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Antimicrobial susceptibility, growth kinetic and pathogenicity of thymidine-requiring Streptococcus species
Abstract:
18 strains of thymidine-requiring streptococcal mutants (thy-) were isolated from urines of patients with urinary tract infection treated with trimethoprim-sulfameth-oxazole (TMP-SMZ) or trimethoprim-sulfadiazine (TMP-SDZ). All thy- mutants were catalase- and beta-lactamase-negative, grew in the presence of bile and esculin, and required from 0.3 to greater than 1280 micrograms/ml of thymidine for normal growth. The antibiotic susceptibility of wild-type and thy- mutants to 21 antimicrobial agents tested were comparable except to trimethoprim (TMP), TMP-SMZ and TMP-SDZ. Ampicillin, penicillin G, erythromycin and rifampin were among the most active compounds tested. Growth kinetic studies with a Streptococcus faecalis thy- mutant in a synthetic basal medium without thymidine resulted in a decrease of 2-3 logarithmic units in viable cells after 24 h of incubation. The addition of thymidine to this thymidine-deprived culture prevented the thymineless death of the cells. In vivo, this thy- mutant was less virulent than the wild-type strain in producing kidney infection in mice.
Insights
Thymidine-requiring streptococcal mutants (thy-) were isolated from patients with urinary tract infections. These mutants exhibited thymineless death when deprived of thymidine, a phenomenon preventable by thymidine supplementation.
Area of Science:
- Microbiology
- Antimicrobial Resistance
- Molecular Biology
Background:
- Trimethoprim-sulfamethoxazole (TMP-SMZ) and trimethoprim-sulfadiazine (TMP-SDZ) are commonly used antibiotics for urinary tract infections.
- The emergence of antibiotic-resistant bacteria is a significant global health concern.
- Understanding bacterial auxotrophy can provide insights into antimicrobial mechanisms and resistance.
Purpose of the Study:
- To investigate the characteristics of thymidine-requiring streptococcal mutants (thy-) isolated from patients with urinary tract infections.
- To evaluate the antibiotic susceptibility profiles of these mutants compared to wild-type strains.
- To assess the impact of thymidine deprivation on bacterial viability and virulence.
Main Methods:
- Isolation and characterization of 18 thymidine-requiring streptococcal mutants (thy-) from patient urine samples.
- Antibiotic susceptibility testing against 21 antimicrobial agents for both wild-type and thy- mutants.
- Growth kinetic studies in synthetic media with and without thymidine.
- In vivo virulence studies in a mouse model of kidney infection.
Main Results:
- All 18 thy- mutants required thymidine for growth and were catalase- and beta-lactamase-negative.
- Mutants showed comparable susceptibility to most antibiotics, except for trimethoprim (TMP), TMP-SMZ, and TMP-SDZ.
- Thymidine deprivation led to a significant decrease in viable cells (2-3 log units) within 24 hours, a phenomenon termed 'thymineless death'.
- Thymidine supplementation prevented thymineless death.
- The thy- mutant exhibited reduced virulence in a mouse kidney infection model compared to the wild-type strain.
Conclusions:
- Thymidine auxotrophy in streptococci can be induced or selected for under antibiotic pressure, particularly with TMP-SMZ or TMP-SDZ treatment.
- Thymineless death is a critical factor affecting the viability of thy- mutants.
- Thymidine auxotrophy may attenuate bacterial virulence, suggesting potential therapeutic implications.