Abstract: The compound N-(.beta.-ketocaproyl)L-homoserine lactone is shown to be an autoinducer that enhances gene expression in a wide variety of microorganisms. Use can be made of this property for diagnostic purposes, e.g., when gene expression causes bioluminescence or antibiotic production, or to promote bacterial growth. The invention claims use for these purposes of the compound and analogs of formula (I) where n is 2 or 3, each of X and Y is O, S or NH, and R is optionally-substituted C1-C12 alkyl or acyl. Some of these are also claimed as new compounds.

Abstract: A method of testing for target bacteria involves adding bacteriophage to a sample to infect the bacteria in the sample; killing extracellular bacteriophage without at the same time killing phage-infected bacteria; amplifying bacteriophage remaining in the sample; and causing the bacteriophage to infect reporter bacteria and thereby produce an observable signal. The reporter bacteria are genetically engineered to have an indicator gene which on expression gives rise to a detectable signal, wherein expression of the indicator gene is initiated on bacteriophage infection of the bacteria.