Search

Aims: Thermophilic spoilage bacteria and their biofilms formed during milk powder processing posed threats to safety and quality of dairy products. This research aims to understand more about the bacterial behaviours and their social models in biofilms. Methods and Results: Interactional effects from both extracellular metabolites and co‐culture on biofilms formation of the contaminating thermophilic bacteria were determined. The results showed that strong biofilm formers always had high AI‐2 activities, including Geobacillus stearothermophilus gs1, Bacillus licheniformis bl1 and Thermoactinomyces vulgaris tv1. Metabolites from themself or other species altered their biofilm biomass detected by crystal violet staining. Dual‐species cultures observed by confocal laser scanning microscope indicated either synergistic or inhibitory effects between B. circulans bc1 and G. stearothermophilus gs1, as well as B. licheniformis bl1 and G. stearothermophilus gs1. Fourier transform infrared spectrometry results revealed the significant diversities in polysaccharides of the biofilm matrix. Conclusions: Cell communication played an important role on biofilm formation in the complex microbial community. Intraspecific and interspecific extracellular metabolites influenced collective bacterial behaviours under mixed circumstances. Significance and impact of study: This research provided evidences on cell communication and biofilm formation of thermophilic bacteria in dairy industry. [ABSTRACT FROM AUTHOR]

Thermophilic spore-forming bacteria are common contaminations in milk powder processing lines. In this study, a remarkable change of bacterial community structure was observed after heat sterilization, and thermophilic bacteria took significant advantages after high temperature treatment. Some culturable thermophilic spores survived from pasteurization and even ultra-high temperature sterilization. Feed tank before spraying drying proved to be a key point for controlling thermophilic bacteria. Benzalkonium chloride (BAC) is an effective disinfectant to remove biofilms formed by the isolated dominant species, Bacillus licheniformis. The synergistic reduction of B. licheniformis biofilm on stainless steel in skimmed milk was 3.89 log CFU/cm2 after combined treatment by 0.0625% (v/v) BAC and cleaning-in-place (CIP). This research provided meaningful proposals on determinations of critical control points in a milk powder processing line and removal strategies of B. licheniformis biofilm, which are of valuable significance on quality guarantees for dairy industry. • Thermophilic bacteria took advantages after high temperature treatment. • Feed tank before spraying drying was a key point for controlling thermophilic bacteria. • Bacillus licheniformis was the most prevailing species in this milk powder processing line. • Routine CIP regime was not efficacious enough to remove B. licheniformis biofilms. • 0.0625% of BAC conjoined with CIP reduced 3.89 log CFU/cm2 of B. licheniformis biofilms. [ABSTRACT FROM AUTHOR]

[Display omitted] • Spoilage effects on milk were superimposed from multiple thermophilic bacteria. • Competitive relationship existed between B. licheniformis and G. stearothermophilus. • Synergistic impacts were observed between B. licheniformis and A. flavithermus. • Interspecific interactions played a role in community structure of mixed-species biofilm. • The predominant strain was dynamic with development of multi-species biofilm. Thermophilic bacteria, such as Bacillus licheniformis , Geobacillus stearothermophilus , Bacillus Subtilis and Anoxybacillus flavithermus , are detected frequently in milk powder products. Biofilms of those strains act as a major contamination to milk powder manufactures and pose potential risks in food safety. In this study, we explored the developing process of multi-species biofilm formed by the four thermophilic bacteria on stainless steel immerged in skimmed milk. The results showed that the thermophilic strains possessed strong capacities to decompose proteins and lactose in skimmed milk, and the spoilage effects were superimposed from multiple strains. B. licheniformis was the most predominant species in the mixed-species biofilm after 12-h incubation. From 24 h to 48 h, G. stearothermophilus occupied the highest proportion. Within the multi-species biofilm, competitive relation existed between B. licheniformis and G. stearothermophilus , while synergistic impacts were observed between B. licheniformis and A. flavithermus. The interspecies mutual influences on biofilm development provided important evidences for understanding colonization of the predominant thermophilic bacteria during milk powder processing. [ABSTRACT FROM AUTHOR]

Bacillus licheniformis is a major source of microbial contamination to dairy industry, and biofilm formation by this spoilage bacterium aggravates the safety issues. Especially for milk powder manufactures, the evaporation process at temperatures between 50 °C and 70 °C before spray drying, is a critical control point against thermophilic bacteria multiplication. In our study, metabolomics analysis was performed to investigate dynamic changes of the metabolites and their roles during process of biofilm development of B. licheniformis at 55 °C for 24 h. Amino acid metabolism was quite active, with cooperation from lipid metabolism, carbohydrate metabolism and nucleotide metabolism. Amino acid biosynthesis provided significant contributions especially during early biofilm development from 8 to 12 h. Metabolites involved in specific pathways of arginine biosynthetic, galactose metabolism and sphingolipid metabolism played a crucial role in building biofilm. This work provided new insights into dynamic metabolic alternations and a comprehensive network during B. licheniformis biofilm development, which will extend the knowledge on the metabolic process of biofilm formation by B. licheniformis. The results are helpful in creating better environmental hygiene in dairy processing and new strategies for ensuring quality of dairy products. • Dynamic metabolic process was established during biofilm formation by Bacillus licheniformis. • The most notable metabolic alternations were detected in early biofilm development. • Arginine biosynthesis played a key role on B. licheniformis biofilm development. • Galactose metabolism and sphingolipid metabolism were crucial for B. licheniformis biofilm. • Amino acid, carbohydrate, lipid metabolism interacted and cooperated in B. licheniformis biofilm. [ABSTRACT FROM AUTHOR]

