta-galactopyranoside
  • detects beta-galactosidase (cleaves lactose into glucose & galactose)
  • also depends on PERMEASE ( transports lactose into cells)
  • yellow is pos
32
Q

Lactose fermenter (ONPG pos)

A

both permease enzyme and beta galactosidase
E. coli, Kleb spp., Enterobacter spp

33
Q

Late lactose fermenter (ONPG pos)

A

only beta galactosidase
Citrobacter spp, Arizona sp

34
Q

Y. enterocolitica motility

A

+ in RT
- in vivo

35
Q

MAC ingredients

A

Peptone
Lactose monohydrate
Bile salts (and CV inhibit GPC)
Sodium chloride
Neutral red
Crystal Violet

36
Q

SMAC

A

E. coli is pink on MAC and pk/ng on SMAC
whereas E. coli O157:H7 is pk on MAc and wt on SMAC

MLSCI 340 (16 decks)

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