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European Journal of Biotechnology and Bioscience
Online ISSN: 2321-9122
Volume 3; Issue 10; October 2015; Page No. 11-13

Susceptibility Pattern of Trimethoprim/ Sulfamethoxazole in Methicillin Resistant Staphylococcus
aureus Isolates of a Tertiary Care Hospital in Karachi
1 Arfa Masihuddin, 2 Mehak Fatima, 3 Syed Bilal Tanvir, 4 Zahra Rehman, 5 Ali Shariq, 6 Arif Hussain
11st Year M.B, B.S student, Ziauddin Medical Univeristy, Karachi, Pakistan.
2 1st Year M.B, B.S student, Ziauddin Medical Univeristy, Karachi, Pakistan.
3 House Officer, Dr Ziauddin Medical University, Karachi Department of Surgery, Sindh, Karachi, Pakistan. 4 1st Year M.B, B.S student, Ziauddin Medical Univeristy, Karachi, Pakistan 5 Assistant Professor Microbiology department, Dr. Ziauddin Medical University Hospital, Sindh, Karachi, Pakistan. 6 Professor, Director Clinical Laboratories, Dr Ziauddin University Hospital, Sindh, Karachi, Pakistan.

To comprehend the frequency, resistance and susceptibility pattern of MRSA isolates to
Trimethoprinin/Sulfamethoxazole in a tertiary care hospital in Karachi
Methods: A prospective cross-sectional study was performed and a total of 369 clinical specimens, which comprised of eye, ear,
wound and pus swabs, blood, urine, sputum samples and tracheal aspirates which were cultured for time frame of 1 year. Standard
and specific microbiological techniques were used to identify positive cultures. Out of a total of 369 isolates 165 were found to be
MRSA. Spss version 22 was used for statistical analysis.
Results: In study it was deduced that 82.4% of the MRSA strains were resistant to Trimethoprim/Sulfamethoxazole as compared to
Clindamycin to which 91.4% of the strains were resistant, while all strains of MRSA were 100% susceptible to Vancomycin.
A slightly higher resistance (83%) to Trimethoprim/Sulfamethoxazole of MRSA strains in age group 31-40yrs was noted when
compared with other age groups. While resistance to Clindamycin was also slightly increased in age group 20-30yrs.
Conclusions: Trimethoprim/Sulfamethoxazole has maintained its susceptibility to MRSA when compared with Clindamycin but
remained inferior to Vancomycin based on data gathered from the antibiogram. Trimethoprim-Sulfamethoxazole can still be
considered as a suitable option for treatment of nosocomial MRSA infections in selected cases as an alternative to Clindamycin and
Keywords: MRSA; Trimethoprim/Sulfamethoxazole, Staphylococcus aureus, resistance pattern.
is community acquired. On further investigation, these strains Staphylococcus aureus is a Gram positive bacteria that is a show the following results: 55% of cellulitis strains, 50% of small, round shaped, non-motile cocci, found in grape-like cutaneous abscess strains, 23% of osteomyelitis strains, and (staphylo-) structures. Found commonly in the environment, the 13% of finger-pulp-infection strains [5].
