The shapeshifting Helicobacter pylori: From a corkscrew to a ball.

There is growing evidence that bacterial morphology is closely related to their lifestyle. The helical Helicobacter pylori relies on its unique shape for survival and efficient colonization of the human stomach. Yet, they have been observed to transform into another distinctive morphology, the spherical coccoid. Despite being hypothesized to be involved in the persistence and transmission of this species, years of effort in deciphering the roles of the coccoid form remain fruitless since contrasting observations regarding its lifestyle were reported. Here, we discuss the two forms of H. pylori with a focus on the coccoid form, the molecular mechanism behind its morphological transformation, and experimental approaches to further develop our understanding of this phenomenon. We also propose a putative mechanism of the coccoid formation in H. pylori through induction of a type-I toxin-antitoxin (TA) system recently shown to influence the morphology of this species.

Ton motor conformational switch and peptidoglycan role in bacterial nutrient uptake.

Active nutrient uptake is fundamental for survival and pathogenicity of Gram-negative bacteria, which operate a multi-protein Ton system to transport essential nutrients like metals and vitamins. This system harnesses the proton motive force at the inner membrane to energize the import through the outer membrane, but the mechanism of energy transfer remains enigmatic. Here, we study the periplasmic domain of ExbD, a crucial component of the proton channel of the Ton system. We show that this domain is a dynamic dimer switching between two conformations representing the proton channel's open and closed states. By in vivo phenotypic assays we demonstrate that this conformational switch is essential for the nutrient uptake by bacteria. The open state of ExbD triggers a disorder to order transition of TonB, enabling TonB to supply energy to the nutrient transporter. We also reveal the anchoring role of the peptidoglycan layer in this mechanism. Herein, we propose a mechanistic model for the Ton system, emphasizing ExbD duality and the pivotal catalytic role of peptidoglycan. Sequence analysis suggests that this mechanism is conserved in other systems energizing gliding motility and membrane integrity. Our study fills important gaps in understanding bacterial motor mechanism and proposes novel antibacterial strategies.

Identification of a muropeptide precursor transporter from gut microbiota and its role in preventing intestinal inflammation.

The gut microbiota is a considerable source of biologically active compounds that can promote intestinal homeostasis and improve immune responses. Here, we used large expression libraries of cloned metagenomic DNA to identify compounds able to sustain an anti-inflammatory reaction on host cells. Starting with a screen for NF-κB activation, we have identified overlapping clones harbouring a heterodimeric ATP-binding cassette (ABC)-transporter from a Firmicutes. Extensive purification of the clone's supernatant demonstrates that the ABC-transporter allows for the efficient extracellular accumulation of three muropeptide precursor, with anti-inflammatory properties. They induce IL-10 secretion from human monocyte-derived dendritic cells and proved effective in reducing AIEC LF82 epithelial damage and IL-8 secretion in human intestinal resections. In addition, treatment with supernatants containing the muropeptide precursor reduces body weight loss and improves histological parameters in Dextran Sulfate Sodium (DSS)-treated mice. Until now, the source of peptidoglycan fragments was shown to come from the natural turnover of the peptidoglycan layer by endogenous peptidoglycan hydrolases. This is a report showing an ABC-transporter as a natural source of secreted muropeptide precursor and as an indirect player in epithelial barrier strengthening. The mechanism described here might represent an important component of the host immune homeostasis.

Activation of Nod2 signaling upon norovirus infection enhances antiviral immunity and susceptibility to colitis.

Over 90% of epidemic non-bacterial gastroenteritis are caused by human noroviruses (NoVs), which persist in a substantial subset of people allowing their spread worldwide. This has led to a significant number of endemic cases and up to 70,000 children deaths in developing countries. NoVs are primarily transmitted through the fecal-oral route. To date, studies have focused on the influence of the gut microbiota on enteric viral clearance by mucosal immunity. In this study, the use of mouse norovirus S99 (MNoV_S99) and CR6 (MNoV_CR6), two persistent strains, allowed us to provide evidence that the norovirus-induced exacerbation of colitis severity relied on bacterial sensing by nucleotide-binding oligomerization domain 2 (Nod2). Consequently, Nod2-deficient mice showed reduced levels of gravity of Dextran sodium sulfate (DSS)-induced colitis with both viral strains. And MNoV_CR6 viremia was heightened in Nod2-/- mice in comparison with animals hypomorphic for Atg16l1, which are prone to aggravated inflammation under DSS. Accordingly, the infection of macrophages derived from WT mice promoted the phosphorylation of Signal Transducer and Activator of Transcription 1 (STAT1) and NOD2's expression levels. Higher secretion of Tumor Necrosis Factor alpha (TNFα) following NOD2 activation and better viral clearance were measured in these cells. By contrast, reduced levels of pSTAT1 and blunted downstream secretion of TNFα were found in Nod2-deficient macrophages infected by MNoV_S99. Hence, our results uncover a previously unidentified virus-host-bacterial interplay that may represent a novel therapeutic target for treating noroviral origin gastroenteritis that may be linked with susceptibility to several common illnesses such as Crohn's disease.

