Elsevier

Food Control

Volume 108, February 2020, 106876
Food Control

Antibacterial activity and mechanism of lactobionic acid against Pseudomonas fluorescens and Methicillin-resistant Staphylococcus aureus and its application on whole milk,☆☆

https://doi.org/10.1016/j.foodcont.2019.106876Get rights and content

Highlights

  • Selected bacteria were completely inactivated after lactobionic acid exposure.

  • Lactobionic acid disrupted cell wall and membrane and proteins content and activity.

  • Lactobionic acid bind to genomic DNA and disturb the normal cellular function.

  • Lactobionic acid exhibited antibiofilm formation activity.

  • Lactobionic acid inhibited the growth of selected bacteria in whole milk.

Abstract

Lactobionic acid (LBA), a polyhydroxy organic acid, is supposed to be a promising candidate for use as multifunctional food additive due to its ability of antibacterial, anti-obesity, etc. The antibacterial activity of LBA has rarely been reported, thus the antibacterial activity and mechanism of LBA against Pseudomonas fluorescens and methicillin-resistant Staphylococcus aureus were investigated. The results of antibacterial activity showed that P. fluorescens was more susceptible to LBA with the lowest minimum inhibitor concentration/minimum bactericidal concentration and that LBA could completely inactivate the selected bacteria. The alkaline phosphatase activity assay, flow cytometry, protein leakage, and sodium dodecyl sulfate polyacrylamide gel electrophoresis demonstrated that LBA could disrupt the integrity of the cell wall and membrane, and the content and activity of bacterial proteins. Scanning electron microscopy and transmission electron microscopy results showed obvious morphological and ultrastructural changes in the bacterial cells, further confirming the cell wall and membrane damages caused by LBA. Moreover, LBA could interact with bacterial DNA via intercalation, to disturb the normal cellular functions. LBA also exhibited antibiofilm formation activity and the ability to inhibit bacterial growth in whole milk. Overall, LBA is expected to be an alternative for novel multifunctional food additive with bacteriostatic action in food industries.

Introduction

Food safety is an important global issue for both food industry and public health sector. The potential risks include food contamination and food-borne diseases by microorganisms (Belli, Cantafora, Stella, Barbieri, & Crimella, 2013). Milk and dairy products are considered a high risk category for potential microbial contamination, and the contamination can originate from the cattle, processing procedures, and environment (Washabaugh, Olaniyan, Secka, Jeng, & Bernstein, 2019). Pseudomonas fluorescens (P. fluorescens) is a psychrophilic bacterium that facilitates the spoilage of dairy products and other food items when stored at 4 °C or during cold-chain transportation (Carminati et al., 2019; Tyagi & Malik, 2010; Wang, Cai, Li, Xu, & Zhou, 2018). The bacterium produces extremely heat-resistant proteases and lipases, which decompose milk proteins and fats, and cause bitterness, fat oxidation, and gelation, seriously affecting the quality of milk and dairy products (Jaspe, Palacios, Fernández, & Sanjosé, 2010; Yao et al., 2012). Methicillin-resistant Staphylococcus aureus (MRSA) is a gram-positive multi-drug resistant food-borne pathogen, which is of significant public health concern because it can enter the human food chain and contaminate milk and dairy products, causing food-borne illnesses (Gloria, Saraiva, Rigueira, & Brandão, 2011; Othman et al., 2018; Unlu et al., 2018). Additionally, MRSA can produce enterotoxin, an α-pore-forming toxin, and it is an important risk factor for the spread of staphylococcal infections (Lin, Mao, Sun, & Cui, 2018).

The use of natural products and ingredients that control food-borne spoilage and pathogenic bacteria in food commodities and improve food quality, flavor, and color is considered a novel antimicrobial strategy (Bajpai, Sharma, & Baek, 2013; Tyagi & Malik, 2011; Xu et al., 2017). Lactobionic acid (LBA) is a polyhydroxy organic acid found in fermented dairy products such as yogurt (Kiryu et al., 2009). LBA is a natural product produced by microorganisms (such as Pseudomonas) in the process of lactose oxidation with various potential applications in food, pharmaceutical, cosmetic, medicine, and chemical industries (De Giorgi, Raddadi, Fabbri, Toschi, & Fava, 2018; Luis-Felipe, Hamoudi, & Belkacemi, 2012). This novel product has received attention as a food additive in recent years owing to its functions, such as promoting mineral absorption; containing bifidus factor; enhancing flavor, moisturizing, and gelling (Alonso, Rendueles, & Díaz, 2013). Additionally, LBA also has versatile biological activities, such as anti-bacterial, anti-oxidant, anti-obesity, anti-aging, and chelating properties (Alonso et al., 2013; Chen & Zhong, 2017; Mukherjee & Yun, 2015). Owing to its health-promoting functions, LBA could improve the safety and quality of food supplies (Chen & Zhong, 2017). Hence, LBA has potential as a novel multifunctional food additive, and understanding its antibacterial performance and mechanism will enhance its application in the future. However, to the best of our knowledge, only one study have been published on antibacterial mode of action of LBA against Staphylococcus aureus up to now (Cao, Fu, Gao, & Zheng, 2019). Therefore, the objectives of the present study were to (1) evaluate the antibacterial activity of LBA against both Gram-negative spoilage bacteria (P. fluorescens) and drug-resistant Gram-positive pathogenic bacteria (MRSA), and (2) investigate the possible mode of action of LBA against these bacteria. The anti-P. fluorescens and anti-MRSA activities of LBA were also investigated in whole milk. The results will promote the application of LBA as an anti-bacterial agent.

Section snippets

Chemicals

LBA and propidium iodide (PI) were purchased from Sigma-Aldrich Corp. (St. Louis, MO, USA). The LBA stock was prepared at 0.625 g/mL in deionized water, filter sterilized, and diluted to the desired concentrations. Tryptone and yeast extract were obtained from Oxoid (Unipath Ltd., Hampshire, UK). Distilled water was purified using an ultra-pure water system (Heal Force Instruments, Shanghai, China). All other chemicals and reagents were of analytical grade.

Bacterial strain and culture condition

P. fluorescens ATCC 13525 and MRSA

In vitro antibacterial activity of LBA

LBA, a high value-added organic acid found in fermented dairy products such as yogurt (Kiryu et al., 2009), has expected to be a candidate for multifunctional food additives due to its versatile functions like antibacterial activities, but its antibacterial performance and mechanism is far from clear. Therefore, we firstly determined the antibacterial activity of LBA against P. fluorescens and MRSA by detection of MIC, MBC in the present study. The result demonstrated that LBA exhibit

Conclusions

In conclusion, the present study elucidated the antibacterial activity and mechanism of LBA against P. fluorescens and MRSA. The results revealed that LBA has obvious antibacterial effects that disrupt the integrity of cell wall and membrane and the content and activity of bacterial proteins and can bind to genomic DNA to disturb the normal cellular function. Furthermore, LBA exhibited antibiofilm formation activity and the ability to inhibit bacterial growth in whole milk. Therefore, LBA might

Conflicts of interest

The authors declare no conflict of interest.

Acknowledgments

We acknowledge Jinzhi Han (Fuzhou University, Fuzhou, China) for valuable suggestions on this study. This work was supported by the National Key R&D Program of China [2018YFC1604302].

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  • Cited by (0)

    This work was support by the [National Key R&D Program of China] under Grant [2018YFC1604302].

    ☆☆

    LBA, lactobionic acid.

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