Characterization of lysine decarboxylase-negative strains of Salmonella enterica serovar Enteritidis disseminated in Japan.
Salmonella enterica serovar Enteritidis is one of the leading causes of food-borne diseases in Japan. Typically, Salmonella spp. test positive for lysine-decarboxylase. However, the number of isolates of serovar Enteritidis without lysine-decarboxylase activity increased in Japan in 2003. Among 109 strains from distinct outbreaks, 10 lacked lysine-decarboxylase activity. Nine of the ten lysine-decarboxylase-negative strains showed quite similar pulsed-field gel electrophoresis profiles. Their lysine-decarboxylase phenotype was recovered by introduction of the cadBA locus from an lysine-decarboxylase-positive strain. Although the cad loci of the lysine-decarboxylase-negative strains seemed to be intact without any insertion sequences, cadC, a positive regulator of cadBA, had a single-base deletion at the same position, the 973rd base (cytosine), in all the nine lysine-decarboxylase-negative strains, whereas the wild-type cadC gene has a 1542 bp coding region (514 amino acids). This deletion was expected to produce a truncated (338 amino acids) form of CadC due to a frameshift. Because CadC senses environmental cues such as external pH and lysine through its putative C-terminal periplasmic domain, it is likely that the truncated CadC is not sensitive enough to external signaling to activate the cadBA operon, resulting in loss of the lysine-decarboxylase activity. Our results suggest that dissemination of these genetically closely related strains of serovar Enteritidis accounts for the unusual increase in the isolation of lysine-decarboxylase-negative strains.
Department of Bacteriology, National Institute of Infectious Diseases, Tokyo, Japan.
Masatomo
M
Morita
Kadumi
K
Mori
Kiyoshi
K
Tominaga
Jun
J
Terajima
Kenji
K
Hirose
Haruo
H
Watanabe
Hidemasa
H
Izumiya
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics; D001434:Bacteriophage Typing; D001483:Base Sequence; D002262:Carboxy-Lyases / Q000235:genetics*; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004196:Disease Outbreaks; D016521:Electrophoresis, Gel, Pulsed-Field; D016368:Frameshift Mutation; D006801:Humans; D007564:Japan / Q000453:epidemiology; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D012480:Salmonella Infections / Q000453:epidemiology / Q000382:microbiology*; D012477:Salmonella enteritidis / Q000145:classification / Q000201:enzymology* / Q000235:genetics
D001426:Bacterial Proteins; C080050:CadC protein, Bacteria; D004269:DNA, Bacterial; D002262:Carboxy-Lyases; C021520:lysine decarboxylase