Ton Motor Conformational Switch and Peptidoglycan Role in Bacterial Nutrient Uptake.

Active nutrient uptake is fundamental for survival and pathogenicity of Gram-negative bacteria, which operate a multi-protein Ton system to transport essential nutrients like metals and vitamins. This system harnesses the proton motive force at the inner membrane to energize the import through the outer membrane, but the mechanism of energy transfer remains enigmatic. Here, we study the periplasmic domain of ExbD, a crucial component of the proton channel of the Ton system. We show that this domain is a dynamic dimer switching between two conformations representing the proton channel's open and closed states. By in vivo phenotypic assays we demonstrate that this conformational switch is essential for the nutrient uptake by bacteria. The open state of ExbD triggers a disorder to order transition of TonB, enabling TonB to supply energy to the nutrient transporter. We also reveal the anchoring role of the peptidoglycan layer in this mechanism. Herein, we propose a mechanistic model for the Ton system, emphasizing ExbD duality and the pivotal catalytic role of peptidoglycan. Sequence analysis suggests that this mechanism is conserved in other systems energizing gliding motility and membrane integrity. Our study fills important gaps in understanding bacterial motor mechanism and proposes novel antibacterial strategies.

Cell envelope growth of Gram-negative bacteria proceeds independently of cell wall synthesis.

All bacterial cells must expand their envelopes during growth. The main load-bearing and shape-determining component of the bacterial envelope is the peptidoglycan cell wall. Bacterial envelope growth and shape changes are often thought to be controlled through enzymatic cell wall insertion. We investigated the role of cell wall insertion for cell shape changes during cell elongation in Gram-negative bacteria. We found that both global and local rates of envelope growth of Escherichia coli remain nearly unperturbed upon arrest of cell wall insertion-up to the point of sudden cell lysis. Specifically, cells continue to expand their surface areas in proportion to biomass growth rate, even if the rate of mass growth changes. Other Gram-negative bacteria behave similarly. Furthermore, cells plastically change cell shape in response to differential mechanical forces. Overall, we conclude that cell wall-cleaving enzymes can control envelope growth independently of synthesis. Accordingly, the strong overexpression of an endopeptidase leads to transiently accelerated bacterial cell elongation. Our study demonstrates that biomass growth and envelope forces can guide cell envelope expansion through mechanisms that are independent of cell wall insertion.

Microbe-mediated intestinal NOD2 stimulation improves linear growth of undernourished infant mice.

The intestinal microbiota is known to influence postnatal growth. We previously found that a strain of Lactiplantibacillus plantarum (strain LpWJL) buffers the adverse effects of chronic undernutrition on the growth of juvenile germ-free mice. Here, we report that LpWJL sustains the postnatal growth of malnourished conventional animals and supports both insulin-like growth factor-1 (IGF-1) and insulin production and activity. We have identified cell walls isolated from LpWJL, as well as muramyl dipeptide and mifamurtide, as sufficient cues to stimulate animal growth despite undernutrition. Further, we found that NOD2 is necessary in intestinal epithelial cells for LpWJL-mediated IGF-1 production and for postnatal growth promotion in malnourished conventional animals. These findings indicate that, coupled with renutrition, bacteria cell walls or purified NOD2 ligands have the potential to alleviate stunting.

Microbiota-induced active translocation of peptidoglycan across the intestinal barrier dictates its within-host dissemination.

