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In-vitro susceptibility and molecular characterisation of macrolide resistance mechanisms among Streptococcus
C Neeleman1, J A De Valk, C H W Klaassen
1Department of Intensive Care, University Hospital St Radboud, Nijmegen, The Netherlands.
Abstract:
In total, 881 presumptive clinical isolates of Streptococcus pneumoniae collected from throughout The Netherlands were analysed to determine their mechanisms of macrolide resistance. Isolates were identified initially by participating laboratories using their own standard identification technique, followed by determination of MICs with Etests. Only 797 isolates were confirmed as pneumococci following bile-solubility tests, lytA PCR and 16S rRNA sequencing. Of these confirmed pneumococci, 59 (7.4%) isolates were macrolide-resistant. Analysis by PCR indicated that 34 (57.6%) isolates harboured only the erm(B) gene and 16 (27.1%) only the mef gene. Three (5.1%) isolates carried both erm(B) and mef, while six (10.2%) isolates were negative for both mechanisms. Of the six negative isolates, three had a mutation in the 23S rRNA gene, and three were negative for all mechanisms tested. No isolates with the erm(A) subclass erm(TR) gene were detected. Among the 19 mef-positive isolates, 14 (73.7%) carried the mef(A) gene, and only five (26.3%) carried the mef(E) gene. No linezolid cross-resistance or multiresistance (resistance to more than two classes of antibiotics) was observed.
Insights
Most macrolide resistance in Streptococcus pneumoniae is due to erm(B) or mef genes. Few resistant isolates showed cross-resistance or multiresistance, indicating specific resistance mechanisms.
Area of Science:
- Microbiology
- Molecular Biology
- Antimicrobial Resistance
Background:
- Macrolide resistance in Streptococcus pneumoniae is a growing public health concern.
- Understanding resistance mechanisms is crucial for effective treatment strategies.
Purpose of the Study:
- To investigate the prevalence and genetic mechanisms of macrolide resistance in clinical isolates of Streptococcus pneumoniae from The Netherlands.
- To identify specific genes responsible for macrolide resistance and assess potential cross-resistance.
Main Methods:
- Analysis of 881 presumptive clinical isolates of Streptococcus pneumoniae.
- Confirmation of isolates using bile-solubility tests, lytA PCR, and 16S rRNA sequencing.
- Determination of macrolide resistance mechanisms via PCR to detect erm(B), mef, and 23S rRNA gene mutations.
Main Results:
- Of 797 confirmed pneumococcal isolates, 59 (7.4%) were macrolide-resistant.
- The erm(B) gene was the most prevalent mechanism (57.6%), followed by the mef gene (27.1%).
- Three isolates (5.1%) harbored both erm(B) and mef genes; three had 23S rRNA mutations; three had no identified resistance mechanism.
Conclusions:
- The erm(B) and mef genes are the primary drivers of macrolide resistance in Dutch Streptococcus pneumoniae clinical isolates.
- The mef(A) gene is more common than mef(E) among mef-positive isolates.
- No significant linezolid cross-resistance or multidrug resistance was observed in the studied isolates.
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