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Microbiology Flashcards

1
Q

What is selective toxicity?

A

Selective inhibition of the growth of the microorganism without damage to host

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2
Q

Name the sources of antibiotics

A

Natural
semisynthetic
Synthetic

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3
Q

Compare the features of gram positive and negative bacteria structurally

A

Gram positive
>one membrane layer
>peptidoglycans close to surface

Gram negative
>double membrane impenetrable to so,e AB
>peptidoglycans not on surface

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4
Q

What component of the cell wall is a good target for selective toxicity?

A

Peptidoglycan (unique to bacteria)

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5
Q

Which classes of antibiotics target the cell wall to inhibit synthesis

A

Beta lactams
Glycopeptides

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6
Q

Examples of beta lactams

A

Penicillin
Beta lactam/Beta lactamase inhibitors combination
Carbapenema
Cephalosporins
Monobactams

All have beta lactam ring

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7
Q

MOA of beta lactams

A

Bind to trans peptides enzyme preventing it from linking the amino acid chains in the cell wall

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8
Q

Further classify penicillins and give an example of each

A

Beta lactamase resistant penecillins eg cloxacillin

Amino penecillins eg amoxicillin (B-road spectrum)

Carboxylate-penecillins

Ureido penecillins eg carbenicillin

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9
Q

How did bacteria adapt to penecillins?

A

Gram + = penecillinase

Gram - = beta lactamase

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10
Q

Examples of beta lactamase inhibitors

A

Clavulanic acid
Sulbactam
Tazobactam
Avibactam

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11
Q

Examples of beta lactam/beta lactamase inhibitor combinations

A

Augmentin (co-amoxicillin-clav)
Piperacillin-tazobactam

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12
Q

How are cephalosporins classified?

A

According to their spectrum of activity and time of development.

1st-5th gen

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13
Q

Which carbapenams have the broadest anti-microbial spectrum and are beta lactamase stable?

A

Group 1 = ergapenem

Group 2 = imipenem, meropenem, doripenem

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14
Q

MOA of glycopeptides

A

Bind to terminal D-ala-D-ala at the end of the pentapeptide chains which are part of the growing bacterial cell wall

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15
Q

Two examples of glycopeptides

A

Vancomycin
Teincoplanin

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16
Q

What is the basis of selective toxicity in cell membrane inhibitors?

A

Bacteria have phospholipids in their membranes but no sterols.

Humans and fungi have sterols (cholesterol, ergosterol)

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17
Q

What is an example of cell membrane inhibitors?

A

Polymyxins (B and E)

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18
Q

What are SE’s of polymyxins?

A

Neuro and nephrotoxic

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19
Q

What bacteria do polymyxins cover?

A

Gram negatives (THEY DO NOT HAVE G+ OR ANAEROBE COVER)

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20
Q

What are the 3 groups of nucleic acid Synthesis inhibitors?

A

Inhibitors of folate synthesis
Inhibitors of DNA synthesis
Inhibitors of mRNA synthesis

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21
Q

What is the MOA of sulfonamides?

A

They compete with PABA for the active site on the enzyme dihydropteroate synthetase (inhibits folic acid synth)

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22
Q

Side effects of sulfonamides

A

> fever, rash, photosensitivity, bone marrow suppression
erythema multi forms, Steven Johnson syndrome
toxic epidermal necrolysis

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23
Q

MOA of trimethroprims

A

Inhibit the synthesis of tetrehydrofolate by inhibiting the enzyme

24
Q

What is sulfamethoxazole-trimethroprim used to treat?

A

UTI’s
Drug prophylaxis in HIV pts
Pneumocystis pneumonia

25
What are the benefits of using sulfonamides and trimethoprim together?
They act on the same pathway at different points. Greater effect in combo. If organism is resistant to one, it won’t be to the other
26
Examples of quinolones
Levofloxacin Ciprofloxacin Moxifloxacin Garenoxacin
27
When are floroquinolones CI?
Pregnancy Children <18y
28
MOA of rifampicin
Blocks mRNA synthesis by RNA polymerase
29
Which AB inhibit protein synthesis?
Tetracyclines Macrolides Aminoglycosides Chloramphenicol Lindosamides Streptogramins
30
Examples of aminoglycosides
Gentamicin Streptomycin Kanamycin
31
MOA of aminoglycosides
Prevent the formation of the initiation complex by preventing fmet binding to the 30s ribosome
32
SE of aminoglycosides
Ototoxicand mephrotoxic
33
MOA of tetracyclines
Inhibit protein synthesis by blocking the attachment of charged aminoacyl-tRNA to the A site on the ribosome
34
CI of tetracyclines
Pregancy Children <8y (yellow staining of teeth)
35
MOA of chloramphenicol
Inhibits peptides transfer at the 50s ribosomal subunit
36
Examples of macrolides
Erythromycin Clarithromhcin Azithromycin
37
MOA of macrolides
Bind exclusively to 50s subunit of ribosome to prevent translocation
38
Examples of lincosamides
Clindamycin Lincomycin
39
Methods of AB susceptibility testing
Kirby Bauer Disc Diffusion Method Agar proportion method Broth microdilution E-test Automated methods Molecular methods (Gene Xpert)
40
Role of practitioner in infection, prevention and control?
Hand hygiene Surveillance data and feedback Healthcare worker education Cleaning/disinfecting equipment Cleaning/disinfecting the health care environment Use of PPE
41
List 5 microbiology lab techniques
1) direct microscopic visualisation (smears, stains) 2) culture and ID 3) detection of antigens or virulence factors 4) detection of microbial DNA/RNA (molecular testing) 5) detection of host immune response
42
Specimen collection guidelines
1) avoid contamination from indigenous flora 2) collect from correct site 3) adequate volume 4) correct transport medium 5) avoid delay in transport 6) label each specimen
43
What can you NOT use for anaerobe culture?
Swabs
44
TB culture turnaround time and specimen
10 days to 3 weeks for positive Swabs are NOT accepted for TB culture **PCR assays in a few hours
45
How many bottles for blood culture?
2 for adults (aerobe and anaerobe) One for paeds
46
Which tube do you fill first for blood culture?
The anaerobic one so that no air gets into the aerobic one
47
What is the protocol for blood cultures of suspected infective endocarditis?
3 sets of cultures, over 2-3 hours from different sites
48
Ova, parasite and cyst specimen protocol
3 stool specimens take, one per day for 3 days recommended
49
Threadworm specimen
Sellotape impression from around anus before or has defaecated or washed in the morning
50
Name the types of TB tests available
TB microscopy Real time PCR (Gene Xpert) Line probe assay Xpert XDR cartridge Liquid culture
51
Method of gene Xpert
Isolated bacteria from sputum Isolated genomic material Amplified with PCR ID’s rifampicin resistance mutations Results in <2hrs
52
What specimens can be processed. Y Gene Xpert?
Nasogastric aspirations Endotracheal aspirations Tissues Pleural fluid Ascetic. Fluid CSF
53
What type of microscopy is used for TB?
Fluorescence microscopy (auramine) = bacilli fluoresce orange-yellow with UV excitation
54
How does liquid culture of TB work?
Glass tube with modified Middlebrook 7H9 broth (7ml) and fluorescence quenching based oxygen sensor at the bottom of the tube. Inoculated with MTB, consume O2 and fluoresce
55
Line probe assay
DNA amplification and reverse hybridisation, iD MTB complex and rifampicin and isoniazid resistance detection
56
First line TB treatment
Rifampicin Isoniazid Ethambutol Pyrazinamide

Chemical Pathology (8 decks)

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