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 this time 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 (two and ten minutes) 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 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 two-minute exposure to 10% dilution of commercial bleach is recommended for disinfection of surfaces and instruments contaminated with N. guarroi.

Nannizziopsis guarroi has prolonged environmental persistence on clinically relevant substrates

“…Prior studies have used the same isolates used in this project to assess antifungal minimum inhibitory concentrations and appropriate disinfection; differences between isolates were demonstrated in each of those studies. 10,12 The differences noted suggest a continuum of N guarroi phenotype; a larger number of isolates evaluated would build upon this knowledge. Finally, the ability to culture N guarroi from contaminated solid substrates was time dependent, and although N guarroi could be isolated from most solid substrates at day 14 after contamination, this finding was often limited to a single isolate or only the highest fungal concentration.…”

“…3 Several other fungi may have a similar colony and cytologic morphology that may have led to occult plate contamination not identified with our methodology. Finally, the fungal concentrations used in this study mirror other in vitro fungal studies 12 ; however, it is unknown how the concentrations evaluated compare to real-life implications of substrate exposure to infected lizards. Further work is required to understand the minimum infective dose for naïve lizards.…”

“…Effective disinfection against N guarroi has recently been described and is limited to sodium hypochlorite (bleach). 12 The environmental persistence of N guarroi on solid substrates was, in general, fungal concentration, isolate, and time dependent. Exposure to higher concentrations of the fungus was associated with a longer environmental persistence while lower concentrations were associated with a shorter environmental persistence.…”

Major Emerging Fungal Diseases of Reptiles and Amphibians

“…These tests, however, have a low sensitivity in asymptomatic animals, meaning that the introduction of carriers in a naive population cannot be fully excluded. There is a paucity of information regarding environmental disinfection for Nannizziopsis sp., but a minimum of two minutes contact with 10% bleach seems to be effective against N. guarroi [ 40 ]. When handling animals with suspected or confirmed infection, it is recommended to dip gloved hands into disinfectant between handling, allowing sufficient contact time to the disinfectant, followed by rinsing with clean water [ 41 ].…”