(P) Lec 3.2: Bacterial Pathogenesis and Epidemiology, Antimicrobials and Mechanism of Bacterial Resistance, and Indigenous Microbial Flora Flashcards
Chapter 13 of Mahon's
1
Q
Performed on bacteria and fungi isolated from clinical specimens to determine which antimicrobial agents might be effective in treating infections caused by these organisms
A
Antimicrobial Susceptibility Testing
2
Q
Only organisms that are likely to be contributing to an infection should be tested
A
Antimicrobial Susceptibility Testing
3
Q
Often performed by a disk diffusion or dilution (minimal inhibitory concentration [MIC]) method
A
Antimicrobial Susceptibility Testing
4
Q
Inoculum concentration of bacteria to be tested must be ______
A
Standardized
5
Q
____ results may occur if too few bacteria are tested
A
False-susceptible
6
Q
____ results may be the outcome of testing too many bacteria
A
False-resistant
7
Q
Name the standard
Standard Suspension
A
McFarland 0.5 standard: contains 99.5 mL of 1% sulfuric acid and 0.5 mL of 1.175% barium chloride.
8
Q
Name the standard
Bacterial Inoculum Size
A
1.5 × 10^8 CFU/mL
9
Q
Name the standard
Standard Medium
A
Mueller-Hinton Heated Agar
10
Q
Name that standard
Standard Depth
A
4-6 mm
11
Q
Name that standard
Standard pH
A
7.2-7.4
12
Q
Name that standard
Atmosphere requirement
A
Aerobic, no CO2
13
Q
Name that standard
Temperature
A
35 - 37°C
14
Q
Disk Diffusion
A
1.5 x 10^8 CFU/mL
15
Q
Broth Dilution
A
5 x 10^5 CFU/mL
16
Q
Agar Dilution
A
1 x 10^4 CFU/mL
17
Q
Composition of Mueller Hinton Agar
A
- Beef infusion solids
- Starch
- Casein hydrolysate agar
18
Q
What are the storage guidelines of Mueller Hinton Agar?
A
- Store prepared media below 8°C
- Protect from direct light
- Store the dehydrated powder in a dry place and tightly sealed containers at 2 - 25°C
19
Q
Main Purpose of 0.5 McFarland Standard
A
To adjust the turbidity of bacterial suspensions to a standardized level
20
Q
Most common composition of 0.5 McFarland Standard
A
- 99.5 mL of 1% sulfuric acid
- 0.5 mL of 1.175% barium chloride
Can be prepared by adding specific volume of 1% sulfuric acid and 1.175% barium chloride to obtain a barium sulfate solution with a specific optical density
21
Q
Storage of 0.5 McFarland Standard
A
Stored in an upright position at 4°C to 25°C and protected from light
22
Q
Under the proper storage conditions, how long does the 0.5 McFarland Standard last?
A
12 weeks from date of manufacture
23
Q
Used to determine the minimum inhibitory concentration (MIC) or the lowest concentration of antimicrobial agent required to inhibit the growth of the bacterium
A
Dilution Susceptibility Testing
24
Q
Those that are attainable in vivo following standard dosing of the respective antimicrobial agent
A
Serial Two Fold-Dilution Concentrations
25
Once the MIC has been determined, the organism is interpreted as ____, ____, ____ or ____ to each agent
Nonsusceptible, susceptible, intermediate, or resistant
26
They described a test that measured the effectiveness with which penicillin in serum killed bacteria associated with endocarditis
Schlichter and MacLean
27
What year did Schlichter and MacLean describe the Serum Bactericidal Test?
1940s
28
Analogous to the MIC-MBC test except that the medium used is patient’s serum
Serum Bactericidal Test
29
Results relate to the amount of antimicrobial agent and any other antibacterial factors *(e.g., antibody, opsonins, complement) present in the patient’s serum)*
Serum Bactericidal Test
30
Also known as oxacillin resistance screening agar
Oxacillin Agar Screen
31
A specialized medium used for the screening of oxacillin-resistant microorganisms, primarily focusing on detecting MRSA
Oxacillin Agar Screen
32
What are the steps involving oxacillin agar screen?
