Neisseria meningitidis colonization of the brain endothelium and cerebrospinal fluid invasion

The brain and meningeal spaces are protected from bacterial invasion by the blood–brain barrier, formed by specialized endothelial cells and tight intercellular junctional complexes. However, once in the bloodstream, Neisseria meningitidis crosses this barrier in about 60% of the cases. This highlights the particular efficacy with which N. meningitidis targets the brain vascular cell wall. The first step of central nervous system invasion is the direct interaction between bacteria and endothelial cells. This step is mediated by the type IV pili, which induce a remodelling of the endothelial monolayer, leading to the opening of the intercellular space. In this review, strategies used by the bacteria to survive in the bloodstream, to colonize the brain vasculature and to cross the blood–brain barrier will be discussed.     

Targeting E. coli invasion of the blood–brain barrier for investigating the pathogenesis and therapeutic development of E. coli meningitis

Escherichia coli is the most common Gram‐negative bacillary organism causing neonatal meningitis. Escherichia coli meningitis remains an important cause of mortality and morbidity, but the pathogenesis of E. coli penetration of the blood–brain barrier remains incompletely understood. Escherichia coli entry into the brain occurs in the meningeal and cortex capillaries, not in the choroid plexus, and exploits epidermal growth factor receptor (EGFR) and cysteinyl leukotrienes (CysLTs) for invasion of the blood–brain barrier. The present study examined whether EGFR and CysLTs are inter‐related in their contribution to E. coli invasion of the blood–brain barrier and whether counteracting EGFR and CysLTs is a beneficial adjunct to antibiotic therapy of E. coli meningitis. We showed that (a) meningitis isolates of E. coli exploit EGFR and CysLTs for invasion of the blood–brain barrier, (b) the contribution of EGFR is upstream of that of CysLTs, and (c) counteracting EGFR and CysLTs as an adjunctive therapy improved the outcome (survival, neuronal injury and memory impairment) of animals with E. coli meningitis. These findings suggest that investigation of host factors contributing to E. coli invasion of the blood–brain barrier will help in enhancing the pathogenesis and development of new therapeutic targets for E. coli meningitis in the era of increasing resistance to conventional antibiotics.     

链球菌突破血脑屏障的作用机制研究进展

血脑屏障(blood-brain barrier,BBB)是中枢神经系统(central nervous system,CNS)的天然结构和功能屏障之一,可有效阻止病原菌的入侵。然而病原菌能通过其自身毒力因子与脑内皮细胞相互作用,诱导宿主免疫应答反应,分泌大量细胞因子、趋化因子等,破坏紧密连接蛋白,最终突破血脑屏障,引起细菌性脑膜炎,产生不可逆的神经系统损伤。链球菌(Streptococcus)作为引起细菌性脑膜炎的重要病原菌,关于其突破血脑屏障分子机制研究已有显著进展。本文针对主要的链球菌,包括肺炎链球菌(Streptococcus pneumoniae)、猪链球菌(Streptococcus suis)、B型链球菌(group B Streptococcus,GBS)、马链球菌等突破血脑屏障的作用机制研究进展进行综述。     

Interactions between Blood-Borne Streptococcus pneumoniae and the Blood-Brain Barrier Preceding Meningitis

Streptococcus pneumoniae (the pneumococcus) is a Gram-positive bacterium and the predominant cause of bacterial meningitis. Meningitis is thought to occur as the result of pneumococci crossing the blood-brain barrier to invade the Central Nervous System (CNS); yet little is known about the steps preceding immediate disease development. To study the interactions between pneumococci and the vascular endothelium of the blood-brain barrier prior to meningitis we used an established bacteremia-derived meningitis model in combination with immunofluorescent imaging. Brain tissue of mice infected with S. pneumoniae strain TIGR4, a clinical meningitis isolate, was investigated for the location of the bacteria in relation to the brain vasculature in various compartments. We observed that S. pneumoniae adhered preferentially to the subarachnoid vessels, and subsequently, over time, reached the more internal cerebral areas including the cerebral cortex, septum, and choroid plexus. Interestingly, pneumococci were not detected in the choroid plexus till 8 hours-post infection. In contrast to the lungs, little to no leukocyte recruitment to the brain was observed over time, though Iba-1 and GFAP staining showed that microglia and astrocytes were activated as soon as 1 hour post-infection. Our results imply that i) the local immune system of the brain is activated immediately upon entry of bacteria into the bloodstream and that ii) adhesion to the blood brain barrier is spatiotemporally controlled at different sites throughout the brain. These results provide new information on these two important steps towards the development of pneumococcal meningitis.     

