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Chemical Pathology > Microbiology > Flashcards

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
Q

What are the benefits of using sulfonamides and trimethoprim together?

A

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
Q

Examples of quinolones

A

Levofloxacin
Ciprofloxacin
Moxifloxacin
Garenoxacin

27
Q

When are floroquinolones CI?

A

Pregnancy
Children <18y

28
Q

MOA of rifampicin

A

Blocks mRNA synthesis by RNA polymerase

29
Q

Which AB inhibit protein synthesis?

A

Tetracyclines
Macrolides
Aminoglycosides
Chloramphenicol
Lindosamides
Streptogramins

30
Q

Examples of aminoglycosides

A

Gentamicin
Streptomycin
Kanamycin

31
Q

MOA of aminoglycosides

A

Prevent the formation of the initiation complex by preventing fmet binding to the 30s ribosome

32
Q

SE of aminoglycosides

A

Ototoxicand mephrotoxic

33
Q

MOA of tetracyclines

A

Inhibit protein synthesis by blocking the attachment of charged aminoacyl-tRNA to the A site on the ribosome

34
Q

CI of tetracyclines

A

Pregancy
Children <8y (yellow staining of teeth)

35
Q

MOA of chloramphenicol

A

Inhibits peptides transfer at the 50s ribosomal subunit

36
Q

Examples of macrolides

A

Erythromycin
Clarithromhcin
Azithromycin

37
Q

MOA of macrolides

A

Bind exclusively to 50s subunit of ribosome to prevent translocation

38
Q

Examples of lincosamides

A

Clindamycin
Lincomycin

39
Q

Methods of AB susceptibility testing

A

Kirby Bauer Disc Diffusion Method
Agar proportion method
Broth microdilution
E-test
Automated methods
Molecular methods (Gene Xpert)

40
Q

Role of practitioner in infection, prevention and control?

A

Hand hygiene
Surveillance data and feedback
Healthcare worker education
Cleaning/disinfecting equipment
Cleaning/disinfecting the health care environment

Use of PPE

41
Q

List 5 microbiology lab techniques

A

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
Q

Specimen collection guidelines

A

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
Q

What can you NOT use for anaerobe culture?

A

Swabs

44
Q

TB culture turnaround time and specimen

A

10 days to 3 weeks for positive
Swabs are NOT accepted for TB culture

**PCR assays in a few hours

45
Q

How many bottles for blood culture?

A

2 for adults (aerobe and anaerobe)
One for paeds

46
Q

Which tube do you fill first for blood culture?

A

The anaerobic one so that no air gets into the aerobic one

47
Q

What is the protocol for blood cultures of suspected infective endocarditis?

A

3 sets of cultures, over 2-3 hours from different sites

48
Q

Ova, parasite and cyst specimen protocol

A

3 stool specimens take, one per day for 3 days recommended

49
Q

Threadworm specimen

A

Sellotape impression from around anus before or has defaecated or washed in the morning

50
Q

Name the types of TB tests available

A

TB microscopy
Real time PCR (Gene Xpert)
Line probe assay
Xpert XDR cartridge
Liquid culture

51
Q

Method of gene Xpert

A

Isolated bacteria from sputum
Isolated genomic material
Amplified with PCR
ID’s rifampicin resistance mutations
Results in <2hrs

52
Q

What specimens can be processed. Y Gene Xpert?

A

Nasogastric aspirations
Endotracheal aspirations
Tissues
Pleural fluid
Ascetic. Fluid
CSF

53
Q

What type of microscopy is used for TB?

A

Fluorescence microscopy (auramine)
= bacilli fluoresce orange-yellow with UV excitation

54
Q

How does liquid culture of TB work?

A

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
Q

Line probe assay

A

DNA amplification and reverse hybridisation, iD MTB complex and rifampicin and isoniazid resistance detection

56
Q

First line TB treatment

A

Rifampicin
Isoniazid
Ethambutol
Pyrazinamide

Chemical Pathology (8 decks)

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