1. Allow medium to reach room temperature.
2. Take the specimen swab and roll it near the edge of the plate.
3. Then, use a sterile loop to perform a four-quadrant streak starting from that area to get isolated colonies.
4. Incubate aerobically at 35°C.
5. Examine after 24 hours for typical MRSA colonies. Re-incubate plates an additional 24 hours before discarding.
33
Used to detect VRSA and Enterococci resistant to VAN
Vancomycin Agar Screen
34
What are the steps involving vancomycin agar screen?
1. Dip the swab into the inoculum (comparable to 0.5 McFarland std) to the plate medium (BHI w 6 mg/L of vancomycin) by streaking over the entire agar surface.
2. Inc. 24 hrs
35
Resistant to VAN if:
They had developed mutations in their cell walls
36
Susceptible to VAN if:
They acquired a plasmid containing vanA vancomycin resistance gene from vancomycin-resistant enterococci
37
Used to detect inducible clindamycin resistance in bacteria, particularly in coagulasenegative staphylococci (CoNS) and Staphylococcus aureus
D-Test
38
The two antibiotics being observed in D-Test are ____ and ____
Erythromycin and clindamycin
39
# Synergy Testing
Its antibacterial activity is significantly greater than that of a single agent
Synergism
40
# Synergy Testing
The activity of the combination less than (and MICs are greater than) that of the single agents
Antagonism
41
# Synergy Testing
The activity of the combination is equal to that of the single agents
Indifference
42
A method used to study the antimicrobial activity of a compound over time. This assay helps determine the bactericidal or bacteriostatic properties of an antimicrobial agent against a particular microorganism
Time-Kill Assay
43
What are the steps involving Time-Kill Assay?
1. Prepare bacterial inoculum
2. Add antimicrobial agent
3. Incubate (on time intervals)
4. Serially diluted, and then plated onto suitable agar
5. Read the number of colonies
44
What are the steps involving E-Test?
1. Prepare bacterial inoculum
2. Uniformly spread bacteria on MHA
3. Impregnate E-test strip
4. Incubate
5. Read
45
A quantitative method used to determine the MIC of antimicrobial agents against specific microorganisms
E-Test
46
It is produced by microorganisms i.e. bacteria and fungi, that it sends outside its cell to harm or kill another microorganism
