|Year : 2014 | Volume
| Issue : 4 | Page : 439-442
Comparison of antibiotic susceptibility pattern of community- and hospital-acquired methicillin-resistant Staphylococcus aureus with special reference to inducible clindamycin resistance in a tertiary care hospital in southern India
Tandra Chadha1, Syeda Nazia Kulsum2, Shashikant Adlekha3, Prabhakar C Mailapur4
1 Department of Microbiology, Sree Narayana Institute of Medical Sciences, Ernakulam, Kerala, India
2 Department of Microbiology, KBNIMS, Gulbarga, Karnataka, India
3 Department of Pathology, Sree Narayana Institute of Medical Sciences, Ernakulam, Kerala, India
4 Department of Microbiology, SRMMC, Kanchipuram, Tamil Nadu, India
|Date of Web Publication||25-Jun-2014|
Department of Microbiology, Sree Narayana Institute of Medical Sciences, Chalakka, North Kuthiyatode - 683 594, Dist: Ernakulam, Kerala
Source of Support: None, Conflict of Interest: None
Background: Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of nosocomial and community infections. Its prevalence varies markedly across different countries and among hospitals of the same country. Aims and Objectives: To estimate the prevalence of MRSA strains and investigate their antibiogram with special reference to inducible clindamycin resistance. Materials and Methods: All S. aureus isolates obtained from the clinical samples of microbiology laboratory were included in the study. All the isolates were identified by standard methods, and antimicrobial susceptibility testing was performed by Kirby Bauer disk diffusion method. Methicillin resistance was detected by combined cefoxitin and oxacillin disk diffusion method. Results were interpreted as per the Clinical and Laboratory Standards Institute (CLSI) guidelines. Results: A total of 362 S. aureus strains were isolated, of which 36.1% (131/362) isolates were MRSA. Of these, 79.4% (104/131) were hospital-acquired MRSA (HA-MRSA) and 20.6% (27/131) were community-acquired MRSA (CA-MRSA). All the isolates were sensitive to vancomycin. Inducible clindamycin [macrolide-lincosamide-streptogramin B (iMLS B )] resistance (D test) among MRSA isolates was 12.3% (16/131). HA-MRSA isolates showed 12.5% (13/104) D test positivity, as compared to 11.2% (3/27) seen in CA-MRSA isolates. Conclusion: The reported rate of MRSA incidence is alarming. Regular surveillance of hospital-acquired infections, isolation nursing of patients who carry MRSA, monitoring of antimicrobial susceptibility pattern, and formulation of a definite antibiotic policy may be helpful.
Keywords: Antibiogram, Clinical and Laboratory Standards Institute, D test, methicillin-resistant Staphylococcus aureus
|How to cite this article:|
Chadha T, Kulsum SN, Adlekha S, Mailapur PC. Comparison of antibiotic susceptibility pattern of community- and hospital-acquired methicillin-resistant Staphylococcus aureus with special reference to inducible clindamycin resistance in a tertiary care hospital in southern India. Med J DY Patil Univ 2014;7:439-42
|How to cite this URL:|
Chadha T, Kulsum SN, Adlekha S, Mailapur PC. Comparison of antibiotic susceptibility pattern of community- and hospital-acquired methicillin-resistant Staphylococcus aureus with special reference to inducible clindamycin resistance in a tertiary care hospital in southern India. Med J DY Patil Univ [serial online] 2014 [cited 2021 Sep 17];7:439-42. Available from: https://www.mjdrdypu.org/text.asp?2014/7/4/439/135257
| Introduction|| |
Methicillin-resistant Staphylococcus aureus (MRSA), first reported in UK in 1961, has emerged in the last decade as one of the most important nosocomial pathogens.  In addition to the dire consequences of infections, MRSA strains are important for their resistance to vancomycin, the drug that has been used to treat MRSA infections for more than three decades.  Once prevalent in health care setup for more than 40 years, MRSA has migrated to the community in recent years.  The prevalence of multidrug-resistant strains in Indian hospitals [hospital-acquired MRSA (HA-MRSA)] ranges from 15 to 70%.  Community-acquired MRSA (CA-MRSA) has evolved as a novel emerging pathogen in patients who had no contact with health care setup.  Unlike HA-MRSA which typically are resistant to multiple antibiotics, CA-MRSA tend to be susceptible to other antibiotic classes and often are resistant to only β lactam antibiotics.  They also differ from HA-MRSA in epidemiological association, drug resistance determinants, putative virulence factors, and genetic background. 