Modern food processing environment provides an ideal condition for biofilms formation by foodborne and spoilage microorganisms on different food contact surfaces. It is widely acknowledged that biofilm has become a serious problem in the food industry, as the biofilm growth mode induces microbial resistance to chemical disinfection. The persistence of biofilms after cleaning and disinfection procedures may result in foodborne illness and food spoilage, emphasizing the importance of preventing biofilms in food production facilities. The use of conventional disinfection technologies alone may not help to achieve the goal of producing safe food products with high quality. Hurdle technology provides a great option for the effective control of biofilms formed on food contact surfaces. Thus, a better understanding of biofilm behavior in response to different disinfectants, as well as seeking potential hurdle technologies to control biofilms are essential. In this review, we discuss the factors that influence the efficiency of disinfectants, and elaborate possible mechanisms which are behind the apparent high antimicrobial resistance of biofilms, and as well as mechanisms which are involved in effective hurdle technologies to control biofilms. [ABSTRACT FROM AUTHOR]

Process biofilms of Bacillus licheniformis present worldwide problem to the dairy industry because of their relevance to food spoilage and quality issues. In this study, metabolites of Lactobacillus plantarum were found to effectively inhibit biofilms formed by B. licheniformis. The biofilm formation was delayed by 10 h by the addition of L. plantarum cell free supernatant and controlling pH of the medium. Confocal laser scanning microscope images showed that L. plantarum metabolites decreased the number of B. licheniformis cells adhered to stainless steel and glass surfaces. Gel filtration chromatography results showed that B. licheniformis utilized the peptides in the growth medium (tryptic soy broth) with the molecular weights ranging from 613 to 1486 Da, and produced plentiful small peptides with the molecular weights ranging from 181 to 613 Da. Moreover, 3–10 kDa components of L. plantarum ultra-filtrates were proved to significantly inhibit biofilm formation by B. licheniformis. Thus, the metabolites produced by L. plantarum provide a novel approach for the prevention of B. licheniformis biofilms in the dairy industry. • Lactobacillus plantarum supernatant effectively inhibited the biofilm formation by Bacillus licheniformis. • L. plantarum inhibited planktonic cell growth of B. licheniformis in co-cultivation. • B. licheniformis preferred an alkaline environment for planktonic growth, and a neutral environment for biofilm formation. • B. licheniformis utilized and decomposed the peptides into smaller ones in tryptic soy broth. • 3–10 kDa components of L. plantarum metabolites obviously weakened biofilm formation of B. licheniformis. [ABSTRACT FROM AUTHOR]

Biofilms on the surface of dairy processing equipment act as potential reservoirs of microbial contamination, which may affect product quality and cause substantial risks for consumer health. Biofilm-forming capacity of a high number of psychrotrophic bacterial species of dairy origin at low temperatures has been poorly reported. This work aimed to explore the biofilm-forming potential of bacterial strains (previously identified from Chinese raw milk) belonging to 72 RAPD based genetic groups (representing 11 predominant genera and 61 species) at 7 °C. Results showed that biofilm formation is a strain-dependent trait, and 25, 10, 19 RAPD groups were weak, moderate and high biofilm formers, respectively, based on results of the crystal violet staining. Isolates of Pseudomonas showed the high tendency to form biofilms. The cell numbers recovered on tryptic soy broth agar plates from surface biofilms ranged from 1.15 to 6.63 log CFU/cm 2 , and the maximum number was detected for Pseudomonas azotoformans (a) (6.63 log CFU/cm 2 ) followed by Serratia quinivorans (6.39 log CFU/cm 2 ) and Pseudomonas libanensis (6.34 log CFU/cm 2 ). In the presence of skim milk, cell numbers decreased to a range from 1.04 to 6.1 log CFU/cm 2 , and high cell number was observed in case of P. azotoformans (a) (6.1 log CFU/cm 2 ), P. libanensis (6.07 log CFU/cm 2 ) and S. quinivorans (5.84 log CFU/cm 2 ). A marked variation in biofilm-forming capacity was observed within the strains belonging to the same species. A moderate correlation (r = 0.42) between the crystal violet assay of polystyrene and methods based on cell enumeration on coupons was observed. Meanwhile, the cell number of Aeromonas hydrophila recovered from stainless steel increased in co-culture with Pseudomonas fluorescens (a). The results expand the knowledge of biofilm-forming capacity of psychrotrophic bacteria of dairy origin. [ABSTRACT FROM AUTHOR]