Increased Persistence of Salmonella enterica Serovar Typhi in the Presence of Acanthamoeba castellanii

Abstract

Salmonella enterica serovar Typhi (S. Typhi) is the etiological agent of the systemic disease typhoid fever. Transmission occurs via ingestion of contaminated food or water. S. Typhi is specific to humans, and no animal or environmental reservoirs are known. As the free-living amoeba Acanthamoeba castellanii is an environmental host for many pathogenic bacteria, this study investigates interactions between S. Typhi and A. castellanii by using cocultures. Growth of both organisms was estimated by cell count, viable count, flow cytometry, and fluorescence microscopy. Results indicate that S. Typhi can survive at least 3 weeks when grown with A. castellanii, as opposed to less than 10 days when grown as singly cultured bacteria under the same conditions. Interestingly, growth rates of amoebae after 14 days were similar in cocultures or when amoebae were singly cultured, suggesting that S. Typhi is not cytotoxic to A. castellanii. Bacteria surviving in coculture were not intracellular and did not require a physical contact with amoebae for their survival. These results suggest that S. Typhi may have a selective advantage when it is associated with A. castellanii and that amoebae may contribute to S. Typhi persistence in the environment.

Mycobacterium gilvum Illustrates Size-Correlated Relationships between Mycobacteria and Acanthamoeba polyphaga

“…polyphaga and Acanthamoeba castellanii are two FLA routinely used to probe mycobacteria-FLA interactions, and A. polyphaga was used in this study (25)(26)(27). We observed that the rapidly growing mycobacteria M. gilvum, M. rhodesiae, and M. thermoresistibile penetrated into A. polyphaga trophozoites, a reproducible result obtained by using a low (1:10) multiplicity of infection.…”

Interactions between Human Norovirus Surrogates and Acanthamoeba spp

“…Two Acanthamoeba species were chosen based on previous studies. A. castellanii is reported to have interactions with nonenveloped viruses (human enteroviruses and adenoviruses) of significance to public health (25,30,31), while both A. castellanii and A. polyphaga play a role in many interactions between acanthamoebae and food-borne bacteria (26)(27)(28).…”

“…Bacteria implicated in food-borne disease outbreaks that have been reported to interact with Acanthamoeba include enterohemorrhagic Escherichia coli (27), Salmonella enterica subsp. enterica, Listeria monocytogenes, Clostridium botulinum, and Campylobacter jejuni (26,28,29). Studies involving Acanthamoeba interactions with viruses are much more limited, including poliovirus, echoviruses 4 and 30 (30), adenoviruses 11 and 41 (31), and coxsackievirus B3 (25).…”

“…Even though FLA primarily feed on bacteria, many are known to contain microbial endosymbionts, including human pathogens. This relationship between human pathogens and FLA has been associated with enhanced environmental survival, increased virulence, and increased resistance to biocides and antibiotics in pathogens that undergo intraprotozoal growth (24)(25)(26). Bacteria implicated in food-borne disease outbreaks that have been reported to interact with Acanthamoeba include enterohemorrhagic Escherichia coli (27), Salmonella enterica subsp.…”

Monitoring F165 1 P-Like Fimbria Expression at the Single-Cell Level Reveals a Highly Heterogeneous Phenotype

“…ON and OFF populations (from 10,000 to 100,000 individual cells) were then resuspended in 1 ml of fresh M9 medium containing 0.2% glycerol and allowed to grow at 37°C for 20 h. These populations were then analyzed by flow cytometry. Bacterial populations were tracked using a logarithmic setting adjusted for bacterial size (forward scatter/side scatter [FSC/SSC]) and by fluorescence with a laser emitting at 488 nm (FL1-H) and collected at wavelengths of 530/30 nm (25).…”