In vitro susceptibility of Salmonella to various antimicrobial agents, including a new cephalosporin, Ro 13-9904.

The in vitro susceptibility of 363 strains of Salmonella isolated in Honk Kong to various antimicrobial drugs was tested, and the minimum inhibitory concentrations of ampicillin, mecillinam, and six cephalosporins (cephalexin, cephradine, cefamandole, cefoxitin, cefuroxime, and Ro 13-9904) for these strains were determined by an agar dilution method. Although strains of the typhoid and paratyphoid group remained susceptible to most antibiotics tested, many strains of the gastroenteric group of salmonellae were found to be resistant to multiple antibiotics, including ampicillin, chloramphenicol, and, occasionally, trimethoprim. Mecillinam and cefamandole, although active against most of the Salmonella strains tested, were shown to be less active against ampicillin-resistant strains. By contrast, Ro 13-9904 exhibited remarkably uniform and high activity against all the Salmonella strains tested, irrespective of their ampicillin resistance.