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Microbiology > Diagnostics > Flashcards

Diagnostics Flashcards

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
Differential media
Distinguishes between different groups of bacteria on the basis of biochemical characteristics
26
Name 2 types of enriched media
Chocolate and blood
27
Name 2 types of selective media
Mannitol salt sugar (NaCl) and MacConkey (bile salt)
28
Name 5 types of differential media
``` Triple sugar iron agar Fermentable carbohydrates Red phenol (pH change) Iron (H2S gas production) Chromoagar (colour formation) ```
29
Name 5 ways of indentifying pure bacteria cultures
Colony morphology, colour, shape, margin, elevation
30
Name the three types of colony morphology
Form, Elevation and Margin
31
Describe a catalase test
Mix H202 and culture Positive reaction shows bubbles Often used to differentiate strep (negative) and staph (positive)
32
Micrococcus identification pathway
Cocci - gram positive - catalase positive - irregular clusters and tetrads - strictly aerobic
33
Staphylococcus and Planococcus identification pathway
Cocci - gram positive - catalase positive - irregular clusters - tetrads - facultative anaerobic
34
Streptococcus identification pathway
Cocci - gram positive - catalase negative - pairs and chain arrangement
35
Neisseria, Branhamella and Moraxella identification pathway
Cocci - gram negative - aerobic - oxidase and catalase positive
36
Veillonella identification pathway
Cocci - gram negative - aerobic - oxidase and catalase negative
37
Bacillus and Clostridium identification pathway
Rods - gram positive - sporeformer
38
Mycobacterium and Nocardia identification pathway
Rods - gram positive - non sporeformer - acid-fast
39
Lactobacillus and Listeria identification pathway
Rods - gram positive - non sporeformer - not acid-fast - regular
40
Corynebacterium and Propionibacterium identification pathway
Rods - gram positive - non sporeformer - not acid-fast - pleomorphic
41
Pseudomonas and Alcaligenes identification pathway
Rods - gram negative - aerobic - oxidase positive
42
Escherichia, Enterobacter, Citrobacter, Proteus, Salmonella and Erwinia identification pathway
Rods - gram negative - facultative anaerobic - oxidase negative - glucose fermentation - motile
43
Shigella and Klebsiella identification pathway
Rods - gram negative - facultative anaerobic - oxidase negative - glucose fermentation - nonmotile
44
Describe a biochemical test
A physiological reaction to nutrients as evidence of the absence of presence of enzymes. If enzyme is present, product forms yielding positive result.
45
Carbohydrate fermentation
Acid formation by fermentation indicated by a colour change, gas formation indicated by bubble in Durham tube
46
Methyl Red Test
Qualitative test for acid production. Bacteria are grown in MR-VP broth, methyl red solution added. Red = positive, yellow = negative
47
Nitrate reduction
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
Starch Hydrolysis
After starch agar incubation plates flooded with iodine solution. Colourless area around growth is positive.
49
Name 2 rapid tests
API Strip and BBL crystal enteric/nonfermenter ID kit
50
Disc diffusion method
lawn of pure bacterial culture inoculated, disc added, zone of inhibition measured
51
Broth Dilution method
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
Etest method (AB biodisc)
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
Name 6 DNA diagnostic systems
``` DNA sequencing Nucleic acid probes PCR Restriction endonuclease analysis Random amplified polymorphic DNA DNA fingerprinting ```
54
What 3 qualities should a good detection system have?
Sensitivity, Specificity and Simplicity
55
Define Sensitivity
The test must be able to detect very small amounts of target even in the presence of other molecules
56
Define Specificity
The test must yield a positive result ONLY for the target molecule
57
Define Simplicity
The test must be able to run efficiently and inexpensively on a routine bias
58
Nucleic Acid Hybridisation
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
Define Membrane Filter Assay
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
Define Dipstick Assay
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
Name 4 advantages of Nucleic Acid Probes
More stable in extreme environments Specimen can be treated harshly Can identify dead microbes More specific than antibodies
62
Describe PCR
2 sequence specific oligonucleotide primers amplify DNA which confirms target presence.
63
Name 4 ways a PCR product can be confirmed
Correct product size Sequence product Hybridisation Nested PCR
64
What can Microarray potentially be used for?
Prenatal screening Testing for specific chromosomal abnormalities Forensics Personalised medicine
65
Enzyme immunoassays
Can be used to detect antigen in a specimen or antibody in a serum sample
66
Serology
The detection of an antibody in a patients serum requiring acute and convalescent samples.
67
Serology Methods
``` Fluorescent Antibody Test Precipitation Reactions Aggluntination reactions Neutralising reactions Complement fixation ```
68
Define a polyclonal antibody
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
Define a monoclonal antibody
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
Name 3 monoclonal antibodies and their associated diseases
Infliximab for Crohns Ibritumomab/rituximab for Non-Hodgkins Lymphoma Trastuzumab for breast cancer
71
Precipitation Reaction
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
Immunodiffusion
Precipitation reaction but in agar.
73
Agglutination reaction
visible clumping of antigen when mixed with specific antibody. Can be direct or passive.
74
Direct agglutination reaction
Soluble antibody results in clumping by interacting with an antigen that is part of the cell surface, used for blood type determination.
75
Passive (indirect) agglutination reaction
Antibody or antigen is absorbed or chemically coupled to call, latex beads or charcoal particles which serve as inert carriers.
76
Haemagglutination
Agglutination of red blood cells
77
Viral Haemagglutination Inhibiton
Some viruses agglutinate red blood cells in vitro, antibodies prevent haemagglutination.
78
Neutralisation reaction
Antitoxin antibody can eliminate the harmful effects of a virus or endotoxin
79
Complement Fixation
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
ELISA
Enzyme-antibody complex produces a coloured product when an enzyme-substrate reaction occurs
81
Radioimmunoassay
Antigens or antibodies labelled with radioactive isotopes
82
Name the 3 types of ELISA and what they detect
Indirect (antibodies) Direct (antigens) Competitive (antigens)

Microbiology (6 decks)

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