AntitbioticsSH1 Flashcards
Definitions
•MIC: minimum inhibitory concentration. ( culture and sensitivity ). Lowest concentration of abx required. The lower the number the more sensitive the bacteria is.
•minimum bactericides concentration: the min concentration that kills an organism. Not really clinically used.
• bacteriostatic: a drug that reduces growth of an organism. Inhibit further growth
• bactericidal: drug that kills organism.
Definitions2
Narrow spectrum : usually one class of bacteria. Eg ) gram + or - 1) aminoglycosides gram neg only
• broad : affects both gram and- and +
Synergy: eg) ampicillin + gentamicin. ( enhance the effect of each other )
• prophylaxis: preventing an infection to a per son with high risk
• empiric therapy : cant wait on lab for results. Have to start something you anticipate like most common that cause that type of infection. Once culture comes back you can use direct therapy.
If we divide based on shape we’ll usually based on shape we’ll usually get either a rod( bacilli) or coccus
And by gram staining we can see which type of stain it’ll pick up. If it picks up the crystal violet ( blue ) stain it’s gram positive. Gram negative pick up saffronin ( red stain )
•Gram positive cocci : very clinically important. Strep, staph and enterococcus.
•Gram + rods: clinically rare. In 20 years of clinical practice, never seen diptheriae, heard about listeria and anthrax very rare. Only exception is clostridium species ( notice it’s an anaerobic rod)
•gram - cocci : nesseriae and moraxella
• gram - rod : GI bugs ( salmonella shingellla campylobacter )
NOTE: both clostridium ( g+ ) and bacteroides fragilis ( g- ) rod both anaerobic
Strep / staph / enterococci
All round. All pick up crystal violet: gram positive
Strep: mean chain forms a chain of round
4 different kinds.
Pyogenes
Agalactiae
Penumoniae
Staph: clusters. Looks like grapes.
Enterococci: could be single double, or chain. comes in different forms.
Streptococcus ( gram + cocci )
Purposes of an exam: number 1 choice ( DOC ) is PCN family.
•Group A strep( pyogenes) : strep throat. Cellulitis ( deep infection of skin: red erythoma swelling, systemic fever sx)
•Group B strep: strep. Agalactiae
-normal vaginal flora 10 to 25% of females. For female pt no problems directly but if pregnant about to deliver when baby exposes to GBS it can enter baby and causes NEONATAL MENINGITIS ( happens within first few days after birth ). So pregnant woman tested by swab ahead of time. By the time they are ready to deliver we know if patient is carry GBS. Done 4-5 weeks before delivery.
—If mild PCN allergy —> IV cefazolin
If severe PCN allergy —> IV clindamycin
•strep. Penumoniae ( pneumococcus ) - seen often. Often associated with pnemonia ( #1 cause of community acquired pnemonia ) but not just pnemonia. ( # 1 cause of meningitis in majority of age groups other than neonates and adolescents).
Otitis media and sinusitis : #1 causes pnemococcus. Middle ear connected to sinuses. ABX for bugs often the same. Duration could be different.
•strep. Vivid as: normal oral flora. During dental infections we have to consider. If very invasive dental procedures with lots of bleeding there is a chance it can go in bloodstream and end up sitting on heart valve : infective endocarditis
Pyogenes/agalactai/pneumoniae
Clinically If infection above the diaphragm ( lungs, sinuses, ears, meningitis ) then chances are it is
Pneumococcus ( strep. Pneumonia )
Gram + cocci
Staphlococci
Gram + cocci
•staph aureus: most important. Clusters of grapes. Blue stain. Staph infections tend to be pyogenic( pus forming ). Majority are staph aureus. Could be MSSA or MRSA
- # 1 cause of infective endocarditis. Other infections: osteomyelitis ( toxic bone syndrome ). COAGULASE POSITIVE ( usually refers to staph auerus. ( how do you know if staph auerus or epidermis or saprophyticus. Lab test: staph auerus generally is the one that is COAGULASE positive ( turn fibrinogen ( factor 1a) to fibrin ( factor 1 = the glue between platelets) ) . Clinically important, within first hour or two we can find out if gram positive if cluster or if COAGULASE positive. Labs can take 2 days. So this info right away tells you staph aureus
•With strep, PCN first choice. With Staph, cant use PCN by itself. It has to B - lactamase - resistant PCN if you use PCN. Staph has betalactamase( ring in PCN. Some bacteria can break it down make PCN down ) in it.
•MSSA : treat with B lactamase- resistant PCN. Remember, We dont use methicillin as an abx. If methicillin sensitive, it means it is sensitive to beta lactamase resistant types of PCN ( dicloxacillin, Nafcillin, Oxacillin, Cloxacillin ( not in us in Canada ) )
- know the forms they come in. Eg) skin abscess, drain, MSSA dx, want a Po abx to send home, need to know dicloxacillin PO, nafcillin (IM /IV ). If infective endocarditis: must use IV abx.
- Nafcillin/ Oxacillin : IM / IV. -Dicloxacillin is PO.
-MRSA: common ABX: VANCOMYCIN/ BACTRIM/DOXYCYCLINE/ ZYVOX
More Staph Aureus infections
•Impetigo : superficial skin ifx w/honey colored crust. Tx: if mild case—> topical —> mupirocin/ retapamulin ( altabax cream( MSSA only) ) if severe then systemic abx ( keflex for example )
•MRSA colonization eradication: say patient has skin abs under armpit. Drain—> pus to culture —> 2 days later MRSA. Tx: flush, abx, and eventually infection resolved. 6 months later same patient now same thing in opposite armpit. We repeat same tx. Few months later same issue in other part of skin. Patient asks how come it comes back as MRSA every time was it ever treated? Yes it was but this person is colonized with MRSA. MRSA lives in this persons nostrils. Without causing ifx in nostril it is the reservoir for MRSA: we can take bactroban and insert in nostrils way deep 3-5 days ( fda approval) clinically seen for like a whole month. And you gotta use hibiclens ( 4% chlorhexidine ).
-% of people colonized with MRSA are much higher today.
MRSA tx
Methicillin-resistant Staph. aureus
-draining the abscess is often enough for small lesions.
PO outpatient abx:
- bactrim: Sulfa allergy
-doxycycline: photosensitivity
-clindamycin: try to avoid unless have to bc high rate causing C. diff
-Linezolid ( zyvox ), tedizolid ( sivextro ) or delafloxacin ( baxdela ) only when necessary
Note: Rifampin only as adjunct to other abx
——-Delafloxacin new fluoroquinolones can be used PO for MRSA
NOTE: Rifampin only as an adjunct to other abx for MRSA
IV abx for MRSA
Enterococci
Gram ( + ) cocci - entero means intestines. Normal GI flora. It can cause ifx as well. Usually elderly in NOSOCOMIAL settings: urine, sepsis, & endocarditis
E. Faecalis & E. Faecium
Tx:
Traditional tx: ampicillin + gentamycin ( synergy )
-newer Tx: ampicillin + ceftriaxone
-if ampicillin allergy or resistance — > vanco + gentamycin
- For Vanco resistant enterococcus ( VRE ) : mostly E faecium
—-use daptomycin, linezolid , tigecycline, relevancin , oritavancin, synercid ( off label for E. Faecium )
Aerobic Gram ( + ) Rods ( bacilli)
1) corynebacteri
