Trimethoprim activity in media selective for Campylobacter jejuni

Area of Science:

• Microbiology
• Antimicrobial Susceptibility Testing

Background:

• Selective media are crucial for isolating specific microorganisms like Campylobacter jejuni.
• Trimethoprim (TMP) is an antimicrobial agent often included in selective media.
• The efficacy of TMP can be influenced by the presence of thymidine in the growth medium.

Purpose of the Study:

• To evaluate the activity of trimethoprim (TMP) in two selective media (Campy-BAP and Skirrow) used for Campylobacter jejuni isolation.
• To compare the minimal inhibitory concentrations (MICs) of TMP in different basal agars.
• To assess the impact of lysed horse blood and thymidine phosphorylase on TMP activity.

Main Methods:

• Evaluated TMP activity in Campy-BAP and Skirrow media.
• Determined MICs of TMP for control organisms in blood agar base, brucella agar, and Mueller-Hinton agar.
• Assessed TMP activity with and without lysed horse blood or thymidine phosphorylase.
• Investigated TMP activity in combination with other antimicrobial agents present in the selective media.

Main Results:

• Trimethoprim (TMP) was inactive in blood agar base and brucella agar, even with added lysed horse blood or thymidine phosphorylase.
• TMP demonstrated activity when combined with other antimicrobials in Skirrow and Campy-BAP media, suggesting potential synergistic effects.
• Sheep blood can replace lysed horse blood in Skirrow medium without affecting TMP activity.

Conclusions:

• Trimethoprim (TMP) alone exhibits limited activity in the basal components of Campy-BAP and Skirrow media.
• The antimicrobial activity of TMP in these selective media is likely due to synergistic interactions with other included agents.
• Optimized formulations of selective media can enhance the efficacy of TMP for Campylobacter jejuni isolation.