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BACTE LAB (FINALS) > AST > Flashcards

AST Flashcards

1
Q

Antibiotic produced by Bacillus subtilis

A

Bacitracin

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2
Q

Antibiotic produced by Bacillus polymyxa

A

Polymyxin

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3
Q

Microorganism that produces Cephalosporin

A

Cephalosporium

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4
Q

Microorganism that produces Penicillin

A

Penicillium notatum

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5
Q

Microorganism that produces Erythromycin

A

Streptomyces erythraeus

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6
Q

Microorganism that produces Neomycin

A

Streptomyces fradiae

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7
Q

Antibiotic produced by Micronospora purpurea

A

Gentamicin

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8
Q

Microorganism that produces Amphotericin B

A

Streptomyces nodusus

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9
Q

Antibiotic produced by Streptomyces noursei

A

Nystatin

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10
Q

Microorganism that produces Chloramphenicol

A

Streptomyces venezuelae

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11
Q

Classification of antibacterial drugs

A

Natural, Semi-synthetic, Synthetic

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12
Q

Drugs produced by bacteria or fungi

A

Natural Drugs

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13
Q

Examples of natural drugs

A

(AKE)
Amphotericin B
Kanamycin
Erythromycin

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14
Q

Define semi-synthetic drugs

A

Modified natural drugs with added chemical groups

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15
Q

Examples of semi-synthetic drugs

A

(CAM)
Carbapenicillin
Ampicillin
Methicillin

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16
Q

Chemically produced drugs

A

Synthetic Drugs

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17
Q

Examples of synthetic drugs

A

(SITC)
Sulfonamides
Isoniazid
Trimethoprim
Ciprofloxacin

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18
Q

1st Gen Drugs

A

(RIPES)
Rifampicin
Isoniazid
Pyrazinamide
Ethambutol
Streptomycin

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19
Q

2nd Gen Drugs

A

(CCOKE)
Capreomycin
Ciprofloxacin
Ofloxacin
Kanamycin
Ethionamide

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20
Q

Antimicrobial agents that inhibit bacterial growth; Stops multiplication via binary fission

A

Bacteriostatic Agents

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21
Q

Examples of bacteriostatic agents

A

(DECTS)
Dapsone
Erythromycin
Chloramphenicol
Tetracycline
Sulfonamides

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22
Q

Antimicrobial agents that kill microorganisms; Treatment for life-threatening conditions; Disrupts bacterial structure

A

Bactericidal Agents

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23
Q

Examples of bactericidal agents

A

Aminoglycosides (GAS)
*Gentamicin
*Amikacin
*Streptomycin

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24
Q

Group A Primary Test (Drugs)

A

(CATG-CATriona Gray)
Cefazolin
Ampicillin
Tobramycin
Gentamicin

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25
Q

Group B Primary Test Selectivity (Drugs)

A

(PICCA)
Piperacillin
Imipenem
Cefuroxime
Ciprofloxacin
Amikacin

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26
Q

Group C Supplemental Report Collectively

A

(CAT)
Chloramphenicol
Aztreonam
Tetracycline

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27
Q

Define MIC

A

(Minimal Inhibitory Concentraton)
Lowest concentration of drug that inhibits bacterial growth

Increasing dilution –> smaller activity of drugs against organisms

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28
Q

Define MBC

A

(Minimal Bactericidal Concentration)
Lowest concentration of drug that kills bacteria

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29
Q

Ratio of the toxic dose to the therapeutic dose; Ratio of how much dosage is safe and lethal

A

Therapeutic Index

Higher TI –> more effective chemotherapeutic agent

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30
Q

What are the mechanisms of action of antibacterial agents?

A

Cell Wall Inhibitors
Protein Synthesis Inhibitors
Nucleic Acid Inhibitors
Cell Membrane Inhibitors
Essential Metabolite Inhibitors

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31
Q

Most selective antibiotics with a higher therapeutic index

A

Cell Wall Inhibitors

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32
Q

Inhibit the activity of transpeptidase enzymes in which cell growth stops and death of cells often follows

A

Cell Wall Inhibitors

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33
Q

These drugs are effective against Gram (+) bacteria

A

Cell Wall Inhibitors

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34
Q

Give the examples of cell wall inhibitors and their action

A

*Bacitracin (inhibits synthesis of peptidoglycan precursors)
*B-lactams (inhibits transpeptidase)
*Isoniazid (can be bactericidal or bacteriostatic)
*Vancomycin (inhibits translocation and elongation of peptidoglycan)

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35
Q

These antibiotics bind to 30S subunit (smaller) that results in the misreading of mRNA.

