MINIMUM INHIBITORY CONCENTRATIONS OF AND ADAPTATION TO FIVE DISINFECTANTS COMMONLY USED AGAINST SALMONELLA IN THE POULTRY INDUSTRY Kim O. Gradel, Danish Veterinary Laboratory Luke Randall, Veterinary Laboratories Agency Weybridge, England

Epidemiological background Since 1992, for all Danish broiler flocks: §Samples for Salmonella examination have been submitted and results registered. §Data, including the use of disinfectants in the preceding download period, have been registered by a visiting veterinarian,. §All data are available in a central database.

Salmonella Infantis in persistently infected broiler houses First isolate selected ”Middle” isolate selected Last isolate selected

Aims of the study §To find minimum inhibitory concentrations (MICs) of five disinfectants for ”non-persistent” and ”persistent” Salmonella serotypes commonly isolated from Danish broiler houses. §To find MICs of five disinfectants for other Salmonella isolates from the poultry sector. §To see if selected strains can be adapted to the five disinfectants in the laboratory.

Sources of bacterial isolates

Disinfectants used in the study §Formaldehyde (24.5%) §Glutaraldehyde (23%) and benzalkonium chloride (5%) compound §Oxidising compound (blend of peroxygen compounds) §Phenol (30-45% high boiling tar acids) §Iodophor ”Danish” disinfectants ”English” disinfectants

MIC-tests (method)

Adaptation and deadaptation (method) Passages of isolate to increasing disinfectant concentrations until there is no growth MIC-tests Six passages of isolate in broth without disinfectant

MIC-tests (Salmonella results) S. Tennessee is a ”non-persistent” serotype. Among ”persistent” types from broiler houses, only S. 4.12:b:- has increased MICs to the iodophor, which is used rarely in Denmark. S. Senftenberg may have a higher intrinsic resistance??

MIC-tests (results for E. coli control strains) The mar response is apparently not involved in increased resistance.

More results (data not shown) No associations between increased MICs for the three disinfectants showing significant differences for some serotypes (formaldehyde, oxidising compound, iodophor). No associations between MICs and use of disinfectants in the preceding download period. Adaptation or deadaptation did not alter any MICs significantly. No significant increases or decreases in MICs during the persistence periods (67 broiler houses with two isolates and 21 broiler houses with more than two isolates), either generally (p = 0.30) or for any individual disinfectants.

Conclusions Resistance to commonly used disinfectants does not play a major role in persistence of Salmonella in Danish broiler houses. In the laboratory, it was not possible to adapt selected strains to the actual disinfectants.

One persistently Salmonella infected broiler house

Use of disinfectants in Danish broiler houses

Changes in MICs during the persistence period 67 broiler houses represented with two isolates. 21 broiler houses represented with more than two isolates. Generally, no significant changes (p = 0.30). Oxidising compound has relatively most increases, but p = 0.10.