Microbiology Flashcards
What is selective toxicity?
Selective inhibition of the growth of the microorganism without damage to host
Name the sources of antibiotics
Natural
semisynthetic
Synthetic
Compare the features of gram positive and negative bacteria structurally
Gram positive
>one membrane layer
>peptidoglycans close to surface
Gram negative
>double membrane impenetrable to so,e AB
>peptidoglycans not on surface
What component of the cell wall is a good target for selective toxicity?
Peptidoglycan (unique to bacteria)
Which classes of antibiotics target the cell wall to inhibit synthesis
Beta lactams
Glycopeptides
Examples of beta lactams
Penicillin
Beta lactam/Beta lactamase inhibitors combination
Carbapenema
Cephalosporins
Monobactams
All have beta lactam ring
MOA of beta lactams
Bind to trans peptides enzyme preventing it from linking the amino acid chains in the cell wall
Further classify penicillins and give an example of each
Beta lactamase resistant penecillins eg cloxacillin
Amino penecillins eg amoxicillin (B-road spectrum)
Carboxylate-penecillins
Ureido penecillins eg carbenicillin
How did bacteria adapt to penecillins?
Gram + = penecillinase
Gram - = beta lactamase
Examples of beta lactamase inhibitors
Clavulanic acid
Sulbactam
Tazobactam
Avibactam
Examples of beta lactam/beta lactamase inhibitor combinations
Augmentin (co-amoxicillin-clav)
Piperacillin-tazobactam
How are cephalosporins classified?
According to their spectrum of activity and time of development.
1st-5th gen
Which carbapenams have the broadest anti-microbial spectrum and are beta lactamase stable?
Group 1 = ergapenem
Group 2 = imipenem, meropenem, doripenem
MOA of glycopeptides
Bind to terminal D-ala-D-ala at the end of the pentapeptide chains which are part of the growing bacterial cell wall
Two examples of glycopeptides
Vancomycin
Teincoplanin
What is the basis of selective toxicity in cell membrane inhibitors?
Bacteria have phospholipids in their membranes but no sterols.
Humans and fungi have sterols (cholesterol, ergosterol)
What is an example of cell membrane inhibitors?
Polymyxins (B and E)
What are SE’s of polymyxins?
Neuro and nephrotoxic
What bacteria do polymyxins cover?
Gram negatives (THEY DO NOT HAVE G+ OR ANAEROBE COVER)
What are the 3 groups of nucleic acid Synthesis inhibitors?
Inhibitors of folate synthesis
Inhibitors of DNA synthesis
Inhibitors of mRNA synthesis
What is the MOA of sulfonamides?
They compete with PABA for the active site on the enzyme dihydropteroate synthetase (inhibits folic acid synth)
Side effects of sulfonamides
> fever, rash, photosensitivity, bone marrow suppression
erythema multi forms, Steven Johnson syndrome
toxic epidermal necrolysis
MOA of trimethroprims
Inhibit the synthesis of tetrehydrofolate by inhibiting the enzyme
What is sulfamethoxazole-trimethroprim used to treat?
UTI’s
Drug prophylaxis in HIV pts
Pneumocystis pneumonia
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
Examples of quinolones
Levofloxacin
Ciprofloxacin
Moxifloxacin
Garenoxacin
When are floroquinolones CI?
Pregnancy
Children <18y
MOA of rifampicin
Blocks mRNA synthesis by RNA polymerase
Which AB inhibit protein synthesis?
Tetracyclines
Macrolides
Aminoglycosides
Chloramphenicol
Lindosamides
Streptogramins
Examples of aminoglycosides
Gentamicin
Streptomycin
Kanamycin
MOA of aminoglycosides
Prevent the formation of the initiation complex by preventing fmet binding to the 30s ribosome
SE of aminoglycosides
Ototoxicand mephrotoxic
MOA of tetracyclines
Inhibit protein synthesis by blocking the attachment of charged aminoacyl-tRNA to the A site on the ribosome
CI of tetracyclines
Pregancy
Children <8y (yellow staining of teeth)
MOA of chloramphenicol
Inhibits peptides transfer at the 50s ribosomal subunit
Examples of macrolides
Erythromycin
Clarithromhcin
Azithromycin
MOA of macrolides
Bind exclusively to 50s subunit of ribosome to prevent translocation
Examples of lincosamides
Clindamycin
Lincomycin
Methods of AB susceptibility testing
Kirby Bauer Disc Diffusion Method
Agar proportion method
Broth microdilution
E-test
Automated methods
Molecular methods (Gene Xpert)
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
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
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
What can you NOT use for anaerobe culture?
Swabs
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
How many bottles for blood culture?
2 for adults (aerobe and anaerobe)
One for paeds
Which tube do you fill first for blood culture?
The anaerobic one so that no air gets into the aerobic one
What is the protocol for blood cultures of suspected infective endocarditis?
3 sets of cultures, over 2-3 hours from different sites
Ova, parasite and cyst specimen protocol
3 stool specimens take, one per day for 3 days recommended
Threadworm specimen
Sellotape impression from around anus before or has defaecated or washed in the morning
Name the types of TB tests available
TB microscopy
Real time PCR (Gene Xpert)
Line probe assay
Xpert XDR cartridge
Liquid culture
Method of gene Xpert
Isolated bacteria from sputum
Isolated genomic material
Amplified with PCR
ID’s rifampicin resistance mutations
Results in <2hrs
What specimens can be processed. Y Gene Xpert?
Nasogastric aspirations
Endotracheal aspirations
Tissues
Pleural fluid
Ascetic. Fluid
CSF
What type of microscopy is used for TB?
Fluorescence microscopy (auramine)
= bacilli fluoresce orange-yellow with UV excitation
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
Line probe assay
DNA amplification and reverse hybridisation, iD MTB complex and rifampicin and isoniazid resistance detection
First line TB treatment
Rifampicin
Isoniazid
Ethambutol
Pyrazinamide
