Published by : PROFESSIONAL MEDICAL PUBLICATIONS
April - June 2009 (Part-II)
Sensitivity pattern of methicillin resistant and methicillin
sensitive Staphylococcus aureus isolates, against several
antibiotics including tigecycline in Iran: A hospital based study
Mohammad Aghazadeh1, Mohammad Rahbar2,
Mohammad Kabeh Monnavar3, Fatemeh Savaheli Moghadam4
Objectives: Methicillin resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen causing significant morbidity and mortality. The aim of this study was to evaluate in vitro activity of tigecycline and other new agents against MRSA, isolated from surgical wound and soft tissue infections in an Iranian 1000-bed tertiary hospital.
Methodology: In vitro activity of tigecycline and other antibiotics were tested against 102 strains of Staphylococcus aureus isolated from different patients hospitalized at Milad hospital from May 2008 to June 2008. All strains were identified according to routine bacteriological methods. Susceptibility testing was performed by disk diffusion methods as recommended by Clinical Laboratory Standards Institute (CLSI). Cefoxitin (30µg) disk used for detection of methicillin resistant strains of S.aureus.
Results: One hundred two strains of S.aureus were isolated from patients admitted to our hospital. The majority of patients was from surgical wards including open heart, orthopedic ward and had post operation wound infections. Of 102 strains 36(35.3%) isolates were MRSA. All isolates including MRSA strains were susceptible to tigecyline, linozolide and vancmycin. Of 102 isolated strains 96 (94.1%) were susceptible to teicoplanine and six stains (5.9%) were intermediate. Resistant rate to other antibiotics including clindamycinm erythromycin pencillin, co-trimoxazole, rifampicin and ciprofloxacin were 35.3%, 27.7%, 97.7%, 26.5%, 16.7%and 33.7% respectively.
Conclusion: All strains of S.aureus, isolated from wound and soft tissue in our hospital were susceptible to tigecyline, linozolide and vancomycin.
KEY WORDS: Methicillin Resistance, Staphylococcus aureus, Wound infection, Antimicrobial agents.
Pak J Med Sci April - June 2009 (Part-II) Vol. 25 No. 3 443-446
How to cite this article:
Aghazadeh M, Rahbar M, Monnavar MK, Moghadam FS. Sensitivity pattern of methicillin resistant and methicillin sensitive Staphylococcus aureus isolates, against several antibiotics including tigecycline in Iran: A hospital based study. Pak J Med Sci 2009;25(3): 443-446
1. Mohammad Aghazadeh
Dept. of Microbiology,
Faculty of Medicine,
Tabriz University of Medical Sciences,
2. Mohammad Rahbar,
Department of Microbiology,
Iranian Reference Health Laboratories,
3. Mohammad, Kabeh - Monnavar,
4. Fatemeh. Savaheli Moghadam
3-4: Dept. of Infection Control,
Mohammad Rahbar (PhD),
Department of Microbiology,
Iranian Reference Health Laboratory,
* Received for Publication: November 10, 2008
* Revision Received: March 16, 2009
* Revision Accepted: April 5, 2009
Staphylococcus aureus is a Gram-positive, non-motile catalase positive, coagulase positive, facultative anaerobe microorganism involved in causing a number of disease including boils pustules, impetigo osteomyelitis, mastitis, septicemia, wound infections, meningitis, food poisoning and toxic shock syndrom.1,2 It produces a variety of pyrogenic toxins and superantigens which contribute to their overall virulence. Methicillin-resistant Staphylococcus aureus (MRSA) is a multidrug-resistant pathogen. Resistance to the macrolides, lincosamides, aminoglycosides, and all beta-lactam agents is also seen with MRSA.3
Methicillin-resistant Staphylococcus aureus (MRSA) is a nosocomial pathogen that causes morbidity and mortality worldwide.4,5 The options for the treatment of MRSA infections are limited to antibiotics such as vancomycin, tigecycline and lineozolid. Tigecycline, a member of the glycocycline class of antibiotics provides good activity against a broad range of gram-positive and gram-negative bacteria, with exception of Pseudomonas aeruginosa, Proteus mirabilis and indol positive Proteus spp.3,5,6
Tigecycline binds to the bacterial 30S ribosome, blocking the entry of transfer RNA. This ultimately prevents protein synthesis but halting the incorporation of amino acids into peptide chains and thus limits bacterial growth.8 The aim of this study was to determine susceptibility of MRSA strains isolated from wound and soft tissue infection to commonly used and new antibiotics such as tigecycline in an Iranian 1000-bed tertiary hospital.
