|Year : 2012 | Volume
| Issue : 2 | Page : 73-75
Prevalence of inducible clindamycin resistance in Staphylococcus aureus
TA Dhanalakshmi1, BL Umapathy2, DR Mohan1
1 Department of Microbiology, Adichunchanagiri Institute of Medical Sciences, B.G. Nagara, Mandya District, Bangalore, Karnataka, India
2 Department of Microbiology, ESIC - Post Graduate Institute of Medical Sciences and Research, Rajaji Nagar, Bangalore, Karnataka, India
|Date of Web Publication||21-Sep-2013|
T A Dhanalakshmi
Department of Microbiology, Adichunchanagiri Institute of Medical Sciences, B.G. Nagara - 571 448, Mandya District, Karnataka
Source of Support: None, Conflict of Interest: None
Background and Objectives: The emergence of methicillin-resistant Staphylococcus aureus (MRSA) has led to the use of Macrolide-Lincosamide-Streptogramin B (MLS B ) antibiotics to treat MRSA infections. Clinical failures can result if resistance to these drugs is inadequately tested. This study was carried out to detect MLS B phenotypes and inducible clindamycin resistance among Staphylococcus aureus (S. aureus).
Materials and Methods: A total of 250 non-duplicate S. aureus isolates were subjected to D-test by placing an erythromycin (15 μg) disc at a distance of 15mm from a clindamycin (2 μg) disc. Results were interpreted using Clinical and Laboratory Standards Institute (CLSI) guidelines. Methicillin resistance was detected by the oxacillin agar dilution method. Results were analyzed using the Chi-square test.
Results: Among 250 isolates of S. aureus, 84 (33.6%) were MRSA and 166 (66.4%) were methicillin-susceptible Staphylococcus aureus (MSSA). Thirty one (36.9%) MRSA and 75 (45.2%) MSSA were sensitive to both erythromycin and clindamycin. Macrolide and Streptogramin B (MS B ) phenotype were observed in 20 (23.8%) of MRSA and 64 (38.6%) of MSSA isolates. Constitutive MLS B resistance and inducible MLS B resistance were observed in 22 (26.2%) and 11 (13.1%) of MRSA, and 17 (10.2%) and 10 (6%) of MSSA isolates, respectively.
Conclusion : D-test should be included as a part of routine antibiotic susceptibility testing to detect inducible clindamycin resistance to prevent treatment failure.
Keywords: Clindamycin, D-test, erythromycin, methicillin-resistant Staphylococcus aureus, methicillin-susceptible Staphylococcus aureus
|How to cite this article:|
Dhanalakshmi T A, Umapathy B L, Mohan D R. Prevalence of inducible clindamycin resistance in Staphylococcus aureus. J Acad Med Sci 2012;2:73-5
|How to cite this URL:|
Dhanalakshmi T A, Umapathy B L, Mohan D R. Prevalence of inducible clindamycin resistance in Staphylococcus aureus. J Acad Med Sci [serial online] 2012 [cited 2019 Dec 14];2:73-5. Available from: http://www.e-jams.org/text.asp?2012/2/2/73/118664
| Introduction|| |
Widespread use of Macrolide-Lincosamide-Streptogramin B (MLS B ) antibiotics to treat Staphylococcus aureus (S. aureus) infections has led to an increase in the number of strains resistant to MLS B antibiotics.  Constitutive resistance (MLS Bc ) can be readily detected but inducible (MLS Bi ) resistance is not detected by routine methods.  D-test identifies inducible resistance and thus avoids treatment failure.  This study was carried out to detect MLS B - resistant phenotypes among S. aureus.
| Materials and Methods|| |
The present study was conducted for a period of 10 months from January 2010 to October 2010 and included a total of 250 non-duplicate consecutive isolates of S. aureus from various clinical specimens. S. aureus was identified using conventional methods.  Methicillin resistance was detected by the oxacillin agar dilution method.  (Hi Media Mumbai, India). D-test was carried out for all S. aureus isolates along with other antibiotic discs in the same routine antibiotic sensitivity plate. During the D-test, an erythromycin 15 μg disc (Hi Media Mumbai, India) was placed at a distance of 15 mm from the clindamycin 2 μg disc (Hi Media Mumbai, India). The plates were incubated at 35o C for 24 h , and results were interpreted using CLSI criteria.  S. aureus ATCC 25923 and 58424 were used as the control strains. Approval from the ethical committee of the institute has been obtained for this study.
