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Microbiology > Diagnostics > Flashcards

Diagnostics Flashcards

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1
Q

Define Clinical Microbiologist

A

A person that works to detect, identify and characterise the microbes that cause infectious disease from a variety of samples collected from sick hosts.

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2
Q

What are some aims of a microbiology lab?

A

To provide accurate information about presence of microorganisms in a specimen that may be involved in a patients disease and to provide information on the antimicrobial susceptibility of isolated microorganisms.

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3
Q

Why are lab tests carried out?

A

To detect microorganisms or their products in patient specimens and to detect evidence of the patients immune response to infection.

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4
Q

What are the three categories of laboratory tests?

A

Identification of microorganisms by isolation and culture
Identification of a specific microbial product
Detection of specific antibodies to a pathogen

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5
Q

Elaborate on isolation and culture labs

A

Microbes may grow on artificial media or cell cultures. The culture is required for antimicrobial susceptibility testing.

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6
Q

Elaborate on microbial product labs

A

These tests yield quicker results. May include cell components, extracellular products and microbe derived nucleic acids.

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7
Q

Elaborate on antibody and pathogen labs

A

Used when the pathogen cannot be cultivated in a lab or is dangerous to staff.

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8
Q

Describe the process of an antibody assay

A

Patient with suspected infectious disease
Blood sample
Search for antibodies using agglutination, RIA, EIA etc
Detection of antibody against specific pathogen

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9
Q

Describe the process of growth dependent microbiology

A

Patient with suspected infectious disease
Blood, faeces, urine, tissue, mucus sample
Enrichment by use of selective, enriched or differential media
Isolation by pure culture
Identification by use of growth dependent, immunological or molecular methods

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10
Q

Describe the process of antigen assay

A

Patient with suspected infectious disease
Blood, faeces, urine, tissue, mucus sample
Search for microbial or virus antigens using fluorescent antibody, EIA etc

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11
Q

Describe the process of molecular assay

A

Patient with suspected infectious disease
Blood, faeces, urine, tissue, mucus sample
Search for key genes of pathogen, nucleic acid hybridisation and PCR

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12
Q

What are sterile body sites?

A

Normally don’t contain bacteria so bacteria found is significant e.g. blood, bone marrow, CSF, serous fluids, tissues, lower respiratory tract, bladder

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13
Q

What are non-sterile body sites?

A

Open to external environment and contain bacteria e.g. mouth, nose, upper respiratory tract, skin, gastrointestinal tract, female genital tract, urethra

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14
Q

Colonisation resistance

A

Competition for space and nutrients with pathogens

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15
Q

Antibacterial substances

A

Release of bacteriocins and colicins to prevent pathogen growth

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16
Q

Antigenic stimulation

A

Continued from commensals cross-reacting protective immunity against pathogens e.g. commensal Neisseriaceae and Neisseria meningitidis

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17
Q

Name 5 types of specimen collection

A

Direct, Culture/Isolation, Immunological and serological tests, In vivo tests, Clinical signs and symptoms

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18
Q

Explain direct testing of the specimen

A

Microscopic (gram stain, acid-fast, fluorescent Ab stain, gene probes) or macroscopic (direct antigen, gene probes)

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19
Q

Explain Culture/Isolation testing of the specimen

A

Biochemical, serotyping, antimicrobic sensitivity, gene probes, phage typing, animal inoculation

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20
Q

What is the most important differential staining technique in microbiology?

A

The gram stain

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21
Q

Alpha haemolysis

A

Greenish brown halo around colony e.g. S. gordonii or S. pneumoniae

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22
Q

Beta haemolysis

A

Complete lysis of blood cells resulting in a clearing effect around the colony e.g. S. aureus or S. pyrogenes

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23
Q

Non haemolytic/gamma haemolysis

A

No change in media e.g. S. epidermidis or S. saprophyticus

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24
Q

Selective Media

A

Favours growth of one type of microorganism and inhibits other growth

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25
Q

Differential media

A

Distinguishes between different groups of bacteria on the basis of biochemical characteristics

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26
Q

Name 2 types of enriched media

A

Chocolate and blood

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27
Q

Name 2 types of selective media

A

Mannitol salt sugar (NaCl) and MacConkey (bile salt)

