*Microbiology 3 (lecture 5) Flashcards
What is the difference between bactericidal and bacteriostatic antibiotics?
Bactericidal = kill bacteria Bcteriostatic = inhibit bacterial growth
Why must antibiotics be selectively toxic?
In order to kill the bacteria without damaging the host
How are antibiotics usually administered?
Usually orally or IV (rarely intramuscularly)
When antibiotics are given orally, when will they reach peak serum levels?
When given IV?
Approx. 1 hour later
Within 15 minutes
Where are antibiotics excreted?
Unchanged antibiotic = in the faeces
Absorbed antibiotic = either in the urine or via the liver, binary tract and into the faeces
Why are antibiotics sometimes given in combination? (3)
To cover a broad range of possible infecting organisms
To prevent the development of resistance e.g. in the treatment of TB
For the synergistic effect of the combination (i.e. 1 + 1 = 3) e.g. in the treatment of some cases of endocarditis
What are the 3 main ways in which antibiotics can work?
Acting on bacterial cell wall
Affecting the bacterial ribosome
Acting on bacterial DNA directly
(all of these structures differ in bacteria and mammalian cells)
What are the 3 groups of antibiotics that act on the bacterial cell wall?
The penicillins
The cephalosporins
The glycopeptides
Name the 6 penicillins?
Penicillin Flucloxacillin Amoxicillin Temocillin Co-amoxiclav Piperacillin/ tazobactam = Tazocin
Name a cephalosporin?
Ceftriaxone
Name 2 glycopeptides?
Vancomycin
Teicoplanin
How do the penicillins work?
They inhibit cell wall synthesis by preventing the cross-linking of peptidoglycan subunits
Are the penicillins bactericidal or bacteriostatic?
Bactericidial
Amount of side effects of penicillins?
Narrow or broad spectrum?
Excreted by?
Very few
Range from narrow to broad spectrum
Rapidly via the kidneys
Are the penicillins safe in pregnancy?
Yes
What are the 2 main drawbacks of the penicillins?
- some patients are hypersensitive to the penicillins. An allergy to one penicillin means allergy to all penicillins (and sometimes also the cephalosporins)
- rapid excretion via the kidney means frequent dosing (usually 4-6 times daily) is necessary
What are the 3 forms of penicillin available? How is each given?
Benzylpenicillin (penicillin G, IV) Phenoxymethyl penicillin (penicillin V, oral) Benzathine penicillin (long actin, IM)
Do organisms that are sensitive to penicillin itself tend to be sensitive to most of the penicillin group of antibiotics?
Yes
What does the penicillin nucleus look like?
A house and a garage
What penicillin is given to gram positive organisms? How can this be given?
Flucloxacillin (IV, oral)
What penicillins are given to both gram positive and gram negative organisms? How re these given?
Amoxicillin (IV, oral)
Co-amoxiclav (IV, oral)
“Tazocin” - IV only (piperacillin/ tazobactam)
What penicillin is given to gram negative organisms?
Temocillin (IV only)
How is flucloxacillin given?
IV and oral
Spectrum of flucloaxicillin?
Very narrow
Useful only for staphylococci and streptococci)
What is flucloxacillin used to treat?
Staphylococci and streptococci infections only e.g.
Skin and soft tissue infection
Wound infection
Cellulitis
How can amoxicillin be given?
IV, oral
Why has amoxicillin become less effective over the years?
Many organisms produce beta-lactamse (an enzyme that destroys amoxicillin)
What is co-amoxiclav?
When is it used?
Amoxicillin plus clavulanic acid which is a beta-lactadase inhibitor
Used when there is an antibiotic resistance to amoxicillin
How can co-amoxiclav be given?
oral and IV
What is tazocin made up of?
Piperacillin (antibiotic)
Tazobactam (beta-lactamase inhibitor)
How is tazocin given?
IV only
How is temocillin given?
IV only
What type of bacteria can temocillin be used to treat?
Colifroms
Can temocillin be used to treat beta-lactamase producing bacteria?
Yes, it is used to treat extended spectrum beta-lactamase producing organisms
What do all cephalosporins have in their name?
“ceph” or “cef”
How do cephalosporins work?
Bactericidal or bacteriostatic?
inhibit cell wall synthesis and are bactericidal (like penicillins)
How are cephalosporins excreted?
Few or many side effects?
Safe in pregnancy?
Excreted via kidneys and urine
Few side effects
Safe in pregnancy
Appearance of a cephalosporin nucleus?
House + garage + garden
Do cephalosporins have a broad or narrow spectrum?
Broad-spectrum
What is the major disadvantage of cephalosporins?