Clinical isolates of S.aureus from wound and soft issue infections between May 2008 to June 2008 in Milad hospital of Tehran were studied .Milad hospital is 1000-bed non teaching tertiary hospital. In total 102 strains of S.aureus isolated from patients admitted to Milad hospital were studied. The majority of patients were hospitalized patients. Briefly, the samples were cultured aerobically in blood and MacConky agar. The plates were incubated overnight. All isolates were identified using gram stain, biochemical tests including ctalase, coagulase and DNase.9 Susceptibility testing were performed by disk diffusion method as recommended by Clinical laboratory Standards Institute (CLSI). Antibiotics were used for susceptibility testing were, tigecycline (15µg), linezolid (30µg), teicoplanin (30µg), penicillin (10 units), oxacillin (1µg), cefoxitin (30µg), vancomycin(30µg), erythromycin(15 µg), clindamycin (2µg), ciprofloxacine, (5µg), Co-trimoxazole, (25µg) and rifampicin. (5µg). All antibiotics disks were provided from Mast diagnostic groups (UK) and tigecyclin provided from Oxoid Company.
Briefly after identification of S.aureus we made a suspension from overnight growth and adjusted turbidly by 0.5MacFarland standard. Sterile swabs were used to inoculate the test organism onto Mueller- Hinton agar. Sterile forceps were used to carefully distribute the antibiotic disks evenly on the inoculated plates. All plates incubated at 35°C for 18 hour. For detection of MRSA all plates were incubated at 35°C for 24 hours. In addition of disk diffusion methods, oxacillin screen agars were used for confirmation of MRSA. The inhibition zone diameter were measured in millimeters and interpreted as a susceptible (S) intermediate (I) or resistant (R) as recommended by CLSI.10 S.aureus ATCC 25923, E.coli ATCC 25922 and P aeruginosa ATCC 27853 were used as a control strains for quality control of antibiotic disks in susceptibility testing .S. aureus ATCC 29213 was used as reference MRSA strain for quality control in MRSA detection process.
One hundred two strains of S.aureus were isolated from specimens including soft tissues, post operative and diabetic foot infections. Of 102 isolates 20 strains isolated from sternum infections flowing heart surgery. A few of patients had diabetic foot infections. Of 102 patients, 60(58/8%) were male and 42 (41.2%) were female. The age of patients ranged between one and 85 years old (mean 43.71, SD ± 20.04). Of 102 patients 84 (82.4%) were hospitalized and 18(17.6%) were outpatients. Twenty (19.6%) of patient were from heart ward, 68 (66. .7%) from other wards such as orthopedic, surgery and the remaining 14(15%) were outpatients.
The results of this study indicated that 36 (35.3%) of all isolates of S.aueus stains were resistant to oxacillin and cefoxitin therefore these strain were methicillin resistant S.aureus (MRSA). All isolated strains of S.aureus including methicillin resistant (MRSA) and methiillin susceptible S.aureus (MSSA) were susceptible to tigecyclin.. Other two antibiotics including linozolid and vancomycins had the high efficacy against both MRSA and MSSA. There were no resistant strains against theses antibiotics. Of 102 isolated strains 96 (94.1%) were susceptible to teicoplanine and six stains (5.9%) were intermediate. There was no resistant strains to this antibiotic. Resistant rate to other antibiotics including clindamycinm, erythromycin pencillin, co-trimoxazole, rifampicin and ciprofloxacin were 35.3.%, 27.7%, 97.7%, 26.5%, 16.7% and 33.7% respectively Table-I.
