[Sensitivity of Streptococcus pneumoniae to antimicrobial drugs]

Abstract

Introduction: Streptococcus pneumoniae is the leading cause of community acquired pneumonia and a frequent cause of otitis media, sinusitis and meningitis. Although most pneumococci remain susceptible to penicillin, relatively less susceptible and resistant strains have been recognized with increasing frequency throughout the world (1). The aim of this study was to determine whether and to what degree pneumococci isolated in our laboratory were resistant to penicillin and other frequently used antimicrobial agents.

Material and methods: During the period from 1991 to 1995 1139 Streptococcus pneumoniae strains isolated from patients with different pneumococcal infections were tested for their susceptibility to antimicrobial agents at the Department of Bacteriology and Parasitology of the Institute of Public Health in Novi Sad. Antimicrobial agents tested included: penicillin, ampicillin, cephalexin, erythromycin, sulfamethoxazole-trimethoprim and clindamycin. Susceptibility test was performed by using Kirby-Bauer disc diffusion technique on Mueller-Hinton agar supplemented with 5% defibrinated bovine blood (5).

Results: Susceptibility of Streptococcus pneumoniae to seven antimicrobial agents used in the study is shown in Table 2. There was a resistance to all antimicrobial agents tested. It was the lowest to erythromycin (1.6%) and the highest to sulfamethoxazole+ trimethoprim (67.3%). The rate of resistance of penicillin was 3.3%. In Table 3 and 4 we can also see that the lowest resistance was to erythromycin, and the highest to sulfamethoxazole+trimethoprim, both for isolates from nose and other sources. Strains of Streptococcus pneumoniae isolated from nasal swabs were more susceptible to penicillin than those isolated from blood, sputum and cerebrospinal fluid.

Discussion: For many years penicillin has been the mainstay of therapy for pneumococcal diseases. Clinical resistance to penicillin was first reported in 1960's. Since this early reported, penicillin resistance has been encountered with increasing frequency in strains of Streptococcus pneumoniae from around the world. In our study resistance to penicillin was low (3.3%). This is in accordance with the authors from Italy, Great Britain, USA and Germany (7, 8, 9, 10). Much higher prevalence of resistant pneumococci we found in the reports from Spain, France and Hungary (13, 14, 15, 17). Many of these strains have been resistant to multiple drugs and have been isolated from patients with invasive infections (meningitis, pneumonia, bacteremia). Percentage of penicillin resistant pneumococci isolated from blood, sputum and cerebrospinal fluid in our study was relatively low (7.7%), but it was higher than the percentage of resistant isolates from nasal swabs (2.0%). These findings are in accordance with other reports (20, 21).

Conclusion: The increasing number of Streptococcus pneumoniae isolates resistant to penicillin and other antimicrobial agents indicates the need to perform susceptibility testing for every isolated strain in order to avoid possible therapeutic failure.