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J Med Microbiol 55 (2006), 689-694; DOI: 10.1099/jmm.0.46497-0
© 2006 Society for General Microbiology
ISSN 1473-5644

Escherichia coli interactions with Acanthamoeba: a symbiosis with environmental and clinical implications

Selwa Alsam1, Seok Ryoul Jeong1, James Sissons1, Ricky Dudley1, Kwang Sik Kim2 and Naveed Ahmed Khan1

1 School of Biological and Chemical Sciences, Birkbeck College, University of London, London WC1E 7HX, UK

2 Pediatric Infectious Diseases, Johns Hopkins University School of Medicine, Baltimore, MD, USA

Correspondence
Naveed Ahmed Khan
n.khan{at}sbc.bbk.ac.uk

Received 3 January 2006
Accepted 24 February 2006

The ability of Acanthamoeba to feed on Gram-negative bacteria, as well as to harbour potential pathogens, such as Legionella pneumophila, Coxiella burnetii, Pseudomonas aeruginosa, Vibrio cholerae, Helicobacter pylori, Listeria monocytogenes and Mycobacterium avium, suggest that both amoebae and bacteria are involved in complex interactions, which may play important roles in the environment and in human health. In this study, Acanthamoeba castellanii (a keratitis isolate belonging to the T4 genotype) was used and its interactions with Escherichia coli (strain K1, a cerebrospinal fluid isolate from a meningitis patient, O18 : K1 : H7, and a K-12 laboratory strain, HB101) were studied. The invasive K1 isolate exhibited a significantly higher association with A. castellanii than the non-invasive K-12 isolate. Similarly, K1 showed significantly increased invasion and/or uptake by A. castellanii in gentamicin protection assays than the non-invasive K-12. Using several mutants derived from K1, it was observed that outer-membrane protein A (OmpA) and LPS were crucial bacterial determinants responsible for E. coli K1 interactions with A. castellanii. Once inside the cell, E. coli K1 remained viable and multiplied within A. castellanii, while E. coli K-12 was killed. Again, OmpA and LPS were crucial for E. coli K1 intracellular survival in A. castellanii. In conclusion, these findings suggest that E. coli K1 interactions with A. castellanii are carefully regulated by the virulence of E. coli.

Abbreviations: CNF1, cytotoxic necrotizing factor-1; OmpA, outer-membrane protein A.




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