It is very essential to know the prevalence of MRSA in any environment because of the public health importance and the threat posed by their infection.  Changing pattern of resistance of S. aureus makes its periodic surveillance mandatory  and formulate treatment protocol accordingly in the hospitals. Hence, the present study was undertaken to find out the prevalence of MRSA isolates, proportion of HA-MRSA and CA-MRSA, and comparison of their antibiotic susceptibility profile, with special reference to inducible clindamycin resistance.
| Materials and Methods|| |
All the clinical samples that came to the microbiology laboratory during the study period from December 2008 to November 2009 constituted the material for this prospective study. Ethical clearance was obtained from the institutional ethical research committee. Three hundred and sixty-two strains of S. aureus were isolated from the various clinical samples such as sputum, urine, blood, exudate/pus, and cerebrospinal fluid (CSF).
MRSA associated, if the original entry criteria of hospitalization for ≥72 h before culture acquisition were met, and if the year before the present hospitalization, the patient had any one of the following: hospitalization, surgery, residency in a long-term care facility, and hemodialysis or peritoneal dialysis, or at the present admission had indwelling percutaneous devices or catheters. 
CA-MRSA is defined as a culture confirmed MRSA infection without any of the above criteria.
Methicillin resistance was determined on Mueller-Hinton Agar (MHA) by modified Kirby Bauer disk diffusion method using oxacillin 1 μg and cefoxitin 30 μg disks.  The MHA plates on which oxacillin disks were applied were supplemented with 4% NaCl and incubated aerobically for 24 h at 30°C, while the one on which cefoxitin was placed was not supplemented with NaCl but incubated aerobically at 35°C for 18 h. Isolates with both inhibition zone diameters ≤13 mm and ≤21 mm around oxacillin and cefoxitin disks, respectively, were considered MRSA strains. Antibiotic sensitivity of the isolates was tested using disks - ampicillin (10 μg), erythromycin (15 μg), gentamicin (10 μg), netilmicin (30 μg), amikacin (30 μg), tetracycline (3 μg), cotrimoxazole (25 μg), ciprofloxacin (5 μg), rifampicin (5 μg), and vancomycin (30 μg).
Detection of Inducible Clindamycin Resistance
Testing for inducible clindamycin [macrolide-lincosamide-streptogramin B (iMLS B )] resistance was accomplished by the agar disk diffusion (D test) method in accordance with the recommendations of the Clinical and Laboratory Standards Institute (CLSI). 
| Results|| |
A total of 3301 samples including 1201 pus samples, 102 wound swabs, 96 blood samples, 1521 urine samples, 209 sputum samples, 33 CSF, and 139 ear discharge, eye discharge, and other body fluids were screened during this period. Out of these samples, staphylococci were isolated in 15.54% (513/3301). Of these, 70.56% (362/513) isolates were identified as S. aureus and 29.43% (151/513) isolates were coagulase-negative staphylococci (CoNS). Out of 362 isolates with S. aureus, 36.18% (131/362) isolates were MRSA and 63.81% (231/362) were methicillin-sensitive S. aureus (MSSA). Among these 131 MRSA isolates, 79.38% (104/131) were HA-MRSA and 20.61% (27/131) were CA-MRSA. Majority of the MRSA isolates were from pus samples [42% (56/131)] and wound swab [27% (35/131)]. Least isolates were from urine samples [2% (3/131)]. All the CA-MRSA isolates [Table 1] were sensitive to vancomycin and rifampin. Sensitivity to netilmicin, erythromycin, and amikacin was 88.8% (24/27). All the isolates were resistant to ampicillin. All the HA-MRSA strains [Table 2] were sensitive to vancomycin [100% (104/104)], followed by rifampin [93.3% (97/104)], netilmicin [81.7% (85/104)], and amikacin [76% (79/104)]. Most of the isolates were multidrug resistant, being resistant to erythromycin [94.2% (98/104)], gentamicin [93.3% (97/104)], and tetracycline [85.6% (89/104)]. None of the isolates were sensitive to ampicillin.
|Table 2: Antibiotic susceptibility pattern of hospital-acquired MRSA (n = 104)|
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MLS resistance is of three phenotypes - constitutive resistance (resistance to both erythromycin and clindamycin), iMLS B (flattening of clindamycin zone adjacent to the erythromycin disk), and MS phenotype (resistant to erythromycin and sensitive to clindamycin). 
The iMLS B resistance by D test was put up for all the erythromycin-resistant and clindamycin-sensitive strains.
The overall D test positivity in MRSA isolates [Table 3] was 12.3% (16/131).
