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Microbiology for Dentists > 7. Bacterial Growth and Identification > Flashcards

7. Bacterial Growth and Identification Flashcards

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1
Q

The name ‘staphylococcus’ comes from where? What does this mean?

A
  • grape in Greek
  • under a microscope appears as clumps of round cells, like a bunch of grapes
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2
Q

Where is Staph.aureus found in body?

A
  • nose/anterior nares
  • throat/nasopharynx
  • skin
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3
Q

How do staph survive in body?

A
  • withstand high concs of salt
  • survive in sweaty areas
  • provide a means of selectively culturing staph using high salt medium
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4
Q

What kind of bacteria is staph?
Exception?

A

commensal
- staph. aureus involved in infections and called opportunistic

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5
Q

What kinds of conditions are caused by staph aureus?

A
  • broad range
  • toxin-mediated conditions like toxic shock syndrome or food poisoning (preformed enterotoxins)
  • localised skin infections like impertigo
  • wound infections
  • systemic infections like infective endocarditis
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6
Q

MRSA is what?

A

methicillin resistant staph aureus

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7
Q

Staph is gram …, … positive cocci.

A
  • positive
  • catalase
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8
Q

Staph and the oxidase test?

A
  • contain cytochrome oxidase
  • a respiratory chain component that’s readily tested by oxidase test
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9
Q

How to distinguish staph aureus from other staph?

A
  • coagulase test
  • enzyme coagulase binds fibrinogen in plasma and triggers cascade of reactions leading to blood clotting
  • most staph aureus produce coagulase but other staph don’t
  • aureus also produces one or more DNase enzymes which can help it escape from host DNA released at sites of infection to trap bacteria
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10
Q

Most oral strep are … as they can cause what?

A
  • pathogenic
  • infective endocarditis
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11
Q

When is S. salivarius used for good?

A
  • sold in some areas as probiotic
  • these strains produce bacteriocins which are peptide antibiotics to help control pathogenic species
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12
Q

Strains of strep produce what? that is used to identify it
Why?

A
  • urease
  • enzyme converts urea into basic (high pH) compound ammonia
  • helps protect against dental caries
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13
Q

Even though strep can protect against dental caries, how can it contribute?

A
  • S.salivarius can produce acid from sugars
  • means levels of this bacteria can be elevated at site of carious lesions
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14
Q

Strep are gram …, non-motile/motile, what shape?

A
  • postive
  • non-motile
  • spherical/cocci
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15
Q

Most oral strep produce … on blood agar culture. Why?

A
  • green tinge
  • hydrogen peroxide’s effect on iron in RBCs
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15
Q

How to differentiate staph and strep?

A
  • strep form chains
  • staph form bunches
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16
Q

Hydrogen peroxide is produced by what bacteria? and isn’t degraded. Why?

A
  • strep
  • lacks catalase
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17
Q

If you can’t see the shapes of staph and strep, how to differentiate?

A
  • strep aren’t degraded as don’t have catalase
  • staph are catalase-positive
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18
Q

Where are E.Coli found?

A
  • human gut
  • animals
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19
Q

Are all E.Coli bad?

A
  • most are harmless
  • well established as lab model
  • pathogenic strains are just not uncommon
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20
Q

Which strains of E.Coli are harmful?

A
  • 157 version of O-antigen and 7 version of H antigen (flagellar protein)
  • cause foodborne outbreaks with diarrhoea and vomiting
  • most common cause of UTIs in women
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21
Q

E.Coli is gram…, what shape? and what oxygen conditions?

A
  • negative
  • rod-shaped/bacillus
  • aerobic
22
Q

Most strains of E.Coli are motile/non-motile and produce fimbriae/don’t

A
  • motile
  • do
23
Q

E.Coli ferments what? and produces large colonies in what agar?

A
  • lactose
  • large red colonies in MacConkey agar
24
Q

How does E.Coli produce energy?

A

aerobic respiration

25
Q

How is E.Coli protected against hydrogen peroxide?

A
  • catalase
26
Q

How do you carry out urease test?

A
  • label agar plates
  • label Eppendorf tubes with urease broth inside to correlate with agar plates
  • take a full loopful of bacterial cells from each agar and add to corresponding tube of 0.5 ml of urease broth
  • colour change is faster if lots of cells are picked
  • add broths to water bath and incubate at 37 degrees at end of practical
27
Q

Possible results of urease test and why?

