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Interpretation of Antibiotic Sensitivity Test

Clinical club talk
by

Anoop Sinha

on 7 November 2012

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Transcript of Interpretation of Antibiotic Sensitivity Test

Dr. Anoop Sinha, MD
Associate Professor
Dept. of Microbiology
SNIMS, Chalakka Antibiotic Sensitivity Test Where is antibiotic "X"? I'm using antibiotic "Y", but that's not been reported: why? Only one or two drugs in an antibiotic class has been reported: why? Where are the higher drugs? If I get you the discs for antibiotic "Z", can you report it? Why are some antibiotics reported while some others not reported in antibiotic sensitivity reports? Choose the ideal antibiotic For a particular isolate From a particular site In a particular patient MIC Minimal Inhibitory Concentration Lowest concentration of antibiotic inhibitory to the organism isolated Antibiotic is regarded as sensitive when:
MIC < serum concentration Methods:
Agar dilution
Broth dilution Disadvantages:
Cumbersome
Labour-intensive
Time-consuming Disc Diffusion Standards for Antibiotic Susceptibility Tests Standards for Antibiotic Susceptibility Tests Which antibiotics for which organism Which antibiotics for which specimen Which antibiotics to report Zone sizes and MICs for labeling an isolate as susceptible or resistant Antibiotics Chosen for a Particular Organism Based on knowledge of intrinsic resistance patterns of the organism in question
Vancomycin: not tested with Gram negatives
II & III generation cephalosporins: not tested with Gram positives
I & II generation cephalosporins: not tested with Pseudomonas
Aminoglycosides: not tested with anaerobes Antibiotics Chosen for a Specimen / Site Based on pharmacokinetic properties of the drugs
Nitrofurantoin: only in urinary isolates
Macrolides: not tested in urinary & CSF isolates Selective Reporting of Antibiotic Susceptibilities To prevent indiscriminate use of higher drugs
Safeguard against development of resistant strains
Make antibiotic therapy cost effective
Examples:
Enterobacteriaceae: II & III generation cephalosporins not reported if susceptible to I generation cephalosporin
Amikacin and netilmicin not reported if isolate is susceptible to gentamicin Interpretation of ABST Reports Drugs reported represent classes of antibiotics All the resistant drugs encountered are reported Within a class of antibiotics: higher drugs not reported if lower drugs are sensitive Drugs chosen as per standards Screening for resistance phenotypes Screening for Resistance Phenotypes MRSA
HLAR
ESBL
AmpC BL
MBL
MLSBi ABST of an Isolate of Staphylococcus aureus Penicillin
Cefoxitin
Gentamicin
Netilmicin
Amikacin
Erythromycin
Clindamycin
Vancomycin
Teicoplanin
Linezolid
Rifampicin R
S
S
S
S
R
R
S
S
S
S Penicillin
Cloxacillin
Cephalexin
Gentamicin
Erythromycin
Clindamycin R
S
S
S
R
R ABST of an Isolate of Escherichia coli Ampicillin
Amox-clav
Cefazolin
Cefalothin
Cefuroxime
Cefotaxime
Ceftazidime
Aztreonam
Piperacillin
Cefepime
Pip-Taz Cefo-Sul
Imipenem
Meropenem
Gentamicin
Tobramycin
Netilmicin
Amikacin
Ciprofloxacin
Ofloxacin
Tetracycline
Cotrimoxazole R
R
R
R
R
R
R
R
R
R
S S
S
S
R
R
S
S
R
R
R
R ABST of an Isolate of Pseudomonas aeruginosa Ceftazidime
Piperacillin
Aztreonam
Cefepime
Pip-Taz
Cefo-Sul
Imipenem
Meropenem
Gentamicin
Tobramycin
Netilmicin
Amikacin
Ciprofloxacin
Ofloxacin S
R
S
S
S
S
S
S
S
S
S
S
S
S Ceftazidime
Piperacillin
Aztreonam
Gentamicin
Tobramycin
Ciprofloxacin
Ofloxacin S
R
S
S
S
S
S ABST of an Isolate of Salmonella typhi Ampicillin
Ceftriaxone
Nalidixic acid
Ciprofloxacin
Chloramphenicol R
S
R
S
S What is wrong with this picture? Cefoxitin
Methicillin
Vancomycin
Penicillin
Clindamycin
Amox-clav R
S
MS
S
S
S A.
B.
C.
D.
E.
F. Thank you
Full transcript