Mutation frequency in antibiotic-resistant and -susceptible isolates of Streptococcus pneumoniae

Area of Science:

• Microbiology
• Genetics
• Molecular Biology

Background:

• Multiple antibiotic resistance in Streptococcus pneumoniae develops through genetic mutations or transformations at various chromosomal locations.
• Deficient DNA repair mechanisms are hypothesized to facilitate the accumulation of these genetic events, leading to increased mutability.

Purpose of the Study:

• To investigate whether clinical isolates of Streptococcus pneumoniae exhibit a higher mutation frequency, particularly those with deficient DNA repair mechanisms.
• To determine if a distinct population of

Main Methods:

• Analysis of mutation frequencies in 27 clinical isolates of Streptococcus pneumoniae, comparing them to a mismatch repair (MMR)-deficient laboratory strain.
• Screening of an additional 180 clinical isolates using a novel rapid method to assess mutation rates.

Main Results:

• A wide spectrum of mutation frequencies was observed across clinical isolates, but none matched the high mutability of the MMR-deficient control.
• No correlation was found between the level of antibiotic resistance and increased mutation frequency in the clinical isolates.
• The rapid screening of 180 isolates did not identify any with mutation frequencies comparable to the MMR-deficient strain.

Conclusions:

• Current evidence does not support the existence of a distinct population of hypermutable strains (mutators) among clinical isolates of Streptococcus pneumoniae.
• The development of multiple antibiotic resistance in S. pneumoniae may not be primarily driven by a subset of highly mutable organisms.