Title: Efficacy of disinfectants against TB
Funder: Department for Environment, Food and Rural Affairs

Abstract: Description The presence and persistence of bovine tuberculosis (bTB) on cattle farms and in wildlife is an ongoing problem, requiring effective interventions on infected farms. The agent which causes bTB is Mycobacterium bovis (MB), which is relatively resistant to many disinfectants due to its fatty cell wall. The disinfectants recommended for use during a farm outbreak are those listed on the Defra Approvals list under the Tuberculosis Order (TBO). The tests used to determine disinfectant efficacy against MB in the UK, under Defra Disinfectant Approvals scheme, and European standards, for assessing chemical disinfectant efficacy, both use surrogate organisms. Surrogate organisms are used mainly because of practical difficulties when working with MB. It has a long growth period and also as it is classified as a Hazard Group 3 pathogen it requires the use of a high containment laboratory in order to culture and test MB. The Defra Disinfectant Approvals scheme uses Mycobacterium fortuitum, a fast growing Hazard Group 2 organism, and the European standard for testing disinfectant efficacy in a veterinary environment (EN14204:2012) uses Mycobacterium avium (MA). MA is also used as a surrogate for the paratuberculosis pathogen which causes chronic intestinal infections in animals and may be involved in Crohn’s disease in humans. Another alternative organism is Mycobacterium terrae which has been used as a surrogate for MB in medical equipment sterilisation scenarios and has been found to be more resistant to hospital disinfectants than MA.It is uncertain whether the surrogate organisms in general use represent a true reflection of the susceptibility of currently circulating M. bovis strains to disinfectants, since no published validation studies are available. This project will compare a panel of surrogate organisms to M. bovis, using a range of available tests for disinfectant efficacy. The aim is to identify a suitable surrogate organism which can be taken forward in the development of simulation trials of field disinfection using realistic laboratory models of surface attachment and faecal interfering substances. The work will be undertaken by Animal and Plant Health Agency, with some parallel testing by Health and Safety Laboratory to validate tests and provide further robustness to the testing protocols. It is unclear whether the currently used disinfectants are effective against M. Bovis, due to the use of the surrogate organisms. This work is aimed at better understanding whether these are suitable surrogates and to identify replacements. Objective Objectives:1.Determine the comparability of M. bovis (MB) and a panel of surrogate mycobacterium isolates through the use of various disinfectant efficacy testing methods: 1.1.Minimum Inhibitory Dilution/Minimum Bactericidal Dilution test using two historic and two recent MB isolates from cattle and from badgers, and compare these to MF (NCIMB10384), MA (ATCC 15769) and MT (ATCC 15755). 1.2.Using the TBO testing method, compare efficacy of disinfectants at a range of concentrations against MF, MA, BCG and MB. Set up annual steering group meetings for Defra and interested parties.Cost for Objectives 1.1, & 1.2 = £134676.021.3.Perform EN14204:2012 Quantitative suspension test for evaluation of mycobactericidal activity of chemical disinfectants using MB, MA and MF.1.4.Perform EN1656:2002 Chemical disinfectants and antiseptics. Quantitative suspension test for the evaluation of bactericidal activity of chemical disinfectants and antiseptics used in the veterinary area including a CL2 mycobacterium strain to compare to the panel of surrogates usually used. This complements work currently funded by Andy Smith in the Disinfectant Policy team at Defra from 2016/17 and work planned for 2017/18 exploring comparisons between this EN method and the Defra approvals General Orders testing scheme which is in draft concept note stage at the moment. Cost for Objective 1.3 & 1.4 (if included as part of the overall project) = £86,360.60


Research activity codes: 2.2 FACTORS RELATING TO PHYSICAL ENVIRONMENT
Health categories: INFECTION