Peptidoglycan, the major structural polymer forming the cell wall of bacteria, is an important mediator of physiological and behavioral effects in mammalian hosts. These effects are frequently linked to its translocation from the intestinal lumen to host tissues. However, the modality and regulation of this translocation across the gut barrier has not been precisely addressed. In this study, we characterized the absorption of peptidoglycan across the intestine and its systemic dissemination. We report that peptidoglycan has a distinct tropism for host organs when absorbed via the gut, most notably by favoring access to the brain. We demonstrate that intestinal translocation of peptidoglycan occurs through a microbiota-induced active process. This process is regulated by the parasympathetic pathway via the muscarinic acetylcholine receptors. Together, this study reveals fundamental parameters concerning the uptake of a major microbiota molecular signal from the steady-state gut.

NOD-like receptors in asthma.

Asthma is an extremely prevalent chronic inflammatory disease of the airway where innate and adaptive immune systems participate collectively with epithelial and other structural cells to cause airway hyperresponsiveness, mucus overproduction, airway narrowing, and remodeling. The nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) are a family of intracellular innate immune sensors that detect microbe-associated molecular patterns and damage-associated molecular patterns, well-recognized for their central roles in the maintenance of tissue homeostasis and host defense against bacteria, viruses and fungi. In recent times, NLRs have been increasingly acknowledged as much more than innate sensors and have emerged also as relevant players in diseases classically defined by their adaptive immune responses such as asthma. In this review article, we discuss the current knowledge and recent developments about NLR expression, activation and function in relation to asthma and examine the potential interventions in NLR signaling as asthma immunomodulatory therapies.

Alive Pathogenic and Saprophytic Leptospires Enter and Exit Human and Mouse Macrophages With No Intracellular Replication.

Leptospira interrogans are pathogenic bacteria responsible for leptospirosis, a zoonosis impacting 1 million people per year worldwide. Leptospires can infect all vertebrates, but not all hosts develop similar symptoms. Human and cattle may suffer from mild to acute illnesses and are therefore considered as sensitive to leptospirosis. In contrast, mice and rats remain asymptomatic upon infection, although they get chronically colonized in their kidneys. Upon infection, leptospires are stealth pathogens that partially escape the recognition by the host innate immune system. Although leptospires are mainly extracellular bacteria, it was suggested that they could also replicate within macrophages. However, contradictory data in the current literature led us to reevaluate these findings. Using a gentamicin-protection assay coupled to high-content (HC) microscopy, we observed that leptospires were internalized in vivo upon peritoneal infection of C57BL/6J mice. Additionally, three different serotypes of pathogenic L. interrogans and the saprophytic L. biflexa actively infected both human (PMA differentiated) THP1 and mouse RAW264.7 macrophage cell lines. Next, we assessed the intracellular fate of leptospires using bioluminescent strains, and we observed a drastic reduction in the leptospiral intracellular load between 3 h and 6 h post-infection, suggesting that leptospires do not replicate within these cells. Surprisingly, the classical macrophage microbicidal mechanisms (phagocytosis, autophagy, TLR-mediated ROS, and RNS production) were not responsible for the observed decrease. Finally, we demonstrated that the reduction in the intracellular load was associated with an increase of the bacteria in the supernatant, suggesting that leptospires exit both human and murine macrophages. Overall, our study reevaluated the intracellular fate of leptospires and favors an active entrance followed by a rapid exit, suggesting that leptospires do not have an intracellular lifestyle in macrophages.

Bacterial sensing via neuronal Nod2 regulates appetite and body temperature.

Gut bacteria influence brain functions and metabolism. We investigated whether this influence can be mediated by direct sensing of bacterial cell wall components by brain neurons. In mice, we found that bacterial peptidoglycan plays a major role in mediating gut-brain communication via the Nod2 receptor. Peptidoglycan-derived muropeptides reach the brain and alter the activity of a subset of brain neurons that express Nod2. Activation of Nod2 in hypothalamic inhibitory neurons is essential for proper appetite and body temperature control, primarily in females. This study identifies a microbe-sensing mechanism that regulates feeding behavior and host metabolism.

Dietary Lactobacillus-Derived Exopolysaccharide Enhances Immune-Checkpoint Blockade Therapy.

