Pathogenicity of clinical Salmonella enterica serovar Typhimurium isolates from Thailand in a mouse colitis model

Probiotic Limosilactobacillus reuteri KUB-AC5 decreases urothelial cell invasion and enhances macrophage killing of uropathogenic Escherichia coli in vitro study

Introduction

Bacterial urinary tract infections (UTI) are among the most common infectious diseases worldwide. The rise of multidrug-resistant (MDR) uropathogenic Escherichia coli (UPEC) UTI cases is a significant threat to healthcare systems. Several probiotic bacteria have been proposed as an alternative to combat MDR UTI. Lactic acid bacteria in the genus Limosilactobacillus are some of the most studied and used probiotics. However, strain-specific effects play a critical role in probiotic properties. L. reuteri KUB-AC5 (AC5), isolated from the chicken gut, confers antimicrobial and immunobiotic effects against some human pathogens. However, the antibacterial and immune modulatory effects of AC5 on UPEC have never been explored.

Methods

Here, we investigated both the direct and indirect effects of AC5 against UPEC isolates (UTI89, CFT073, and clinical MDR UPEC AT31) in vitro. Using a spot-on lawn, agar-well diffusion, and competitive growth assays, we found that viable AC5 cells and cell-free components of this probiotic significantly reduced the UPEC growth of all strains tested. The human bladder epithelial cell line UM-UC-3 was used to assess the adhesion and pathogen-attachment inhibition properties of AC5 on UPEC.

Results and discussion

Our data showed that AC5 can attach to UM-UC-3 and decrease UPEC attachment in a dose-dependent manner. Pretreatment of UPEC-infected murine macrophage RAW264.7 cells with viable AC5 (multiplicity of infection, MOI = 1) for 24 hours enhanced macrophage-killing activity and increased proinflammatory (Nos2, Il6, and Tnfa) and anti-inflammatory (Il10) gene expression. These findings indicate the gut-derived AC5 probiotic could be a potential urogenital probiotic against MDR UTI.

Controlling the bacterial load of Salmonella Typhi in an experimental mouse model by a lytic Salmonella phage STWB21: a phage therapy approach

BACKGROUND

Salmonella enterica serotype Typhi is one of the major pathogens causing typhoid fever and a public health burden worldwide. Recently, the increasing number of multidrug-resistant strains of Salmonella spp. has made this utmost necessary to consider bacteriophages as a potential alternative to antibiotics for S. Typhi infection treatment. Salmonella phage STWB21, isolated from environmental water, has earlier been reported to be effective as a safe biocontrol agent by our group. In this study, we evaluated the efficacy of phage STWB21 in reducing the burden of salmonellosis in a mammalian host by inhibiting Salmonella Typhi invasion into the liver and spleen tissue.

RESULTS

Phage treatment significantly improved the survival percentage of infected mice. This study also demonstrated that oral administration of phage treatment could be beneficial in both preventive and therapeutic treatment of salmonellosis caused by S. Typhi. Altogether the result showed that the phage treatment could control tissue inflammation in mice before and after Salmonella infection.

CONCLUSIONS

To the best of our knowledge, this is the first report of phage therapy in a mouse model against a clinically isolated Salmonella Typhi strain that includes direct visualization of histopathology and ultrathin section microscopy images from the liver and spleen sections.

Multidrug resistance plasmids underlie clonal expansions and international spread of Salmonella enterica serotype 1,4,[5],12:i:- ST34 in Southeast Asia

