Quorum Sensing and Spoilage Potential of Psychrotrophic Enterobacteriaceae Isolated from Milk

Table 4

Activation of the AHL monitor strains in cross-streak experiments.

Isolate and controls	Monitor strains
	CV 026	pSB403	F117 (pAS-C8)	F117 (pKR-C12)	A 136	NTL4
Pantoea sp. 039	-	-	-	-	+	++
H. alvei 059	+++	+++	++	-	+++	+++
Enterobacter sp. 067	+	++	-	-	+	++
H. alvei 068	+++	+++	++	-	+++	+++
H. alvei 071	+++	+++	+	-	+++	+++
A. hydrophila 099	++	++	+	-	+	+++
B. cepacia H111	Nd	+++	+++	Nd	Nd	Nd
B. vietnamiensis	Nd	Nd	Nd	+++	Nd	Nd
P. aeruginosa PAO1	+++	Nd	Nd	Nd	+++	+++

The six monitor strains were cross-streaked against different psychrotrophic strains on LB agar plates. Following up to 48 hours of incubation at 30°C, the production of violacein by C. violaceum CV026, bioluminescence by E. coli pSB403, green fluorescent protein gfp (ASV) by P. putida F117, and β-galactosidase activity by A. tumefaciens A136 and NTL4 was visualized as described in the Material and Methods. Levels of activation are indicated as follows: +++, strong activation, diffusion of AHL of > 1 cm; ++, activation, diffusion of AHL of 0.5 to 1 cm; +, weak activation, diffusion of AHL of < 0.5 cm; -, no detectable activation. Nd: not determined.