Molecular identification and probiotic potential characterization of lactic acid bacteria isolated from the pigs with superior immune responses - PubMed (original) (raw)

. 2024 Mar 21:15:1361860.

doi: 10.3389/fmicb.2024.1361860. eCollection 2024.

Wenli Zhang # 1 2, Xinrong Wang # 1 2 3, Yu Pan 1 2, Mengjie Wang 1 2, Yunfei Xu 1 2, Junxin Gao 1 2, Hongyu Cui 1 2, Changwen Li 1 2, Hongyan Chen 1 2, He Zhang 1 2, Changyou Xia 1 2, Yue Wang 1 2 3 4

Affiliations

Molecular identification and probiotic potential characterization of lactic acid bacteria isolated from the pigs with superior immune responses

Wenjie Ma et al. Front Microbiol. 2024.

Abstract

Lactic acid bacteria (LAB) belong to a significant group of probiotic bacteria that provide hosts with considerable health benefits. Our previous study showed that pigs with abundant LAB had more robust immune responses in a vaccination experiment. In this study, 52 isolate strains were isolated from the pigs with superior immune responses. Out of these, 14 strains with higher antibacterial efficacy were chosen. We then assessed the probiotic features of the 14 LAB strains, including such as autoaggregation, coaggregation, acid resistance, bile salt resistance, and adhesion capability, as well as safety aspects such as antibiotic resistance, hemolytic activity, and the presence or absence of virulence factors. We also compared these properties with those of an opportunistic pathogen EB1 and two commercial probiotics (cLA and cLP). The results showed that most LAB isolates exhibited higher abilities of aggregation, acid and bile salt resistance, adhesion, and antibacterial activity than the two commercial probiotics. Out of the 14 strains, only LS1 and LS9 carried virulence genes and none had hemolytic activity. We selected three LAB strains (LA6, LR6 and LJ1) with superior probiotic properties and LS9 with a virulence gene for testing their safety in vivo. Strains EB1, cLA and cLP were also included as control bacteria. The results demonstrated that mice treated LAB did not exhibit any adverse effects on weight gain, organ index, blood immune cells, and ileum morphology, except for those treated with LS9 and EB1. Moreover, the antimicrobial effect of LR6 and LA6 strains was examined in vivo. The results indicated that these strains could mitigate the inflammatory response, reduce bacterial translocation, and alleviate liver, spleen, and ileum injury caused by Salmonella typhimurium infection. In addition, the LR6 treatment group showed better outcomes than the LA6 treatment group; treatment with LR6 substantially reduced the mortality rate in mice. The study results provide evidence of the probiotic properties of the LAB isolates, in particular LR6, and suggest that oral administration of LR6 could have valuable health-promoting benefits.

Keywords: antimicrobial activity; immune responses; lactic acid bacteria; probiotic characteristics; safety assessment.

Copyright © 2024 Ma, Zhang, Wang, Pan, Wang, Xu, Gao, Cui, Li, Chen, Zhang, Xia and Wang.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1

Figure 1

Percentages of autoaggregation (A) and coaggregation with enteropathogenic E. coli (B), Salmonella typhimurium (C), and Staphylococcus aureus (D) in the 14 LAB isolates with better antimicrobial capacity, along with EB1 and two commercial strains (cLA, cLP). Data represent means ± standard deviations.

Figure 2

Figure 2

Survival rates of the 14 LAB isolates with better antimicrobial capacity, along with EB1 and two commercial strains in acid for 2 h (A) and 4 h (B) and in bile salt for 2 h (C) and 4 h (D).

Figure 3

Figure 3

Adhesion of the 14 LAB isolates with better antimicrobial capacity, along with EB1 and two commercial strains to HT-29 (A) and Caco-2 (B) cells. Data represent means ± standard deviations.

Figure 4

Figure 4

Effect of LAB supplementation on body weight gain and organ indices of experimental mice. (A) ADG of mice gavaged with selected strains. (B–F) The heart (B), liver (C), spleen (D), lung (E), and kidney (F) indices in the experimental groups. Data represent means ± standard deviations. *p < 0.05, ***p < 0.001.

Figure 5

Figure 5

Effects of strains supplementation on blood immune cells and the ileum of experimental mice. (A–D) The numbers of leukocytes, lymphocytes (B), neutrophils (C), and eosinophils (D) in the blood of mice. (E) HE staining of ileal tissue sections to evaluate the general morphological changes. Data represent means ± standard deviations. *p < 0.05, ***p < 0.001.

Figure 6

Figure 6

Effects of LR6 and LA6 on mortality and bacterial translocation in mice infected with S. typhimurium (ATCC14028). (A) The survival rate of mice in each group after infection. (B–E) Day 3 and day 5 after challenge, the number of bacteria in the spleen (B,C) and liver (D,E). Data represent means ± standard deviations. *p < 0.05, **p < 0.01, ***p < 0.001.

Figure 7

Figure 7

Effect of LR6 and LA6 on inflammatory cytokines in mice infected with S. typhimurium (ATCC 14028). (A,D) TNF-α levels in mice serum at day 3 and day 5 after challenge. (B,E) Expression of TNF-α in spleen on day 3 and day 5 after challenge. (C,F) Expression of TNF-α in liver on day 3 and day 5 after challenge. Data represent means ± standard deviations. *, p < 0.05; **, p < 0.01; ***, p < 0.001.

Figure 8

Figure 8

Effect of LR6 and LA6 on alleviating the liver, spleen, and ileum injury caused by S. typhimurium (ATCC 14028) infection in mice. Histological morphology of the (A–D) liver, (E–H) spleen, and (I–L) ileum (H&E staining). (A,E,I) Mice fed LR6 and challenged with S. typhimurium, (B,F,J) mice fed LA6 and challenged with S. typhimurium, (C,G,K) control mice challenged with S. typhimurium, (D,H,L) control mice fed PBS.

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