1. Antimicrobial susceptibility patterns of Polish invasive isolates of Neisseria meningitidis in the years 1997-2006 Marcin Kadłubowski 1, Anna Skoczyńska 1, Tomasz Wołkowicz 2, Waleria Hryniewicz 1 1 National Reference Centre for Bacterial Meningitis, Department of Epidemiology and Clinical Microbiology, National Medicines Institute, Warsaw, Poland 2 Department of Bacterial Genetics, Institute of Microbiology, Faculty of Biology, Warsaw University, Warsaw, Poland INTRODUCTION Monitoring of antimicrobial susceptibility of invasive bacterial pathogens, such as Neisseria meningitidis is extremely important for establishment of therapeutic and prophylactic recommendations. In Poland antimicrobial susceptibility determination of the leading community- acquired invasive bacterial pathogens has been performed in the National Reference Centre for Bacterial Meningitis (NRCBM). AIM The aim of this study was to determine the susceptibility of meningococcal invasive isolates to drugs commonly used in both therapy and prophylaxis of the invasive meningococcal disease (IMD). MATERIALS AND METHODS The analysis was performed on all, over seven-hundred invasive isolates of N. meningitidis, collected in the NRCBM between 1997 and 2006. Susceptibility to penicillin G, ceftriaxone, chloramphenicol, rifampin and ciprofloxacin was evaluated by agar dilution method, using Mueller-Hinton agar supplemented with 5% of defibrinated sheep blood. For co-trimoxazole the susceptibility was performed by the same method, using Mueller-Hinton agar with 5% of lysed horse blood. The Streptococcus pneumoniae ATCC 49619 was used for quality control purposes. The results were interpreted according to the Clinical and Laboratory Standards Institute (CLSI) guidelines for N. meningitidis. The percentages of susceptible, intermediate and resistant isolates were analysed for each drug and each year. Also, the MIC50 and MIC90 values were calculated. Susceptibility of isolates to antimicrobial drugs was analysed for major serogroups as well as for particular clonal complexes. RESULTS More than ninety percent of the isolates studied were fully susceptible to penicillin. There was no change in penicillin susceptibility pattern despite the increase in prevalence of serogroup C isolates. Even the occurrence and dissemination of ST-8/A-4 Cluster meningococci in Poland in 2003- 2005 has not influenced the overall penicillin susceptibility results. There is still full susceptibility of Polish N. meningitidis invasive isolates to ceftriaxone, chloramphenicol, rifampin and ciprofloxacin. No significant changes in MIC50 and MIC90 values of these drugs were observed in the 10-years study period. MIC50 and MIC90 values for each year are presented in the following graphs. There is a high percentage of the isolates non-susceptible to co-trimoxazole and MIC50 as well as MIC90 values of this drug correspond to the resistant phenotype during all the study period. MIC 50 and MIC 90 values of different antimicrobials for N. meningitidis in Poland, 1997-2006. ACKNOWLEDGEMENTS The study was supported by unrestricted grants from Polish Ministry of Health and Ministry of Science. None part of this was supported by any industrial grant. The attendance of the presenting author to the Meningitis and Septicaemia Conference was kindly supported by Glaxo Smith Kline Biologicals. CONCLUSIONS Susceptibility of invasive meningococcal isolates to antimicrobial drugs has been very stable in Poland. There is still almost full susceptibility to penicillin, and this antibiotic is recommended as the drug of choice for treatment of IMD. In contrast to other European countries, the emergence of ST-8/A-4 cluster meningococci has not changed the penicillin susceptibility pattern in Poland. One hundred percent susceptibility of the isolates to ceftriaxone, chloramphenicol, rifampin and ciprofloxacin provides a good coverage for both therapy and chemoprophylaxis of meningococcal infections. Frequent resistance of meningococci to co-trimoxazole suggests, that this drug should not be used neither in treatment, nor in prophylaxis, and its testing can have only epidemiological value. Author’s contact details: Marcin Kadłubowski National Reference Centre for Bacterial Meningitis, Dept. of Epidemiology and Clinical Microbiology, National Medicines Institute Chelmska 30/34 Street, 00-725 Warsaw Email: kadlubek@cls.edu.pl