Vol 43 # 2 June 2011 - Kma.org.kw

June 2011
KUWAIT MEDICAL JOURNAL 105
Original Article
Inducible Clindamycin Resistance in Staphylococcus Aureus:
A Study from a Tertiary Care Hospital of North India
Neha Bansal 1 , Uma Chaudhary 2 , Vivek Gupta 3
1
Department of Microbiology, Government Medical College and Hospital, Chandigarh, India
2
Department of Microbiology, Pt. BDS University of Health Sciences, Rohtak, Haryana, India
3
Department of General Medicine, National Institute of Medical Sciences, Jaipur, Rajasthan, India
Kuwait Medical Journal 2011; 43 (2): 105-108
ABSTRACT
Objectives: Clindamycin is a preferred therapeutic option
in erythromycin resistant Staphylococcus aureus skin and soft
tissue infections. However, a major concern regarding its
use for staphylococcal infections is the possible presence
of inducible resistance to clindamycin. The present study
was aimed to determine the incidence of constitutive and
inducible clindamycin resistance in S.aureus isolates in our
hospital.
Design: Retrospective study
Setting: Pt. BDS University of Health Sciences, Rohtak,
Haryana, India
Subjects: A total of 250 consecutive, non-duplicate S.aureus
strains were isolated from various clinical specimens, both
from inpatients and outpatients.
Intervensions: Antibiotic susceptibility tests were
performed using Kirby-Bauer disc diffusion method.
Methicillin resistance was detected by oxacillin disc on
Mueller-Hinton Agar (MHA) plate supplemented with 2%
NaCl. D-test was performed on all erythromycin-resistant
and clindamycin-sensitive isolates to detect inducible
clindamycin resistance.
Main Outcome Measures: Observed and counted were
methicillin resistance in S.aureus, constitutive and inducible
resistance of the isolates to clindamycin, origin of the MLSBi
isolates that is “community” or “hospital” and resistance of
MLSBi isolates to other drugs.
Results: Among 250 S.aureus strains, 112 (44.8%) were found
to be Methicillin-resistant Staphylococcus aureus (MRSA) and
20% had MLSBi phenotype. MRSA isolates showed higher
inducible as well as constitutive resistance (p < 0.0001) to
clindamycin as compared to methicillin-sensitive S.aureus
(MSSA). All S.aureus isolates having MLSBi phenotype
were sensitive to vancomycin and linezolid.
Conclusions: The study strongly recommends the routine
testing of in vitro inducible clindamycin resistance in
S.aureus isolates as it will help in guiding therapy.
KEY WORDS: erythromycin, D-test, lincosamide, MLSBi phenotype
INTRODUCTION
The increasing incidence of methicillin-resistant
Staphylococcus aureus (MRSA) infections and changing
patterns in antimicrobial resistance have led to
renewed interest in the use of macrolide-lincosamidegroup
B streptogramin (MLSB) antibiotics to treat
such infections [1] . The MLSB antibiotics are chemically
distinct but exert similar action by binding to 50S
ribosomal subunit inhibiting bacterial protein
synthesis [2] . Macrolide resistance in staphylococci
may be due to an active efflux mechanism encoded
by msrA gene (conferring resistance to macrolides
and group B streptogramins only) or may be due
to ribosomal target modification, mediated via erm
gene, which encodes enzymes that confer inducible
or constitutive resistance to MLSB agents (MLSB
resistance). In constitutive MLSB resistance, rRNA
methylase is always produced, compared to inducible
MLSB resistance where methylase is produced only in
the presence of an effective inducer [3,4] . In vitro, S. aureus
isolates with constitutive resistance (MLSBc strains)
are resistant to erythromycin and clindamycin, while,
isolates with inducible resistance (MLSBi strains) are
resistant to erythromycin but appear susceptible to
clindamycin. Failure to identify MLSBi resistance may
lead to clinical failure of clindamycin therapy due to
selection of constitutive erm mutants [5] . This inducible
MLSB resistance is not recognized by using standard
susceptibility test methods, including standard broth
- based or agar dilution susceptibility tests. However,
it can be detected by a simple disc approximation
test (D-test) by placing erythromycin (inducer) and
clindamycin discs in adjacent positions. Flattening or
blunting of the zone around clindamycin disc adjacent
to erythromycin disc indicates the presence of inducible
resistance to clindamycin [3] .
Address correspondence to:
Dr. Neha Bansal, MBBS, MD, Demonstrator, Department of Microbiology, Government Medical College and Hospital, Sector-32 D, Chandigarh,
India. Tel: +919216588849, +91172-5097461, E-mail: drneha_bansal@yahoo.com