Tolerance mechanisms of human-residential bifidobacteria against lysozyme

• Published in: Anaerobe Vol. 47; pp. 104 - 110
• Main Authors: Sakurai, Takuma, Hashikura, Nanami, Minami, Junichi, Yamada, Akio, Odamaki, Toshitaka, Xiao, Jin-zhong
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.10.2017
• Subjects: Acetylation; Anti-Infective Agents - metabolism; Bifidobacterium - chemistry; Bifidobacterium - drug effects; Bifidobacterium - physiology; Cell Wall - chemistry; Humans; Hydrolysis; Muramidase - metabolism; Peptidoglycan - chemistry; Peptidoglycan - isolation & purification; Peptidoglycan - metabolism
• ISSN: 1075-9964; 1095-8274
• DOI: 10.1016/j.anaerobe.2017.05.001

We previously reported that lysozyme present in breast milk is a selection factor for bifidobacterial colonization in infant human intestines. This study is aimed at examining their underlying mechanisms. Human-residential bifidobacteria (HRB) generally exhibited higher tolerance than non-HRB to lysozymes, except B. bifidum subspecies. To assess the involvement of enzymatic activity of lysozyme, peptidoglycan (PG) was isolated and the degree of O-acetylation (O-Ac) in 19 strains, including both HRB and non-HRB, was determined. Variety in the degree of O-Ac was observed among each of the Bifidobacterium species; however, all purified PGs were found to be tolerant to lysozyme, independent of their O-Ac degree. In addition, De-O-Ac of PGs affected the sensitivity to lysozyme of only B. longum-derived PG. To examine the non-enzymatic antibacterial activity of lysozyme on bifidobacteria, lysozyme was heat-denatured. The HRB and non-HRB strains exhibited similar patterns of susceptibility to intact lysozyme as they did to heat-denatured lysozyme. In addition, strains of B. bifidum (30 strains), which showed various tolerance of lysozyme, also exhibited similar patterns of susceptibility to intact lysozyme as they did to heat-denatured lysozyme. These results suggest that bifidobacteria are resistant to the peptidoglycan-degrading property of lysozyme, and the tolerance to lysozyme among some HRB strains is due to resistance to the non-enzymatic antibacterial activity of lysozyme. •Human-residential bifidobacteria (HRB) generally exhibited higher tolerance to lysozymes than non-HRB.•All bifidobacteria were resistant to the peptidoglycan-degrading property of lysozymes.•The varied susceptibility of bifidobacteria to lysozyme was due to their tolerance to the cationic cytotoxicity of lysozymes.