Phage Endolysins as an Alternative Biocontrol Strategy for Pathogenic and Spoilage Microorganisms in the Food Industry

Abstract

Food contamination by pathogenic and spoilage bacteria causes approximately 47 million cases of foodborne diseases in the United States and leads to tons of food spoilage, worsening the food loss situation worldwide. In addition, conventional preservation treatments implemented in the food industry decrease food's nutritional and organoleptic quality. Therefore, there is a need for new alternatives to counteract food contamination without altering its characteristics. Endolysins are a promising strategy due to their unique properties, such as host specificity, synergism with other antibacterial agents, mode of action, and low probability of resistance development. These characteristics differentiate them from other antibacterial agents used in the food industry. Endolysins are enzymes produced by bacteriophages during the process of bacterial infection and lysis. This review describes the advances related to endolysin application systems in food, considering their potential for food safety and an overview of the application conditions according to the type of food and bacteria to be controlled. We also highlight the need for new studies on endolysin encapsulation and prolongation of the action time in cases of outbreaks that allow obtaining key information to improve the application of endolysins in different food matrices during food processing and storage.

Keywords: antibacterial agents; bacterial lysis; bacteriophages; biocontrol; endolysins; muralitic activity; phage enzymes.

Figure 1

(A) Lytic cycle: (1) phage attachment to the bacterium; (2) injection of genetic material; (3) replication of the phage genome; (4) production of phage protein structures; (5) phage assembly; (6) lysis and release of virions. (B) Activity of the enzymes VAPGH, endolysins, and holins. Adapted from Gutiérrez et al. [41].

Figure 2

Exogenous application of an endolysin. (A) Application to a Gram-positive cell: The endolysin binds to the peptidoglycan and cleaves the peptidoglycan bonds, leading to cell lysis. (B) Application to a Gram-negative cell: The outer membrane (OM) acts as a selective barrier that protects the peptidoglycan.

Figure 3

Methods to help endolysins access the OM of Gram-negative bacteria: (A) Gram-negative bacteria possess an OM that acts as a barrier, preventing direct contact with natural endolysins when externally applied. This barrier prevents peptidoglycan degradation and cell lysis. (B) (1) Identification of lysins with intrinsic capacity for OM penetration; (2) Endolysin in combination with OMPs; (3) Lysins modified by protein engineering (4) Endolysins in OM-penetrating carrier systems.