Antibiotics
47
A drug used to treat infections caused by bacteria and other microorganism
Antibiotics
48
# Name the antibiotic
Bacillus subtilis
Bacitracin
49
# Name the antibiotic
Bacillus polymyxa
Polymyxin
50
# Name the antibiotic
Streptomyces nodosus
Amphotercin B
51
# Name the antibiotic
Streptomyces venezuelae
Chloramphenicol
52
# Name the antibiotic
Streptomyces erythraeus
Erythromycin
53
# Name the antibiotic
Streptomyces griseus
Streptomycin
54
# Name the antibiotic
Micromonospora purpurea
Gentamicin
55
# Name the antibiotic
Cephalosporium spp. *(fungi)*
Cephalothin
56
# Name the antibiotic
Penicillium notatum *(fungi)*
Penicillin
57
# Inhibitors of Cell Wall Synthesis
**Antibiotic:** B-lactams
| Give the **examples, principles, and any additional notes.**
**Examples:** Penincillins, Cephalosporins, Carbapenams *(Imipenem)*, Monobactams *(Azotreonam)*
**Principle:** Targets the enzyme mediating the transpeptidation
**Additional Notes:** Methicillin for penincillin-resistant Staph.
58
# Inhibitors of Cell Wall Synthesis
**Antibiotic:** Glycopeptides
| Give the **examples, principles, and any additional notes.**
**Example:** Vancomycin
**Principle:** Binds into the substrate of the transpeptidation enzyme
**Additional Notes:** DOC for Clostridium difficile and for MRSA
59
# Inhibitors of Protein Synthesis
**Antibiotic:** Aminoglycosides
| Give **examples and principles.**
**Examples:** Gentamicin, Tobramycin, Kanamycin
**Principle:** Acts on **30S subunit**; not active against anaerobes, used with a penicillin for Enterococcus
60
# Inhibitors of Protein Synthesis
**Antibiotic:** Tetracyclines
| Give **examples and principles.**
**Examples:** Tetracycline, Doxycycline
**Principle:** Reversible binding to **30S subunit**
**Contraindication:** tetracyclin affects bone and teeth in infants
61
# Inhibitors of Protein Syntheis
**Antibiotic:** Phenicols
| Give **examples and principles.**
**Examples:** Chloramphenicol
**Principle:** Acts on **50S subunit**
62
# Inhibitors of Protein Synthesis
**Antibiotic:** Macrolides
| Give **examples and principles.**
**Examples:** Erythromycin, Azithromycin, Clindamycin
**Principles:** Acts on 50S subunit; clindamycin for gram (+) and gram (-) anaerobes
63
# Inhibitors of DNA
**Antibiotic:** Quinolones
| Give **the examples.**
* Ciprofloxacin
* Norfloxacin
| For P. aeruginosa and other anaerobes
64
# Give the resistance and disease.
**Agent:** S. pneumoniae
**Resistance:** Penicillin
**Disease:** Pneumonia
65
# Give the resistance and disease.
**Agent:** Shigella
**Resistance:** Multiple Resistance
**Disease:** Dysentery
65
# Give the resistance and disease.
**Agent:** Salmonella typhi
**Resistance:** Multiple Resistance
**Disease:** Typhoid
66
# Give the resistance and disease.
**Agent:** Neisseria gonorrhoeae
**Resistance:** Penicillin and Tetracycline
**Disease:** Gonorrhea
66
# Give the resistance and disease.
**Agent:** Mycobacterium tuberculosis
**Resistance:** Multiple Resistance
**Disease:** Tuberculosis
67
# Give the resistance and disease.
**Agent:** S. aureus
**Resistance:** Methicillin and Cancomycin
**Disease:** Skin and soft tissue infections
68
# Give the resistance and disease.
**Agent:** Klebsiella, Pseudomonas
**Resistance:** Multiple Resistance
**Disease:** Pneumonia, UTI
69
* Presence of genes responsible for resistance to its own antibiotic
* Lack transport system or target for that antibiotic
* Due to increase efflux activity
Natural Antimicrobial Resistance
70
* Gene changes or exchanges that result from acquired resistance are usually caused by genetic mutation(s)
* Acquisition of genes from other organisms via gene transfer mechanisms, or a combination of mutational and gene transfer events
Acquired Antimicrobial Resistance
71
# Acquired Antimicrobial Resistance
Process by which bacteria take up free, extracellular DNA from their environment and incorporate it into their own genome
Transformation
72
# Acquired Antimicrobial Resistance
A process of horizontal gene transfer where genetic material is transferred directly from one bacterial cell to another through a physical connection known as a pilus or conjugation bridge
Conjugation
73
# Acquired Antimicrobial Resistance
Process by which bacterial DNA is transferred from one bacterium to another by a bacteriophage (a virus that infects bacteria)
Transduction
74
# Specific Antimicrobial Resistance
Aminoglycosides
| Inactivation of Drugs by Enzymes
* Acetyltransferases
* Phosphotransferases
* Adenylyltransferase
75
# Specific Antimicrobial Resistance
Chloramphenicol
| Inactivation of Drugs by Enzymes
* Chloramphenicol
* Acetyltransferases
76
# Specific Antimicrobial Resistance
Macrolide
| Inactivation of Drugs by Enzymes
* Esterases
* Methyltransferases
* Hydrolytic enzymes
77
# Specific Antimicrobial Resistance
Tetracycline, B-lactams, aminoglycosides, quinolone
| Alteration of Membrane Permeability
Changes in porins, efflux pumps, altered membrane composition, biofilm formation, membrane lipid modifications
78
# Specific Antimicrobial Resistance
Macrolide
| Alteration of Intracellular Target Site
* Methylation of 23S rRNA
* Blocking erythromycin binding site
79
# Specific Antimicrobial Resistance
Aminoglycosides
| Alteration of Intracellular Target Site
* Altered protein in 30S ribosome
80
# Specific Antimicrobial Resistance
B-lactams
| Alteration of Intracellular Target Site
* Alteration in penicillin binding proteins
81
# Specific Antimicrobial Resistance
Rifampin
| Alteration of Intracellular Target Site
* Altered DNA-dependent RNA polymerase
82
# Specific Antimicrobial Resistance
Quinolones
| Alteration of Intracellular Target Site
* Modified DNA gyrase
* Topoisomerase IV
83
# Specific Antimicrobial Resistance
Sulfonamides
| Overproduction of Target Enzyme
* Increased levels of Dihydropteroate synthase
84
# Specific Antimicrobial Resistance
Trimethoprim
| Overproduction of Target Enzymes
* Increased levels of Dihydrofolate reductase (DHFR)