As they are broad spectrum, they significantly affect the normal bowel flora
They kill the normal gut bacteria allowing overgrowth of clostridium difficile which causes a nasty gastroenteritis
Many hospitals now try to avoid using them meaning they have very limited indications for use in Tayside
How are the glycopeptides (vancomycin and teicoplanin) given?
Both IV
How does vancomycin work?
Are the glycopeptides bactericidal or bacteriostatic?
Cell-wall active antibiotics but in a slightly different way to the penicillins and cephalosporins
Binds to the end of the growing pentapeptide chain during peptidoglycan synthesis preventing cross-linking and weakening the bacterial cell wall
Bactericidal
How are the glycopeptides excreted?
Via the kidneys and urine
What can happen to patients taking vancomycin with kidney failure?
Toxic levels can build up in the blood causing further kidney damage
What type of organisms are glycoproteins active against?
Only gram positive cell walls - active against all (most?) gram positive bacteria
What antibiotic can treat MRSA?
Vancomycin (if becomes resistant to this, we would have very few options to treat it)
Gentamicin
Antibiotics that inhibit protein synthesis? (5)
The macrolides
The tetracyclines
The aminoglycosides
Others (Clindamycin, chlorampheicol)
What are 3 macrolides?
Erythromycin
Clarythromycin
Azinthromycin
What is an example of a teracycline?
Doxycycline
What is an example of an aminoglycoside?
Gentamicin
How do antibiotics inhibit protein synthesis?
By attaching to bacterial ribosomes (structurally different from mammalian ribosomes)
Are antibiotics that inhibit protein synthesis (act on ribosomes) bactericidal or bacteriostatic?
Why?
What is the exception to this?
Bacteriostatic
Usually protein synthesis can resume when the antibiotic is removed
The amino glycoside group - binding of these antibiotics to ribosome are lethal
How are the macrocodes excreted?
Via the liver, biliary tract and into the gut
Is Erythromycin safe in pregnancy?
Yes
What type of infections are macrolides especially useful for treating?
As the antibiotics are lipophilic they can pass through the cell membranes easily
They are therefore useful for treating certain infections where bacteria hide from the host’s immune system by getting into the host cell
What kind of bacterial infections is erythromycin/ clarythromycin useful for treating?
Clostridium spp. Streptococcus spp. Staph. aureus Neisseria spp. (partly sensitive) Haemophils infleunzae (partly sensitive)
Why must gentamicin be given IV?
It is not absorbed from the gut
What is gentamicin used to treat?
Active mainly against gram negative aerobic organisms such as coliforms and Pseudomonas aeruginosa
Used in hospital for treating serious gram negative infeciton
How is gentamicin excreted?
In the urine
What can gentamicin cause?
Causes damage to kidneys and VIIIth cranial nerve (deathless and dizziness) so need to monitor blood levels of ahminoglycosides
Examples of antibiotics that act on material DNA? (3)
Metronidazole
Trimethoprim (+/- sulphonamide) - shown to cause synergy in the lab
Fluoroquinolones
How can metronidazole be given?
Oral or IV
How does metronidazole work?
Causes strand breakage of bacterial DNA
What type of infections is metronidazole used to treat?
Anaerobic (and some protozoal) infections
How if Trimethoprim given?
Oral
How does trimethoprim work?
It inhibits bacterial folic acid synthesis
What is the name when trimethoprim is given in combination with sulphamethoxazole?
How is this given?
Co-trimoxazole (septrin)
IV or orally
How is trimethoprim excreted?
Via the urine
What type of bacteria does trimethoprim have activity against?
Some gram negative and some gram positive bacteria
What are 2 examples of fluoroquinolones?
How are each given?
Ciprofloxacin (IV, oral)
Levofloxacin (IV)
How do fluoroquinolone act?
By preventing “supercoiling of bacterial DNA”
Are fluoroquinolones bactericidal or bacterostatic?
Bactericidal
Why is the use of Fluoroquinolones severely restricted in tayside?
In an attempt to reduce the risk of clostridium difficile
How are fluoroquinolones excreted?
Via the urine
What are the common side effects of all antibiotics?
Nausea, vomiting and diarrhoea (all antibiotics disrupt the gut bacterial flora)
What antibiotic causes renal and VIII nerve damage?
Gentamicin
What antibiotic causes tendonitis?
Ciprofloxacin
What antibiotic interacts with alcohol?
Metronidazole
What group of antibiotics increase the risk of C. diff. in elderly patients?
Broad spectrum antibiotics
What 4 antibiotics do we try to avoid?
Why?
Cephalosporins
Co-amoxiclav
Ciprofloxacin
Clindamycin