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28
Q

Name 5 types of differential media

A 
Triple sugar iron agar
Fermentable carbohydrates
Red phenol (pH change)
Iron (H2S gas production)
Chromoagar (colour formation)
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29
Q

Name 5 ways of indentifying pure bacteria cultures

A

Colony morphology, colour, shape, margin, elevation

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30
Q

Name the three types of colony morphology

A

Form, Elevation and Margin

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31
Q

Describe a catalase test

A

Mix H202 and culture
Positive reaction shows bubbles
Often used to differentiate strep (negative) and staph (positive)

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32
Q

Micrococcus identification pathway

A

Cocci - gram positive - catalase positive - irregular clusters and tetrads - strictly aerobic

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33
Q

Staphylococcus and Planococcus identification pathway

A

Cocci - gram positive - catalase positive - irregular clusters - tetrads - facultative anaerobic

34
Q

Streptococcus identification pathway

A

Cocci - gram positive - catalase negative - pairs and chain arrangement

35
Q

Neisseria, Branhamella and Moraxella identification pathway

A

Cocci - gram negative - aerobic - oxidase and catalase positive

36
Q

Veillonella identification pathway

A

Cocci - gram negative - aerobic - oxidase and catalase negative

37
Q

Bacillus and Clostridium identification pathway

A

Rods - gram positive - sporeformer

38
Q

Mycobacterium and Nocardia identification pathway

A

Rods - gram positive - non sporeformer - acid-fast

39
Q

Lactobacillus and Listeria identification pathway

A

Rods - gram positive - non sporeformer - not acid-fast - regular

40
Q

Corynebacterium and Propionibacterium identification pathway

A

Rods - gram positive - non sporeformer - not acid-fast - pleomorphic

41
Q

Pseudomonas and Alcaligenes identification pathway

A

Rods - gram negative - aerobic - oxidase positive

42
Q

Escherichia, Enterobacter, Citrobacter, Proteus, Salmonella and Erwinia identification pathway

A

Rods - gram negative - facultative anaerobic - oxidase negative - glucose fermentation - motile

43
Q

Shigella and Klebsiella identification pathway

A

Rods - gram negative - facultative anaerobic - oxidase negative - glucose fermentation - nonmotile

44
Q

Describe a biochemical test

A

A physiological reaction to nutrients as evidence of the absence of presence of enzymes. If enzyme is present, product forms yielding positive result.

45
Q

Carbohydrate fermentation

A

Acid formation by fermentation indicated by a colour change, gas formation indicated by bubble in Durham tube

46
Q

Methyl Red Test

A

Qualitative test for acid production. Bacteria are grown in MR-VP broth, methyl red solution added. Red = positive, yellow = negative

47
Q

Nitrate reduction

A

Red diazonium dye indicated nitrite reduced to nitrate. Colourless broths get zinc dust added, if it goes red it is negative if it stays colourless nitrates have been reduced to other products

48
Q

Starch Hydrolysis

A

After starch agar incubation plates flooded with iodine solution. Colourless area around growth is positive.

49
Q

Name 2 rapid tests

A

API Strip and BBL crystal enteric/nonfermenter ID kit

50
Q

Disc diffusion method

A

lawn of pure bacterial culture inoculated, disc added, zone of inhibition measured

51
Q

Broth Dilution method

A

Each row has different antibiotic
End point is well with lowest concentration of antibiotic that shows no visible growth
Highest concentration in left well
Serial twofold dilutions made in right wells

52
Q

Etest method (AB biodisc)

A

Strip tests for antibiotic susceptibility
Each strip calibrated in terms of the minimum inhibitory concentration in micrograms per microlitre
Lowest concentration at centre of plate
Lowest concentration of antibiotic that inhibits bacterial growth is MIC value for that particular agent

53
Q

Name 6 DNA diagnostic systems

A 
DNA sequencing
Nucleic acid probes
PCR
Restriction endonuclease analysis
Random amplified polymorphic DNA
DNA fingerprinting
54
Q

What 3 qualities should a good detection system have?

