| Abstract |
The increasing incidence of penicillin resistance and multi-drug resistance in Streptococcus pneumoniae and its global spread is a cause of great concern. Differences in resistance rates have been reported not only for various geographical areas, but also for different regions of the same country. Studies conducted in Greece report different rates of resistance to antibiotics, because of the different specimens examined, the different ages of the patients included and the various methods used for susceptibility testing.
The present study included 450 S. pneumoniae isolates recovered from clinical specimens submitted to the Laboratory of Clinical Microbiology, at the University Hospital of Heraklion, over a 9-year period (1997-2005). The origin of the strains was: upper respiratory tract (n=168), lower respiratory tract (n=97), ocular secretions (n=77), blood (n=43), middle ear (n=34), pus (n=15), cerebrospinal fluid (n=8), pleural fluid (n=3), synovial fluid (n=1) and other sites (n=4).
Serotyping was performed by the capsular swelling method with specific antisera. Susceptibility testing used the disk diffusion method described by the Clinical and Laboratory Standards Institute (CLSI). The minimal inhibitory concentration (MIC) of penicillin was determined by the broth dilution method and the MICs of 18 antibiotics were determined by E- test.
Eighty-seven (19.3%) isolates showed intermediate resistance and 67 (14,9%) high level resistance to penicillin. The yearly percentage of isolates with intermediate and high level resistance to penicillin increased from 17.1% in 1997 to 28.5% in 2005, with the highest value (38.3%) observed in 2001.
The rates of resistance to cefuroxime, cefepime, imipenem, meropenem, erythromycin, clindamycin, azithromycin, sparfloxacin, moxifloxacin,
chloramphenicol, tetracycline and trimethoprim/sulfamethoxazole were 22.9, 0.9, 1.8, 0.9, 30, 30, 10.7, 44.7, 0.2, 0.2, 6.4, 24.4 and 18.9%, respectively. Almost 3% of the isolates were intermediately resistant to ceftriaxone and cefotaxime. Isolates were uniformly susceptible to levofloxacin and vancomycin.
Comparing the activity of penicillin with that of other β-lactamss and additional antimicrobial agents, we found that resistance to these agents was significantly more common among penicillin-resistant strains than among penicillin-sensitive ones. Isolates not susceptible to penicillin were encountered significantly more often in children with localized infections than in adults with invasive disease.
Multi-drug resistance was present in 135 (30%) isolates. Of the multiresistant strains, 19.2% were resistant to penicillin, erythromycin, clindamycin, tetracycline and trimethoprim/sulfamethoxazole. Serotyping was performed in 406 (90.2%) isolates. The most prevalent serogroups were: 19, 14, 6, 3 and 9. Serogroup 7 was significantly more common in invasive isolates.
In conclusion, the results of the present study indicate the presence of increased penicillin resistance and multi-drug resistance among clinical isolates of S. pneumoniae in our region. Continuous surveillance of pneumococcal resistance, judicious use of antibiotics and prevention of pneumococcal disease through use of effective vaccines, will likely reduce the spread of antibiotic resistant pneumococci.
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