Microbes and their byproducts have been reported to regulate host health and immune functions. Here we demonstrated that microbial exopolysaccharide produced by Lactobacillus delbrueckii subsp. bulgaricus OLL1073R-1 (EPS-R1) induced CCR6+ CD8+ T cells of mice and humans. In mice, ingestion of EPS-R1 augmented antitumor effects of anti-CTLA-4 or anti-PD-1 monoclonal antibody against CCL20-expressing tumors, in which infiltrating CCR6+ CD8+ T cells were increased and produced IFNγ accompanied by a substantial immune response gene expression signature maintaining T-cell functions. Of note, the antitumor adjuvant effect of EPS-R1 was also observed in germ-free mice. Furthermore, the induction of CCR6 expression was mediated through the phosphorylated structure in EPS-R1 and a lysophosphatidic acid receptor on CD8+ T cells. Overall, we find that dietary EPS-R1 consumption induces CCR6+ CD8+ T cells in Peyer's patches, favoring a tumor microenvironment that augments the therapeutic effect of immune-checkpoint blockade depending on CCL20 production by tumors. SIGNIFICANCE: Gut microbiota- and probiotic-derived metabolites are attractive agents to augment the efficacy of immunotherapies. Here we demonstrated that dietary consumption of Lactobacillus-derived exopolysaccharide induced CCR6+ CD8+ T cells in Peyer's patches and improved the tumor microenvironment to augment the therapeutic effects of immune-checkpoint blockade against CCL20-producing tumors. See related commentary by Di Luccia and Colonna, p. 1189. This article is highlighted in the In This Issue feature, p. 1171.

Multifaceted modes of action of the anticancer probiotic Enterococcus hirae.

A deviated repertoire of the gut microbiome predicts resistance to cancer immunotherapy. Enterococcus hirae compensated cancer-associated dysbiosis in various tumor models. However, the mechanisms by which E. hirae restored the efficacy of cyclophosphamide administered with concomitant antibiotics remain ill defined. Here, we analyzed the multifaceted modes of action of this anticancer probiotic. Firstly, E. hirae elicited emigration of thymocytes and triggered systemic and intratumoral IFNγ-producing and CD137-expressing effector memory T cell responses. Secondly, E. hirae activated the autophagy machinery in enterocytes and mediated ATG4B-dependent anticancer effects, likely as a consequence of its ability to increase local delivery of polyamines. Thirdly, E. hirae shifted the host microbiome toward a Bifidobacteria-enriched ecosystem. In contrast to the live bacterium, its pasteurized cells or membrane vesicles were devoid of anticancer properties. These pleiotropic functions allow the design of optimal immunotherapies combining E. hirae with CD137 agonistic antibodies, spermidine, or Bifidobacterium animalis. We surmise that immunological, metabolic, epithelial, and microbial modes of action of the live E. hirae cooperate to circumvent primary resistance to therapy.

LpxT-Dependent Phosphorylation of Lipid A in Escherichia coli Increases Resistance to Deoxycholate and Enhances Gut Colonization.

The cell surface of Gram-negative bacteria usually exhibits a net negative charge mostly conferred by lipopolysaccharides (LPS). This property sensitizes bacterial cells to cationic antimicrobial peptides, such as polymyxin B, by favoring their binding to the cell surface. Gram-negative bacteria can modify their surface to counteract these compounds such as the decoration of their LPS by positively charged groups. For example, in Escherichia coli and Salmonella, EptA and ArnT add amine-containing groups to the lipid A moiety. In contrast, LpxT enhances the net negative charge by catalyzing the synthesis of tri-phosphorylated lipid A, whose function is yet unknown. Here, we report that E. coli has the intrinsic ability to resist polymyxin B upon the simultaneous activation of the two component regulatory systems PhoPQ and PmrAB by intricate environmental cues. Among many LPS modifications, only EptA- and ArnT-dependent decorations were required for polymyxin B resistance. Conversely, the acquisition of polymyxin B resistance compromised the innate resistance of E. coli to deoxycholate, a major component of bile. The inhibition of LpxT by PmrR, under PmrAB-inducing conditions, specifically accounted for the acquired susceptibility to deoxycholate. We also report that the kinetics of intestinal colonization by the E. coli lpxT mutant was impaired as compared to wild-type in a mouse model of infection and that lpxT was upregulated at the temperature of the host. Together, these findings highlight an important function of LpxT and suggest that a tight equilibrium between EptA- and LpxT-dependent decorations, which occur at the same position of lipid A, is critical for the life style of E. coli.

