Since the introduction of antibacterial agents, serious infections due to enteric pathogens have occurred with increasing frequency.1 Because these microorganisms are quite often resistant to the commonly employed, safe antibacterial agents, therapy frequently requires the use of agents with significant potential for serious human toxicity. Specifically, the treatment of infections due to Salmonella species other than Salmonella typhosa are frequently not cured with chloramphenicol2; Proteus mirabilis is resistant to the clinically usable concentrations of most antibiotics with the exception that large doses of penicillin G may be effective in some circumstances.3 Recently, Noall et al4 emphasized the difficulty in attaining success in treatment of Proteus infections.
Approximately ten years ago the antibiotic penicillin N (cephalosporin N) was isolated and identified as D-4-amino-4-carboxy-n-butyl penicillin. When compared with penicillin G (benzyl penicillin), this penicillin was not very active as an inhibitor of Gram-positive microorganisms. However, it was surprisingly