Effectiveness of Common Disinfecting Agents against Isolates of Nannizziopsis guarroi

Abstract Nannizziopsis guarroi, a keratinophilic fungus, is an important cause of dermatomycosis in companion lizards. At present, effective disinfection protocols are unknown and additional information is needed to prevent contamination of surfaces and equipment used in the care of these animals. To this aim, the qualitative in vitro–disinfecting capability of eight commonly used household and laboratory disinfectants (Novalsan®, 3% and 10% dilutions of commercial bleach, Virkon®-S, Lysol® household cleaner with hydrogen peroxide, 70% ethanol, 409®, and household cleaning ammonia) were tested at two different contact times (2 and 10 min) with three different aqueous fungal concentrations of four molecularly confirmed N. guarroi isolates. A positive control after contact with saline was also grown. After contact with disinfectant or saline, the isolates were incubated, and photographic images were taken of plate growth on day 10. Images of each plate were scored using a semiquantitative scoring system. The only disinfectant that completely inhibited growth for all four isolates at both contact times and at all three isolate dilutions was the 10% dilution of commercial bleach. All four isolates grew after contact with ammonia, regardless of contact time or isolate dilution, and the other disinfectants showed variable inhibition of growth that was either isolate or concentration dependent, or both. In conclusion, a minimum of 2 min of exposure to a 10% dilution of commercial bleach is recommended for disinfection of surfaces and instruments contaminated with N. guarroi.