Disclosed herein are pharmaceutical compositions comprising an effective amount of an isolated Chp peptide having an amino acid sequence selected from the group consisting of SEQ ID NOs. 1-4, 6-26 and 54-66, or a modified Chp peptide having about 80% sequence identity therewith, wherein the modified Chp peptide inhibits growth, reduces the population, or kills at least one species of Gram-negative bacteria; and a pharmaceutically acceptable carrier. Further disclosed herein are isolated Chp peptides, as well as vectors comprising a nucleic acid molecule that encode the Chp peptides and host cells comprising a vector. Also disclosed herein are methods of inhibiting the growth, reducing the population, or killing of at least one species of Gram-negative bacteria and methods of treating a bacterial infection in a subject.

Disclosed herein are methods of inhibiting the growth, reducing the population, or killing of at least one species of Gram-negative bacteria comprising contacting the bacteria with a composition comprising an effective amount of a Chp peptide, lysin, or lysin-AMP construct or active fragments or variants thereof for a period of time sufficient to inhibit said growth, reduce said population, or kill said at least one species of Gram-negative bacteria. Also disclosed herein are methods of inhibiting a Gram-negative bacteria present in sputum; methods of preventing, disrupting or eradicating a Gram-negative bacterial biofilm; and methods of treating a bacterial infection caused by a Gram-negative bacteria.