Compounds for use in antibacterial therapy

A method of sensitizing Gram-negative bacteria to antibacterial agents and to the host defence mechanism complement, comprising subjecting said Gram-negative bacteria to the action of a compound having the general formula ##STR7## in which Dab is diaminoburyric acid;

• A is selected from a group comprising leucine, threonine, isoleucine and phenylalanine;
• B is selected from a group comprising leucine and threonine;
• D is selected from a group comprising D-leucine and D-phenylalanine;
• and C is a substituent selected from the group comprising --Dab--Thr, --Dab--Thr--Dab, --Dab, --Dab--Thr--Acyl and H, in which Thr is threonine, Acyl is a lower acyl group of 1 to 5 carbon atoms and Dab is as defined above.

A pharmaceutical composition for use in sensitizing Gram-negative bacteria to antibacterial agents, complement or both, comprising a therapeutically effective amount of a compound having the general formula ##STR8## in which Dab is diaminobutyric acid;

• A is selected from a group comprising leucine, threonine, isoleucine and phenylalanine;
• B is selected from the group comprising leucine and threonine;
• D is selected from a group comprising D-leucine and D-phenylalanine;
• and C is a substituent selected from the group comprising --Dab--Thr, --Dab--Thr--Dab, --Dab, --Dab--Thr--Acyl and H, in which Thr is threonine, Acyl is a lower acyl group of 1 to 5 carbon atoms and Dab is as defined above, or an acid addition salt thereof with a pharmaceutically acceptable acid;
• in admixture with a pharmaceutically acceptable carrier.