The effect of Baquacil on pathogenic free‐living amoebae (PFLA) 1. In axenic conditions

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Abstract
The amoebicidal properties of Baquacil, a 20% solution of polyhexamethylene biguanide hydrochloride (PHMB), was tested against 4 strains of Naegleria and 2 of Acanthamoeba in axenic conditions at 25, 30, and 37°C. In the control cultures all the strains grew equally well at 30°C, whereas the non‐pathogenic strains of Naegleria (Pl200f) and Acanthamoeba (1501) grew best at 25°C, and the pathogenic strains of Naegleria (MsM, MsT, and Northcott) and Acanthamoeba (A‐1) showed stimulated growth at 37°C. At 37°C MsM, MsT, and Northcott respectively showed 2.25, 1.5, and 0.0% survival after 30 minutes’ exposure to 50 mg L‐1 Baquacil. The survival rates of Pl200f, A ‐ 1, and 1501 were respectively 0.0, 1.5, and 0.75%. At 30°C the same treatment produced the survival rates MsM, 7.5%; MsT, 3.0%; Northcott, 0.0%; Pl200f & A ‐ 1, 3.0%; and 1501, 3.0%. At 25°C the survival rates were all zero with the exception of MsT (2.25%) and 1501 (1.5%). Increasing the exposure time to 240 minutes against strains with high survival rates after 30 minutes’ exposure showed N. fowleri (MsM) to have the greatest potential to survive Baquacil. Increasing the initial Baquacil concentration at an exposure time of 30 minutes showed only N. gruberi (Pl200f) able to survive 80 mg L‐1. Isolation of resistant strains showed N. fowleri (MsM,br3) and (MsT,br1) to be almost totally resistant to Baquacil.