Influence of Temperature, Source, and Serotype on Biofilm Formation of Salmonella enterica Isolates from Pig Slaughterhouses

Quantitative assessment of in vitro biofilm formation by 40 Salmonella enterica isolates isolated in pig abattoirs from animal and environmental sources (surfaces in contact and not in contact with meat) and classified in eight seroytpes was carried out by using a microtiter plate assay with spectrophotometric reading (optical density at 620 nm). Biofilm-forming ability was statistically correlated with the temperature of incubation (22 and 35 degrees C), the source of the isolates, and the antimicrobial resistance profile. After incubation at 35 degrees C, 9 isolates (22.5 %) were classified as weak biofilm producers. After incubation at 22 degrees C, 25 isolates (62.5%) were classified as weak producers and 3 (7.5%) as moderate producers. The quantity of biofilm formed after incubation at 22 degrees C was significantly higher (P < 0.01) than at 35 degrees C. This result is notable because 22 degrees C is a common temperature in meat processing facilities and in slaughterhouses. At 35 degrees C, isolates detected from surfaces in contact with meat showed significantly higher (P < 0.1) optical density values compared to isolates from other samples, highlighting the risk of cross-contamination for carcasses and offal. No correlation was detected between quantity of biofilm and serotype or between biofilm formation and resistance to antimicrobials.