Cellular stress promotes NOD1/2-dependent inflammation via the endogenous metabolite sphingosine-1-phosphate.

Cellular stress has been associated with inflammation, yet precise underlying mechanisms remain elusive. In this study, various unrelated stress inducers were employed to screen for sensors linking altered cellular homeostasis and inflammation. We identified the intracellular pattern recognition receptors NOD1/2, which sense bacterial peptidoglycans, as general stress sensors detecting perturbations of cellular homeostasis. NOD1/2 activation upon such perturbations required generation of the endogenous metabolite sphingosine-1-phosphate (S1P). Unlike peptidoglycan sensing via the leucine-rich repeats domain, cytosolic S1P directly bound to the nucleotide binding domains of NOD1/2, triggering NF-κB activation and inflammatory responses. In sum, we unveiled a hitherto unknown role of NOD1/2 in surveillance of cellular homeostasis through sensing of the cytosolic metabolite S1P. We propose S1P, an endogenous metabolite, as a novel NOD1/2 activator and NOD1/2 as molecular hubs integrating bacterial and metabolic cues.

Acute monoarthritis in young children: comparing the characteristics of patients with juvenile idiopathic arthritis versus septic and undifferentiated arthritis.

Acute arthritis is a common cause of consultation in pediatric emergency wards. Arthritis can be caused by juvenile idiopathic arthritis (JIA), septic (SA) or remain undetermined (UA). In young children, SA is mainly caused by Kingella kingae (KK), a hard to grow bacteria leading generally to a mild clinical and biological form of SA. An early accurate diagnosis between KK-SA and early-onset JIA is essential to provide appropriate treatment and follow-up. The aim of this work was to compare clinical and biological characteristics, length of hospital stays, duration of intravenous (IV) antibiotics exposure and use of invasive surgical management of patients under 6 years of age hospitalized for acute monoarthritis with a final diagnosis of JIA, SA or UA. We retrospectively analyzed data from < 6-year-old children, hospitalized at a French tertiary center for acute mono-arthritis, who underwent a joint aspiration. Non-parametric tests were performed to compare children with JIA, SA or UA. Bonferroni correction for multiple comparisons was applied with threshold for significance at 0.025. Among the 196 included patients, 110 (56.1%) had SA, 20 (10.2%) had JIA and 66 (33.7%) had UA. Patients with JIA were older when compared to SA (2.7 years [1.8-3.6] versus 1.4 [1.1-2.1], p < 0.001). Presence of fever was not different between JIA and SA or UA. White blood cells in serum were lower in JIA (11.2 × 109/L [10-13.6]) when compared to SA (13.2 × 109/L [11-16.6]), p = 0.01. In synovial fluid leucocytes were higher in SA 105.5 × 103 cells/mm3 [46-211] compared to JIA and UA (42 × 103 cells/mm3 [6.4-59.2] and 7.29 × 103 cells/mm3 [2.1-72] respectively), p < 0.001. Intravenous antibiotics were administered to 95% of children with JIA, 100% of patients with SA, and 95.4% of UA. Arthrotomy-lavage was performed in 66.7% of patients with JIA, 79.6% of patients with SA, and 71.1% of patients with UA. In children less than 6 years of age with acute mono-arthritis, the clinical and biological parameters currently used do not reliably differentiate between JIA, AS and UA. JIA subgroups that present a diagnostic problem at the onset of monoarthritis before the age of 6 years, are oligoarticular JIA and systemic JIA with hip arthritis. The development of new biomarkers will be required to distinguish JIA and AS caused by Kingella kingae in these patients.

NOD1 sensing of house dust mite-derived microbiota promotes allergic experimental asthma.