A
  • urease broth has medium of 2% urea and phenol red as indicator
  • any organism that produces urea should change pH indicator from yellow to pink due to production of ammonia
  • (NH2)2CO and water becomes carbon dioxide and 2 ammonia
  • takes 6-24 hrs to full develop but colour change seen after around an hour
28
Q

Explain catalase test

A
  • hydrogen peroxide strongly oxidising agent
  • using Pasteur pipette, place 3 drops of it on microscope slide and do for and label each bacteria
  • take a loopful of cells from each and add to corresponding slide
  • dip loop in 6% hydrogen peroxide solutionE
29
Q

Explain possible results of catalase test

A
  • if bacteria is catalase-positive, bubbles develop in liquid when loop dipped in hydrogen peroxide
  • detects catalase enzyme
  • 2H2O2 becomes 2 water and oxygen
  • bubbles seen are oxygen liberated by catalase
30
Q

Explain DNase test

A
  • use tripartite plate with 3 species
  • using Pasteur pipette, flood each section with Toluidine Blue
  • gently rock plate to spread solution evenly
  • after a few mins, check for lighter pinkish colour around each bacterial colony
31
Q

Explain results of DNase test

A
  • DNase test plate contains high molecular weight DNA incorporated into agar
  • DNase enzymes produced during bacterial growth degrade DNA around colonies
  • toluidine blue turns pink in the presence of free nucleotides or oligonucleotides released by degradation of DNA
32
Q

Under a microscope, Gram Neg bacteria appear … and positive appear …

A
  • pink
  • dark purple
33
Q

Explain coagulase test

A
  • commercial Staph Latex Agglutination kit and one plate with two species of bacteria as pos and neg control
  • resuspend latex reagent by inverting a few times
  • dispense 1 drop of latex reagent into each well of test card
  • with a sterile toothpick, transfer 2 colonies of each bacteria into respective well and mix
  • gently rock to allow mixture to flow over whole test area
  • watch for agglutination for 20 seconds
34
Q

Explain results of coagulase test

A
  • detects for presence of coagulase which is a clumping factor
  • in our case, the blue polystyrene latex particles are coated with human fibrinogen
  • bacterial cells with clumping factor will bind to fibrinogen and cause them to agglutinate
35
Q

Results of urease test for
- staph aureus
- E.Coli
- strep salivarius

A
  • neg
  • neg
  • pos
36
Q

Results of catalase test for
- staph aureus
- E.Coli
- strep salivarius

A
  • pos
  • neg
  • neg
37
Q

Results of DNase test for
- staph aureus
- E.Coli
- strep salivarius

A
  • pos
  • neg
  • neg
38
Q

Results of Gram stain test for
- staph aureus
- E.Coli
- strep salivarius

A
  • blue cocci clusters
  • red rods
  • blue cocci (more highly branched than staph though)
39
Q

Results of coagulase test for
- staph aureus
- E.Coli
- strep salivarius

A
  • pos
  • no test
  • no test
40
Q

Why in the coagulase test did we not test E.Coli or strep?

A
  • because we had confirmed them already
  • just needed to confirm staph
41
Q

Brilliance E.Coli/coliform agar
- selects what species?
- selective agent
- indicator

A
  • Gram-neg bacteria
  • sodium lauryl sulfate
  • rose-Gal/X-Glu
42
Q

Schaedler Anaerobe agar
- selects what species?
- selective agent
- indicator

A
  • fastidious anaerobes
  • reducing agents cysteine and hydrochloride/glucose
  • none
43
Q

Pseudomonas C-N Selective Agar
- selects what species?
- selective agent
- indicator

A
  • pseudomonas
  • cetrimide
  • cetrimide
44
Q

Brilliance Candida agar
- selects what species?
- selective agent
- indicator

A
  • candida
  • cloramphenicol
  • enzyme substrate
45
Q

XLD agar
- selects what species?
- selective agent
- indicator

A
  • enterobacteria
  • deoxycholate
  • xylose, lactose, lysine, thiosulfate
46
Q

Brilliance Salmonella agar
- selects what species?
- selective agent
- indicator

A
  • salmonella
  • novobiocin, cefsulodin
  • enzyme substrates
47
Q

What feature of the cell retains a crystal violet stain?

A

peptidoglycan

48
Q

What is the virulence factor in staph?

A

enterotoxin

49
Q

What can be seen under a microscope to identify bacteria?

A
  • shape
  • size
  • capsules
  • colour of stain
  • structure
  • gram neg/pos
50
Q

Role of fimbriae

A
  • hair like filamentous protein
  • sticks cells and aids biofilms
51
Q

What kind of bacteria grow on a blood agar?

A

complex

52
Q

What is the criteria for a good bacteria test?

A
  • specific
  • clear to read
  • sensitive to low numbers of bacteria
  • fast
  • easy
  • cheap
  • reproducible

Microbiology for Dentists (37 decks)

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