Spatial Variation and Survival of Salmonella enterica Subspecies in a Population of Australian Sleepy Lizards (Tiliqua rugosa).

The life cycles of many enteric bacterial species require a transition between two very distinct environments. Their primary habitat is the gastrointestinal tract of the host, while their secondary habitat, during transmission from one host to another, consists of environments external to the host, such as soil, water, and sediments. Consequently, both host and environmental factors shape the genetic structure of enteric bacterial populations. This study examined the distribution of four Salmonella enterica subspecies in a population of sleepy lizards, Tiliqua rugosa, in a semiarid region of South Australia. The lizards living within the 1,920-m by 720-m study site were radio tracked, and their enteric bacteria were sampled at regular intervals throughout their active seasons in the years 2001, 2002, and 2006. Four of the six subspecies of S. enterica were present in this population and were nonrandomly distributed among the lizards. In particular, S. enterica subsp. diarizonae was restricted to lizards living in the most shaded parts of the study site with an overstorey of Casuarina trees. Experiments undertaken to investigate the survival of S. enterica cells under seminatural conditions revealed that cell survival decreased with increased exposure to elevated temperatures and UV light. Among the three S. enterica subspecies tested, S. enterica subsp. diarizonae consistently had an average expected life span that was shorter than that observed for the other two subspecies. There was no indication in the data that there was any competitive dominance hierarchy among the S. enterica subspecies within individual hosts. Thus, the nonrandom distribution of S. enterica subspecies in this population of lizards appears to be driven by their different survival characteristics in the external environment.

Substructure within Salmonella enterica subsp. enterica isolates from Australian wildlife.

Multilocus sequence typing of 56 Salmonella enterica subsp. enterica strains isolated from Australian wildlife hosts was performed. The results of population assignment algorithms revealed that the 56 strains could be subdivided into two distinct clades. Strains belonging to the two clades were further distinguished phenotypically, genotypically, and with respect to host distribution.

Low prevalence of Salmonella enterica in Australian wildlife.

A total of 2489 wildlife hosts from Australia were sampled in order to determine the fraction of hosts that harboured Salmonella enterica as a dominant member of the host's enteric community. Hosts sampled included fish, frogs, reptiles, birds and mammals from the four main climatic regions of Australia: desert, grassland, temperate and tropical. Salmonella enterica was predominately isolated from reptiles, in particular, lizards. It was also isolated from mammals, though not from any fish, frog or bird host. Salmonella enterica was more likely to be isolated from lizards living in desert or grassland regions of Australia compared with lizards inhabiting tropical or temperate regions. The low prevalence of S. enterica isolated from wildlife hosts in Australia indicates that Australian wildlife are unlikely to play a large role in disseminating S. enterica to humans and livestock.