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Diagnostic Microbiology > Media Characteristics > Flashcards

Media Characteristics Flashcards

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Biology 101 flashcards
1
Q

what is bacitracin used for

A

distinguish S.pyogenes (sensitive) from other beta-haemolytic Streptococci

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2
Q

what is bacitracin most effective against

A

most effective against Gram-positive bacteria, especially Staphylococci and some alpha and beta haemolytic Strep

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3
Q

what organisms is CHOC agar suitable for

A

more fastidious organisms, e.g. Haemophilus influenzae, Neisseria gonorrhoeae, Neisseria meningitidis

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4
Q

what type of haemolysis does Strep. pyogenes display on BA

A

Beta haemolysis

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5
Q

what type of haemolysis does Step. viridans display on BA

A

alpha haemolysis

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6
Q

what type of agar is CHROMagar and how does it differentiate between species

A

selective medium for the isolation and presumptive ID of yeast (Candida)
differentiates between species using chromogenic substrates in the medium giving colonies different colours
differentiates between C. albicans, C. tropicalis and C. krusei

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7
Q

what colour is C. albicans on CHROMagar

A

colonies are light to medium green

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8
Q

what colour is C. tropicalis on CHROMagar

A

colonies are dark blue to metalic blue

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9
Q

what colour is C. krusei on CHROMagar

A

colonies are light pink to pink, flat with a whiteish border

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10
Q

what type of agar would you use to select for and differentiate Candida species

A

CHROMagar

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11
Q

what is BSA (bismuth sulphite agar) used for

A

highly selective agar for isolation of Salmonella typhi from other Salmonella species

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12
Q

what are the active ingredients in BSA agar

A

bismuth sulphite and brilliant green inhibit the growth of most coliforms and Gram positive bacteria
Ferrous sulphite causes production of H2S, presence of H2S gives positive colonies a characteristic brown to black colour with a metalic sheen (iron)

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13
Q

how does Pseudomonas aerunginosa appear on BSA

A

colourless pin point colonies

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14
Q

how do coliforms appear on BSA

A

most are inhibited, small colourless, green or black

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15
Q

what agar would you use to differentiate S. typhi from other Salmonella species

A

use BSA (bismuth sulphite agar)
S. typhi will have black colonies with surrounding black zone, sheen
other Salmonella sp. will be black or brown to green, flat, moist

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16
Q

what is CAMP agar used for

A

(Campylobacter agar)
enrichment medium made selective for Campylobacter by inclusion of antibiotics: vancomycin, trimethoprim, Polymyxin B, Amphotericin, Cephalothin
these antibiotics inhibit enteric flora

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17
Q

what is CNA agar used for

A

(Colistin Nalidixic Acid)
selective isolation of GPC
antibiotics (Colistin and Nalidixic Acid) suppress growth of Enterobacteriaceae and Psuedomonas sp.
allow growth of: yeast, Stahylococci, Streptococci, enterococci

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18
Q

what organisms grow on CNA

A

GPC

yeasts, Staphylococci, Streptococci, enterococci

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19
Q

what organisms are inhibited on CNA

A

Enterobacteriaceae and Psuedomonas sp.

inhibited by antibiotics (colistin + nalidixic acid)

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20
Q

what is CLED agar designed for

A

use in urine bacteriology, supports growth of most urinary pathogens
prevents swarming of Proteus sp.

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21
Q

what does CLED stand for

A

Cysteine lactose electrolyte deficient

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22
Q

what does the agar colour change indicate on CLED

A

lactose fermentation indicated by agar colour change from blue to yellow

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23
Q

how does E.coli and Klebsiella sp. appear on CLED

A

E.coli: yellow, opaque, flat/rough

Klebsiella sp. : yellow to white, mucoid

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24
Q

how do Proteus sp. appear on CLED

A

blue, translucent

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25
Q

how do Salmonella sp. appear on CLED

A

blue, flat, smooth

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26
Q

how do Corynebacterium and Lactobacillus appear on CLED

A

grey, <0.25mm

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27
Q

what is DCA used for

A

(Deoxycholate citrate agar)

used for isolation and max recovery of intestinal pathogens

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28
Q

how is DCA agar selective

A

deoxycholate and sodium citrate incorporated in media inhibit or greatly suppress Gram-positive bacteria and coliform bacteria