Salmonella enterica serotype 1,4,[5],12:i:- (Typhimurium monophasic variant) of sequence type (ST) 34 has emerged as the predominant pandemic genotype in recent decades. Despite increasing reports of resistance to antimicrobials in Southeast Asia, Salmonella ST34 population structure and evolution remained understudied in the region. Here we performed detailed genomic investigations on 454 ST34 genomes collected from Vietnam and diverse geographical sources to elucidate the pathogen's epidemiology, evolution and antimicrobial resistance. We showed that ST34 has been introduced into Vietnam in at least nine occasions since 2000, forming five co-circulating major clones responsible for paediatric diarrhoea and bloodstream infection. Most expansion events were associated with acquisitions of large multidrug resistance plasmids of IncHI2 or IncA/C2. Particularly, the self-conjugative IncA/C2 pST34VN2 (co-transferring blaCTX-M-55, mcr-3.1, and qnrS1) underlies local expansion and intercontinental spread in two separate ST34 clones. At the global scale, Southeast Asia was identified as a potential hub for the emergence and dissemination of multidrug resistant Salmonella ST34, and mutation analysis suggests of selection in antimicrobial responses and key virulence factors.

Clinical Characteristics, Antimicrobial Resistance, Virulence Genes and Multi-Locus Sequence Typing of Non-Typhoidal Salmonella Serovar Typhimurium and Enteritidis Strains Isolated from Patients in Chiang Mai, Thailand

Non-typhoidal salmonellosis (NTS) caused by ingesting Salmonella enterica contaminated food or drink remains a major bacterial foodborne disease. Clinical outcomes of NTS range from self-limited gastroenteritis to life-threatening invasive NTS (iNTS). In this study, we isolated Salmonella spp. from the stool and blood of patients hospitalized at Maharaj Nakorn Chiang Mai Hospital, Chiang Mai, Thailand, between 2016-2021 (a total of 395 cases). Then, serovar Typhimurium and Enteritidis were identified and further characterized by multiplex PCR, and multi-locus sequence typing. Our data show that multidrug resistance (MDR) sequence type 34 (ST34) and ST11 are the predominant sequence types for serovars Typhimurium and Enteritidis, respectively. Most S. Typhimurium ST34 lacks spvB, and most S. Enteritidis ST11 harbor sseI, sodCI, rpoS and spvB genes. NTS can be found in a wide range of ages, and anemia could be a significant factor for S. Typhimurium infection (86.3%). Both S. Typhimurium (6.7%) and S. Enteritidis (25.0%) can cause iNTS in immunocompromised patients. S. Typhimurium conferred MDR phenotype higher than S. Enteritidis with multiple antibiotic resistance indexes of 0.22 and 0.04, respectively. Here, we characterized the important S. Typhimurium, S. Enteritidis, and human clinical factors of NTS within the region.

phoP maintains the environmental persistence and virulence of pathogenic bacteria in mechanically stressed desiccated droplets

Despite extensive studies on kinematic features of impacting drops, the effect of mechanical stress on desiccated bacteria-laden droplets remains unexplored. In the present study, we unveiled the consequences of the impaction of bacteria-laden droplets on solid surfaces and their subsequent desiccation on the virulence of an enteropathogen Salmonella typhimurium (STM). The methodology elucidated the deformation, cell-cell interactions, adhesion energy, and roughness in bacteria induced by impact velocity and low moisture because of evaporation. Salmonella retrieved from the dried droplets were used to understand fomite-mediated pathogenesis. The impact velocity-induced mechanical stress deteriorated the in vitro viability of Salmonella. Of interest, an uninterrupted bacterial proliferation was observed in macrophages at higher mechanical stress. Wild-type Salmonella under mechanical stress induced the expression of phoP whereas infecting macrophages. The inability of STM ΔphoP to grow in nutrient-rich dried droplets signifies the role of phoP in sensing the mechanical stress and maintaining the virulence of Salmonella.

