title: Spurious sulfamethoxazole-trimethoprim resistance of Salmonella typhi.
abstract: Several studies have identified thymidine excess in susceptibility test media as the cause of spurious resistance of various bacteria to sulfamethoxazole-trimethoprim. We document the phenomenon in Salmonella typhi and Salmonella paratyphi-A and demonstrate its occurrence in 3 of 17 (18%) lots of Mueller-Hinton agars now in use in major medical laboratories in Lima, Peru. The findings are particularly significant because sulfamethoxazole-trimethoprim is an important alternative to chloramphenicol or ampicillin for the treatment of typhoid and paratyphoid fevers.
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003470:Culture Media; D004338:Drug Combinations / Q000494:pharmacology; D004352:Drug Resistance, Microbial; D008826:Microbial Sensitivity Tests; D012482:Salmonella paratyphi A / Q000187:drug effects*; D012485:Salmonella typhi / Q000187:drug effects*; D013420:Sulfamethoxazole / Q000494:pharmacology*; D014295:Trimethoprim / Q000494:pharmacology*; D015662:Trimethoprim, Sulfamethoxazole Drug Combination
chemical_list: D000900:Anti-Bacterial Agents; D003470:Culture Media; D004338:Drug Combinations; D015662:Trimethoprim, Sulfamethoxazole Drug Combination; D014295:Trimethoprim; D013420:Sulfamethoxazole