Flashcards in Microbiology Deck (260)
Why do we culture blood?
to look for bacteraemia - it is normally bacteria free without bacteria flora
How can blood be contaminated?
patient's skin, surface of the items used to take the culture, fingers of the person taking the blood, laboratory
How long does it take for a blood culture to identify an organism?
1 day to do gram stain and coccsu/bacillus
2-3 days to identify organism and assess whether this is likely to be a contaminant
Why are contaminants a problem?
give wrong treatment, waste of money, side effects for patients, unnecessary equipment, increased length of stay, mislead clinicians, not always able to identify whether it is a contaminant or not, don't meet contamination targets
What organism is resistant to all B lactams?
Disadvantage of using B lactam antibiotics?
can predispose to C.difficile and colonization with resistant bacteria e.g. MRSA, many people report allergies to this group, especially penicillin
What is the most widely used class of antibiotics and how do they work?
B lactams which includes penicillins, cephalosporins, carbapenems and combinations - bind to cell wall and inhibit cells wall sunthesis
Two main types of penicillins?
What antibiotic is used for enterococci and H.influenzae?
amoxcillin - but most enterobacteria are resistant to it
What is flucloxacillin used for?
anti staphylococcal agent as stability to penicillinase
What are B lactamase inhibitors used for?
bacteria resistance is through B lactamase production, so these antibiotics prevent this resistance, so use combinations e.g. co-amoxiclav, tazocin
What are monobactams used for?
e.g. Aztreonam, for gram negative bacilli, including pseudomonas and preferably aerobes, safer for C.diff
What are carbapenems used for?
e.g. imipenem for very broad spectrum hospital acquired infections
Disadvantages of carbapenems e.g. imipenem?
expensive, CI in CNS disorders and can predispose to C.diff
What are cephalosporins used for?
e.g. cefotaxime, ceftazidime for gram negative activity, good CNS penetration and good anti pseudomonal
What are glycopeptides used for?
e.g. vancomycin for gram positive only and reserved for serious, resistant ones e.g. MRSA (Iv only and toxic)
What are macrolides used for?
e.g. erythromysin, clarithromycin for staph and strep activity, used to soft tissue and throat infections if allergic to penicillins (no gram negative cover)
What are lincosamindes used for?
e.g. clindamycin for staph, strep and anaerobes and C.diff and PMC good bone concentrations and well absorbed orally
What are tetracyclines used for?
mild MRSA infections and chlamydias
What are aminoglycosides used for and how do they work?
e.g. gentamicin for enterobacteriaceae, pseudomonas and staphylococci, synergy with cell wall antibiotics against streptococci and enterococci - inhibit ribosomal activity and protein synthesis
Disadvantages of aminoglycosides?
more toxic than glycoproteins so nephro and oto toic levels must be monitored carefullly
What is fusidic acid used for?
serious anti staphylococcal agents e.g. osteomyelitis, only used in combination
What is oxazolidinone used for and how does it work?
grampositive including MRSA and VRE - inhibits bacterial protein synthesis and blocks initiatio complex formation
Disadvantages of oxazolidinone?
only 1 class e.g. linezolid and are expensive and can cause bone marrow suppression if used for >2 weeks
What are nuclei acids/quinolones used for and how do they work?
e.g. ciprofloxacin - UTIs, enterobacteriacease pseudomonas and staph - inhibitt DNA gyrase
What is rifampicin used for and how do they work?
TB and general Staph's and meningitis prophylaxis - must be used in combination - interfere with nuclei acid synthesis or function
What is metronidazole used for?
anti anaerobic for bacteria and protozoa
What likely organisms are seen in UTIs?
e coli, staph sparophyticus, enterococci
Antibiotics for UTIs?
trimethoprim, amoxicillin, clavulanate, cephalosporin