Suitability of two commercial preparations for disinfections against methicillin-resistant Staphylococcus aureus in veterinary medicine.

Two commercially available preparations from the disinfectants list of the German Veterinary Association (Deutsche Veterinärmedizinische Gesellschaft e. V. (DVG)) were tested against a methicillin-resistant Staphylococcus aureus (MRSA) field isolate in a concentration as recommended in the list for disinfection of bacteria. The "Guidelines of DVG for testing of disinfection methods and chemical disinfectants" were used as methodical base. Initially, the examinations for determination of the minimal inhibitory concentrations (MIC) and suitable inactivation substances were carried out. The bactericidal effect of both commercial preparations--a formic acid preparation (55 g per 100 g) and a preparation containing 21 g glutaraldhyde plus 17 g per 100 g formaldehyde--as well as reference disinfectants (37% formaldehyde and 99.5% phenol) were examined in suspension and carrier tests. The suspension tests were performed without and with protein load (20% FBS). Pieces of linden wood were used as carriers. The recommendation of DVG for both Venno Vet 1 super and M&enno Veterinär B neu as bactericide (except of bacterial spores) is 30 min (for preventive disinfections) as well as 120 min contact (for specific disinfections) of 1% concentration. The results show that the disinfection of MRSA do not require higher concentrations and longer contact times as recommended in the disinfectant list of DVG for both commercial disinfectants. Both products were effective in suspension tests in a 1% concentration and within five minutes independent of protein load. In contrast, 1% phenol (reference disinfectant for suspension tests) needed 30 min reaction time without protein load as well as 60 min with protein load for complete inactivation of the MRSA field strain. In carrier tests, a 30 min contact of 1% concentration of both commercial disinfectants and 3% concentration of formalin (reference disinfectant for carrier tests) was sufficient for complete disinfection.