An Infection Model And Antimicrobials Flashcards
Name the different mechanisms of infection
Contiguous (direct) spread Inoculation Haematogenous Ingestion Inhalation Vector Vertical transmission
What factors affect the patient’s risk of infection?
Age Gender Physiological state Genetics/epigenetics Pathological state/co-morbidities Social factors
What are the 2 types of time in relation to infection?
Calendar time (time of year) Relative time (since pt exposure)
What is the difference between exotoxins and endotoxins?
Exotoxins: deliberately released by microorganisms as a virulence factor
Endotoxins: released in bacterial cell breakdown
What are the 2 general types of treatment?
Specific
Supportive
What are the different outcomes of infection?
Cure
Chronic infection (+/- disability)
Death
Describe the different ways of classifying antibacterials
Bactericidial or Bacteriostatic
Broad vs Narrow spectrum
Target site
Chemical structure
Describe the ideal features of antimicrobials
Selectively toxic Few adverse effects Reaches site of infection Oral/IV formulation Long half-life No interference with other drugs
What are the different target sites for antimicrobials?
Cell wall synthesis
Protein synthesis
Nucleic acid synthesis
Cell membrane function
Name the classes of antimicrobials that interfere with cell wall synthesis
Beta lactams
Glycopeptides
Name the classes of antimicrobials that interfere with protein synthesis
Tetracyclines
Aminoglycosides
Macrolides
Name an antimicrobial class that interferes with nucleic acid synthesis and give some examples
Quinolones (rifampicin and trimethoprim)
Name an antimicrobial class that interferes with cell membrane function
Polymyxins (colistin)
How does penicillin work?
Binds to penicillin binding protein to prevent it linking parts of the cell wall together
Without it there is no rigidity of cell wall therefore the organism does not remain viable
How does vancomycin work?
Active against gram positive organisms
Sits on the cross linking chains and prevents penicillin binding protein from doing its job
How do fluoroquinolones work?
Inhibit 2 enzymes which deal with replication of nucleic acids
Prevents the organism from multiply
Broad spectrum Abx for gram positive and negative bacteria
Describe the mechanisms of resistance of bacteria
Drug inactivating enzymes
Altered target
Altered uptake of drug (decreased permeability or increased efflux)
Genetic (mutation and horizontal gene transfer)
Name the 3 mechanisms of horizontal gene transfer
Conjugation
Transduction (bacteriophages)
Transformation (directly through the cell wall)
Define minimum inhibitory concentration
The lowest concentration of antibiotic that will have an inhibitory effect on the organism
Name the 4 main classes of beta lactams
Penicillins
Cephalosporins
Carbopenems
Monobactams
Penicillin is mainly activated against which organisms?
Mainly gram positive streptococci
Used to be staphylococci but most are resistant now
Amoxicillins are mainly active against which organisms?
Gram negatives
Flucloxacillin is active against…
Staphylococci and streptococci
Except MRSA
Describe cephalosporins
Broad spectrum Abx but not active against anaerobes
Ceftriaxone has good activity in the CSF (therefore good for meningitis)
Describe carbapenems
Very broad spectrum
Active against most gram negatives
Generally safe in a penicillin allergy
Vancomycin is what type of Abx?
Glycopeptide
Describe the features of vancomycin
Active against most gram positive
Some enterococci are resistant
Resistance in staphylococci is rare
Narrow therapeutic window
Describe the features of tetracyclines
Broad spectrum not specifically used when there is a penicillin allergy
Usually for gram positives
Active against atypical pathogens in pneumonia
Active against chlamydia and some protozoa
Shouldn’t be given to children under 12 (stain teeth and bones)
Describe the features of aminoglycosides
Eg. Gentamicin Profoundly active against gram negatives Good activity in the blood and urine Potentially nephrotoxic Narrow therapeutic window Reserved for severe gram negative sepsis
Describe the features of macrolides
Eg. Erythromycin
Alternative to penicillin for mild gram positive infections
Active against atypical respiratory pathogens
Describe the features of quinolones
Eg. Ciprofloxacin Inhibit DNA gyrase Very active against gram negatives Active against atypical pathogens Increasing resistance and risk of Clostridium difficile
What is the mechanism of trimethoprim?
Inhibitor of folic acid synthesis
Describe azoles (antifungals)
Active against yeasts and moulds
Inhibit cell membrane synthesis
Describe polyenes (antifungals)
Inhibit cell membrane function
Topical treatment of candida
Can get some for IV treatment of systemic fungal infections
Describe aciclovir (antiviral)
Inhibits viral DNA replication
Active against herpes simplex and varicella zoster
How does Tamiflu work? (Oseltamivir)
Inhibits viral neuraminidase
Used for influenza A and B
What is metronidazole?
An antibacterial and anti protozoal against
Describe the features of cellulitis
Often caused by strep pyogenes
Spread through superficial dermis
Enzymatically breaks down the CT of the dermis - allowing the organism to spread
Swollen, hot, red, painful
Describe the features of necrotising fasciitis
Mixed synergistic bacterial infections
‘Flesh-eating’
Death of the body’s soft tissue
Red/purple skin, severe pain, fever and vomiting
Most common areas = limbs and perineum
Typically enters through a break in the skin eg. Cut or burn