A

Protein Synthesis Inhibitors

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36
Q

These drugs target aerobic and anaerobic, gram (+) and gram (-) bacteria

A

Protein Synthesis Inhibitors

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37
Q

Protein synthesis inhibitors are effective against what examples of microorganisms?

A

(FIMPT)
Bacteroides fragilis
Haemophilus influenzae
Neisseria meningitidis
Streptococcus pneumoniae
Mycobacterium tuberculosis

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38
Q

Examples of protein synthesis inhibitors

A

Aminoglycosides, Tetracycline

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39
Q

Examples of nucleic acid inhibitors and their action

A

*Rifampicin (inhibits RNA polymerase and synthesis)
*Quinolones (effective against enteric bacteria like E. coli)
*Metronidazole (treatment for amoeba, disrupts DNA, effective for anaerobic bacteria)

40
Q

What drugs are effective against Gram (-) bacteria

A

Cell Membrane Inhibitors

41
Q

Examples of cell membrane inhibitors

A

Polymyxin B and E

42
Q

First mutant bacteria

A

Pseudomonas aeruginosa

43
Q

This targets the permeability of cell walls

A

Cell Membrane Inhibitors

44
Q

Examples of essential metabolite inhibitors

A

Folic Acid (Sulfamethoxazole)
Cord Factor (Isoniazid)
*For TB; Virulence Factor

45
Q

Principle of AST

A

Measures the ability of an antibiotic or other microbial agent to inhibit bacterial growth

46
Q

What is an antibiogram

A

Profile of the susceptibilities of specific pathogenic bacteria against antimicrobial agents

47
Q

Primary goal of AST

A

To determine whether the bacterial isolate is capable of expressing resistance to the antimicrobial agents selected for treatment

48
Q

Purpose of AST

A

*To guide the clinician in selecting appropriate antimicrobial agent
*To gather epidemiologic data on microbial resistance

49
Q

Purpose of standardization

A

*To optimize bacterial growth conditions
*To optimize conditions for antimicrobial integrity and activity
*To maintain reproducibility and consistency of the resistance profile

50
Q

Most common method in Antimicrobial Susceptibility Testing

A

Disk Diffusion Method (Kirby-Bauer Test)

51
Q

Medium used in Kirby-Bauer Test

A

Mueller-Hinton Agar

52
Q

Standard used in DDM and its components

A

0.5 Mcfarland/Barium Sulfate Suspension
*99.5 mL of 1% Sulfuric Acid
*0.5 mL or 1.175% Barium Chloride

53
Q

Standard inoculum in DDM

A

1.5 x 10^8 organisms/mL

54
Q

pH of DDM

A

7.2-7.4 (slightly alkaline)

55
Q

Depth of plate in DDM

A

4 mm

56
Q

Condition of DDM

A

Aerobic (NO CO2)

57
Q

Temperature of DDM

A

35-37*C

58
Q

Incubation time in DDM

A

16-18 hours

59
Q

Diameter of antibiotic disk

A

6 mm

60
Q

Bacterial count in DDM

A

Petroff-Hausser

61
Q

If sample is too turbid then Mcfarland, what do you do?

A

Dilute and add NSS

62
Q

If sample is too diluted than Mcfarland, what do you do?

A

Add colony

63
Q

The standard susceptibility medium for non-fastidious bacteria

A

Mueller-Hinton Agar

64
Q

Composition of MHA

A

(BANCV)
Beef infusion
Agar
Nucleic Acid
Casein
Vitamins

65
Q

Used to improve the detection of oxacillin resistant staphylococc

A

MH broth with 2% NaCl

66
Q

Utilized for testing susceptibility for streptococci, N. meningitidis, and other fastidious organisms

A

MH broth with 5% lysed horse or sheep blood

67
Q

Where is sheep’s blood collected?

