Background: Acanthamoeba can interact with a wide range of microorganisms such as viruses, algae, yeasts, protists and bacteria including Legionella pneumophila, Pseudomonas aeruginosa, Vibrio cholerae, Helicobacter pylori, Listeria monocytogenes, Mycobacterium spp., and Escherichia coli. In this capacity, Acanthamoeba has been suggested as a vector in the transmission of bacterial pathogens to the susceptible hosts. Methods: Here, we used a keratitis isolate of A. castellanii of the T4 genotype and studied its interactions with two bacterial genera which have not been tested before, Enterobacter aerogenes, and Aeromonas hydrophila, as well as E. coli. Assays were performed to determine bacterial association with and invasion of A. castellanii. Additionally, bacterial survival intracellular of A. castellanii trophozoites as well as cysts was determined. Results: All three bacterial isolates tested, associated, invaded, and survived inside A. castellanii trophozoites as well as A. castellanii cysts. However, E. aerogenes and E. coli exhibited significantly reduced association with and invasion of A. castellanii as compared with A. hydrophila (P < 0.01 using paired T-test, one tail distribution). In the long term survival assays, all three bacterial isolates tested remained viable inside A. castellanii trophozoites, while amoeba remained intact; however A. hydrophila exhibited higher survival inside amoebae (14.54 ± 3.3 bacteria:amoeba ratio) compared with E. aerogenes (3.96 ± 0.7 bacteria:amoeba ratio) and E. coli (5.85 ± 1.1 bacteria:amoeba ratio). A. hydrophila, E. coli, and E. aerogenes remained viable during the encystment process and exhibited higher levels of recovery from mature cysts (14.13 ± 0.89 A. hydrophila:amoeba ratio, 10.13 ± 1.17 E. aerogenes:amoeba ratio, and 11.95 ± 0.7 E. coli:amoeba ratio). Conclusions: A. hydrophila and E. aerogenes also joined the ranks of other bacteria that could benefit from A. castellanii. Because cysts can be airborne, these findings suggest that Acanthamoeba is a potential vector in the transmission of A. hydrophila and E. aerogenes to susceptible hosts.

The ability of pathogenic free-living amoebae to produce infections is a growing concern. In this study, we investigated the presence of free-living amoebae (Acanthamoeba spp., Naegleria fowleri, Balamuthia mandrillaris) in drinking water supplies in Karachi, Pakistan. Fifty-two domestic tap water samples were examined. Amoebae were identified by morphological characteristics and polymerase chain reaction. Thirty percent of the examined samples were positive for Acanthamoeba spp., 8% for N. fowleri while B. mandrillaris were not recovered. Additionally we examined secretory IgA antibody to Acanthamoeba and B. mandrillaris. Acanthamoeba antibody prevalence rate was 100% in both males and females, while B. mandrillaris antibody prevalence rate was 5.5% in males only (females were negative). Our findings suggest that free-living amoebae are a potential health hazard in domestic water supplies in Karachi, Pakistan.

A B S T R A C TAcanthamoeba cysts are highly resistant to contact lens disinfecting solutions. Acanthamoeba cyst wall is partially made of 1,4 b-glucan (i.e., cellulose) and other complex polysaccharides making it a hardy shell that protects the resident amoeba. Here, we hypothesize that targeting the cyst wall structure in addition to antiamoebic compound would improve the efficacy of marketed contact lens disinfecting solutions. Using chlorhexidine as an antiamoebic compound and cellulase enzyme to disrupt cyst wall structure, the findings revealed that combination of both agents abolished viability of Acanthamoeba castellanii cysts and trophozoites. When tested alone, none of the agents nor contact lens disinfecting solutions completely destroyed A. castellanii cysts and trophozoites. The absence of cyst wall-degrading enzymes in marketed contact lens disinfecting solutions render them ineffective against Acanthamoeba cysts. It is concluded that the addition of cyst wall degrading molecules in contact lens disinfecting solutions will enhance their efficacy in decreasing the incidence of Acanthamoeba effectively.

The majority of children in Karachi have blood lead levels above 10 micrograms/dl, the upper safety limit set by the United States Centers for Disease Control and Prevention. A study was undertaken to evaluate chronic lead exposure in children by measuring lead levels in shed primary teeth collected from primary school children in Karachi. A total of 309 teeth were collected from nine different schools, and analysed for lead content by atomic absorption spectrophotometry with electrothermal atomization. The mean (SD) age of the subjects was 7.6 (1.2) years and the mean lead level was 5.78 micrograms/g of whole tooth (dry weight), ranging from 0.42 to 39.75 micrograms/g. Incisor teeth had a significantly higher mean (SD) lead level, 6.42 (4.19) micrograms/g, than canines and molars which contained 4.91 (5.12) micrograms and 4.50 (2.67) micrograms lead whole tooth (dry weight), respectively. Significant differences were observed between different schools. No difference was observed between boys and girls and the accumulation of lead in teeth was not correlated with chronological age.

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