Co-trimoxazole sensitivity testing: comparison of separate and combined disk agar diffusion techniques

Area of Science:

• Microbiology
• Clinical Pharmacy
• Infectious Diseases

Background:

• Urinary tract infections (UTIs) are common, often caused by bacteriuria.
• Co-trimoxazole (trimethoprim/sulfamethoxazole) is a frequently used antibiotic for UTIs.
• Accurate antibiotic sensitivity testing is crucial for effective treatment.

Purpose of the Study:

• To evaluate the reliability of combined disk testing for co-trimoxazole sensitivity in bacteria causing significant bacteriuria.
• To compare the results of combined disk testing with separate disk testing for trimethoprim and sulphamethoxazole.

Main Methods:

• Agar diffusion technique was used to test 507 bacterial strains from patient urine samples.
• Organisms were tested with a combined disk of trimethoprim and sulphamethoxazole.
• A standardized inoculum was used for testing with both combined and separate antibiotic disks.

Main Results:

• Combined disk testing for co-trimoxazole sensitivity did not consistently match the sensitivity patterns observed with separate disks.
• Discrepancies were noted between the primary sensitivity test using a combined disk and more detailed testing.

Conclusions:

• Combined disk testing for co-trimoxazole may not be a fully reliable method for determining bacterial sensitivity in cases of significant bacteriuria.
• Clinicians should be aware of potential inaccuracies when interpreting co-trimoxazole sensitivity results from combined disk tests.