From Exit to Entry: Long-term Survival and Transmission of Salmonella

Abstract

Salmonella spp. are a leading cause of human infectious disease worldwide and pose a serious health concern. While we have an improving understanding of pathogenesis and the host-pathogen interactions underlying the infection process, comparatively little is known about the survival of pathogenic Salmonella outside their hosts. This review focuses on three areas: (1) in vitro evidence that Salmonella spp. can survive for long periods of time under harsh conditions; (2) observations and conclusions about Salmonella persistence obtained from human outbreaks; and (3) new information revealed by genomic- and population-based studies of Salmonella and related enteric pathogens. We highlight the mechanisms of Salmonella persistence and transmission as an essential part of their lifecycle and a prerequisite for their evolutionary success as human pathogens.

Figure 1

Survival of Salmonella ser. Typhimurium in Rdar Morphotype Colonies Compared to Liquid Cultures. Dots represent the total CFU from 1 mL aliquots of cells grown for 18 h in Luria broth at 37 °C (overnight) or rdar morphotype colonies grown on 1% tryptone agar for two days at 28 °C. To ensure consistency, overnight cultures were normalized to an optical density of 1.0 at 600 nm prior to removing aliquots. The “overnight lyophilized” samples represent 1 mL aliquots of cells that were frozen and lyophilized for 48 h prior to measurement. Rdar morphotype colonies were stored for two weeks or 30 months, one colony per well, in a plastic, 24-well tissue culture plate [43] prior to measurement. Each grey dot represents the average CFU value from at least four biological replicates. Cells samples were stained using a Live/Dead bacterial viability kit (Invitrogen, Carlsbad, CA, USA, cat. No. L-7012) and enumerated by manual scanning on a fluorescent microscope; n represents the total number of cells that were counted from two to three biological replicates of each sample type. The bars reflect the percentage of cells that were scored as live (green) or dead (magenta), with a combined total of 100%.