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Media Characteristics 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
how do Salmonella sp. appear on CLED
blue, flat, smooth
26
how do Corynebacterium and Lactobacillus appear on CLED
grey, <0.25mm
27
what is DCA used for
(Deoxycholate citrate agar) | used for isolation and max recovery of intestinal pathogens
28
how is DCA agar selective
deoxycholate and sodium citrate incorporated in media inhibit or greatly suppress Gram-positive bacteria and coliform bacteria
29
how is DCA agar differentiative
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
30
what would a colony with a black centre indicate on DCA agar
indicate H2S producing bacteria | by the reduction of ferric ammonium citrate to iron sulphide
31
how do E.coli and Klebsiella appear on DCA
most strains inhbited E. coli, pink, 1-2mm Klebsiella, pink, mucoid, 3-4mm
32
how do Shigella sonnei and Shigella flexneri appear on DCA
colourless to pale pink, smooth, 1-2mm
33
how do Salmonella sp. appear on DCA
colourless or black centred, 2-4mm
34
ho do P. aeruginosa and Proteus sp. appear on DCA
colourless, flat, lemon shaped | Proteus sp. have characteristic odour
35
what is CHOC agar + bacitracin used for
used to distinguish S. pyogenes (sensitive to bacitracin) from other beta-haemolytic strep
36
what is GC agar used for
(Gonococcus agar) | used for isolation of pathogenic Neisseria sp. from clinical specimens
37
how is GC selective
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
what is GLU agar used for
(glucose agar) | used for differentiating fermentation reactions of Enterobacteriaceae
39
what does GLU agar contain
contains tryptone and yeast extract: nitrogen source sodiumchloride: maintains osmotic balance glucose: energy source, when fermented produces acid, causes colour change (yellow)
40
what colour indicator is present in GLU and what is the observed colour change
indicator: bromocresol purple | colour change: purple to yellow (glucose fermentation, acidic conditions)
41
what is the difference between Mac3 and Mac7 agar
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
what is HE agar used for
(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
how is HE agar differential
contains ferric ammonium citrate | reduction of citrate to iron sulphide by H2S producers results in blackening of colony centre
44
how do Shigella sp. appear on HE agar
green to blue, moist, raised
45
how do Salmonella sp. appear on HE agar
green colonies, some with black centres
46
what does a blackened centre of a colony indicate
indicates bacterium is a H2S producer | due to reduction of ferric ammonium citrate to iron sulphide
47
what is HTM agar used for
Haemophilus Test medium | used for antimicrobial disk susceptibility tests for Haemophilus sp.
48
what is LBAG agar used for
used for isolation of anaerobic organisms from sites contaminated with intestinal flora contains lysed blood which facilitates anaerobe growth
49
how is LBAG selective
contains gentamicin which inhibits most facultative bacteria without affecting anaerobic organisms
50
what is MSA agar used for
(Mannitol Salt Agar) | selective medium for the isolation of Staphylococcus species
51
how is MSA selective and differential
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
how does Staph. aureus, Staph. saprophyticus and Staph. epidermidis appear on MSA
S. aureus & S. saprophyticus: yellow | S. epidermidis: pink/white
53
what is Mannitol selinite broth used for
selective isolation of Salmonella typhi, Salmonella paratyphi B can also be used for selective isolation of Salmonella from water and foodstuffs
54
what does MAC (MCA) agar contain
contains peptone, lactose, bile salts, NaCl, neutral red indicator
55
what is MAC (MCA) agar used for
differential medium for Enterobacteria
56
what does Crystal violet do in MAC 3 agar
in combination with bile salts, inhibits Gram positive bacteria
57
what is characteristic of MHA agar
(Mueller Hinton agar) does not contain heat labile compounds can be autoclaved
58
what is MHA agar used for
recommended standard agar for antibiotic disc diffusion susceptibility testing
59
what does MHA agar contain
contains beef infusion, casamino acids and starch
60
what is nutrient agar used for
used for X + V testing for Haemophilus species | used for less fastidious organisms
61
what is purple starch agar used for
to test for starch hydrolysis starch hydrolysed: yellow starch not hydrolysed: purple or white
62
what is PVT agar and what is it used for
blood agar with the addition of polymyxin, vancomycin and trimethrophrim used to inhibit instestial flora used to isolate Campylobacter sp from faecal specimens
63
what is Regan Lowe agar used for and what are the characteristic ingredients
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
what is SAB + C agar used for + characteristics of media
(Sabouraud + Chlorophenicol agar) acidic medium used for isolation of dermathophytes, other fungi and yeasts (e.g. Candida) Chlorophenicol enhances bacterial growth inhibition
65
what is TCBS agar used for
isolation of Vibiro sp. from faecal samples | most other enteric bacteria are suppressed for at least 24hrs
66
how is TBS agar differential
sucrose fermentation: indicated by blue/green to yellow colour change
67
what is Tellurite agar used for
selective medium for isolation and differnetiation of Corynebacterium diptheriae (var; mitis, intermedius, gravis) other bacteria inhibited by sodium tellurite presence
68
how to differentiate Corynebacterium diptheriae variants
on Tellurite agar: var. gravis: small, grey var. intermedius: small, brownish grey var mitis: small, black
69
what is Tryptone soya agar (TSA) used for
general laboratory use highly nutritious and versatile contains tryptone and peptone supports growth of many fastidious organisms
70
what is XLD agar used for
selective medium for the isolation of enteric pathogens from faecal specimens
71
why is Xylose included in XLD media
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
why is Sodium deoxycholate included in XLD media
to inhibit coliforms and Gram positive bacteria
73
what does the hydrogen sulphide indicator differentiate between in XLD media
differentiates between Shigella and Salmonella species
74
how is Salmonella sp. differentiated from non-pathogenic xylose fermentors in XLD media
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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