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29
Q

how is DCA agar differentiative

A

fermentation of lactose indicated by opaque pink to red colonies
reduction of ferric ammonium citrate to iron sulphide (H2S producing bacteria) indicated by blackening of colony centres

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30
Q

what would a colony with a black centre indicate on DCA agar

A

indicate H2S producing bacteria

by the reduction of ferric ammonium citrate to iron sulphide

31
Q

how do E.coli and Klebsiella appear on DCA

A

most strains inhbited
E. coli, pink, 1-2mm
Klebsiella, pink, mucoid, 3-4mm

32
Q

how do Shigella sonnei and Shigella flexneri appear on DCA

A

colourless to pale pink, smooth, 1-2mm

33
Q

how do Salmonella sp. appear on DCA

A

colourless or black centred, 2-4mm

34
Q

ho do P. aeruginosa and Proteus sp. appear on DCA

A

colourless, flat, lemon shaped

Proteus sp. have characteristic odour

35
Q

what is CHOC agar + bacitracin used for

A

used to distinguish S. pyogenes (sensitive to bacitracin) from other beta-haemolytic strep

36
Q

what is GC agar used for

A

(Gonococcus agar)

used for isolation of pathogenic Neisseria sp. from clinical specimens

37
Q

how is GC selective

A

contains antibiotic to inhibit growth of commensal organisms, dependent on laboratory preference and local strain differences
antibiotics used inhibit Gram-neg and Gram-pos organisms

38
Q

what is GLU agar used for

A

(glucose agar)

used for differentiating fermentation reactions of Enterobacteriaceae

39
Q

what does GLU agar contain

A

contains tryptone and yeast extract: nitrogen source

sodiumchloride: maintains osmotic balance
glucose: energy source, when fermented produces acid, causes colour change (yellow)

40
Q

what colour indicator is present in GLU and what is the observed colour change

A

indicator: bromocresol purple

colour change: purple to yellow (glucose fermentation, acidic conditions)

41
Q

what is the difference between Mac3 and Mac7 agar

A

Mac3 contains Crystal violet
Mac7 does not contain Crystal violet
Crystal violet in combination with bile salts inhibit the growth of Gram positive bacteria

42
Q

what is HE agar used for

A

(Hektoen Enteric Agar)
used for the isolation of Shigella and Salmonella sp. from enteric pathological specimens
bile salts and indicatior inhibit much of normal intestinal flora
Shigella is still able to grow due to increase carbohydrate and peptone content

43
Q

how is HE agar differential

A

contains ferric ammonium citrate

reduction of citrate to iron sulphide by H2S producers results in blackening of colony centre

44
Q

how do Shigella sp. appear on HE agar

A

green to blue, moist, raised

45
Q

how do Salmonella sp. appear on HE agar

A

green colonies, some with black centres

46
Q

what does a blackened centre of a colony indicate

A

indicates bacterium is a H2S producer

due to reduction of ferric ammonium citrate to iron sulphide

47
Q

what is HTM agar used for

A

Haemophilus Test medium

used for antimicrobial disk susceptibility tests for Haemophilus sp.

