Ampicillin-chloramphenicol interaction against enteric gram-negative organisms

Basim I. Asmar, Adnan S. Dajani

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


Because two children with Salmonella osteomyelitis responded differently to a combination of ampicillin and chloramphenicol, we investigated the activity of each antibiotic and the combination against 21 enteric organisms including Salmonella sp. and other Gram-negative bacilli. Ampicillin was bactericidal against all 21 organisms (minimal bactericidal concentration (MBC) range, 0.25 to 16 μg/ml). Chloramphenicol was bactericidal against 5 (MBC range, 2 to 16 μg/ml) and bacteriostatic against 16 (MBC, ≥64 μg/ml). Fractional lethal indices indicated that chloramphenicol and ampicillin were antagonistic (fractional lethal concentration, >1.2) against all 16 bacteria for which chloramphenicol was bacteriostatic, and the ampicillin MBC increased from a mean of 2.2 μg/ml to 37.2 μg/ml. The two antibiotics were synergistic (fractional lethal concentration, <0.8) against the five organisms for which chloramphenicol was bactericidal, and the ampicillin MBC was lowered from a mean of 3.0 μg/ml to 0.4 μg/ml. Our data indicate that the combination of ampicillin and chloramphenicol can be synergistic or antagonistic against Gram-negative enteric bacteria depending on whether chloramphenicol is bactericidal or bacteriostatic against the specific organism.

Original languageEnglish
Pages (from-to)39-42
Number of pages4
JournalPediatric Infectious Disease
Issue number1
StatePublished - 1983


Dive into the research topics of 'Ampicillin-chloramphenicol interaction against enteric gram-negative organisms'. Together they form a unique fingerprint.

Cite this