Free-living amoeba live in close association with other microorganisms
in the same ecological niches, feeding on bacteria and fungi. The eff
iciency of consumption is different, depending on protozoan type and g
rowth state, temperature, bacterial abundance, and size and nature of
bacterial prey. Many of the bacteria are digested, especially enteroba
cteria which are used as nutriment. Gram positive bacteria seem to be
digested slower, owing to their thick cell wall. Some bacteria may avo
id digestion by liberation out of the phagosome before lysosomal fusio
n or resist the cellular mechanisms of digestion in phagosomes and esc
ape into the host cell cytoplasm where they multiply. A number of bact
eria have been reported to survive as parasites or endosymbionts of fr
ee-living amoeba, and some of these bacteria are also potential pathog
ens to vertebrates. Free-living amoeba are incriminated in the ecology
and epidemiology of legionellosis. They are also likely to be natural
hosts for well-known pathogens like Vibrio cholerae and Listeria mono
cytogenes, or nosocomial new pathogens, like Xanthomonas maltophilia a
nd Flavobacterium sp. Their interacting with protozoa in biofilms asso
ciated to intracellular replication and inclusion of pathogen bacteria
in cysts give these pathogens a possibility of survival and transmiss
ion in unfavourable conditions.