Differential Legionella spp. survival between intracellular and extracellular forms in thermal spring environments

Abstract

Legionella are commonly found in natural and man-made aquatic environments and are able to inhabit various species of protozoa. The relationship between the occurrence of Legionella spp. within protozoa and human legionellosis has been demonstrated; however, the proportions of intracellular and extracellular Legionella spp. in the aquatic environment were rarely reported. In this study, we developed a new method to differentiate intracellular and extracellular Legionella spp. in the aquatic environment. Water samples from three thermal spring recreational areas in southeastern Taiwan were collected and analyzed. For each water sample, concurrent measurements were performed for Legionella spp. and their free-living amoebae hosts. The overall detection rate was 32 % (16/50) for intracellular Legionella spp. and 12 % (6/50) for extracellular Legionella spp. The most prevalent host of Legionella spp. was Hartmannella vermiformis. The identified Legionella spp. differed substantially between intracellular and extracellular forms. The results showed that it may be necessary to differentiate intracellular and extracellular forms of Legionella spp.

Legionella pneumophila and Protozoan Hosts: Implications for the Control of Hospital and Potable Water Systems

“…Other protozoan genera; Balamuthia [97], Dictyostelium [98], Echinamoeba [31], Naegleria [99], Paramecium [100], and Vermamoeba [32], facilitate intracellular replication of L. pneumophila. The second method is used to detect naturally co-existing Legionella-protozoans from environment, but microscopically it is very difficult to find protozoans containing Legionella in the natural environment [101]. As an alternative approach, a sample is screened for the presence of both Legionella and protozoan hosts.…”

Legionella Occurrence beyond Cooling Towers and Premise Plumbing

“…Amoeba co-culturing greatly increased the detection rates in certain samples. Legionella were also detected in sodium bicarbonate and sulfur springs in Taiwan at similar levels [40]). Here, 38% of the samples that were collected from three springs tested positive for Legionella within host amoebae.…”

“…Even with common occurrence, higher concentrations of Legionella in lakes may be caused by specific environmental conditions. During an environmental study to assess the impact of seasonal effects on the presence and species in Taiwanese reservoirs, extremely high concentrations of up to 1.6 × 10 6 cells/mL and 7.35 × 10 8 cells/mL were measured [36,40]. Although positivity was the highest in fall, the concentrations tended to peak in summer, with warmer regions in the south having more stable populations.…”

From Many Hosts, One Accidental Pathogen: The Diverse Protozoan Hosts of Legionella

“…Co-isolation studies attempt to address this issue by examining the co-existence of protozoa and Legionella in environmental samples. In rare cases, protozoa harboring Legionella have been isolated from environmental samples providing direct evidence of their interaction in the environment (Thomas et al, 2006 ; Hsu et al, 2011 ; Kao et al, 2013 ). More commonly, Legionella are identified by 16S sequencing of DNA extracts from bacteria isolated by Legionella -selective culture methods on bacteriological medium (Salloum et al, 2002 ; Sheehan et al, 2005 ) or enrichment through co-culture of environmental samples with amoebae (Pagnier et al, 2008 ).…”

“…While this is not surprising for Acanthamoeba, Hartmannella , and Naegleria , as these are some of the most abundant protozoa in nature, in many cases co-isolation studies identified the same species of these genera. In particular, three of the protozoa identified, A. palestinensis, N. lovaniensis , and V. vermiformis that had been shown to support L. pneumophila replication in co-culture experiments (Anand et al, 1983 ; Rowbotham, 1986 ; Declerck et al, 2005 ; Thomas et al, 2006 ) were isolated from water samples harboring L. pneumophila (Kao et al, 2013 ). Similarly, amoebal enrichment assays resulted in the isolation of Acanthamoeba jacobsi harboring L. pneumophila directly from a thermal spring water sample (Hsu et al, 2011 ).…”