Comparative in vitro activity of chloramphenicol and thiamphenicol against Haemophilus influenzae, Neisseria gonorrhoeae and the typhoid and paratyphoid bacilli.

Chloramphenicol and thiamphenicol were tested by the agar dilution method against 105 Salmonella typhi, 15 S. paratyphi A, 6 S. paratyphi B, 8 S. paratyphi c, 57 Haemophilus influenzae and 60 Neisseria gonorrhoeae strains. The two drugs showed similar in vitro activity against strains of H. influenzae and N. gonorrhoeae irrespective of their beta-lactamase production. In contrast, while all the tested isolatels of typhoid and paratyphoid fever Salmonella were susceptible to chloramphenicol, most of these strains showed resistance to thiamphenicol with MICs greater than or equal to 8 microgram/ml. The significance of these findings are discussed.