Table 1.

Bacterial strains and plasmids used in this study.

Strain	Plasmid	Description	Reference or source
Aeromonas hydrophila 099		Wild type, psychrotrophic isolated from cooled raw milk	[10]
Agrobacterium tumefaciens A136	pCF373, pCF218, Tcr, Spcr	Monitor strain: detects AHL with 3-oxo, 3-hydroxy, and 3-unsubstituted side chain	[16]
Agrobacterium tumefaciens NTL4	pZLR4, Gmr	Monitor strain: detects AHL with 3-oxo, 3-hydroxy, and 3-unsubstituted side chain	[17]
Burkholderia cepacia H111		Positive control in the cross-streak to E. coli pSB403, and P. putida F117 pAS-C8	[18]
Burkholderia vietnamiensis		Positive control in the cross-streak to P. putida F117 pKR-C12	[19]
Chromobacterium violaceum CV026		Monitor strain: detects AHL compounds with unsubstituted side chains from C4 to C8 in length.	[20]
Enterobacter sp. 067		Wild type, psychrotrophic isolated from cooled raw milk	[10]
Escherichia coli MT102	pSB403, Tcr	Monitor strain: exhibits the highest sensitivity for 3-oxo-C6-HSL. However, several other AHL molecules are detected by this sensor	[21]
Escherichia coli XL1-Blue	pQE30-Xa	Cloning and subcloning host. supE44, hsdR17, endA1, recA1, gyrA96, thi1, relA1, lac- F′[proAB+, lacIq, lacZ∆M15, Tn10 (tetF)]	[22]
Escherichia coli XL1-Blue	pQE30-Xa-halI068	It expresses AHL synthase, HalI, from H. alvei 068	This study
Hafnia alvei 059		Wild type, psychrotrophic isolated from cooled raw milk	[10]
Hafnia alvei 068		Wild type, psychrotrophic isolated from cooled raw milk	[10]
Hafnia alvei 071		Wild type, psychrotrophic isolated from cooled raw milk	[10]
Pantoea sp. 039		Wild type, psychrotrophic isolated from cooled raw milk previously identified as Serratia liquefaciens	[10]
Pseudomonas aeruginosa PAO1		Positive control in the cross-streak to C. violaceum CV026, A. tumefaciens NTL4, and A. tumefaciens A136	Laboratory of Microbiology, University of Zürich
Pseudomonas putida F117	pAS-C8, Gmr	Monitor strain: exhibits the highest sensitivity for OHL	[19]
Pseudomonas putida F117	pKR-C12, Gmr	Monitor strain: it detects 3-oxo-C12- and 3-oxo-C10-HSL	[19]
Vibrio harveyi BB120		Positive control: AI2 producer	[23]
Vibrio harveyi BB170		Monitor strain: detects AI2	[23]