mode of transmission for S. aureus is via air droplets and Emerging as a nosocomial pathogen in the 1970s, MRSA has aerosols. Approximately a third of healthy individuals carry this become highly prevalent and is a cause of many community bacterium in their pharynx, noses and on their skin [1]. acquired infections. MRSA is primarily an altered form of Staphylococcus aureus can be termed as one of the predominant S.aureus that allows it to become resistant to beta lactam pathogens of nosocomial infections – infections occurring antibiotics by expressing a modified version of a penicillin within 48 hours of hospitalization, 30 days of an operation or 3 binding protein (PBP2a) [6]. Over many years, S.aureus has
days of discharge. Up to 60% of all nosocomial infections in the acquired resistance to several antibiotics by developing a ICU are caused by Methicillin-resistant S. aureus (MRSA) [2]. resistance pattern. These patterns include horizontal gene In acute care hospital Staphylococcus aureus is a major cause transfer, spontaneous mutations leading to resistance in of health care associated infections, including nosocomial fluoroquinolones and linezolid and antibiotic trapping for pneumonia, surgical site infection, skin infections, vancomycin [7]. While it is known that S.aureus is susceptible to osteomyelitis, food poisoning, endocarditis and toxic shock Vancomycin, Trimethoprim/sulfamethoxazole is a viable syndrome. Other infections such as those of the bloodstream, option for alternative treatment of S.aureus infections as it has cardiovascular, and eye, ear, nose, and throat are also included retained its susceptibility worldwide. For soft tissue infections, [3, 4]. 5% of Staphylococcus aureus strains produces a cytotoxin
Trimethoprim/sulfamethoxazole is recommended but for know as Panton-Valentine leukocidin (PVL) which causes severe MRSA infections, Vancomycin is preferred [8].
tissue necrosis and leukocyte destruction. 85% of these are associated with severe necrotic hemorrhagic pneumonia which Material and Methods
Linezolid group and 52/59 (88.1%) in the A prospective cross-sectional study was performed and a total Trimethoprim/Sulfamethoxazole and Rifampicin group (risk of 369 clinical specimens, which comprised of eye, ear, wound difference 6.3%, 95% CI −6.8% to 19.2%). They concluded and pus swabs, blood, urine, sputum samples and tracheal Trimethoprim/sulfamethoxazole was non-inferior in the aspirates and were cultured for time frame of March 2014 to treatment of MRSA infection [13].
Nov 2014. Positive cultures for S. Aureus were identified. Brain Another randomized controlled trial studied the effectiveness of heart infusions Broth were used to process all specimens which Trimethoprim/Sulfamethoxazole against Vancomycin of the were incubated at 35 0C. Macroscopically the cultures were 228 intravenous drug users, 101 had proven infections. Out of observed for progress for 7 days. On the 7th day Subcultures of these, 54 had Methicillin susceptible S aureus and 47 had all the blood specimens were done before reporting the culture MRSA. Positive results were seen in 57 of 58 Vancomycin as negative. For 18-24 hours plates were incubated aerobically recipients and in 37 of 43 TMP-SMZ recipients (P less than at 37 0C. All other specimens (wound swabs, ear swabs, eye 0.02). The authors concluded that swabs, sputum, aspirates) were inoculated onto sheep blood, Trimethoprim/Sulfamethoxazole could be used to treat certain chocolate and Mac Conkey agar plates and incubated at 37 oC MRSA cases [14]. for 18-24 hours. In addition all specimens were inoculated on However, in another randomized trial conducted in Israel, the mannitol-salt agar and the incubation was extended to at least authors concluded that Trimethoprim/Sulfamethoxazole did not 48-72 hours for discernible colony development. Standard achieve non-inferiority against Vancomycin.252 patients took procedures were used to identify the isolates part in the trial (92 had bacteremia).Treatment failure for For statistical analysis SPSS version 22 was utilized. Out of Trimethoprim-Sulfamethoxazole (51/135, 38%) versus total 369 specimens 165 specimens were found to be MRSA. Vancomycin (32/117, 27%)—risk ratio 1.38 (95% confidence Sensitivity of clindamycin and trimethoprim along with interval 0.96 to 1.99) was not significant. However, vancomycin to MRSA isolates was deduced as well. Trimethoprim-Sulfamethoxazole did not meet the non- inferiority criterion [8].
