Thymidine-dependent Escherichia coli infection and some associated laboratory problems

Area of Science:

• Microbiology
• Clinical Medicine
• Antimicrobial Resistance

Background:

• Co-trimoxazole is a common antibiotic used to treat bacterial infections.
• Emergence of drug-dependent bacterial strains can complicate treatment.
• Escherichia coli can develop resistance or altered growth requirements during therapy.

Purpose of the Study:

• To describe the rapid emergence of a thymidine-dependent Escherichia coli strain during co-trimoxazole treatment.
• To investigate the cultural characteristics of thymidine-dependent E. coli strains.
• To identify factors influencing the growth of these emergent strains.

Main Methods:

• Case report of a patient treated with co-trimoxazole.
• Isolation and identification of Escherichia coli from blood cultures.
• Characterization of thymidine-dependent E. coli strains.
• Growth studies on various blood agar batches with differing ages and agar bases.

Main Results:

• A thymidine-dependent strain of Escherichia coli rapidly emerged in a patient receiving co-trimoxazole.
• The organism was isolated from blood cultures during a septicaemia event.
• Significant variation in growth was observed among three thymidine-dependent strains on different blood agar preparations.
• Growth variability correlated with the age of blood agar plates and the type of agar base used.

Conclusions:

• Co-trimoxazole treatment can rapidly select for thymidine-dependent Escherichia coli.
• The growth of thymidine-dependent E. coli is highly sensitive to nutrient availability in culture media.
• Variations in blood agar composition and age significantly impact the detection and study of such emergent strains.