Infection Session 2 Flashcards
Why is physiological state relevant in gestational diabetes?
During pregnancy bacteria in the large bowel can cause gestational diabetes
What is the difference in calendar and relative time when considering a patient with a suspected infection?
Calendar time considers seasonal diseases e.g. Flu or chickenpox
Relative considers time since a potential exposure
By what 7 mechanisms can infection occur?
Contiguous spread Inoculation Haematogenous Ingestion Inhalation Vector Vertical transmission
How do aerosols form?
Around a ‘seed’ e.g. a dust particle
Why is chickenpox so contagious?
Virus rapidly multiplies in lungs and is transmitted via inhalation
What sequence does management of infection usually take?
History –> examination –> diagnosis –> specific+/- supportive Tx –> infection prevention in hospital and community
How are the vast majority of infection diagnoses made?
History alone
Why is debridement of tissue sometimes used to treat infection?
Dead tissue has a low redox potential and bloodflow so is a perfect environment for anaerobic bacteria
Why does the dead space left following debridement often need packing?
Blood/serosa can accumulate here and promote microbial growth
What outcomes are possible following an infection?
Resolution
Chronic infection –> potential disability
Death
What is an antibiotic?
Antimicrobial produced by a living organism
What are the four main types of antimicrobials?
Antibacterial
Antiviral
Antiprotozoal
Antifungal
What is the difference between a bactericidal and bacteriostatic antibacterial agent?
Bactericidals kill, bacteriostatics inhibit
What are the ideal features of antimicrobial agents?
Selectively toxic Few adverse effects Reach site of infection Oral/IV formulation Long half-life for infrequent dosing No interference w/other drugs
How do beta-lactams act as antibacterials?
Inhibit cell wall regeneration by binding to penicillin binding protein so new X-links cannot be formed
How do glycopeptides act as antibacterials?
Bind to peptidoglycan thus blocking cell wall X-linking enzyme
What mechanisms can bacteria use to be resistant to beta-lactams?
Decrease their permeability to them
Express beta-lactamases to inactivate drug
Alter target enzyme so it has a lower affinity
Which classes of antibacterials inhibit protein synthesis by blocking a variety of enzymes?
Tetracyclines
Aminoglycosides
Macrolides
How can bacteria be resistant to tetracyclines?
Increase efflux to actively pump out before it takes effect
Alter target enzyme
Which class of antibacterials do trimethoprim and rifampicin belong to and how do they act?
Quinolones (floroquinolones clinically)
Bind to DNA gyrase to interfere with DNA supercoiling
What are polymixins?
Antibacterials that inhibit cell membrane function
Will a bacterium only ever have one mechanism of resistance to one particular drug?
No, might have different mechanisms for same class as well as multiple mechanisms for different classes
Does there need to be a high level of antibiotic exposure for a chromosomal gene mutation resulting in antibiotic resistance to occur?
No
What two methods form the basis of antibiotic resistance?
Chromosomal gene mutation
Horizontal gene transfer
What is the qualitative method of measuring antibiotic activity?
Disc sensitivity to examine zone of inhibition around disc
What is the quantitative measure of antibiotic sensitivity?
Minimum inhibitory concentration
How is minimum inhibitory concentration measured?
Bacterial broth is cultured in a serial dilution of antibiotic
Are carbapenems broad or narrow spectrum?
Broad - including anaerobes and most G-ve
What are penicillins mainly active against?
Streptococci
What is flucoxacillin active against?
Staph and streptococci
Give an example of a commonly used beta-lactamase inhibitor combination therapy.
Co-amoxiclav
How do new generation of cephalosporins compare to old generations?
Increased G-ve spectrum and decreased G+ve activity
Are cephalosporins active against anaerobes?
No
What is the relevance of cephalosporins to C.diff infection?
Broad spectrum so widespread use –> resistant C.diff strains
How does the activity of vancomycin against G+ve bacteria compare to its activity against G-ve?
Active against most G+ve but not G-ve
Why is vancomycin given orally for intestinal infections?
Not normally absorbed into the blood
Why must care be taken with vancomycin use?
It has a narrow therapeutic window
What class of antimicrobials does vancomycin belong to?
Glycopeptides
Why are tetracyclines not widely used in hospitals?
Broad spectrum
In what common situation might carbapenems, tetracyclines or macrolides be used?
Penicillin allergy
What are tetracyclines active against?
Chlamydia
Some protozoa
Atypical pneumonia pathogens
Why are tetracyclines not given to children under 12 y.o.?
Stain bones and teeth yellow
Which antimicrobial is reserved for severe G-ve sepsis?
Gentamicin
Why is gentamicin reserved as a last resort for severe G-ve sepsis?
Profound activity against G-ve but is potentially nephrotoxic
What is used in primary care as an alternative to penicillin for mild G+ve infections?
Macrolides
Why are macrolides used in combination with drugs for typical respiratory pathogens?
They are active against atypical respiratory pathogens
Name two macrolides.
Erythromycin
Clarithromycin
What activity do quinolones have?
Very active against G-ve and atypical pathogens
Why is there a concern with quinolones and C.diff infection?
Rapidly increasing resistance
What action do trimethoprim and sulphonamides have?
Inhibit folic acid synthesis
What is trimethoprim most commonly used for in the UK?
UTI
When might you use a combination of trimethoprim and sulphonamides?
In a specific and unusual infection
What class of antifungals acts by inhibiting cell-membrane synthesis?
Azoles
What is an over-the-counter antifungal used to treat Candida?
Fluconazole
How does the activity of Azoles and Polyenes differ even though their mechanism of action is the same?
Azoles active against yeasts +/- moulds
Polyenes active against more complicated moulds
Why can aciclovir be used against Herpes simplex and Varicella Zoster viruses?
Upon phosphorylation it inhibits viral DNA polymerase
How does Tamiflu work?
Inhibits viral neuraminidase
What is metronidazole active against?
Anaerobic bacteria and several protozoa
What are the 7 patient factors which can affect disease?
Age Gender Physiological state Pathological state Social factors Time Place