BACKGROUND: Asthma severity has been linked to exposure to gram-negative bacteria from the environment that are recognized by NOD1 receptor and are present in house dust mite (HDM) extracts. NOD1 polymorphism has been associated with asthma. OBJECTIVE: We sought to evaluate whether either host or HDM-derived microbiota may contribute to NOD1-dependent disease severity. METHODS: A model of HDM-induced experimental asthma was used and the effect of NOD1 deficiency was evaluated. Contribution of host microbiota was evaluated by fecal transplantation. Contribution of HDM-derived microbiota was assessed by 16S ribosomal RNA sequencing, mass spectrometry analysis, and peptidoglycan depletion of the extracts. RESULTS: In this model, loss of the bacterial sensor NOD1 and its adaptor RIPK2 improved asthma features. Such inhibitory effect was not related to dysbiosis caused by NOD1 deficiency, as shown by fecal transplantation of Nod1-deficient microbiota to wild-type germ-free mice. The 16S ribosomal RNA gene sequencing and mass spectrometry analysis of HDM allergen, revealed the presence of some muropeptides from gram-negative bacteria that belong to the Bartonellaceae family. While such HDM-associated muropeptides were found to activate NOD1 signaling in epithelial cells, peptidoglycan-depleted HDM had a decreased ability to instigate asthma in vivo. CONCLUSIONS: These data show that NOD1-dependent sensing of HDM-associated gram-negative bacteria aggravates the severity of experimental asthma, suggesting that inhibiting the NOD1 signaling pathway may be a therapeutic approach to treating asthma.

Effect of gut microbiota on depressive-like behaviors in mice is mediated by the endocannabinoid system.

Depression is the leading cause of disability worldwide. Recent observations have revealed an association between mood disorders and alterations of the intestinal microbiota. Here, using unpredictable chronic mild stress (UCMS) as a mouse model of depression, we show that UCMS mice display phenotypic alterations, which could be transferred from UCMS donors to naïve recipient mice by fecal microbiota transplantation. The cellular and behavioral alterations observed in recipient mice were accompanied by a decrease in the endocannabinoid (eCB) signaling due to lower peripheral levels of fatty acid precursors of eCB ligands. The adverse effects of UCMS-transferred microbiota were alleviated by selectively enhancing the central eCB or by complementation with a strain of the Lactobacilli genus. Our findings provide a mechanistic scenario for how chronic stress, diet and gut microbiota generate a pathological feed-forward loop that contributes to despair behavior via the central eCB system.

Cross-reactivity between tumor MHC class I-restricted antigens and an enterococcal bacteriophage.

Intestinal microbiota have been proposed to induce commensal-specific memory T cells that cross-react with tumor-associated antigens. We identified major histocompatibility complex (MHC) class I-binding epitopes in the tail length tape measure protein (TMP) of a prophage found in the genome of the bacteriophage Enterococcus hirae Mice bearing E. hirae harboring this prophage mounted a TMP-specific H-2Kb-restricted CD8+ T lymphocyte response upon immunotherapy with cyclophosphamide or anti-PD-1 antibodies. Administration of bacterial strains engineered to express the TMP epitope improved immunotherapy in mice. In renal and lung cancer patients, the presence of the enterococcal prophage in stools and expression of a TMP-cross-reactive antigen by tumors correlated with long-term benefit of PD-1 blockade therapy. In melanoma patients, T cell clones recognizing naturally processed cancer antigens that are cross-reactive with microbial peptides were detected.

Study of the cwaRS-ldcA Operon Coding a Two-Component System and a Putative L,D-Carboxypeptidase in Lactobacillus paracasei.

The cell surface is the primary recognition site between the bacterium and the host. An operon of three genes, LSEI_0219 (cwaR), LSEI_0220 (cwaS), and LSEI_0221 (ldcA), has been previously identified as required for the establishment of Lactobacillus paracasei in the gut. The genes cwaR and cwaS encode a predicted two-component system (TCS) and ldcA a predicted D-alanyl-D-alanine carboxypeptidase which is a peptidoglycan (PG) biosynthesis enzyme. We explored the functionality and the physiological role of these three genes, particularly their impact on the bacterial cell wall architecture and on the bacterial adaptation to environmental perturbations in the gut. The functionality of CwaS/R proteins as a TCS has been demonstrated by biochemical analysis. It is involved in the transcriptional regulation of several genes of the PG biosynthesis. Analysis of the muropeptides of PG in mutants allowed us to re-annotate LSEI_0221 as a putative L,D-carboxypeptidase (LdcA). The absence of this protein coincided with a decrease of two surface antigens: LSEI_0020, corresponding to p40 or msp2 whose implication in the host epithelial homeostasis has been recently studied, and LSEI_2029 which has never been functionally characterized. The inactivation of each of these three genes induces susceptibility to antimicrobial peptides (hBD1, hBD2, and CCL20), which could be the main cause of the gut establishment deficiency. Thus, this operon is necessary for the presence of two surface antigens and for a suitable cell wall architecture.