Microbiology Lecture 8 Flashcards
Define sterilisation.
Kills all viable organisms including endospores
Define disinfection.
Kills all vegetative organisms, but not endospores
Does everything need to be sterilised?
No, items like cutlery, thermometers, plates etc
Why arent thermometers sterilised?
Doesnt penetrate the body, just mouth. Swallowed endospores typically not a problem.
What does an antiseptic chemical do?
Kills or inhibits microbial growth, but nontoxic enough to be used on living tissue.
What is the difference between an antiseptic and disinfectant?
Antiseptic is non-toxic.
What affects sterilisation/disinfection efficacy? How is this prevented?
Affected by presence of fat/protein on the item. Important to preclean beforehand.
How do biofilms affect disinfection/sterilisation?
Less penetration of chemicals
Order the following from most resistant to least resistant. Lipid/medium viruses Mycobacteria Non-lipid/small viruses Vegetative bacteria Fungi Bacterial spores
Bacterial spores Mycobacteria Nonlipid/small viruses Fungi Lipid/medium viruses Vegetative bacteria
Are hypochlorites effective when dilute or concentrated? What are they particularly effective against?
Must be diluted to be effective (1/10 dilution needed).
Excellent against viruses
What are hypochlorites inactivated by? How can this be a problem during cleanup?
Organic matter. ie. a blood spill must be visibly removed first before disinfection.
Is alcohol well suited for use on skin, or is it an irritant? Is pure alcohol more effective than a lower ww%? Why is this so?
Suitable for skin, less irritating than soap.
70% is better than 100%. This is because pores close at 100%, better entry at 70%.
What are 3 properties of a good handwash? Name one.
Good wetting properties
Rinses well
Has residual activity
Chlorhexidine
When is soap usually used?
When hands are visibly soiled.
Describe the handwashing process in 5 steps.
Wet hands Add handwash Rub hands Scratch palms to reach fingernails Rinse well, and pat dry
Why must hands be wet first before adding handwash?
Prevents skin irritation.
Name 3 advantages of alcohol handrub. Name one disadvantage.
Convenient, dries quick, less irritating than handwashing
No good if hands are visibly soiled.
Name 2 properties of a good antimicrobial.
Must be effective at low concentrations, and selectively toxic.
What is a therapeutic index, and what is it in penicillin vs gentamycin?
Therapeutic index describes suitability of antimicrobial.
Penicillin has high selective toxicity - high index.
Gentamycin has toxicity to both host and target pathogen - lower index.
Gentamycin is used on resistant bacteria. How is it usually administerd given all its side effects?
Blood levels rise quickly and can kill auditory nerves.
Typically given in 8h periods, and levels in blood monitored before the next dose is administered.
Define microbiostatic agent.
Inhibits microbe growth.
Define broad spectrum antibiotic.
Effective against many groups of microbes, but disrupts natural flora
Define narrow spectrum antibiotic.
Effective against a specific target microbe. Leaves more natural flora intact.
How are penicillin resistant gram positive bacteria killed?
Vancomycin.
Where are antibiotics made naturally, and why? If there are so many antibiotics in nature, why do we have a shortage clinically?
Made by fungi and bacteria in nature, for competition.
Less than 1% of these are clinically useful as they are typically too toxic to be used in vivo.
Which antibiotic group accounts for more than 50% of the worlds use? Name 3 examples.
Beta lactam antibiotics, including penicillins, cephalosporins, and cephamycins.
What bond links cell wall units together? What about cell wall interlinks?
Unit links - glycosidic bonds
Interlinks peptide bonds
What is the mechanism of action for aminoglycoside antibiotics? Which bacteria is it effective against, and what are two side effects?
Inhibits protein synthesis by targeting small ribosomal subunits.
Effective against gram negative bacteria
Is neutotoxic and nephrotoxic.
What is the mechanism of action for macrolide antibiotics?
Inhibits protein synthesis by targeting large ribosomal subunits.
What is tetracycline made by, and what is it effective against?
Made by streptomyces, broad spectrum, effective against almost all gram positive and negative bacteria.
Name 6 mechanisms of action for antibiotics.
Injury to membrane Inhibit synthesis of essential metabolites Inhibit transcription Inhibit DNA replication Inhibit cell wall synthesis Inhibit protein synthesis
How can antibiotic resistance be spread?
Bacteria that make antibiotic resistance have mechanisms to resist their own antibiotics.
Can be transferred to other microbes via transformation.
Name 2 ways resistance to penicillin can be achieved.
B lactam ring in penicillin cleaved by B lactamase
Can make pumps to pump it out.
