A pilot programme of MRSA surveillance in India. (MRSA Surveillance Study Group).
AA Mehta, CC Rodrigues, RR Kumar, AA Rattan, HH Sridhar, VV Mattoo, VV Ginde
PD Hinduja Hospital and Medical Research Centre, Bombay.
A A Mehta
PD Hinduja Hospital and Medical Research Centre, Bombay.
This surveillance study was conducted simultaneously at three centres across India. A total of 13,610 test samples from various sites were obtained. Microbiological methods employed were similar at the three centres. Identification of S aureus was based on the recognition of the production of coagulase with positive isolates being recorded as S aureus. Both tube coagulase tests and slide coagulase test were performed. Antimicrobial susceptibility testing of the isolated strains of staphylococcus aureus and staphylococcus epidermidis to various antimicrobial discs were carried out according to standardized disk diffusion method recommended by NCCLS. Of the total 739 cultures of S aureus, 235 (32%) were found to be multiply resistant with the individual figures for resistance being 27% (Bombay), 42.5% (Delhi) and 47% (Bangalore). MRSA is emerging to be a significant problem pathogen in the surgical setting with vancomycin probably the only reliable choice for these infections.
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Mehta A A, Rodrigues C C, Kumar R R, Rattan A A, Sridhar H H, Mattoo V V, Ginde V V. A pilot programme of MRSA surveillance in India. (MRSA Surveillance Study Group). J Postgrad Med 1996;42:1-3
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Mehta A A, Rodrigues C C, Kumar R R, Rattan A A, Sridhar H H, Mattoo V V, Ginde V V. A pilot programme of MRSA surveillance in India. (MRSA Surveillance Study Group). J Postgrad Med [serial online] 1996 [cited 2022 May 18 ];42:1-3
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Staphylococcus aureus in the most frequently isolated gram-positive pathogen and is increasingly implicated as a cause of nosocomial infections world wide. Recent increase of methicillin-resistant and multipleresistant strains at large hospitals started to pose great difficulty in selecting antimicrobial agents for the management of the infections they cause. Cephalosporins and other beta-lactam antibiotics have been shown to be clinically ineffective even though certain in vitro tests such as the standard disk diffusion test would suggest that the strains are susceptible. Heterogeneous resistance to the beta-lactam antibiotics and cephalosporins is also responsible for the problems encountered in detecting MRSA,. Resistance to erythromycin, clindamycin, tetracycline, aminoglycosides, and chloramphenicol has also been reported with MRSA strains,. This intractable difficulty in the detection of staphylococcal resistance to beta-lactam antibiotics has resulted in the adoption of carefully defined laboratory test procedures directed towards providing the clinical microbiology laboratory the ability to detect and accurately assess the antibiotic susceptibility of methicillinresistant staphylococci. In India, there have been reports of MRSA from different institutes. However, to the best of our knowledge, this is the first surveillance programme using the same methodology, in different centres. Spread well over the country. The present investigation was carried out as a pilot to find out the incidence of MRSA in Indian hospitals and to compare the antimicrobial activity of currently available antibiotics including vancomycin against Staphylococcus aureus.
The study was conducted over a 6 month period beginning September 1994 in Ail India Institute of Medical Sciences. New Delhi, PD Hinduja National Hospital and Medical Research Centre, Mumbai and Kidwai Memorial Institute of Oncology, Bangalore. A total of 13,610 samples from variety of sources such as wound swabs, arterial and central line lips, catheter tips, blood, pus and respiratory tract were received during the study period. Only the first isolates from the patients were considered for screening.
Specimens were cultured according to standard practice appropriate to the type of specimen. Positive cultures showing gross morphology consistent with staphylococci were Gram stained and observed microscopically for clusters of Grampositive cocci Identification of S aureus was based on the recognition of the production of coagulase. Coagulase positive isolates were recorded as S aureus. Both tube coagulase tests and slide coagulase test were performed.