Modeling tuberculous meningitis in zebrafish using Mycobacterium marinum

Tuberculous meningitis (TBM) is one of the most severe extrapulmonary manifestations of tuberculosis, with a high morbidity and mortality. Characteristic pathological features of TBM are Rich foci, i.e. brain- and spinal-cord-specific granulomas formed after hematogenous spread of pulmonary tuberculosis. Little is known about the early pathogenesis of TBM and the role of Rich foci. We have adapted the zebrafish model of Mycobacterium marinum infection (zebrafish–M. marinum model) to study TBM. First, we analyzed whether TBM occurs in adult zebrafish and showed that intraperitoneal infection resulted in granuloma formation in the meninges in 20% of the cases, with occasional brain parenchyma involvement. In zebrafish embryos, bacterial infiltration and clustering of infected phagocytes was observed after infection at three different inoculation sites: parenchyma, hindbrain ventricle and caudal vein. Infection via the bloodstream resulted in the formation of early granulomas in brain tissue in 70% of the cases. In these zebrafish embryos, infiltrates were located in the proximity of blood vessels. Interestingly, no differences were observed when embryos were infected before or after early formation of the blood-brain barrier (BBB), indicating that bacteria are able to cross this barrier with relatively high efficiency. In agreement with this observation, infected zebrafish larvae also showed infiltration of the brain tissue. Upon infection of embryos with an M. marinum ESX-1 mutant, only small clusters and scattered isolated phagocytes with high bacterial loads were present in the brain tissue. In conclusion, our adapted zebrafish–M. marinum infection model for studying granuloma formation in the brain will allow for the detailed analysis of both bacterial and host factors involved in TBM. It will help solve longstanding questions on the role of Rich foci and potentially contribute to the development of better diagnostic tools and therapeutics.KEY WORDS: Tuberculous meningitis, Tuberculosis, Zebrafish, Mycobacterium marinum, Blood-brain barrier, ESX-1 mutant     

Extracellular Bacterial Pathogen Induces Host Cell Surface Reorganization to Resist Shear Stress

Bacterial infections targeting the bloodstream lead to a wide array of devastating diseases such as septic shock and meningitis. To study this crucial type of infection, its specific environment needs to be taken into account, in particular the mechanical forces generated by the blood flow. In a previous study using Neisseria meningitidis as a model, we observed that bacterial microcolonies forming on the endothelial cell surface in the vessel lumen are remarkably resistant to mechanical stress. The present study aims to identify the molecular basis of this resistance. N. meningitidis forms aggregates independently of host cells, yet we demonstrate here that cohesive forces involved in these bacterial aggregates are not sufficient to explain the stability of colonies on cell surfaces. Results imply that host cell attributes enhance microcolony cohesion. Microcolonies on the cell surface induce a cellular response consisting of numerous cellular protrusions similar to filopodia that come in close contact with all the bacteria in the microcolony. Consistent with a role of this cellular response, host cell lipid microdomain disruption simultaneously inhibited this response and rendered microcolonies sensitive to blood flow–generated drag forces. We then identified, by a genetic approach, the type IV pili component PilV as a triggering factor of plasma membrane reorganization, and consistently found that microcolonies formed by a pilV mutant are highly sensitive to shear stress. Our study shows that bacteria manipulate host cell functions to reorganize the host cell surface to form filopodia-like structures that enhance the cohesion of the microcolonies and therefore blood vessel colonization under the harsh conditions of the bloodstream.     

Type IV pilus retraction enables sustained bacteremia and plays a key role in the outcome of meningococcal sepsis in a humanized mouse model

