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The emergence of Streptococcus pneumoniae resistant to macrolide antimicrobial agents: a 6-year population-based
1Departments of Medicine and of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia, USA. kgay@emory.edu
Abstract:
From 1994 through 1999, the available isolates (4148 isolates) from active population-based surveillance of invasive pneumococcal disease in metropolitan Atlanta were serotyped and were tested for antimicrobial susceptibility. Macrolide-resistant isolates were studied for the presence of ermAM (a ribosomal methylase gene), mefE (a macrolide efflux gene), and tetM (the class M tetracycline resistance gene). Macrolide resistance increased from 16% of all invasive isolates in 1994 to 32% in 1999. Of the macrolide-resistant pneumococcal isolates studied, 99% contained genomic copies of mefE or ermAM. Isolates with ermAM were mainly serotypes 6B, 23F, 14, or 19F and contained tetM; mefE-associated isolates were predominantly serotypes 14, 6A, or 19F, and most did not contain tetM. The frequency of the ermAM-mediated phenotype in invasive Streptococcus pneumoniae remained stable over the 6-year surveillance. However, the mefE-mediated phenotype increased from 9% in 1994 to 26% of all isolates in 1999 and was noted in new serotypes. By 1999, 93% of the mefE-containing strains had minimum inhibitory concentrations >/=8 microgram/mL. Dissemination of the mefE determinant accounted for the rapid increase in the rate of macrolide resistance in our S. pneumoniae population.
Insights
Macrolide resistance in invasive Streptococcus pneumoniae increased significantly from 1994 to 1999, primarily driven by the spread of the mefE gene. This rise in antimicrobial resistance poses a growing public health concern.
Area of Science:
- Microbiology
- Infectious Diseases
- Genetics
Background:
- Invasive pneumococcal disease (IPD) surveillance is crucial for monitoring antimicrobial resistance trends.
- Macrolide resistance in Streptococcus pneumoniae has emerged as a significant public health challenge.
- Understanding the genetic mechanisms of macrolide resistance is essential for effective treatment strategies.
Purpose of the Study:
- To investigate the prevalence and genetic determinants of macrolide resistance in invasive pneumococcal isolates in metropolitan Atlanta.
- To track changes in macrolide resistance patterns over a six-year period (1994-1999).
- To identify the specific genes (ermAM, mefE, tetM) associated with macrolide resistance.
Main Methods:
- Population-based surveillance of IPD isolates in metropolitan Atlanta.
- Serotyping of Streptococcus pneumoniae isolates.
- Antimicrobial susceptibility testing.
- Molecular detection of resistance genes (ermAM, mefE, tetM).
Main Results:
- Macrolide resistance in invasive pneumococcal isolates increased from 16% in 1994 to 32% in 1999.
- The mefE gene, encoding a macrolide efflux pump, was identified as the primary driver of this increase, rising from 9% to 26% of all isolates.
- While ermAM was associated with specific serotypes and the tetM gene, mefE-associated resistance expanded to new serotypes and showed high minimum inhibitory concentrations by 1999.
Conclusions:
- The rapid increase in macrolide resistance in Streptococcus pneumoniae during the study period was largely attributed to the dissemination of the mefE determinant.
- The emergence and spread of mefE-mediated resistance highlight the dynamic nature of antimicrobial resistance.
- Continued surveillance and molecular characterization are vital for understanding and combating evolving resistance patterns in bacterial pathogens.