Effect of surfactants, temperature, and sonication on the virucidal activity of polyhexamethylene biguanide against the bacteriophage MS2

Background: Virucidal compounds are essential in preventing the transmission of viral infection in the health care environment. Understanding their mechanisms of action is necessary to improve their efficacy. Inactivation of viruses is less documented than that of bacteria notably because different types of virus have diverse response to microbicides, making difficult to establish an inactivation pattern. Methods: The effect of viral aggregates on the virucidal activity of polyhexamethylene biguanide-based microbicide VANTOCIL (TM) TG (Arch Chemicals, Manchester, UK) against the bacteriophage MS2 was investigated by using in combination a standard suspension efficacy test under different conditions and dynamic light scattering measuring the presence and size of aggregates. Results: Temperature had a key role in increasing significantly the virucidal activity of VANTOCIL (TM) TG, reducing virus concentration by 4-log(10) within 10 minutes at 40 degrees C. The high temperature was linked to a reduction of viral aggregates despite the exposure to the biguanide. In addition, the viral inactivation kinetic became significantly more linear at 30 degrees C and 40 degrees C. Such results were also observed with sonication during treatment, where a first-order kinetic was observed. However, the addition of surfactants, even though there was evidence of a decrease in viral clumps, did not enhance the virucidal activity of polyhexamethylene biguanide. Conclusion: The presence of viral aggregates was an important factor in the virucidal efficacy of the biguanide as demonstrated by the correlation among high temperature, decrease in aggregates, and increase in activity, although it is possible that high temperatures might also cause conformational changes of the viral capsid, increasing the sensitivity of virions to the microbicide.