title: Biofilm Formation and Disinfectant Susceptibility of Persistent and Nonpersistent Listeria monocytogenes Isolates from Gorgonzola Cheese Processing Plants.
abstract: The aim of this study was to investigate whether the biofilm-forming ability and/or the disinfectant susceptibility accounted for the persistence of Listeria monocytogenes in Gorgonzola cheese processing plants. For this purpose, a set of 16 L. monocytogenes isolates collected in the 2004-2007 period was analyzed, including 11 persistent isolates collected in different years, within the collection period, and displaying identical or highly correlated pulsotypes. The evaluation of biofilm-forming ability was assessed using crystal violet (CV) staining and the enumeration of viable cells on stainless steel coupons (SSC). Absorbance values obtained with CV staining for persistent and nonpersistent isolates were not significantly different (rm-ANOVA p > 0.05) and the cell counts from nonpersistent isolates showed to be higher compared with persistent isolates (rm-ANOVA p < 0.05). A simulation of disinfectant treatments was performed on spot inoculated coupons in clean and dirty conditions, according to EN 13697, and on biofilms on SSC, grown in nutrient-rich (dirty) and limiting (clean) conditions using acid acetic-hydrogen peroxide (P3) and acid citric-hydrogen peroxide (MS) commercial disinfectants. The treatment was considered effective when a 4 Log reduction in viable cell count was observed. The Log reductions of persistent and nonpersistent isolates, obtained with both the assays in clean and dirty conditions, were compared and no significant differences were detected (rm-ANOVA p > 0.05). A greater influence of organic matter on MS could explain why P3 was efficient in reducing to effective levels the majority of the isolates at the lowest concentration suggested by the manufacturer (0.2% [v/v]), while the same purpose required a higher concentration (1% [v/v]) of MS. In conclusion, our results demonstrate that the persistence of these isolates in Gorgonzola cheese processing plants was linked neither to the biofilm-forming ability nor to their susceptibility to hydrogen peroxide-based disinfectants; therefore, other factors should contribute to the persistent colonization of the dairies.
authors.affiliation: 1 Dipartimento di Scienze Veterinarie, University of Turin , Grugliasco, Italy .
authors.forename: Annalisa
authors.initials: A
authors.lastname: Costa
authors.affiliation: 1 Dipartimento di Scienze Veterinarie, University of Turin , Grugliasco, Italy .
authors.forename: Luigi
authors.initials: L
authors.lastname: Bertolotti
authors.affiliation: 2 LEAF-Linking Landscape, Environment, Agriculture and Food/Laboratório de Microbiologia, DRAT-Departamento dos Recursos Naturais, Ambiente e Território, Instituto Superior de Agronomia, University of Lisbon , Lisbon, Portugal .
authors.forename: Luisa
authors.initials: L
authors.lastname: Brito
authors.affiliation: 1 Dipartimento di Scienze Veterinarie, University of Turin , Grugliasco, Italy .
authors.forename: Tiziana
authors.initials: T
authors.lastname: Civera
mesh_terms: D019342:Acetic Acid / Q000494:pharmacology; D058491:Bacterial Load / Q000187:drug effects; D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development; D002611:Cheese / Q000382:microbiology*; D019343:Citric Acid / Q000494:pharmacology; D004396:Coloring Agents / Q000737:chemistry; D003612:Dairying / Q000295:instrumentation*; D004202:Disinfectants / Q000494:pharmacology*; D024901:Drug Resistance, Multiple, Bacterial; D004866:Equipment Contamination / Q000517:prevention & control; D005506:Food Contamination / Q000517:prevention & control; D005840:Gentian Violet / Q000737:chemistry; D006861:Hydrogen Peroxide / Q000737:chemistry / Q000494:pharmacology; D025301:Hyphae / Q000254:growth & development / Q000378:metabolism; D007558:Italy; D008089:Listeria monocytogenes / Q000187:drug effects* / Q000254:growth & development / Q000302:isolation & purification / Q000502:physiology; D050296:Microbial Viability / Q000187:drug effects; D010407:Penicillium / Q000254:growth & development / Q000378:metabolism; D012499:Sanitation; D062211:Spatio-Temporal Analysis; D013194:Staining and Labeling; D013193:Stainless Steel
chemical_list: D004396:Coloring Agents; D004202:Disinfectants; D013193:Stainless Steel; D019343:Citric Acid; D006861:Hydrogen Peroxide; D005840:Gentian Violet; D019342:Acetic Acid
keywords: Gorgonzola cheese; Listeria monocytogenes; biofilms; hydrogen peroxide-based disinfectants; persistence; susceptibility