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

The 1976 outbreak of Legionnaires' disease led to the discovery of the intracellular bacterial pathogen Legionella pneumophila. Given their impact on human health, Legionella species and the mechanisms responsible for their replication within host cells are often studied in alveolar macrophages, the primary human cell type associated with disease. Despite the potential severity of individual cases of disease, Legionella are not spread from person-to-person. Thus, from the pathogen's perspective, interactions with human cells are accidents of time and space—evolutionary dead ends with no impact on Legionella's long-term survival or pathogenic trajectory. To understand Legionella as a pathogen is to understand its interaction with its natural hosts: the polyphyletic protozoa, a group of unicellular eukaryotes with a staggering amount of evolutionary diversity. While much remains to be understood about these enigmatic hosts, we summarize the current state of knowledge concerning Legionella's natural host range, the diversity of Legionella-protozoa interactions, the factors influencing these interactions, the importance of avoiding the generalization of protozoan-bacterial interactions based on a limited number of model hosts and the central role of protozoa to the biology, evolution, and persistence of Legionella in the environment.

Effect of UV irradiation (253.7 nm) on free Legionella and Legionella associated with its amoebae hosts

Water systems are the primary reservoir for Legionella spp., where the bacteria live in association with other microorganisms, such as free-living amoebae. A wide range of disinfection treatments have been studied to control and prevent Legionella colonization but few of them were performed considering its relation with protozoa. In this study, the effectiveness of UV irradiation (253.7 nm) using low-pressure lamps was investigated as a disinfection method for Legionella and amoebae under controlled laboratory conditions. UV treatments were applied to 5 strains of Legionella spp., 4 strains of free-living amoeba of the genera Acanthamoeba and Vermamoeba, treating separately trophozoites and cysts, and to two different co-cultures of Legionella pneumophila with the Acanthamoeba strains. No significant differences in the UV inactivation behavior were observed among Legionella strains tested which were 3 logs reduced for fluences around 45 J/m(2). UV irradiation was less effective against free-living amoebae; which in some cases required up to 990 J/m(2) to obtain the same population reduction. UV treatment was more effective against trophozoites compared to cysts; moreover, inactivation patterns were clearly different between the genus Acanthamoeba and Vermamoeba. For the first time data about Vermamoeba vermiformis UV inactivation has been reported in a study. Finally, the results showed that the association of L. pneumophila with free-living amoebae decreases the effectiveness of UV irradiation against the bacteria in a range of 1.5-2 fold. That fact demonstrates that the relations established between different microorganisms in the water systems can modify the effectiveness of the UV treatments applied.

Encystment of Vermamoeba (Hartmannella) vermiformis: Effects of environmental conditions and cell concentration

Vermamoeba vermiformis is a free-living amoeba (FLA) which is widely distributed in the environment. It is known to colonize water systems and to be a reservoir of pathogenic bacteria, such as Legionella pneumophila. For these reasons the control of V. vermiformis represents an important health issue. However, FLA may be resistant to disinfection treatments due to the process of encystment. Thereby, it is important to better understand factors influencing this process. In this aim, we investigated the effect of temperature, pH, osmotic pressure and cell concentration on the encystment of two V. vermiformis strains. Encystment was quite fast, with a 100% encystment rate being observed after 9h of incubation. For the two strains, an optimal encystment was obtained at 25 and 37°C. Concerning pH and osmotic pressure, there were different effects on the encystment according to the tested strains. For the reference strain (ATCC 50237), the patterns of encystment were similar for pH comprised between 5 and 9 and for KCl concentrations ranging from 0.05 to 0.2 mol L(-1). For the environmental strain (172A) an optimal encystment was obtained for basic pH (8 and 9) and for a concentration in KCl of 0.1 mol L(-1). The results also clearly demonstrated that the encystment rate increased with cell concentration, suggesting that there is an inter-amoebal communication. The present study establish for the first time environmental conditions favoring encystment and would lay the foundations to better control the encystment of V. vermiformis.

Potentially pathogenic free-living amoebae in contact lenses of the asymptomatic contact lens wearers

BACKGROUND

Free-living amoebae (FLA) including Acanthamoeba spp. and Hartmannella spp. are the causative agents of serious corneal infection especially within contact lens wearers. Thus contact lenses and their storage case could be a suitable niche for potentially pathogenic amoebae. The main objective of the present study was to evaluate the contamination of contact lenses to free living amoebae using morphological and sequencing based methods.

