Academic journal article Central European Journal of Public Health

Discrepancies between Various Methods in Susceptibility Testing and Epidemiological Analysis of Stenotrophomonas Maltophilia Clinical Isolates

Academic journal article Central European Journal of Public Health

Discrepancies between Various Methods in Susceptibility Testing and Epidemiological Analysis of Stenotrophomonas Maltophilia Clinical Isolates

Article excerpt

SUMMARY

The susceptibility of 25 Stenotrophomonas maltophilia (S. maltophilia) clinical isolates to four different antimicrobials (trimethoprim/sulfomethoxazole, piperacillin/tazobactam, ceftazidime, ciprofloxacin) were investigated by disk diffusion, E-test and commercial Sensititre and PASCO broth microdilution techniques. Discrepancies between the results of broth microdilution and the other methods studied were characterized as very major, major and minor errors. Using the broth microdilution as the reference method, 24% of the isolates were found susceptible to trimethoprim/ sulfamethoxazole, 24% to ceftazidime, 0% to piperacillin/tazobactam and 12% to ciprofloxacin. Good correlation was observed between the two broth microdilution Sensititre and PASCO for all antibiotics tested. Disc diffusion and E-test generated inconsistent results for all agents except trimethoprim/sulfamethoxazole. A great genomic diversity was demonstrated within the S. maltophilia strains tested. Although our results confirm that trimethoprim-sulfamethoxazole had some in vitro activity against S. maltophilia, further clinical studies are necessary to evaluate the clinical efficacy of these compounds for the treatment of S. maltophilia infections, since no randomized controlled trials have been carried out and no correlation between the clinical response and susceptibility testing results has been reported. Furthermore, the high genomic diversity observed in the S. maltophilia strains indicates the need for careful epidemiological evaluation especially in nosocomial outbreaks.

Key words: E-test, disk diffusion, broth microdilution, epidemiological analysis

INTRODUCTION

Stenotrophomonas maltophilia has emerged over the last decade as an important opportunistic pathogen with intrinsic resistance to many antimicrobials implicated in a variety of infections. Predisposing factors for S. maltophilia infections are consumption of broad spectrum antibiotics, use of central venous catheter, leucopenia and use of cytotoxic agents, prolonged hospitalization especially in the Intensive Care Unit (ICU), mechanical ventilation or tracheotomy, hématologie malignancies, cancer and prolonged use of corticosteroids (1,2). Since it remains a concern for public health, especially for immunocompromised hosts and for patients with cystic fibrosis, various antibiotics alone or in combination have been tested. Trimethoprim-sulfamethoxazole remains the treatment of choice for S. maltophilia infections despite the bacteriostatic action and the emergence of resistant strains (3-5).

Although in vitro susceptibility methods for S. maltophilia have not been so far fully standardized, E-test is a simple method of susceptibility testing and has been shown to be reliable and accurate although Clinical Laboratory Standard Institute (CLSI) recommends broth and agar dilution for the determination of MICs in S. maltophilia (6-9).

Therefore and because of the increasing pathogenic potential of this microorganism, we investigated the resistance patterns of 25 not clonal S. maltophilia clinical isolates and we compared broth microdilution (Sensititre) results with those from disc diffusion, PASCO broth microdilution and E-test.

MATERIALS AND METHODS

Bacterial Isolates

A total of 25 S. maltophilia isolates collected from five Greek hospitals were included in the study. Isolates were collected from individual patients in one year period from pus (2), wound infection (3), sputum (7), blood (1), BAL (1), bronchial secretions (9) and urine (2). They were lyophilized and stored at room temperature. Five of the 25 strains studied were obtained from ICUs whereas the rest from medical wards. All isolates were identified by the API 20 NE System (Bio Merieux, Marcy-IEtoile, France).

Molecular Typing

The molecular typing of the S. maltophilia isolates was carried out using the Pulse Field Gel Electrophoresis (PFGE) technique. …

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