Chromosomally mediated high-level gentamicin resistance in Streptococcus mitis

Area of Science:

• Microbiology
• Genetics
• Infectious Diseases

Background:

• Streptococcus mitis is a common bacterium, part of the normal oral flora.
• Antibiotic resistance in bacteria poses a significant global health threat.
• Penicillin and gentamicin are commonly used antibiotics for bacterial infections.

Purpose of the Study:

• To investigate the antibiotic resistance profiles of Streptococcus mitis blood culture isolates.
• To identify the genetic basis for penicillin and gentamicin resistance in these strains.
• To determine the in vitro synergy between penicillin and gentamicin against resistant S. mitis.

Main Methods:

• Antibiotic susceptibility testing (MIC determination) for penicillin and gentamicin.
• Polymerase chain reaction (PCR) assays to detect specific resistance genes.
• Oligonucleotide probing and DNA hybridization to analyze gene location.

Main Results:

• Four S. mitis isolates showed high-level resistance to both penicillin and gentamicin.
• The gene encoding high-level gentamicin resistance, typically found in other bacteria, was present in all resistant S. mitis strains.
• No in vitro synergy was observed between penicillin and gentamicin.
• Resistance genes appear to be chromosomally integrated, as plasmid isolation was unsuccessful.

Conclusions:

• Certain Streptococcus mitis strains can acquire and harbor genes for high-level antibiotic resistance.
• The genetic mechanisms of resistance in these S. mitis strains may involve chromosomal integration.
• Understanding resistance mechanisms is crucial for effective treatment strategies against S. mitis infections.