Therapeutic effects of oral administration of lytic Salmonella phages in a mouse model of non-typhoidal salmonellosis

Acute non-typhoidal salmonellosis (NTS) caused by a Gram-negative bacterium Salmonella enterica serovar Typhimurium (S. Tm) is one of the most common bacterial foodborne diseases worldwide. Bacteriophages (phages) can specifically target and lyse their host bacteria, including the multidrug-resistant strains, without collateral damage to other bacteria in the community. However, the therapeutic use of Salmonella phages in vivo is still poorly investigated. Salmonella phages ST-W77 and SE-W109 have previously been shown by our group to be useful for biocontrol properties. Here, we tested whether phages ST-W77 and SE-W109 can reduce Salmonella invasion into cultured human cells and confer a therapeutic benefit for acute NTS in a mammalian host. Human colonocytes, T84 cells, were treated with phages ST-W77, SE-W109, and its combination for 5 min before S. Tm infection. Gentamicin protection assays demonstrated that ST-W77 and SE-W109 significantly reduced S. Tm invasion and inflammatory response in human colonocytes. Next, streptomycin-pretreated mice were orally infected with S. Tm (108 CFU/mouse) and treated with a single or a combination of ST-W77 and SE-W109 (1010 PFU/mouse for 4 days) by oral feeding. Our data showed that phage-treated mice had lower S. Tm numbers and tissue inflammation compared to the untreated mice. Our study also revealed that ST-W77 and SE-W109 persist in the mouse gut lumen, but not in systemic sites. Together, these data suggested that Salmonella phages ST-W77 and SE-W109 could be further developed as an alternative approach for treating an acute NTS in mammalian hosts.

Lactobacillus plantarum synergistically regulates M1 macrophage polarization in resistance against Salmonella enterica serovar Typhimurium infection

Macrophage polarization affects the progression of pathogenic bacterial infections. Lactobacillus is widely used to interact with macrophages and to exert specific immunomodulatory activities. In this study, we investigated the regulation of macrophage polarization against Salmonella enterica serotype Typhimurium (STM) by Lactobacillus plantarum JL01 (LP), to explore prevention and treatment strategies for salmonellosis. We assessed the in vitro differential polarization of RAW 264.7 macrophages and mouse bone marrow macrophages (BMMs) by LP against STM, by measuring protein and cytokine levels, and bactericidal activity. In addition, we assessed the protective effects of LP against STM by evaluating weight loss, survival, the burden of STM in tissues, the polarization of macrophages in the spleen and mesenteric lymph nodes (MLNs), intestinal histopathology, and cytokine production. LP slightly affected the polarization of RAW 264.7, a slight M1-skewing. LP promoted the RAW 264.7 bactericidal activity against STM. In BMMs, M1 polarization induced by LP was significantly lower than the M1-positive phenotype. The combination of LP with M1 synergistically improved M1 polarization and bactericidal activity against STM compared to the individual effects. LP promoted the activation of the NF-κB signaling pathway. Supplementation with the NF-κB inhibitor decreased M1 polarization induced by LP. We observed the protective effect of LP against STM in C57BL/6 mice, through a decrease in weight loss, mortality, STM burden in the liver, and promotion of macrophage M1 and M2 polarization in the spleen and MLNs; though M1 was higher, it did not cause inflammatory damage. In summary, LP can synergistically promote M1 polarization in combination with the M1 phenotype through the NF-κB signaling pathway and increases resistance against S. Typhimurium infection. These findings will lay the foundation for the prevention and treatment of S. Typhimurium infections in the future.

Deferiprone has less benefits on gut microbiota and metabolites in high iron-diet induced iron overload thalassemic mice than in iron overload wild-type mice: A preclinical study

AIMS

This study aimed to investigate the changes in gut microbiota in iron-overload thalassemia and the roles of an iron chelator on gut dysbiosis/inflammation, and metabolites, including short-chain fatty acids (SCFAs) and trimethylamine N-oxide (TMAO).

MAIN METHODS

Adult male C57BL/6 mice both wild-type (WT: n = 15) and heterozygous β-thalassemia (BKO: n = 15) were fed on either a normal (ND: n = 5/group) or a high‑iron diet for four months (HFe: n = 10/group). HFe-treated WT and HFe-treated BKO groups were further subdivided into two subgroups and each subgroup given either vehicle (n = 5/subgroup) or deferiprone (n = 5/subgroup) during the last month. Gut microbiota profiles, gut barrier characteristics, levels of proinflammatory cytokines, and plasma SCFAs and TMAO were determined at the end of the study.