Among the HA-MRSA strains, 62.5% (65/104) showed constitutive resistance (resistant to both erythromycin and clindamycin), 19.2% (20/104) showed MS phenotype (resistant to erythromycin and sensitive to clindamycin), and 12.5% (13/104) showed iMLS B resistance (blunting of clindamycin zone adjacent to erythromycin disk).
Among the CA-MRSA isolates, 11.2% (03/27) exhibited iMLS B resistance and none of the strains showed constitutive resistance and MS phenotype.
There was significant difference in the susceptibility pattern of CA-MRSA and HA-MRSA for all the antibiotics except for amikacin, and rifampin. All the MRSA isolates were sensitive to vancomycin and resistant to ampicillin. All the CA-MRSA isolates were sensitive to rifampin. Majority of the HA-MRSA isolates were sensitive to rifampin [93.3% (97/104)], netilmicin [81.7% (85/104)], and amikacin [76% (79/104)]. Majority of them were resistant to erythromycin [94.2% (98/104)], and gentamicin [93.3% (97/104)].
| Discussion|| |
The high proportion of MRSA isolates (36%) found in this study is alarming. This is comparable to the prevalence in different parts of India: 38.4% in Varanasi,  35% in Kanchipuram,  and 34.7% in Dibrugarh.  In the present study, the prevalence of HA-MRSA was 79.4% and CA-MRSA was 20.6%. This finding is in concordance with the studies of Naimi et al. who showed the prevalence of CA-MRSA to be 12% and HA-MRSA to be 85%.  Several authors have reported the prevalence of CA-MRSA ranging from <1 to 36%. ,
In the present study, majority of the MRSA isolates were obtained from pus (42.74%), followed by wound swab (26.71%). This is comparable to the study results of Kumari et al. showing the majority of MRSA isolates to be obtained from pus and wound swab (65.3%)  and Tiwari et al. showing 66.6% of MRSA isolated from pus and wound swab. 
Antibiotic susceptibility of CA-MRSA revealed that majority of the isolates were sensitive to the routinely used antibiotics except β lactams. In the present study, there was statistically significant difference in the susceptibility pattern of CA-MRSA and HA-MRSA to most of the antibiotics - erythromycin, gentamicin, netilmicin, tetracycline, cotrimoxazole, ciprofloxacin, and clindamycin. There was no significant difference observed in the susceptibility pattern of the isolates to ampicillin, amikacin, and rifampin. This is in concordance with the study results of Timothy et al., who revealed statistically significant difference in the susceptibility pattern of CA-MRSA and HA-MRSA isolates to ciprofloxacin, clindamycin, erythromycin, and gentamicin.  Several other reports have quoted similar antibiotic susceptibility pattern, suggesting CA-MRSA to have wider antimicrobial susceptibility pattern compared to HA-MRSA. ,,, In contrast to the present study, a study conducted by Tiwari et al. did not show any significant difference in the antibiotic susceptibility pattern of CA-MRSA and HA-MRSA.  Because of the easy availability and indiscriminate use of antibiotics, the chances of emergence of resistant strains are increasing. Lack of public awareness has further deteriorated the situation.
In the present study, D test positivity was seen in 12.3% (16/131) of the MRSA isolates. D test was positive in 11.2% of CA-MRSA and 12.5% of HA-MRSA isolates. Comparable results were obtained in a study by Saikia et al., showing the prevalence of inducible clindamycin resistance by D test to be 9.38% among MRSA isolates.  A study by Patel et al. showed the prevalence of inducible clindamycin resistance to be 49.64% among the MRSA isolates, and the prevalence of CA-MRSA was reported to be 33% and HA-MRSA was 56%.  The iMLS B resistance test should be carried out routinely in laboratories so as to prevent therapeutic failures. The reasons for the increasing incidence of MRSA in the hospitals and community could be multifactorial. Selection pressure due to overuse of antibiotics could have contributed to the emergence of these pathogens.
| Conclusion|| |
Staphylococcus, particularly MRSA, has emerged as a major global health problem both in community and hospitals. The emergence of MRSA poses a major health threat. Since these are resistant to the commonly used antibiotics which are used to treat a variety of infections, there is a need for the development, adoption, and enforcement of appropriate control policies in our hospital. Regular surveillance of hospital-associated infections including monitoring of antimicrobial (especially vancomycin) susceptibility pattern of MRSA and formulation of a definite antimicrobial policy may be helpful in reducing the incidence of these infections. A further study of MRSA may be conducted for the epidemiological mapping of these infections.
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[Table 1], [Table 2], [Table 3]
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