METHODS

Overall, 90 volunteers provided their contact lenses. All volunteers wore soft contact lenses. Both lenses were cultured in the same plate. Forty-eight of the volunteers were medical and dentistry student and 42 were ophthalmology attendees of hospitals in Tehran, Iran. All of the samples were inoculated to non-nutrient medium and monitored daily for the outgrowth of the amoebae. PCR and sequencing were performed using various primer pairs.

RESULTS

Of the 90 volunteers, 9 (10%) were positive for free-living amoebae outgrowth. Morphological analysis revealed that 3 isolates were belonged to Hartmannella genus according to small round cysts and 6 isolates were belonged to Acanthamoeba genus based on the star shape of endocysts. Sequencing revealed that Acanthamoeba belonged to T4, T3 and T5 genotype. Hartmannella were also belonged to vermiformis species.

DISCUSSION

The presence of potentially pathogenic free living amoebae including Acanthamoeba and Hartmannella could be a high risk for people using soft contact lenses. These results revealed that improved clarification and professional recommendations for contact lens wearers is of utmost importance.

Effect of thermal treatment on free-living amoeba inactivation

AIMS

To evaluate the effect of temperature on two amoeba strains of the genera Acanthamoeba and two amoeba strains of the genera Hartmannella separately treated depending on their life stage, trophozoite or cyst, when cells are directly exposed under controlled conditions.

METHODS AND RESULTS

For thermal treatments, three temperatures were selected 50, 60 and 70°C, and a microcosm was designed using dialysis bags. The inactivation of each strain was determined using a method based on the most probable number quantification on agar plates. The results showed that for all amoeba strains, thermal treatment was more effective against trophozoites compared with cyst stages. The inactivation patterns showed statistical differences between the two genera analysed at temperatures above 50°C. The effectiveness of the thermal treatments at 60 and 70°C was higher for both life stages of Hartmannella vermiformis strains compared with Acanthamoeba strains, being the most resistant Acanthamoeba cysts.

CONCLUSIONS

Free-living amoebae have been isolated in a wide range of environments worldwide due to their capacity to survive under harsh conditions. This capacity is mainly based on the formation of resistant forms, such as double-walled cysts, which confers a high level of resistance as shown here for thermal treatments.

SIGNIFICANCE AND IMPACT OF STUDY

Free-living amoebae survival can promote a rapid recolonization of drinking water systems and is a likely source of emerging opportunistic pathogens such as Legionella. Because of that a better understanding of the factors that affect micro-organism inactivation in water systems would allow more efficient application of disinfection treatments.

First Report of Hartmannella keratitis in a Cosmetic Soft Contact Lens Wearer in Iran

BACKGROUND

Poor hygiene will provide good condition for corneal infections by opportunistic free-living amoebae (FLA) in soft contact lens wearers. In the present study an amoebic keratitis due to Hartmannella has been recognized in a 22-year-old girl with a history of improper soft contact lens use. She had unilateral keratitis on her left eye. Her clinical signs were eye pain, redness, blurred vision and photophobia. The round cysts of free-living amoebae were identified in non-nutrient agar medium by light microscopy. These cysts were suspected to be Hartmannella using morphological criteria. A PCR assay has been confirmed that the round cysts were belonged to H. vermiformis.

in Hot Springs of Ardebil Province, Northwest Iran

BACKGROUND

Geothermal waters could be suitable niches for thermophilic free living amoebae including Naegleria and Hartmannella. Ardebil Province, northwest Iran is popular for having many hot springs for recreational and health purposes activity. The present research is the first molecular based investigation regarding the presence of Naegleria and Hartmannella in the hot springs of Ardebil Province in Iran.

METHODS

Overall, 30 water samples were taken from waters of thermal hot springs in Ardebil Province, Iran during 2010-2011. All collected samples were transferred to Dept. of Parasitology and Mycology, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Cultivation of concentrated water samples was performed using culture-enrichment method. Cloning of the target amoebae was obtained and morphological and molecular analysis was done using page key combined with two sets of primers, respectively. Sequence analysis and homology search was used for strains identification.

RESULTS

Of 30 water samples, 8 (26.7%) were positive for thermotolerant Vahlkampfiids and Hartmannella based on morphological characteristics of vegetative form and double walled cysts. Cloning of the target amoebae were done successfully. Sequencing of the positive isolates revealed that the strains belonged to Naegleria (N. carteri and N. spp) and H. vermiformis.

CONCLUSION

The result highlights a need for improved filtration and disinfection and periodic monitoring of recreational thermal waters in order to prevent disease related to free- living amoebae. This is the first comprehensive molecular study of thermophilic Naegleria and Hartmannella in hot springs of Iran.