Table 1 Gram-negative bacterial species and plasmids used in this study ^# Ap ^r : ampicillin resistance; Cm ^r : chloramphenicol resistance; Gm ^r : gentamicin resistance; Km ^r : kanamycin resistance; Str ^r : streptomycin resistance

E. coli TOP10

ΔlacX74 ara Δ139 Δ(ara-leu)

Invitrogen®

Salmonella Typhimurium

OU5045

Wild type with a virulence plasmid

Ou and Chu [10]

OU5046

A virulence plasmidless strains derived from OU5045

Ou and Chu [10]

OU5045△sipB

OU5045 with sipB deletion; Cm^r

This study

OU5046△sipB

OU5046 with sipB deletion ; Cm^r

This study

Salmonella Choleraesuis OU7085

Clinical isolate; drug-susceptible

Ou and Chu [10]

Serratia marcescens

CB40

Encapsulated clinical isolate; Cm^r

This study

CB47

Encapsulated clinical isolate; Cm^r

This study

Acinetobacter baumannii

AB08

Encapsulated clinical isolate; Cm^r

This study

AB23

Encapsulated clinical isolate; Cm^r

This study

Klebsiella pneumoniae CG354

Encapsulated clinical isolate; Cm^r

This study

Plasmids

p3ZLux4

ColE1-typed replicon and lux operon; Ap^r; Km^r;

This study

pKD46Gm

A temperature-sensitive plasmid of λ

Red mutagenesis vector; Gm^r

Doublet et al. [11]

pSE-Lux1

46.3-kb conjugative plasmid with IncX- and ColE1-typed replicon and lux operon; Ap^r, Km^r;

Chen et al.[7]