Results & Discussion
Four teaching hospitals in Pakistan collected data on 1102 Occurring in microscopic clusters that resemble grapes, S.aureus isolates. MRSA accounted for 41.9% of the S.aureus Staphylococcus aureus are spherical, Gram-positive bacteria. isolates. According to the study nosocomial MRSA was multi- Found mainly in the nasal passages, S. aureus also colonizes in drug resistant whereas community acquired MRSA showed other anatomical sites like the oral cavity, skin and the susceptibility to Trimethoprim-Sulfamethoxazole (3.9%) and gastrointestinal tract. It is a non-motile, non-spores forming Clindamycin (63%) [15]. bacteria that causes a variety of supparative, nosocomial Whereas in our own study we found out 82.4% of the MRSA infections [9]. Nosocomial infections are those that occur within
strains were resistant to Trimethoprim-Sulfamethoxazole as 72 hours of hospitalization, and were not present or incubating compared to Clindamycin to which 91.4% of the strains were prior to it [10].
resistant, while all strains of MRSA were 100% susceptible to Hospitalized patients are at a greater risk of infection by S. Vancomycin. This indicates Trimethoprim-Sulfamethoxazole aureus due to surgical or other wounds. The infection can can still be considered as a potential treatment option when aggravate if it is resistant to most types of antibiotics, and may compared with Clindamycin. In males 85.9% of the stains were require isolation from other patients [11]. Since the infection is
resistant to Trimethoprim-Sulfamethoxazole while in females only caused by antibiotic resistant strains, it is only treated with 79% of the strains were resistant to it as shown in table 1. The vancomycin [12].
age distribution of MRSA and antibiotic resistance pattern is In Switzerland, a study was conducted to test the non-inferiority depicted in table 2. It shows that there is a slightly higher of Trimethoprim/Sulfamethoxazole and Rifampicin against resistance (83%) to Trimethoprim-Sulfamethoxazole of MRSA linezolid for treating MRSA infection.150 adult patients strains in age group 31-40yrs as compared to other age groups. participated in the trial and the authors confirmed with PP While resistance to Clindamycin was also slightly increased in analysis that 54/66 (81.8%) showed positive results in the age group 20-30yrs. Table 1: Resistance pattern of MRSA according to Gender (n=165)
Resistance pattern of MRSA according to Gender (n=165)
Average Total
Antibiotics Male Co-trimoxazole(TMP/SLZ) 85.9% Table 2: Drug Resistance against MRSA in different Age group
Age group
Age group
Age group
Age group
Age group
20-30 31-40 41-50 51-60 >60 Oxacillin 100% 100% 100% 100% 100% Cotrimoxazole 82% 83% 82.1% 82.2% 82.1% Clindamycin 94.8% 87.8% 91.9% 90.8% 91.9% In 1961 the first strain of Staphylococcus aureus that resisted 7. Pantosti A, Sanchini A, Monaco M. Mechanisms of Methicillin was found, marking the beginning of MRSA. Also, antibiotic resistance in Staphylococcus aureus. Future resistance was developed against Penicillin, Amoxicillin, Microbiol. 2007; 2(3):323-34 Oxacillin, and other beta lactams. In 2002, this also showed 8. Paul M, Bishara J, Yahav D. Trimethoprim- resistance against the antibiotic Vancomycin in the United sulfamethoxazole versus vancomycin for severe infections caused by meticillin resistant Staphylococcus aureus: Therefore, MRSA needs to be treated as it causes acute randomised controlled trial. BMJ. 2015; 14(350):h2219 infection like boils, cellulitis, impetigo and chronic infections 9. Todar K. Staphylococcus aureus [Internet], 2015 [cited 20 like blood poisoning (sepsis), UTI, pneumonia, septic arthritis, July 2015]. Available from: osteomyelitis and endocarditis [17]. Trimethoprim-
