Herpes simplex virus-1 entrapped in Candida albicans biofilm displays decreased sensitivity to antivirals.

BACKGROUND AND AIM Biofilms represent a serious clinical problem because of the increased resistance of biofilm-associated organisms to antimicrobial agents and the potential for these organisms to cause infections in patients with indwelling medical devices. The presence of some pathogenic viruses in water biofilms underlines the ability of viruses to attach and cling to biofilms retaining their infectivity. Recently we demonstrated that, in vitro, human pathogenic viruses, including HSV-1, can be encompassed in C. albicans biofilm. This biofilm is responsible for severe device-related disseminated infections causing invasive candidemias with a very high rate of mortality. The aim of this in vitro study was to ascertain whether encompassment of Herpes Simplex Virus type 1 (HSV-1) in Candida biofilm impacts virus sensitivity to acyclovir and foscarnet. METHODS VERO cells were infected with HSV-1 and added to mature Candida biofilms in the presence and the absence of acyclovir or foscarnet. After 24h incubation, the amount of infectious virus embedded in biofilm was titrated on VERO cells. Similarly, different drug scalar concentrations were tested in order to determine the inhibiting dose 50 (ID50). In order to evaluate whether the impact on drug antiviral activity is related to the presence of biofilm matrix or to the steric obstruction of the hyphal mass, the efficacy of antiviral drugs were also tested comparing the virus inhibition growth in the presence of Candida biofilm with that obtained in cultures of the same candida strain grown in planktonic hyphal form. RESULTS Acyclovir 50 µM caused a 2,3 Log reduction (99.5%) of virus yield in the control cultures whereas in the presence of Candida biofilm the reduction was only 05 Log (68.5%); foscarnet determined a reduction of 1.4 Log (96%) in the controls and 0.2 Log (36.9%) in biofilm cultures. IDs50 for acyclovir were 5.4µM and 22.6 µM in the absence and in the presence of Candida biofim respectively; for foscarnet IDs50 were 54 µM and 661 µM, respectively. DISCUSSION Encompassment of HSV1-infected cells within the biofilm causes a dramatic decrease in antiviral efficacy of ayclovir and foscarnet. We can speculate that circulating HSV-1 infected cells might be retained in the biofilm and, later on, released as either single cells or within biofilm small fragments. Therefore, Candida biofilm on medical devices may be a source of viral infections with a reduced drug sensitivity.