Preservative tolerance and resistance
Authors: CHAPMAN J.S. , DIEHL M.A. , FEARNSIDE K.B. 
Published: March 2003

Preservative tolerance is defined as a situation in which a formerly effective preservative system no longer controls microbial growth. Tolerance can have several potential causes: destabilization of the preservative, establishment of biofilms in the manufacturing system, and the development of resistance. As part of an effort to understand and control tolerance, a collection of preservative‐resistant bacteria was established. Pseudomonas and related genera constitute 92% of the isolates in the collection. The collection includes bacteria isolated from products preserved with dimethoxy dimethyl hydantoin (DMDMH), dibromodicyanobutane (DBCB), glutaraldehyde (GLUT), benzisothiazolone (BIT), and methylchloroisothiazolone/methylisothiazolone (MCI/MI). Several isolates were also obtained from products preserved with combinations of DMDMH/iodopropargyl butylcarbamate (IPBC) and DMDMH/IBPC/MCI/MI. Bacteria were deemed resistant if they were isolated from a matrix in which the preservative was stable, and their minimal inhibitory concentrations (MIC) were significantly elevated as compared to a group of conspecific strains from the American Type Culture Collection. Isolates resistant to DMDMH, DBCB, or GLUT had normal outer membrane protein (OMP) profiles, and were cross‐resistant to formaldehyde (FA) and several other FA‐releasing preservatives, a pattern typical of strains producing elevated levels of FA dehydrogenase. The BIT‐resistant isolates were cross‐resistant to a number of structurally dissimilar preservatives but retained susceptibility to MCI. MCI‐resistant isolates had altered OMP profiles, displayed reduced uptake of MCI, and were cross‐resistant to some other preservatives. Restoration of sensitivity to MCI by treatment with EDTA confirmed the role of the outer membrane in MCI resistance. Resume La tolerance due conservateur est definie comme une situation dans laquelle un systeme conservateur precedemment efficace ne maitrise plus le developpement microbien. La tolerance peut avoir plusiers causes potentielles: destablisation du conservateur, survenue de biofilms dans le systeme de fabrication, et developpement d'une resistance. Dans le cadre d'une campagne pour comprendre et maitriser la tolerance, nous avons constitue un echantillon de bacteries resistantes aux conservateurs. Pseudomonas et apparentes constituent 92% des isolats de l'echantillon. L'echantillon comprend des bacteries isolees a partir de produits conserves a l'aide de dimethoxydimethyl‐hydantoine (DMDMH), dibromodicyanobutane (DBCB), glutaraldehyde (GLUT), benzothiazolone (BIT) et methylchloroisothiazolone/methylisothiazolone (MCI/MI). Plusieurs des isolats ont aussi ete obtenus a partir de produits conserves par des associations de DMDMH/iodopropargyl‐butylcarbamate (IPBC) et de DMDMH/IBPC/MCI/MI. Les bacteries ont ete considerees comme resistantes si elles ont ete isolees d'une matrice dans laquelle le conservateur est stable, et si leurs concentrations minimales d'inhibition (MIC) sont significativement elevees par comparaison a un groupe de souches conspecifiques de l'American Type Culture Collection. Les isolats resistants a la DMDMH, au DBCB, ou au GLUT ont des profils proteiniques de membrane externe (OMP) normaux, et sont conjointement resistants au formaldehyde (FA) et a plusiers autres conservateurs generants du FA, schema classique de souches produisant des teneurs elevees de FA‐dehydrogenase. Les isolats resistants a la BIT sont conjointement resistants a plusieurs conservateurs structurellement dissimilaires mais demeurent susceptibles a la MCI. Les isolats resistants a la MCI ont des profils OMP alteres, montrent une consommation reduite de MCI, et sont conjointement resistants a d'autres conservateurs. Le retour a la sensibilite a la MCI par traitement avec de l'EDTA confirme le role de la membrane externe dans la resistance a la MCI.