Interspecific plasmid transfer and modification of heat-stable enterotoxin expression by klebsiella pneumoniae from infants with diarrhea

Abstract

We have previously described two heat-stable enterotoxins (ST) produced by Cltrobacter freundii and by Klebsiella pneumoniae. To see whether transfer of toxigenic ability may occur between different bacterial species, conjugal mating experiments were performed using strains isolated from children. Donors and recipients were incubated together. ST production by the recipients was tested by the suckling mouse assay, which is the standard biologic method for detecting ST, and also by an ELISA test. The latter is based on MAb directed to Escherichia coli 18- or 19-amino acid toxin. Citrobacterand E. coli strains producing an ELISA-positive ST were used as plasmid donors. Recipients were E. coli, Klebsiella P89, and Klebsiella AL55. The latter had been previously shown to be capable of producing an ELISA-negative ST, but had spontaneously lost this ability. After conjugation, all strains gave positive results in the suckling mouse assay. However, E. coli and Klebsiella P89 ST were positive in the ELISA test, whereas Klebsiella AL55 ST was negative. The same three strains were transformed by inserting the plasmid pSLM004 encoding an ELISA-positive ST. Klebsiella P89 and E. coli became capable of producing an ELISA-positive ST, whereas Klebsiella AL55 cells were positive in the suckling mouse assay but negative in the ELISA. To assess whether the toxigenicity acquired was itself transmissible, the new ST-producing strains were incubated with a nontoxigenic Citrobacter strain. The latter became capable of producing an ELISA-positive ST in all cases. In conclusion: 1) different enterobacteria may transmit ST plasmids by conjugation; 2) the ability to produce ST is acquired together with the ability to transfer it to other bacteria; and 3) selected strains of Klebsiellaare capable of modifying toxin expression through a posttrans-lational, yet unknown, mechanism. © 1993 International Pediatric Research Foundation, Inc.