| Results|| |
Among 250 clinical isolates of S. aureus, 84 (33.6%) were methicillin-resistant Staphylococcus aureus (MRSA) and 166 (66.4%) were methicillin-susceptible Staphylococcus aureus (MSSA). Inducible clindamycin resistance (erythromycin resistant, clindamycin sensitive and D-test positive, MLS Bi ) was observed in 11 (13.1%) of MRSA and 10 (6%) of MSSA isolates [Table 1]. Results were analyzed using Chi-square test.
|Table 1: *Macrolide‑lincosamide‑streptogramin B resistant and sensitive phenotypes among|
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| Discussion|| |
S. aureus is one of the important pathogens causing community-acquired and nosocomial infections. It facilitates disease by its propensity to develop resistance to multiple antibiotics which complicates treatment, well exemplified by MRSA, leaving few therapeutic options.  Clindamycin is a good substitute to treat both MRSA and MSSA infections. Its advantages are its low cost, fewer side effects, availability of oral and parenteral forms, lack of need for renal adjustment, good tissue penetration, ability to directly inhibit toxin production, and the fact that it is not impeded by high bacterial burden.  Furthermore, it is a useful option in the treatment of penicillin allergy.  One of the major concerns with regard to the use of clindamycin is the presence of inducible resistance to clindamycin.  Resistance to MLS B antibiotics can occur by either of two different mechanisms: Due to an active efflux mechanism encoded by msrA gene (conferring resistance to macrolides and type B streptogramins only-MS B phenotype) or due to ribosomal target modification, affecting macrolides, lincosamides and type B streptogramins (MLS B resistance).  The erm genes encode enzymes that confer inducible or constitutive resistance to MLS B agents via methylation of the 23S rRNA, reducing the binding of MLS B agents to the ribosome. , In vitro, S. aureus isolates with constitutive resistance (MLS Bc ) are resistant to erythromycin and clindamycin, and isolates with inducible resistance (MLS Bi ) are resistant to erythromycin but appear susceptible to clindamycin. The erm gene expression is normally minimal;  low levels of erythromycin induces the production of methylase,  which allows clindamycin resistance to be expressed.  Hence, it is noted that treatment of patients harboring MLS Bi Staphylococci with clindamycin leads to the development of constitutive resistance, subsequently leading to therapeutic failure.  Conversely, labeling all erythromycin-resistant Staphylococci as clindamycin resistant will disrupt the use of clindamycin in infections caused by truly clindamycin-susceptible Staphylococcal isolates.  Inducible clindamycin resistance cannot be detected by standard broth micro-dilution testing, automated susceptibility testing devices, and the standard disc diffusion test or E-test.  The D-test identifies MLS Bi resistance.  If the D-test was delayed until erythromycin resistance and clindamycin susceptibility were noted in the isolate, the results may not be available for maximum clinical utility.  The incidence of MLS Bi and MS B phenotypes was significantly higher in MRSA than in MSSA isolates (Chi-square test, P less than 0.01). This denotes the importance of carrying out the D-test in MRSA isolates so that the use of clindamycin is judiciously undertaken before switching over to vancomycin in treating such infections.
| Conclusion|| |
The increasing frequency of Staphylococcal infection and the changing pattern of antimicrobial resistance have led to the interest in the use of clindamycin therapy in the treatment of Staphylococcal isolates.  Laboratories and clinicians must be aware of the local prevalence of MLS Bi isolates.  The early detection of MLS Bi resistance helps in the use of clindamycin only in infections caused by truly clindamycin susceptible S. aureus and thus helps mitigate treatment failure.  The D-test identifies MLS Bi resistance, is simple, inexpensive, easy-to-perform, reproducible, and it can be included as a part of routine antibiotic susceptibility testing. ,
| Acknowledgment|| |
We are thankful to all our colleagues and technicians for their support.
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