Survival of Acinetobacter baumannii with Acanthamoebasp.

Abstract number: R2269

Objective:Acinetobacter baumannii, potentially found in water sources, is an important emerging hospital-acquired pathogen, affecting patients in intensive care units. It is also known that protozoa can influence the growth of microorganisms as bacteria or yeasts, but little is known about the influence of free-living amobae on A. baumannii. We therefore explore in this study the relationships during a coculture of two strains of Acanthamoeba (A. castellanii or A. culbertsoni) and one strain of A. baumannii.

Methods:

–The first experiment was a coculture of A. castellanii (ATCC 30234) or A. culbertsoni (ATCC 30171) trophozoites and A. baumannii in PBS at 27°C. After 24, 48 or 72 h, the cocultures were plated on Mueller Hinton medium to count CFU. Controls were realized by incubating bacteria in the same conditions without amoebae.

–The same experiment was then conducted, but after 24 h, the cocultures were transferred in encystment medium, and CFU of A. baumannii were counted after 1, 3, 5, 7, 14, 21, 30 and 60 days of incubation at 27°C. Moreover, at various times, samples of the suspensions were examined in electron microscopy.

Results:

–In the coculture experiments realized in PBS at 27°C, the presence of A. castellanii or A. culbertsoni induced a major increase in A. baumannii growth, compared to the control.

–Concerning the incubation in encystment medium after 24 h of coculture, the results showed a marked persistance of the viability of A. baumannii in the presence of Acanthamoeba. The electron microscopy showed internalized bacteria in trophozoites after 24 h of coculture. After 10 days in encystment medium, bacteria were found within cyst wall.

Conclusion: Under certain conditions, the survival and growth of A. baumannii is favored by Acanthamoeba strains. So, in hospital water systems, a special attention should be paid to the presence of free living amoebae, which can promote A. baumannii growth.