MRSA is a major nosocomial pathogen causing significant morbidity and mortality. The important reservoirs of MRSA in hospitals/institutions are infected or colonized patients and transient hand carriage on the hands of health care workers.4,5,10 In Islamic Republic of Iran, the significance of MRSA had been recognized relatively late and it emerged as a problem in the1980s and in the 1990s. Epidemic strains of these MRSA are usually also resistant to several other antibiotics. During the past 15 years, the appearance and world-wide spread of many such clones have caused major therapeutic problems in many hospitals, as well as diversion of considerable resources to attempts at controlling their spread.11
In our study, the prevalence of MRSA isolated from different wound infections was 35.3%. This is not in line with our previous reports.12 Similar observation was made by Mehta, in India who in his study on control of MRSA in a tertiary care center, had reported an isolation rate of 33% from pus and wound swabs.13 However, Qureshi from Pakistan reported a high isolation rate of up to 83% MRSA from pus. The result of this study revealed that all isolates of both MRSA and MSSA were susceptible to vancomycin, tigecycline and linozolid.14 There is some reports regarding reduced susceptibility or resistance of S.aureus to vancomycin. The first reported isolation of vancomycine intermediate S aureus (VISA) occurred in Japan in 1997 and more than 100 VISA isolates have since been reported.15 In 2002, three vancomycin-resistant S. aureus (VRSA) from clinical specimens of American patients were found to have high-level resistance to vancomycin [minimal inhibitory concentration (MIC) >32 µg/ml] although a few more cases of VRSA have since been described.16 Fortunately, these isolates have not yet become widespread.17 Linezolid is an oxazolidinone antibiotic with activity against gram-positive pathogens including vancomycin resistant (VRE), MRSA, and vancomycin intermediate (VISA). The unique mechanism of action involves inhibition of bacterial protein synthesis through binding to the domain V regions of the 23S rRNA gene.18 Resistance to linezolid requires mutations of multiple gene copies. Linezolid is currently approved for skin and soft tissue infections and pneumonia due to susceptible pathogens.9 Based on in vitro susceptibility data, tigecycline has a broad spectrum of activity against both gram-positive cocci including MRSA. Clinical trials have been conducted in patients with complicated skin and soft tissue infections and intra abdominal infections for which the drug has been approved by FDA.20,21 In our county there is no published documents for treatment of soft tissue infections caused by MRSA. However these antibiotics can be used for treatment of infections caused by multidrug –resistant organisms such as MRSA.
Our study showed that nearly 36% isolates of S.aureua were methicillin resistant .Vancomycin, tigecycline and linozolid were effective against both methicillin resistant and susceptible strains of S.aureus.
1. Ikeagwu IJ. Amadi ESand Iroha IR., Antimicrobial sensitivity pattern of Staphlococcus aureus in Abakalki, Nigeria. Pak J Med Sci 2008;24:231-5.
2. Lentino JR, Narita M, Yu VL. New antimicrobial agent’s therapy for resistant gram-negative cocci. Eur J Clin Microbiol Infect Dis 2008;27:3-15.
3. Bouchillon SK, Johnson BM, Hoban DJ, Johnson JL, Dowzicky MJ, Wu DH, et al. Determining incidence of extended spectrum beta-lactamase producing Enterobacteriaceae, vancomycin-resistant Enterococcus faecium and methicillin-resistant Staphylococcus aureus in 38 centers from 17 countries: the PEARLS study 2001-2002 Int J Antimicrob Agents 2004;24:119-24.
4. Rahbar M, Babazadeh H, Zargami N. High methicillin resistance of Staphylococcus aureus in imam Khomeini hospital of Uremia, Iran. Infect Control Hosp Epedemiol 2001;22:196-7.
5. Rahbar M, Karamiyar M, Gra-Agaji R. Nasal carriage of Methicillin-resistant Staphylococcus aureus among Healthcare workers of an Iranian hospital. Infect Control Hosp Epedemiol 2003;24:337-23.
