A simple technique for suppressor detection in Escherichia coli.

Area of Science:

• Microbiology
• Genetics
• Molecular Biology

Background:

• Ciprofloxacin resistance in Escherichia coli is a growing public health concern.
• Mutations in the gyrA gene, such as S83, are frequently associated with reduced susceptibility to fluoroquinestones.
• The presence of stop mutations in essential genes can lead to cell death unless suppressed.

Purpose of the Study:

• To investigate the viability of Escherichia coli strains harboring a gyrA S83 stop mutation.
• To determine if clinical isolates possess tRNA suppressor activity capable of rescuing viability.
• To assess the prevalence of this suppressor activity in diverse clinical E. coli isolates.

Main Methods:

• Construction of a pBR322 derivative with a TAG mutation in the bla gene to assess ampicillin resistance.
• Utilizing the engineered plasmid to evaluate the suppressor activity in an E. coli J53 ciprofloxacin-resistant strain (J53 CipR27).
• Application of the method to 22 unique clinical E. coli isolates to determine the presence of suppressor activity.

Main Results:

• Restoration of ampicillin resistance in the engineered strain indicated successful suppression of the TAG stop codon in gyrA.
• The study confirmed that the E. coli J53 CipR27 strain possesses tRNA suppressor activity.
• All 22 unique clinical E. coli isolates tested exhibited low-level tRNA suppressor activity.

Conclusions:

• The gyrA S83 stop mutation in Escherichia coli does not necessarily lead to inviability due to endogenous tRNA suppressor activity.
• This low-level suppressor activity is a common trait among clinical E. coli isolates.
• Understanding tRNA suppressor activity is crucial for interpreting genetic resistance mechanisms and bacterial viability.