A

Jugular vein

68
Q

Preferable when preparing culture media for BAB due to the large RBC compared to humans

A

Sheep’s blood

69
Q

Alternative method of testing for MRSA aside from adding 2% NaCl

A

Plate containing 6 ug/ml of oxacilin in Mueller-Hingon Agar supplemented with 4% NaCl

70
Q

Factors affecting disk diffusion

A

(ATGpNC)
*Amount of inoculum
*Thickness of susceptibility plate
*Growth rate of microbe
*pH of medium
*Number of disks per plate
*Concentration of divalent bonds

71
Q

If the agar is too thick –>

A

Smaller ZOI

72
Q

If the agar is too thin –>

A

Larger ZOI

73
Q

If the temperature is higher than 35*C –>

A

False detection of MRSA (due to mutated mecA gene)

74
Q

If the temperature is lower than 35*C –>

A

Larger ZOI

75
Q

Incubation of plates in CO2 leads to –>

A

Decreased pH

76
Q

Increased pH –>

A

Decreased activity of tetracycline drugs

77
Q

Decreased pH –>

A

Decreased activity of aminoglycosides and erythromycin

78
Q

Placement of more than 12 may result in –>

A

Overlapping of zones

79
Q

Can affect the testing of aminoglycosides and
tetracycline against PAE.

A

Concentration of divalent bonds (Ca ang Mg)

80
Q

Procedure for AST

A
  1. Pure inoculum are obtained by selecting 4-5 colonies of the same morphology.
  2. Colonies are being suspended into 0.05% NSS to achieve a turbid suspension.
  3. Bacterial suspension & Mcfarland solution are compared by matching the turbidity of the tubes against a dark background.
  4. Perform Lawn Streaking. Turn the plate 60 degrees between each streaking
  5. Within 15 minutes of inoculation antimicrobial agents are applied into your MHA.
  6. Within 15 minutes. of disk placement, plates are inverted & incubated at 35C for 16-18hrs.
  7. Diameter of each inhibition zone is measured using a caliper or ruler.
81
Q

If there is no ZOI –>

A

Measure the size of the antibiotic disk in mm. Do NOT report as zero

82
Q

Distance between each disk

A

15 mm

83
Q

How many discs fit in 150 mm?

A

12

84
Q

How many discs fit in 100 mm?

A

5-6

85
Q

Causes of false resistant AST

A

*15 mins delay (disc application)
*increased moisture
*too thick medium
*increased organisms –> decrease ZOI

86
Q

Causes of false sensitive

A

*15 mins delay (incubation)
*increased drying
*too thin
*decreased organisms –> larger ZOI

87
Q

Define susceptible

A

Microorganisms should respond to therapy with that antimicrobial agent; Effective against the microorganism

88
Q

Define intermediate

A

*MIC approaches or exceeds the level of antimicrobial agent that can be achieved
*Clinical response is likely to be less than with a susceptible strain
*Can be both effective or resistant against the organism

89
Q

Define resistant

A

No or small ZOI. Antibiotic is not the appropriate choice for treatment

90
Q

In case the organism is susceptible to 2 antibiotics, what should you do?

A

Determine the drug that works best for the px

91
Q

It uses manual gravity based inoculation technique; Has mechanism to read ESBL; Results after 8-12 Hours

A

Phoenix System

92
Q

Inocula are manually introduced to the broth microdilution tray

A

Microscan Walkaway System

93
Q

Fully automated equipment that is designed for the identification of bacteria and AST; Optical readings every 15 minutes; Final reading is 6-8 hours

A

Vitek System

94
Q

2 types of MRSA and define

A

*Healthcare Associated MRSA (due to invasive procedures or devices such as surgeries, artificial joints, intravenous tubing)
*Community Associated MRSA (begins as a painful skin boil, spread by skin-to-skin contact, at risk populations are crowded areas)

95
Q

The only difference between CA and HA MRSA

A

location where it is acquired

96
Q

Tests for MRSA that are recommended by CLSI

A

(BCLPCN)
*Broth microdilution testing
*Cefoxitin disk screen test
*Latex agglutination for PBP2a (Penicillin‐binding protein 2a)
*Plate containing 6 ug/ml of oxacilin in Mueller-Hingon Agar supplemented with 4% NaCl
*Chromogenic agars
*Nucleic acid amplification test (PCR) –> detects mecA gene

BACTE LAB (FINALS) (2 decks)

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