6. Bouchillon SK, Hoban DJ, Johnson BM, Johnson JL, Hsiung A, Dowzicky MJ. Tigecycline Evaluation and Surveillance Trial (TEST) Group. In vitro activity of tigecycline against 3989 Gram-negative and Gram-positive clinical isolates from the United States Tigecycline Evaluation and Surveillance Trial (TEST Program; 2004). Diagn Microbiol Infect Dis 2005;52:173.
7. Souli M, Kontopidou FV, Koratzanis E, Antoniadou A, Giannitsioti E, Evangelopoulou P, et al. In vitro activity of tigecycline against multiple-drug-resistant, including pan-resistant, gram-negative and gram-positive clinical isolates from Greek hospitals Antimicrob Agents Chemother 2006;50:3166.
8. Nickie D. Tigecycline (Tygacil): The first in the glycycline class of antibiotics. Proc (Bayl Univ Med Cent) 2006;19:155-61.
9. "Harison LS. Text book of diagnostic microbiology. (Third edition) Mahon CR, Lehman DC, Manselis G (Eds), Saunders Philadelphia, PA, USA. pp 367-381, 2007".
10. Clinical and Laboratory Standards Institute (CLSI) 2006.Performance standards for antimicrobial susceptibility testing; 16th informational supplement M100- S 16 CLSI, USA, Wayne. PA
11. Li F De, Wolf Miller F. Epidemiology, surveillance and control of methicilillin resistant Staphylococcus aureua. An overview. Asian Pac J Trop Med 2008;1:50-5.
12. Rahbar M, Yaghoobi, Fattahi A. Comparison of different laboratory methods for detection of Methicillin Resistant Staphylococcus aureus Pak J Med Sci 2006;22:442-5.
13. Mehta AP, Rodrigues C, Sheth K, Jani S, Hakimiyan A, Fazalbhoy N. Control of methicillin resistant Staphylococcus aureus in a tertiary care Centre–A five–year study. J Med Microbiol 1998;16:31-4.
14. Qureshi AH, Rafi S, Qureshi SM, Ali AM. The current susceptibility patterns of methicillin resistant Staphylococcus aureus to conventional anti Staphylococcus antimicrobials at Rawalpindi. Pak J Med Sci 2004;20:361-4.
15. Appelbaum PC. MRSA, the tip of the iceberg. Clin Microbiol Infect 2006;12 Suppl 2:3-10.
16. Chang S, Sievert DM, Hageman JC. Infection with vancomycin - resistant Staphylococcus aureus containing the vanA resistance gene. N Engl J Med 2003;348:1342–134.
17. Centers for Disease Control and Prevention (CDC) Staphylococcus aureus resistant to vancomycin-United States. MMRW Morb Mortal Wkly Rep 2002;51(26):565-7.
18. Meka VG, Pillai SK, Sakoulas G. Linezolid resistance in sequential Staphylococcus aureus isolates associated with a T2500A mutation in the 23S rRNA gene and loss of a single copy of rRNA. J Infect Dis 2004;190:311-17
19. Weigelt J, Itani K, Stevens D, Lau W, Dryden M, Knirsch C. Linezolid versus vancomycin in treatment of complicated skin and soft tissue infections. Antimicrob Agents Chemother 2005;49:2260-6.
20. Lentino JR, Narita M, Yu VL. New antimicrobial agents as therapy for resistant gram-positive cocci. Eur J Clin Microbiol Infect Dis 2008;27:3-15.
21. Sakoulas G, Moellering RC Jr, Eliopoulos GM. Adaptation of methicillin-resistant Staphylococcus aureus in the face of vancomycin therapy Clin Infect Dis 2006;42:Suppl 1:S40-50.
HOME | SEARCH | CURRENT ISSUE | PAST ISSUES
Room No. 522, 5th Floor, Panorama Centre
Building No. 2, P.O. Box 8766, Saddar, Karachi - Pakistan.
Phones : 5688791, 5689285 Fax : 5689860