Antimicrobial susceptibility Testing
Antimicrobial susceptibility testing of the isolated strains of staphylococcus aureus and staphylococcus epidermidis to various antimicrobial discs were carried out according to standardised disk diffusion method recommended by National Committee for Laboratory Standards, M2A5, 1993. MuellerHinton Agar plates (pH 7.27.4) were uniformly surface inoculated by cotton swab lightly saturated from a suspension of visual equivalence to the 0.5 Macfariand nephelometric. Within 5 to 20 minutes, the standard antibiotics disks were applied to the agar surface at least 24 mm apart. These plates were incubated at 35?C for 24 hours. Zone diameters to the nearest milli meters were measured and recorded. For disk susceptibility testing methicillin/oxacillin, amoxicillin/clavulanic acid, cefazolin, cefotaxime, gentamicin, netilmicin, tobramycin, amikacin, cefoperazone, cefaclor, lincomycin, ciprofloxacin, rifampicin and vancomycin were the antibacterials tested.
Out of the total 13,610 samples received in the three participating centres, 739 Staphylococci were isolated [Table:1] Out of these 739 staphylococcal isolates 235 (31.8%) were methicillin resistant. In Mumbai, out of 516 Staphylococci 137 (26.6%) were methicillin resistant. The centre in Bangalore showed 33 (47.1%) methicillin resistant strains out of 70 Staphylococci isolated and the centre in New Delhi isolated 65 (42.5%) methicillin resistant strains from 153 Staphylococci.
MRSA now accounts for an important cause of nosocomial infections. MRSA and MSSA are equally pathogenic and are capable of causing the same spectrum of nosocomial infection,. The major determinant of MRSA resistance to betalactam antibiotics is chromosomally mediated and involves production of an unusually low affinity penicillin binding proteins PBP2a or PBP 2,. Most strains of MRSA produce betalactamase, but it does not appear to contribute significantly to their level of resistance to methicillin or oxacillin. Most strains are heterogeneously resistant to methicillin, oxacillin, and the cephalosporins. This unusual form of resistance is resistance for many problems that clinical microbiology laboratories encounter in detecting MRSA.
Our study revealed that, overall the rate of methicillinresistance among large hospitals in India with S aureus is nearly 32%. Similar data reported in other studies over the world in tertiary care centres, support this high incidence found in our study. In Bangalore, the incidence was highest i.e. 47.1% perhaps because it is an oncology hospital and use of antibacterials is more frequent.
MRSA is resistant to all the beta lactam antibacterials, as well as to the cephalosporins despite the fact that standard disk susceptibility testing may indicate sensitivity to cephalosporin drugs. Boyce also suggests that Staphylococci that are resistant to methicillin, oxacillin and naficillin should also be considered resistant to cephalosporins.
In our study, MRSA showed 100% susceptibility to vancomycin. To date and for the past 35 years all strains of MRSA are uniformly susceptible to vancomycin and our study confirms this finding.
Rifampicin and lincomycin showed 78% and 70% sensitivity respectively whereas all other antibacterials tested showed variable sensitivity pattern from 0 to 50%. Ciprofloxacin showed 44% susceptibility in the present study. Several quinolone antimicrobials have good antistaphylococcal activity in vitro. Ciprofloxacin has been most widely used in MRSA infections in the past, but a high level of ciprofloxacin resistance has emerged very rapidly after introduction of the agent into general use,. Chambers and Lyon et al have also shown that the majority of strains are also resistant to erythromycin, clindamycin, tetracycline and aminoglycosides. If this is so, then vancomycin is the drug of first and the only choice in the management of MRSA infections.
Prevention of MRSA infections merit discussion as once introduced in a hospital MRSA is very difficult to eradicate. After introduction within hospital, MRSA spreads rapidly by hands of medical personnel. Colonized employees of the hospital such as asymptomatic nasal carriers and infected patients acting as reservoirs are important sources in the spread of this organism,. Multiple, prolonged use of antibiotics and prolonged hospitalisation are other important factors which make hospitals an ideal place for transmission and perpetuation of MRSA.
The resistance of MRSA to a wide range of antibacterials is well documented. This makes the empirical use of antibacterials effective against M RSA imperative. Vancomycin has been clearly shown to be the drug of choice for the treatment of MRSA infections.
The present MRSA surveillance programme has given a result, which is consistent in all three centres well spread across the country as well as consistent with data published elsewhere in the world. Similar programmes are necessary to monitor the future trend of MRSA.
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