Evaluation of microbial ecology, Listeria monocytogenes and Salmonella sp. in food processing industries, multispecies biofilm formation and control methods

Author(s)

Leonardo Ereno Tadielo

• Document type: Doctoral Thesis
• Press: Botucatu. 2023-07-07.
• Institution: Universidade Estadual Paulista (Unesp). Faculdade de Medicina Veterinária e Zootecnia. Botucatu
• Defense date: 2023-06-30
• Advisor: José Paes de Almeida Nogueira Pinto

Abstract

The objectives of the study were to evaluate the hygienic-sanitary quality, presence, virulence, and factors related to biofilm formation of L. monocytogenes and Salmonella sp. and identify the microbial ecology on surfaces of equipment and utensils of Brazilian industries of poultry, pork, and dairy; evaluate the effectiveness of the Sanitation Standard Operating Procedure (SSOP) of a poultry slaughterhouse; to evaluate the dynamics of biofilm formation in pure and multispecies cultures of L. monocytogenes, Salmonella spp., and accompanying microbiota on a polypropylene surface and evaluate the action of Thymol and Carvacrol (THY+CAR), Silver and Zinc Oxide nanoparticles (AgNPs+ZnONPs) and lactic and acetic acid (AL+AA) in inhibiting the formation of multispecies biofilms. Counts of mesophilic aerobes, enterobacteria, Escherichia coli, and Pseudomonas sp., research of L. monocytogenes and Salmonella sp., and identification of microbial ecology through 16S rRNA gene sequencing. The dynamics of pure and multispecies biofilm formation were evaluated on polypropylene surfaces for up to 360 h at 10 °C and the inhibitory effects of THY+CAR, AgNPs+ZnONPs, and AL+AA on multispecies biofilm formation were measured at 3 h, 24 h, 120 h, 216 h, and 360 h, through viable cell count, microbial ecology and architecture. The mesophilic aerobic count was higher in the dairy, followed by the pork and poultry slaughterhouses. L. monocytogenes was detected in the three industries, the pork slaughterhouse had the highest occurrence, followed by poultry and dairy. Salmonella sp. was detected only in dairy. Pseudomonas, Acinetobacter, and Aeromonas were frequent contaminants in the poultry slaughterhouse; Acinetobacter, Pseudomonas, and Brevundimonas for pork and Pseudomonas, Kocuria, and Staphylococcus for dairy. The SSOP from the poultry slaughterhouse was able to reduce the count of all indicator microorganisms and eliminate Salmonella sp., however, L. monocytogenes remained on some surfaces. The microbial ecology before SSOP was composed of microorganisms that are associated with the process of obtaining and preparing meat cuts, such as Aneurinibacillus, Anoxybacillus, and Enterococcus. After SSOP, there was a change in the microbial ecology, highlighting microorganisms that are more adapted to industrial conditions, such as Pseudomonas, Acinetobacter, and Aeromonas. The dynamics of the formation of pure and multispecies biofilms showed punctual differences according to the evaluation times, however, all biofilms presented similar counts in evaluations over 216 h, indicating a synergistic effect of the bacterial consortium of multispecies biofilms. THY+CAR were the compounds that showed the greatest inhibition of multispecies biofilms, followed by AL+AA and AgNPs+ZnONPs. These compounds also inhibited the development of L. monocytogenes and Salmonella spp. in multispecies biofilms. Regarding the architecture of biofilms, THY+CAR, AgNPs+ZnONPs, and AL+AA affected the development of biofilms, demonstrating low numbers of bacterial cells and EPS under the surfaces. Our results provide important information to understand the microbiological risk of contamination and its impacts on the effectiveness of sanitation programs. (AU)

• FAPESP's process: 20/01529-9 - Evaluation of microbial ecology on the presence of Listeria monocytogenes and Salmonella sp. in food processing industries, the formation of multispecies biofilms and control methods
• Grantee: Leonardo Ereno Tadielo
• Support Opportunities: Scholarships in Brazil - Doctorate