Ambler Prions Flashcards
BSA (blood sheep agar)
routine. most things GP, GN and candida grow here
MacConkey
For Gram negatives/enterics (bile tolerant).
Chocolate
lysed red cell media to release nutrients for picky (fastidious) organisms
Sabouraud
for dermatophytes and other fungi
Antibiotic Resistance
Decreased penetration to target
Gram negs. like P.aero has thick outer membrane (wall)
Alteration of target site
change in PBP by strep and staph so it is not recognized
Inactivation by enzyme
enzyme eats abx renderning ineffective. ‘ase’. ie penicillinase, carbapenimase
chromosomal - ie inducible by Enterobacter
plasmid – can be a moving target as non chromosomal
transposon – non chromosomal like plasmid. ‘jumping genes’
Beta-Lactam Resistance types
Penicillinase Cephalosporinase ESBL (Extended Spectrim Beta-lactamase) AMP-C Carbapenemase. ‘CRE’ has been in the news a lot recently.
Micro plate tests
Kirby Bauer
abx discs and read zone of clearing; CLSI has breakpoints for S, I or R
e-Test
graduated concentration of abx and read point
Urine
diagnosis of presumed UTI difficult.
Pyuria = >10wbc
Leukocyte esterase great at detecting very small WBC’s so despite decent sens/spec:75-96%/94-98%, it is not diagnostic
Nitrates – tells if nitrate splitting bacteria (ie Ecoli) is there. does not tell if problematic
Blood – not common in uti compared to non infectious causes
how about bacteria?
>100k only applies to enterobactericiae and only predicts persistant colonization or infection. Kass, MD in the 1950’s studied this extensively.
to comfortably dx UTI you need
1) symptoms. we only treat asymptomatic bacteria in the urine in the pregnant patient as it reduces pyelonephritis and preterm labor
2) pyuria (increase in wbc’s)
3) bacteria suggestive of infection. ie Staph epi = no.
again >100k suggest persistence and MAY mean infection that needs treatment.
Blood culture
major problem is it is usually collected through skin or through a catheter, both of which get colonized with bacteria.
pearls:
always try 2 separate sites of draw
if rigors/chills. Get 2 sets stat as rigors signify clearing of the bacteremia
if fever then q 15 min is fine
if thinking endocarditis or persistent bacteremia, showing persistence over time necessary.
Newer blood culture machines are better at culturing the ‘fastidious- (ie HACEK group).
Not many instances for holding blood cultures >5 days. Propionibacterium is one common exception
Fungal blood cultures very low yield except candida which grows on normal culture stuff.
Sputum
need deep specimen.
gingival scraping has 1012 anaerobic orgs.
again need inflammation (ie inc WBC’s)
Need to have a favorable ratio of wbc’s to respiratory epithelial cells. Bronchial epithelial cells more significant in indicating ‘deep’ specimen.
eg 4+ PMN’s and 0+ epithelial cells would be ideal.
thought that 104 -105 orgs needed for gram stain positivity.
Encapsulated
Worry for splenectomized patients
Typeable Haemophilus influenzae (ie type B) Strep pneumo Neisseria meningiditis Strep agalactiae (group B) Klebsiella Salmonella Capnocytophaga - means dog death. Splenectomy patient bitten by a dog that dies, think of this. Crytptococcus
Community Acquired Pneumonia
85% of bacterial cases: (also major causes of ear infections)
Strep pneumoniae
Haemophilus influenzae
Moraxella catarrhalis
Rest (atypicals)
Legionella pneumophila
Mycoplasma pneumoniae
Chlamydophila pneumoniae
Respiratory viruses*
Haemophilus influenzae
small non motile gnr. needs factors ‘V’ and ‘X’ so chocolate agar better.
2nd most common CAP bacterial org.
common in smoker/copd patients
clinically nontypeable and type B strains have capsule
H. influ type B
kids = life threatening complication/disease of epiglottitis
fever, sore throat, leaning forward with mouth open and drooling.
medical emergency as they can lose airway fast.