In Vitro Sensitivity of Salmonella to Ten Antimicrobial Agents Including Sulfamethoxazole and Trimethoprim, Alone and in Combination

AUTOR(ES)

Marks, Melvin I.

RESUMO

The activities of trimethoprim (TMP) and sulfamethoxazole (SMZ), alone and in combination (SMZ-TMP), and of the following antibiotics were tested against 115 clinical isolates of nontyphoid Salmonella species: tobramycin, gentamicin, ampicillin, amoxicillin, neomycin, kanamycin, chloramphenicol, and tetracycline. The methods of disk diffusion, microtiter broth dilution, and agar dilution were employed for all single antimicrobial agents as well as for SMZ-TMP studies. Growth curves were performed in broth. SMZ-TMP, TMP, gentamicin, tobramycin, and neomycin were the most active drugs in vitro. All strains were inhibited by ≤1 μg of TMP per ml, but >100 μg of SMZ per ml was required for at least 10% of strains. SMZ and TMP in a ratio of 10:0.5, respectively, inhibited all isolates and were synergistic for 105 strains. All strains inhibited by the combination of 10:0.5 SMZ-TMP had a zone diameter of ≥22 mm by using a combination disk containing 1.25 μg of TMP and 23.75 μg of SMZ. Seven isolates were resistant to >100 μg/ml of ampicillin or amoxicillin; all isolates were sensitive to chloramphenicol at ≤6.3 μg/ml. SMZ-TMP appears to be active against nontyphoid salmonellae in vitro; this is usually due to a synergistic effect.

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