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Antibiotic susceptibility of Streptococcus pneumoniae isolates in Portugal. A multicenter study between 1989 and 1993
M V Pato1, C B Carvalho, A Tomasz
1Instituto Nacional de Saúde Dr. Ricardo Jorge, Lisbon, Portugal.
Abstract:
A total of 1,104 strains of Streptococcus pneumoniae were isolated from hospitalized patients (75.5%) and from colonization sites at the Public Health Institute (24.5%) during the last 4 years (1989-1993). Penicillin resistance (defined as MIC > or = 0.1 microgram/liter) was found to increase in time: 4.6% in 1989, 4.9% in 1990, 6.4% in 1991, 11.3% in 1992, and 17% in 1993. In 1992, 0.8% of the strains had penicillin MIC = 2 mg/liter. Increase in penicillin resistance was also evident among invasive strains [blood, cerebrospinal fluid (CSF), pleura]: 2/92 isolates from 1989-1992 (2.3%) were penicillin resistant as compared to 7/101 isolates from 1992 (6.9%). Multiresistance (resistance to three or more antibiotics) was 4.4% with penicillin, tetracycline, chloramphenicol being the predominant resistant phenotype at the end of 1992. In 1993, strains with resistance to penicillin plus chloramphenicol plus tetracycline increased further. Erythromycin resistance was usually associated with clindamycin resistance, but the majority of such strains remained susceptible to penicillin. Drift in the direction of increasing MIC values was also noted during this 3-year period among "susceptible" isolates: bacteria with MIC of 6-10 ng/ml representing the majority of isolates in 1990-1991 decreased and were replaced by cells with MIC of 20 ng/ml. The most frequent pneumococcal serotypes were 23, 19, 3, 6, 14, 9, and 8, with the frequency of type 9 increasing from 2.9% (in 1989) through 3.2% (1990) to 6.4% (1992). Among all antibiotic resistant strains, the prevalent serotypes were 23, 9, 14, and 6. The chromosomal backgrounds of resistant isolates tested by pulsed-field gel electrophoresis showed close resemblance to the background of the serotype 23F multiresistant clone first identified in Spain. The data suggest that the recent large increase in the frequency of penicillin-resistant pneumococci represents the import of this clone into Portugal during the early 1990s. The increased frequency of drug-resistant pneumococci highlights the importance of continued surveillance of these dangerous pathogens.
Insights
Penicillin resistance in Streptococcus pneumoniae increased significantly from 1989 to 1993, with a multiresistant clone likely imported from Spain. Continued surveillance of these drug-resistant pathogens is crucial.
Area of Science:
- Medical Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Streptococcus pneumoniae is a leading cause of bacterial infections worldwide.
- The emergence and spread of antibiotic resistance in S. pneumoniae pose a significant public health threat.
- Understanding resistance patterns and genetic relatedness is crucial for effective treatment and control strategies.
Purpose of the Study:
- To investigate the trends in penicillin resistance and multiresistance among Streptococcus pneumoniae isolates in Portugal from 1989 to 1993.
- To identify prevalent pneumococcal serotypes and their association with antibiotic resistance.
- To determine the genetic relatedness of resistant isolates to known resistant clones.
Main Methods:
- Isolation and antimicrobial susceptibility testing of 1,104 Streptococcus pneumoniae strains from hospitalized patients and colonization sites.
- Phenotypic characterization of multiresistance (resistance to three or more antibiotics).
- Pulsed-field gel electrophoresis (PFGE) to analyze the chromosomal backgrounds of resistant isolates.
Main Results:
- Penicillin resistance increased from 4.6% in 1989 to 17% in 1993, including a rise in resistance among invasive strains.
- Multiresistance (to penicillin, tetracycline, chloramphenicol) became more prevalent, with specific serotypes (23, 9, 14, 6) being predominant among resistant strains.
- PFGE analysis revealed that resistant isolates shared chromosomal backgrounds similar to a previously identified multiresistant serotype 23F clone from Spain.
Conclusions:
- The study suggests the introduction and spread of a specific penicillin-resistant clone from Spain contributed to the observed increase in resistance in Portugal.
- The rising frequency of drug-resistant pneumococci underscores the need for ongoing surveillance programs.
- Effective monitoring is essential to track the evolution of antimicrobial resistance in this important pathogen.