Neisseria meningitidis (the meningococcus) remains a major cause of bacterial meningitis and fatal sepsis. This commensal bacterium of the human nasopharynx can cause invasive diseases when it leaves its niche and reaches the bloodstream. Blood-borne meningococci have the ability to adhere to human endothelial cells and rapidly colonize microvessels. This crucial step enables dissemination into tissues and promotes deregulated inflammation and coagulation, leading to extensive necrotic purpura in the most severe cases. Adhesion to blood vessels relies on type IV pili (TFP). These long filamentous structures are highly dynamic as they can rapidly elongate and retract by the antagonistic action of two ATPases, PilF and PilT. However, the consequences of TFP dynamics on the pathophysiology and the outcome of meningococcal sepsis in vivo have been poorly studied. Here, we show that human graft microvessels are replicative niches for meningococci, that seed the bloodstream and promote sustained bacteremia and lethality in a humanized mouse model. Intriguingly, although pilus-retraction deficient N. meningitidis strain (ΔpilT) efficiently colonizes human graft tissue, this mutant did not promote sustained bacteremia nor induce mouse lethality. This effect was not due to a decreased inflammatory response, nor defects in bacterial clearance by the innate immune system. Rather, TFP-retraction was necessary to promote the release of TFP-dependent contacts between bacteria and, in turn, the detachment from colonized microvessels. The resulting sustained bacteremia was directly correlated with lethality. Altogether, these results demonstrate that pilus retraction plays a key role in the occurrence and outcome of meningococcal sepsis by supporting sustained bacteremia. These findings open new perspectives on the role of circulating bacteria in the pathological alterations leading to lethal sepsis.     

Spin trapping agent,phenyl N-tert-butylnitrone,reduces nitric oxide production in the rat brain during experimental meningitis

Phenyl N-tert-butylnitrone (PBN) is a spin trapping agent previously shown to exert a neuroprotective effect in infant rat brain during bacterial meningitis. In the present study, we investigated the effect of systemic PBN administration on nitric oxide (NO) production in a rat model of experimental meningitis induced by lipopolysaccharide (LPS). We assessed the NO concentration in rat brain tissues with an electron paramagnetic resonance (EPR) NO trapping technique. In this model, rats receiving intracisternal LPS administration showed symptoms of meningitis and cerebrospinal fluid (CSF) pleocytosis. The time course study indicated that the concentration of NO in the brain reached the maximum level 8.5h after injection of LPS, and returned to the control level 24 h after the injection. When various doses of PBN (125–400 mg/kg) were injected intraperitoneally 30 min prior to LPS, NO production in the brain was reduced with increasing PBN dose (250 mg/kg suppressed 80% at 8.5h after LPS injection), and white blood cells (WBC) in CSF were significantly decreased. We concluded that reduction of NO generation during bacterial meningitis contributes to the neuroprotective effect of PBN in addition to its possible direct scavenging of reactive oxygen intermediate (ROI).     

Rapid separation of bacteria from blood—review and outlook

The high morbidity and mortality rate of bloodstream infections involving antibiotic‐resistant bacteria necessitate a rapid identification of the infectious organism and its resistance profile. Traditional methods based on culturing the blood typically require at least 24 h, and genetic amplification by PCR in the presence of blood components has been problematic. The rapid separation of bacteria from blood would facilitate their genetic identification by PCR or other methods so that the proper antibiotic regimen can quickly be selected for the septic patient. Microfluidic systems that separate bacteria from whole blood have been developed, but these are designed to process only microliter quantities of whole blood or only highly diluted blood. However, symptoms of clinical blood infections can be manifest with bacterial burdens perhaps as low as 10 CFU/mL, and thus milliliter quantities of blood must be processed to collect enough bacteria for reliable genetic analysis. This review considers the advantages and shortcomings of various methods to separate bacteria from blood, with emphasis on techniques that can be done in less than 10 min on milliliter‐quantities of whole blood. These techniques include filtration, screening, centrifugation, sedimentation, hydrodynamic focusing, chemical capture on surfaces or beads, field‐flow fractionation, and dielectrophoresis. Techniques with the most promise include screening, sedimentation, and magnetic bead capture, as they allow large quantities of blood to be processed quickly. Some microfluidic techniques can be scaled up. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:823–839, 2016     