48
Q

what is LBAG agar used for

A

used for isolation of anaerobic organisms from sites contaminated with intestinal flora
contains lysed blood which facilitates anaerobe growth

49
Q

how is LBAG selective

A

contains gentamicin which inhibits most facultative bacteria without affecting anaerobic organisms

50
Q

what is MSA agar used for

A

(Mannitol Salt Agar)

selective medium for the isolation of Staphylococcus species

51
Q

how is MSA selective and differential

A

selective: high salt content, inhibits growth of most bacteria except Staphylococcus sp. and some halophilic marine organisms
differential: contains phenol red indicator, fermentation of mannitol cause red to yellow colour change

52
Q

how does Staph. aureus, Staph. saprophyticus and Staph. epidermidis appear on MSA

A

S. aureus & S. saprophyticus: yellow

S. epidermidis: pink/white

53
Q

what is Mannitol selinite broth used for

A

selective isolation of Salmonella typhi, Salmonella paratyphi B
can also be used for selective isolation of Salmonella from water and foodstuffs

54
Q

what does MAC (MCA) agar contain

A

contains peptone, lactose, bile salts, NaCl, neutral red indicator

55
Q

what is MAC (MCA) agar used for

A

differential medium for Enterobacteria

56
Q

what does Crystal violet do in MAC 3 agar

A

in combination with bile salts, inhibits Gram positive bacteria

57
Q

what is characteristic of MHA agar

A

(Mueller Hinton agar)
does not contain heat labile compounds
can be autoclaved

58
Q

what is MHA agar used for

A

recommended standard agar for antibiotic disc diffusion susceptibility testing

59
Q

what does MHA agar contain

A

contains beef infusion, casamino acids and starch

60
Q

what is nutrient agar used for

A

used for X + V testing for Haemophilus species

used for less fastidious organisms

61
Q

what is purple starch agar used for

A

to test for starch hydrolysis
starch hydrolysed: yellow
starch not hydrolysed: purple or white

62
Q

what is PVT agar and what is it used for

A

blood agar with the addition of polymyxin, vancomycin and trimethrophrim used to inhibit instestial flora
used to isolate Campylobacter sp from faecal specimens

63
Q

what is Regan Lowe agar used for and what are the characteristic ingredients

A

used for the isoation of Bordetella and Haemophilus sp.
contains charcoal (inhibits free fatty acids) and nicotinic acid (essential for B. pertussis, B. parapertussis and bronchiseptica)
broad spectrum antibiotic may be added to inhbit normal flora from URT and mouth

64
Q

what is SAB + C agar used for + characteristics of media

A

(Sabouraud + Chlorophenicol agar)
acidic medium
used for isolation of dermathophytes, other fungi and yeasts (e.g. Candida)
Chlorophenicol enhances bacterial growth inhibition

65
Q

what is TCBS agar used for

A

isolation of Vibiro sp. from faecal samples

most other enteric bacteria are suppressed for at least 24hrs

66
Q

how is TBS agar differential

A

sucrose fermentation: indicated by blue/green to yellow colour change

67
Q

what is Tellurite agar used for

A

selective medium for isolation and differnetiation of Corynebacterium diptheriae (var; mitis, intermedius, gravis)
other bacteria inhibited by sodium tellurite presence

68
Q

how to differentiate Corynebacterium diptheriae variants

A

on Tellurite agar:
var. gravis: small, grey
var. intermedius: small, brownish grey
var mitis: small, black

69
Q

what is Tryptone soya agar (TSA) used for

A

general laboratory use
highly nutritious and versatile
contains tryptone and peptone
supports growth of many fastidious organisms

70
Q

what is XLD agar used for

A

selective medium for the isolation of enteric pathogens from faecal specimens

71
Q

why is Xylose included in XLD media

A

rapid xylose fermentation is almost universal across enteric bacteria, except: Shigella, Providencia, Edwardsiella
Shigella species can be identified on the media by their negative xylose reaction

72
Q

why is Sodium deoxycholate included in XLD media

A

to inhibit coliforms and Gram positive bacteria

73
Q

what does the hydrogen sulphide indicator differentiate between in XLD media

A

differentiates between Shigella and Salmonella species

74
Q

how is Salmonella sp. differentiated from non-pathogenic xylose fermentors in XLD media

A

incorporation of lysine into the media; Salmonellae exhaust the xylose and decarboxylate the lysine, this alters the pH to alkaline, mimicking the Shigella reaction

Diagnostic Microbiology (2 decks)

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