A

Sensitivity, Specificity and Simplicity

55
Q

Define Sensitivity

A

The test must be able to detect very small amounts of target even in the presence of other molecules

56
Q

Define Specificity

A

The test must yield a positive result ONLY for the target molecule

57
Q

Define Simplicity

A

The test must be able to run efficiently and inexpensively on a routine bias

58
Q

Nucleic Acid Hybridisation

A

Detects a specific DNA sequence associated with an organism by using an organism specific nucleic acid probe. A gene probe is a short specific sequence of DNA used to see whether a sample contains target or complementary DNA.

59
Q

Define Membrane Filter Assay

A

Colonies from plates or infected tissues treated with strong alkali to lyse cell then fixed to filter. Hybridisation by incubating at stable duplex temperature between target and probe.

60
Q

Define Dipstick Assay

A

Dual reporter and capture probes are used. Capture probe contains polydA tail that hybridises to poldT oligonucleotide affixed to dipstick binding to oligonucleotide target reporter complex.

61
Q

Name 4 advantages of Nucleic Acid Probes

A

More stable in extreme environments
Specimen can be treated harshly
Can identify dead microbes
More specific than antibodies

62
Q

Describe PCR

A

2 sequence specific oligonucleotide primers amplify DNA which confirms target presence.

63
Q

Name 4 ways a PCR product can be confirmed

A

Correct product size
Sequence product
Hybridisation
Nested PCR

64
Q

What can Microarray potentially be used for?

A

Prenatal screening
Testing for specific chromosomal abnormalities
Forensics
Personalised medicine

65
Q

Enzyme immunoassays

A

Can be used to detect antigen in a specimen or antibody in a serum sample

66
Q

Serology

A

The detection of an antibody in a patients serum requiring acute and convalescent samples.

67
Q

Serology Methods

A 
Fluorescent Antibody Test
Precipitation Reactions
Aggluntination reactions
Neutralising reactions
Complement fixation
68
Q

Define a polyclonal antibody

A

Contains many antibodies recognising many determinants on an antigen
Various antibody classes present
Can make a specific antibody only with pure antigen
Reproducibility and standardisation are difficult

69
Q

Define a monoclonal antibody

A

Contains a single antibody recognizing only a single determinant
Single class of antibody produced
Can make a specific antibody using impure antigen
Highly reproducible

70
Q

Name 3 monoclonal antibodies and their associated diseases

A

Infliximab for Crohns
Ibritumomab/rituximab for Non-Hodgkins Lymphoma
Trastuzumab for breast cancer

71
Q

Precipitation Reaction

A

The interaction of a soluble antigen with a soluble antibody to form an insoluble complex - aggregate of antigen and antibody. Reaction occurs maximally only when the optimal proportions of antigen and antibody are present

72
Q

Immunodiffusion

A

Precipitation reaction but in agar.

73
Q

Agglutination reaction

A

visible clumping of antigen when mixed with specific antibody. Can be direct or passive.

74
Q

Direct agglutination reaction

A

Soluble antibody results in clumping by interacting with an antigen that is part of the cell surface, used for blood type determination.

75
Q

Passive (indirect) agglutination reaction

A

Antibody or antigen is absorbed or chemically coupled to call, latex beads or charcoal particles which serve as inert carriers.

76
Q

Haemagglutination

A

Agglutination of red blood cells

77
Q

Viral Haemagglutination Inhibiton

A

Some viruses agglutinate red blood cells in vitro, antibodies prevent haemagglutination.

78
Q

Neutralisation reaction

A

Antitoxin antibody can eliminate the harmful effects of a virus or endotoxin

79
Q

Complement Fixation

A

Lysin-mediated haemolysis
Antigen, antibody, complement, sensitised sheep red blood cells
Test antigen and antibody reaction
Contents mixed with sheep red blood cells. If complement is used in first stage no haemolysis
Unfixed complement = haemolysis

80
Q

ELISA

A

Enzyme-antibody complex produces a coloured product when an enzyme-substrate reaction occurs

81
Q

Radioimmunoassay

A

Antigens or antibodies labelled with radioactive isotopes

82
Q

Name the 3 types of ELISA and what they detect

A

Indirect (antibodies)
Direct (antigens)
Competitive (antigens)

Microbiology (6 decks)

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