CLINICAL UTILITY OF ANTIBIOGRAMS

1. CLINICAL UTILITY OF ANTIBIOGRAMS
Dr.T.V.Rao MD
If we look at our responsibilities as medical Microbiologists, the little work we do in diagnostic
laboratories remain with bacterial cultures, and Antibiotic Sensitivity testing pattern of Aerobic
isolates from common specimens sent to our laboratories, with emerging automation the clinical
microbiologists have greater role to interpret the matters on antibiotic resistance and sensitivity
pattern and certainly helps to forecast the events on emerging Antibiotic resistance clinical setting
where we work with many terminally ill and patients lodged in super speciality care , As
Antibiograms are important tools for health care professionals involved in prescribing empiric
antibiotics for suspected bacterial infections. Going to the basics, what is Antibiogram? An overall
profile of antimicrobial susceptibility of a microbial species to a battery of antimicrobial agents. A
tool for healthcare providers to use local antibiotic susceptibility data as recommended by the CDC
to provide guidance in their prescribing practice. Only the first isolate from the patient is to be
included in the analysis. However it has its own controversies bigger area of understanding is in
need, The analysis should be done on the basis of patient location and specimen type. The
percentage susceptibility of the most frequently isolated bacteria should be presented in the
antibiogram, preferably in a tabular form. The antibiogram must be printed or put up in the intranet
for easy access to all clinicians Collaborating with hospitals Hospital antibiograms are commonly
used to help guide empiric antimicrobial treatment and are an important component of detecting
and monitoring trends in antimicrobial resistance. To serve these purposes, antibiograms must be
constructed using standardized methods that allow inter- and intra-hospital comparisons These tools
utilize micro biologic data from patient specimens from a Medical establishment or nursing facility to
estimate the ward- or facility-wide prevalence of antibiotic susceptibilities for common Bacterial
pathogens. The hospital antibiogram is a periodic summary of antimicrobial susceptibilities of local
bacterial isolates submitted to the hospital's clinical microbiology laboratory. Antibiograms are often
used by clinicians to assess local susceptibility rates, as an aid in selecting empiric antibiotic therapy,
and in monitoring resistance trends over time within an institution. Anti-microbial susceptibility data
are often considered when deciding if a particular antimicrobial will be included in the anti-infective
section of a drug formulary Antibiograms are also used to compare susceptibility rates across
institutions and track resistance trend they are also an important component of monitoring trends in
antimicrobial resistance within different areas of a facility. Hospitals use antibiograms as part of their
infection control measures to classify types of bacteria found in cultures, to identify patterns of
antibiotic susceptibility in those bacteria, and to track changes in antibiotic susceptibility over time.
Hospitals use these cumulative antimicrobial susceptibility test data reports to determine the most
appropriate agents for initial empirical antimicrobial therapy and to target efforts to reduce
inappropriate antibiotic use. Selection of empiric therapy in a particular patient should not be based
solely on an antibiogram. Patient’s particular infection history, including past antimicrobial use, must
also be considered. Antibiograms provide guidance for empiric antibiotic use in patients, but other
factors including patient characteristics and prevalence of other risk factors should be incorporated
when making therapeutic decisions. They do not even reveal if the organism was causing infection or
was simply a colonizing strain. Antibiograms reveal qualitative measures of susceptibility (i.e.,
whether a pathogen is resistant or susceptible) but do not provide quantitative data, such as
minimum inhibitory concentrations (MICs). Hospital antibiograms can be a useful means for guiding
empiric therapy and tracking the emergence of bacterial resistance among nosocomial isolates.
However, variability in the manner in which antibiograms are constructed and reported introduces
confounding that impedes intra- and inter hospital comparisons. Although the CLSI published the

2. M39-A guidance document on standardizing anti-biogram construction and reporting, data suggest
that few medical centres have adopted all elements of this document. Until there is greater and
more predictable compliance with the M39-A document, it would be extremely valuable to have the
construction methodologies notated on the antibiogram so that the approach is transparent.
Notations should specify the methodology applied to duplicate isolates and the time frame
designated for excluding duplicate isolates. This way, when antibiogram data are used to compare
antimicrobial resistance rates among hospitals, different methodologies used to generate
susceptibility data can be accounted for. The recommendations in M39-A3 are intended to be used
by individuals involved in the following: analysing and presenting antimicrobial susceptibility test
data utilizing cumulative antimicrobial susceptibility test data to make clinical decisions ; and
designing information systems for the storage and analysis of antimicrobial susceptibility test data
One of the recommendations for prevention and control of multi drug-resistant organisms is for
institutions to have a multidisciplinary process in place to review local antibiograms and
antimicrobial drug use to enhance appropriate antimicrobial use, The WHONET software can be
freely downloaded and used for analysis. Consensus guidelines have been developed by the Clinical
and Laboratory Standards Institute (CLSI) to standardise methods used in constructing antibiograms.
However all the matters related to what to prescribe, and best the best option remain with clinician
as the test results can be used to guide antibiotic choice. The results of antimicrobial susceptibility
testing should be combined with clinical information and experience when selecting the most
appropriate antibiotic for patients. Despite the statistical limitations, some conclusions remain valid:
AST is nuanced and complex, and automated instrumentation does not eliminate the need for well-
trained, experienced clinical microbiologists to oversee testing and review data.
I WISH MANY CLINICAL MICROBIOLOGISTS TO ASCERTAIN ROLE IN THE CLINICAL CARE OF THE
PATIENTS, AND INTERPRETATION ON MATTERS RELATED TO ANTIBIOGRAMS
Ref 1 CLSI Publishes Guideline for Analysis and Presentation of Cumulative Antimicrobial
Susceptibility Test Data
2 Systematic Review of Antibiograms: A National Laboratory System Approach for Improving
Antimicrobial Susceptibility Testing Practices in Michigan Martha S. Boehme, MLS (ASCP)CMaPatricia
A. Somsel, DrPHbFrances Pouch Downes, DrPHa - Public Health Laboratories
Dr.T.V.Rao MD Professor of Microbiology Freelance writer