Sterilise
To kill all microbes
Sanitise
To kill most microbes
Aseptic
Absence of microbes
Disinfectant
o Non-selective chemical for killing microbes
o Unsuitable for use on living tissue
o High concentrations required
o E.g. sodium hypochlorite
Antiseptic
o Non-selective chemical for killing microbes
o Appropriate for use on living tissue, usually skin
o High concentrations required
o E.g. betadine
Antibiotics
o Target particular pathways
o Pathways are unique to bacteria or group of bacteria
o Very small concentrations required
o For use on or in living tissues
Broad spectrum antibiotics
Effective against many bacterial groups
Narrow spectrum antibiotics
Effective against only a few bacterial groups
Bactericidal antibiotics
Kill bacteria
Bacteriostatic antibiotics
Inhibit growth of microbes, immune system kills.
Complication in the definition of bactericidal and bacteriostatic.
Decreasing concentration: bactericidal becomes bacteriostatic.
Increasing concentration: bacteriostatic becomes bacteriocidal.
Prophylactic therapy
- Before the infection risk occurs e.g. surgery
- Antimicrobial choice based on known or likely pathogen
- Use only if: there is evidence for effectiveness or an infection is disasterous
Empirical therapy
• Best guess
• Use only when:
o Bacterial infections are very likely
o Treatment has substantial benefit
o ID, sensitivity unknown
• Use narrowest spectrum antibiotic for most likely pathogen
• First obtain specimens for MC&S testing
• Change to directed therapy when laboratory results are available.
Directed therapy
• Antimicrobial therapy with evidence from laboratory testing
o Microbial pathogen has been identified
o Antimicrobial sensitivity has been determined
• Then choose the antimicrobial that is:
o Most effective
o Least toxic
o Narrowest spectrum
• Directed therapy is the most desirable antimicrobial therapy
The antimicrobial creed
Microbiology guides therapy wherever possible
Indications should be evidence-based
Narrowest spectrum required
Dosage appropriate to the site and type of infection
Minimise duration of therapy
Ensure monotherapy in most situations
Oral antimicrobial administration
- Preferred
- Less serious adverse effects
- Cheaper products
- Lower costs to administer
- Just as ‘powerful’ as injections
- Drugs must have good oral bioavailability
Parenteral antimicrobial administration
• When oral administration is ineffective
o Poor oral bioavailability
o Swallowing difficulties
o Absorption problems (e.g. vomiting, diarrhoea)
o Higher concentrations are required than possible oral route
o Time critical (rare)
• Reassess daily and convert to oral ASAP
Topical antimicrobial administration
- Use only when effectiveness is proven
* Antimicrobial different from oral and parenteral types, for avoidance of resistance
Adverse effects
• All microbials can cause adverse effects
• Adverse effects are usually mild, self-limiting
• Adverse effects more likely in:
o Elderly
o Patients with renal or hepatic impairment
Antimicrobial hypersensitivity (allergy)
- Very commonly reported, esp. to penicillin
- 5 to 10% of patients
- But often vague details, inaccurate
- Usually from parenteral administration
- True anaphylaxis in 0.01% to 0.04% of courses of penicillin
- 10% of anaphylaxis fatal
When can a patient be given allergy causing antibiotics?
- The antibiotics is clearly the most effective
- Patient is carefully observed
- Patient undergoes desensitisation therapy
Multi-drug resistant bacteria
o Myobacterium tuberculosis o Staphylococcus aureus o Enterococcus o Enterics (E. coli, Klebsiella, Enterobacter) o Pseudomonas aeruginosa
Antibiotic resistant mechanisms
- Enzymes that degrade antibiotics e.g. beta-lactamases
- Decreased inner cell membrane permeability
- Decreased outer membrane permeability
- Efflux pumps removing antibiotic from inside cells
- Alteration of the binding site e.g. MRSA
How to bacteria gain resistance genes?
• Inherent (natural) e.g. many Gram-negs to penicillin
• Vertical gene transfer
o Mutations after selection pressure of antibiotics
o Then transferred ‘vertically’ to progeny
• Horizontal gene transfer
o Genes transferred to related bacteria
o Mechanisms