KEY FINDINGS

HFe-fed WT mice showed distinct gut microbiota profiles from those of ND-fed WT mice, whereas HFe-fed BKO mice showed slightly different gut microbiota profiles from ND-fed BKO. Gut inflammation and barrier disruption were found only in HFe-fed BKO mice, however, an increase in plasma TMAO levels and decreased levels of SCFAs were observed in both WT and BKO mice with HFe-feeding. Treatment with deferiprone, gut dysbiosis and disturbance of metabolites were attenuated in HFe-fed WT mice, but not in HFe-fed BKO mice. Increased Verrucomicrobia and Ruminococcaceae were associated with the beneficial effects of deferiprone.

SIGNIFICANCE

Iron-overload leads to gut dysbiosis/inflammation and disturbance of metabolites, and deferiprone alleviates those conditions more effectively in WT than in those that are thalassemic.

Effect of Inonotus obliquus polysaccharide on composition of the intestinal flora in mice with acute endometritis

Inonotus obliquus Polysaccharide (IOP) is a large molecule extracted from Inonotus obliqus, a medicinal fungus, which has a wide range of biological activities and has been shown to be associated with inflammation. The purpose of this study is to investigate whether IOP can help to reduce acute endometritis by regulating intestinal flora. We observed pathological changes in mice with endometritis following treatment with IOP and evaluated changes in the levels of interleukin-6 (IL-6), interleukin-1β (IL-1β) and tumor necrosis factor α (TNF-α), and further studied the effects of IOP on the intestinal flora of endometritis mice using 16S rRNA high-throughput sequencing. The results showed that IOP improved the condition of uterine tissues and reduced the release of pro-inflammatory cytokines. Meanwhile, the 16S rRNA sequencing results showed that IOP could regulate the changes in intestinal microflora at the level of genera, possibly by changing the relative abundance of some genera.

Anti-inflammatory Effect of Probiotic Limosilactobacillus reuteri KUB-AC5 Against Salmonella Infection in a Mouse Colitis Model

Acute non-typhoidal salmonellosis (NTS) caused by Salmonella enterica Typhimurium (STM) is among the most prevalent of foodborne diseases. A global rising of antibiotic resistance strains of STM raises an urgent need for alternative methods to control this important pathogen. Major human food animals which harbor STM in their gut are cattle, swine, and poultry. Previous studies showed that the probiotic Limosilactobacillus (Lactobacillus) reuteri KUB-AC5 (AC5) exhibited anti-Salmonella activities in chicken by modulating gut microbiota and the immune response. However, the immunobiotic effect of AC5 in a mammalian host is still not known. Here, we investigated the anti-Salmonella and anti-inflammatory effects of AC5 on STM infection using a mouse colitis model. Three groups of C57BL/6 mice (prophylactic, therapeutic, and combined) were fed with 10⁹ colony-forming units (cfu) AC5 daily for 7, 4, and 11 days, respectively. Then, the mice were challenged with STM compared to the untreated group. By using a specific primer pair, we found that AC5 can transiently colonize mouse gut (colon, cecum, and ileum). Interestingly, AC5 reduced STM gut proliferation and invasion together with attenuated gut inflammation and systemic dissemination in mice. The decreased STM numbers in mouse gut lumen, gut tissues, and spleen possibly came from longer AC5 feeding duration and/or the combinatorial (direct and indirect inhibitory) effect of AC5 on STM. However, AC5 attenuated inflammation (both in the gut and in the spleen) with no difference between these three approaches. This study demonstrated that AC5 confers both direct and indirect inhibitory effects on STM in the inflamed gut.