Sulfamethoxazole may be a useful alternative to Vancomycin 10. Medicine Net. com. Definition of Nosocomial [Internet]. for treatment of severe S. aureus infections [18] 2015 [cited 20 July 2015]. Available from: Treatment of endocarditis, joint infection and meningitis caused due to these infections respond well to Trimethoprim/Sulfamethoxazole. These antibiotics act by 11. Better Health Channel. Staphylococcus aureus - golden inhibiting dihydropteroate synthetase, dihydrofolate reductase, staph [Internet]. [cited 22 July 2015]. Available from: as well as bacterial folic acid synthesis [19]. Hence, due to this unique mechanism this antibiotic can be utilized for the pages/Staphylococcus_aureus_golden_staph, 2015 treatment of complicated MRSA infections as an alternative to 12. Foster T. Staphylococcus. In: Baron S, editor. Medical other antibiotics. Microbiology. 4th edition. Galveston (TX): University of Texas Medical Branch at Galveston, 1996. Chapter 12. Conclusion
Emerging resistance of MRSA to antimicrobial agents is a growing concern, especially in the developing countries where 13. Harbarth S, von Dach E, Pagani L. Randomized non- there is excessive unmonitored usage of antibiotics. This issue inferiority trial to compare trimethoprim/sulfamethoxazole has narrowed down our options for usage of different antibiotics plus rifampicin versus linezolid for the treatment of MRSA to treat severe nosocomial MRSA infections in patients. Despite infection. J Antimicrob Chemother. 2015; 70:264-72 high resistance pattern of MRSA to antimicrobials agents in our 14. Markowitz N, Quinn EL, Saravolatz LD. Trimethoprim- research it was determined that Trimethoprim- sulfamethoxazole compared with vancomycin for the Sulfamethoxazole has a comparatively lower resistance to treatment of Staphylococcus aureus infection. Ann Intern MRSA when compared with Clindamycin, but remained Med. 1992; 117:390-8. inferior to Vancomycin based on data gathered from the 15. Bukhari SZ, Ahmed S, Zia N. Antimicrobial susceptibility antibiogram. Hence, It can be ascertained that Trimethoprim- pattern of Staphylococcus aureus on clinical isolates and Sulfamethoxazole is still a suitable option for treatment of efficacy of laboratory tests to diagnose MRSA: a multi- nosocomial MRSA infections in selected cases as an alternative centre study. J Ayub Med Coll Abbottabad. 2011; to Clindamycin and Vancomycin which have been used non judiciously in developing countries for the treatment of the 16. National institute of Allergy and Infectious Diseases. aforementioned pathogen. Methicillin-Resistant Staphylococcus aureus (MRSA) [Internet] 2015 [cited 22 July 2015]. Available from: References
1. Mandal A. What is Staphylococcus Aureus? [Internet]. [cited 8 July 2015]. Available from: 17. NHS. MRSA infection – Symptoms, 2015. [cited 24 July 2015]. Available from: Staphylococcus-Aureus.aspx), 2010 2. Inweregbu K, Dave J, Pittard A. Nosocomial infections. Contin Educ Anaesth Crit Care Pain 2005; 5(1):14-17. 18. Andra M, Lawrence KR. Trimethoprim/sulfamethoxazole 3. Ali MA, Abbasi SA, Arif S, Mirza IA. Nosocomial for treatment of severe Staphylococcus aureus infections. infections due to methicillin resistant Staphylococcus Ann Pharmacother. 2004; 38(2):338-41. aureus in hospitalized patients Pak J Med Sci. 2007; 19. Chernyshev A, Fleischmann T, Kohen A. Thymidyl biosynthesis enzymes as antibiotic targets. Appl Microbiol 4. Noskin GA, Rubin RJ, Schentag JJ. The Burden of Biotechnol 2007; 74:282-9. Staphylococcus aureus Infections on Hospitals in the United States: An Analysis of the 2000 and 2001 Nationwide Inpatient Sample Database. Arch Intern Med 2005; 165(15):1756-61. 5. Lina G, Piemont Y, Godail-Gamot F. Involvement of Panton-Valentine Leukocidin--Producing Staphylococcus aureus in Primary Skin Infections Pneumonia and Clin Infect Dis. 1999; 29(5):1128-32. 6. Kali A, Stephen S, Umadevi S. Changing Trends in Resistance Pattern of Methicillin Resistant Staphylococcus aureus. J Clin Diagn Res. JCDR. 2013; 7(9):1979-1982 


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