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Year : 2002  |  Volume : 56  |  Issue : 7  |  Page : 330--334

Methicillin resistance among isolates of Staphylococcus aureus : Antibiotic sensitivity pattern & phage typing

Supriya S Tahnkiwale, S Roy, SV Jalgaonkar 
 Department of Microbiology, Indira Gandhi Medical College, Nagpur-440 018,

Correspondence Address:
Supriya S Tahnkiwale
Department of Microbiology, Indira Gandhi Medical College, Nagpur-440 018

How to cite this article:
Tahnkiwale SS, Roy S, Jalgaonkar S V. Methicillin resistance among isolates of Staphylococcus aureus : Antibiotic sensitivity pattern & phage typing.Indian J Med Sci 2002;56:330-334

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Tahnkiwale SS, Roy S, Jalgaonkar S V. Methicillin resistance among isolates of Staphylococcus aureus : Antibiotic sensitivity pattern & phage typing. Indian J Med Sci [serial online] 2002 [cited 2014 Apr 19 ];56:330-334
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Staphylococcus aureus has been reported to the a major cause of community and hospital acquired infection.[1] Methicillin resistant Staphylococcus aureus (MRSA) has become endemic world wide, over the past two decades. It is now a major nosocomial pathogen in many hospitals. Indiscriminate use of multiple antibiotics, prolonged hospital stay, intravenous drug abuse, carriage of MRSA in nose are some of the important risk factors of MRSA acquisition.[2]

Control of MRSA in hospital is essential. It can be achieved by proper implementation of hospital infection control measures and regular surveillance activity. Not much work about incidence of MRSA has been done in this region. Present communication deals with prevalence of MRSA In tertiary care hospital and their phage typing pattern.


The study was carried out between Nov­1999 to Oct-2000 at Indira Gandhi Medical College, Nagpur. A total of 3988 samples of pus, wound swabs, sputum, blood, vaginal swabs and conjunctival swabs were processed for Isolation of Staphylococcus aureus.

Specimens were screened by preliminary Gram's stain and were inoculated on 10% sheep blood agar and MacConkey's agar. Staphylococcus aureus was identified by conventional techniques .[3]

Antimicrobial sensitivity was performed on all the Staphylococcus aureus isolates by Kirby-Baur's disc diffusion method.[4] Oxacillin sensitivity was performed on Muller-Hinton agar with 4% sodium chloride. The strains were reported as sensitive, intermediate sensitive or resistant, to oxacillin with inhibition zone diameter equal or more than to 13mm and less than or equal to 10mm respectively.

All the oxacillin resistant strains were subjected for testing of beta lactamase production by rapid acidimetric method[5]. All these strains were also subjected to estimation of minimum inhibitory concen­tration against oxacillin using E-strips (AB BIO DISK, Sweden). The oxacillin resistant strains were sent to National Staphylococcal Phage-typing Centre, Maulana Azad Medical College, New Delhi for phage typing.


Forty-five out of 230 isolates (19.56%) of S' aureus were MRSA. Maximum number of MRSA (26.92%) were: from pus and wound swabs. All MRSA strains were beta lactamase producers. Multidrug resistance was observed in MRSA strains. Maximum strains were resistant to penicillin (100%), cotrimoxazole (97%) and chloramphenicol (93.33). Least resistance was observed against gentamicin (6.66%). All strains were found to be sensitive to vanco­mycin. [Table 1].

Multidrug resistance was found to be less common amongst the Methicillin Sensitive Staphylococcus aureus (MSSA) strains. Maximum resistance was observed against co-trimoxazole (55.67%) followed by penicillin (40.54%). Least resistance was observed against ciprofloxacin 4.86% while none of the MSSA strains were resistant to gentamycin. [Table 1].

28 out of 44 strains were nontypeable by phage values less than tug/ml for oxacillin. Majority (34 out of 45) showed MIC values 4ug/ml. Nine showed MIC of 12ug/nil and two strains showed MIC values of 250 ug/ml.

Out of 44 strains subjected to phage typing, maximum (28) were nontypeable. Eleven belonged to mixed group, while 4 belonged to group three indicating hospital strains. [Table 2] Out of 44, twenty three strains typed additionally by MRSA phage revealed that all three typeable strains with MRSA phages were also typeable with the routine phages all of which belonged to group three.


Methicillin was indicated for treatment of Staphylococcal infections due to penicillinase producing staphylococci. Methicillin resistant strains gradually evolved during last three decades which accounted for less than 0.1% of Staphylococcus aureus in 1960s. Since then MRSA have become well established as hospital acquired pathogen.[6]

In our study 19.56% of the total isolates of the Staphylococcus aureus were MRSA. The reported incidence of MRSA in India was found to range from 6.9% to 51.6%.[7]

Antibiotic sensitivity results showed that all MRSA strains were significantly more resistant to antibiotics compared to Methicillin Sensitive Staphylococcus aureus (MSSA) isolates. Resistance of MRSA to penicillin (100%), cotrimox­azole (97%), chloramphenicol (93.33%), erythromycin (68.68%) was marked. High resistance to these drugs has also been reported in other studies.[8],[9]

Low ciprofloxacin resistance of MRSA strains (33.33%) was found in the present study. High resistance to this antibiotic was reported in some studies[9] and low resistance in other studies.[10] High resistance of MRSA to gentamycin has been reported.[11] In our study only 6.6% resistance to gentamycin was found. All MRSA strains of present study were sensitive to vancomycin.

MIC values to oxacillin > or = to 250 ugm/ ml were found only in two strains, while MIC of majority strains ranged between 2 ugm/ml to 12 ugm/ml. High MIC values were recently found in one of the studies.[12]

Bacteriophage typing of Staphylococcus aureus is an established epidemiological marker. Four of the 44(9.0%) MRSA strains in the present study belonged to group three & 11 strains (25%) showed a mixed group pattern while a large number of strains (28) were nontypeable (63.6%)

Interestingly 23 strains were also typed by new MRSA phages. Three of these strains also belonged to group three while 20 nontypeable strains couldn't be typed by the new phages. Due to high level of nontypeability alternative methods such as biochemical reactions have been used. The present study indicates that the new scheme of phage typing is also not very helpful in the local strains. There is a need to develop local set of MRSA phages for improvement and typability.


Out of 3988 clinical specimens from hospital admitted patients 230 strains of Staphylococcus aureus were isolated. 45 strains (19.56%) were Methicillin resistance Staphylococcus aureus (MRSA). All MRSA strains were beta lactamase producers. Multidrug resistance was observed among MRSA strains more commonly than in methi­cillin sensitive strains of Staphylococcus aureus (MSSA). Maximum strains were resistant to penicillin (100%), cotrimoxazole (97%) & chloramphenicol (93.33%). As least resistant to gentamicin & ciprofloxacin shown by MRSA, these drugs can be used in few situations after susceptibility test. All strains of MRSA were sensitive to vancomycin (100%).

Majority of strains (34 out of 45) showed MIC values of 4 ug/ml. Twenty eight out of 44 strains were non typable using routine phages. Study revealed that MRSA with associated multidrug resistance is common in this region. There is need to develop local set of MRSA' phages for improvement of typability.


Authors are thankful to Professor of Microbiology & Incharge, Staphyloco­ccus Phage Typing Centre, Maulana Azad Medical college, New Delhi for phage typing of strains. Authors are grateful to Dr. W.B.Tayade, Dean, Indira Gandhi Medical college, Nagpur for permitting to carry out and publish this work.


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