AgResearch and ESR scientists work to prevent salmonella epidemics

New Zealand has strict quarantine requirements at the border, but these have not prevented the emergence of two major pandemics of Salmonellosis in the last few years. AgResearch and ESR scientists are investigating why these pandemics occurred.

Salmonellosis is an internationally significant disease of humans and animals. In recent times, there have been two global pandemics caused by Salmonella enterica serovar Enteritidis and S. enterica serovar Typhimurium definitive type (DT) 104. Strict biosecurity measures prevented the extension of these pandemics to our shores. However, New Zealand has experienced epidemics of Salmonella enterica serovar Brandenburg and S. enterica serovar Typhimurium DT160 over the last few years. These two serovars have caused significant disease in both humans and animals. The former serovar has caused major losses in sheep flocks from abortions and ewe deaths and the latter has caused the deaths of large numbers of wild birds, principally sparrows. Also, S. Typhimurium DT160 has been the most common serovar isolated from humans over the last four years and S. Brandenburg has also been a predominant serovar isolated from humans in New Zealand. Interestingly, neither of these two serovars is a significant cause of disease in humans or animals overseas.

In 2005, a collaborative research programme was established by Geoffrey de Lisle at AgResearch and Philip Carter at ESR. Piklu Bhattacharya, a postdoctoral scientist, was jointly employed by AgResearch and ESR to investigate why certain serovars of Salmonella cause epidemics. One likely explanation is that a new Salmonella epidemic is the result of a Salmonella strain having increased its disease-causing potential by acquiring new genes from other bacteria by horizontal gene transfer. Piklu investigated this hypothesis using sophisticated DNA and protein techniques to compare New Zealand and overseas strains of S. Typhimurium DT160 with other S. Typhimurium strains.

Piklu made a comparison of DNA from New Zealand strains of S. Typhimurium DT160 and DNA from S. Typhimurium LT2, for which the genome has been sequenced. Over 30 genes were present in the New Zealand DT 160 strain but not in the sequenced strain, S. Typhimurium LT2. Many of these genes coded for bacterial viruses (phage) that have been acquired by the New Zealand strains of DT160. In a parallel investigation, Piklu examined the proteins expressed by DT160 and LT2. This study has revealed greater expression of some proteins in the New Zealand DT 160 strains than in the LT2 strain.

This work is currently being continued by Marian Price-Carter at AgResearch and Chris Pope at ESR, who are concentrating on characterising the phage present in the New Zealand strain of DT 160. A major question that is being addressed is whether the acquisition of this phage has been pivotal in this Salmonella type causing a pandemic in New Zealand.

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Page last updated: 12 June 2008