脑脊液检查在早产儿及足月儿细菌性脑膜炎的诊断价值

目的:评价脑脊液检查在早产儿及足月儿细菌性脑膜炎诊断中的价值。方法:选取2014年6月1日至2016年12月31日上海市儿童医院新生儿科收治的行腰椎穿刺检查的447例新生儿,回顾性分析新生儿的一般资料、脑脊液常规生化、培养等指标,根据胎龄将患儿分为早产儿167例与足月儿280例,再根据有无患发细菌性脑膜炎分为早产儿细菌性脑膜炎27例(早产儿观察组)、早产儿非细菌性脑膜炎140例(早产儿对照组)、足月儿细菌性脑膜炎38例(足月儿观察组)、足月儿非细菌性脑膜炎242例(足月儿对照组),采用受试者工作特征(ROC)曲线评估蛋白定量、白细胞计数、葡萄糖对早产儿及足月儿细菌性脑膜炎的诊断价值。结果:与同组对照组相比,足月儿观察组和早产儿观察组蛋白定量和白细胞计数均明显升高,而葡萄糖含量显著下降,且差异均具有统计学意义(P0.05);本研究65例细菌性脑膜炎患儿脑脊液培养分离出11株细菌(16.9%)。足月儿脑脊液白细胞计数、蛋白定量以及葡萄糖诊断细菌性脑膜炎的ROC曲线下面积分别为0.995、0.846、0.703。早产儿脑脊液白细胞计数、蛋白定量以及葡萄糖诊断细菌性脑膜炎ROC曲线下面积分别为0.970、0.711、0.705。结论:脑脊液白细胞计数、蛋白定量在足月儿和早产儿细菌性脑膜炎中具有较高的诊断价值。     

Escherichia coli K1 utilizes host macropinocytic pathways for invasion of brain microvascular endothelial cells

Eukaryotic cells utilize multiple endocytic pathways for specific uptake of ligands or molecules, and these pathways are commonly hijacked by pathogens to enable host cell invasion. Escherichia coli K1, a pathogenic bacterium that causes neonatal meningitis, invades the endothelium of the blood‐brain barrier, but the entry route remains unclear. Here, we demonstrate that the bacteria trigger an actin‐mediated uptake route, stimulating fluid phase uptake, membrane ruffling and macropinocytosis. The route of uptake requires intact lipid rafts as shown by cholesterol depletion. Using a variety of perturbants we demonstrate that small Rho GTPases and their downstream effectors have a significant effect on bacterial invasion. Furthermore, clathrin‐mediated endocytosis appears to play an indirect role in E. coli K1 uptake. The data suggest that the bacteria effect a complex interplay between the Rho GTPases to increase their chances of uptake by macropinocytosis into human brain microvascular endothelial cells.      

Identification of CiaR Regulated Genes That Promote Group B Streptococcal Virulence and Interaction with Brain Endothelial Cells

Group B Streptococcus (GBS) is a major causative agent of neonatal meningitis due to its ability to efficiently cross the blood-brain barrier (BBB) and enter the central nervous system (CNS). It has been demonstrated that GBS can invade human brain microvascular endothelial cells (hBMEC), a primary component of the BBB; however, the mechanism of intracellular survival and trafficking is unclear. We previously identified a two component regulatory system, CiaR/H, which promotes GBS intracellular survival in hBMEC. Here we show that a GBS strain deficient in the response regulator, CiaR, localized more frequently with Rab5, Rab7 and LAMP1 positive vesicles. Further, lysosomes isolated from hBMEC contained fewer viable bacteria following initial infection with the ΔciaR mutant compared to the WT strain. To characterize the contribution of CiaR-regulated genes, we constructed isogenic mutant strains lacking the two most down-regulated genes in the CiaR-deficient mutant, SAN_2180 and SAN_0039. These genes contributed to bacterial uptake and intracellular survival. Furthermore, competition experiments in mice showed that WT GBS had a significant survival advantage over the Δ2180 and Δ0039 mutants in the bloodstream and brain.     

The bacterial community of entomophilic nematodes and host beetles

Insects form the most species‐rich lineage of Eukaryotes and each is a potential host for organisms from multiple phyla, including fungi, protozoa, mites, bacteria and nematodes. In particular, beetles are known to be associated with distinct bacterial communities and entomophilic nematodes. While entomopathogenic nematodes require symbiotic bacteria to kill and reproduce inside their insect hosts, the microbial ecology that facilitates other types of nematode–insect associations is largely unknown. To illuminate detailed patterns of the tritrophic beetle–nematode–bacteria relationship, we surveyed the nematode infestation profiles of scarab beetles in the greater Los Angeles area over a five‐year period and found distinct nematode infestation patterns for certain beetle hosts. Over a single season, we characterized the bacterial communities of beetles and their associated nematodes using high‐throughput sequencing of the 16S rRNA gene. We found significant differences in bacterial community composition among the five prevalent beetle host species, independent of geographical origin. Anaerobes Synergistaceae and sulphate‐reducing Desulfovibrionaceae were most abundant in Amblonoxia beetles, while Enterobacteriaceae and Lachnospiraceae were common in Cyclocephala beetles. Unlike entomopathogenic nematodes that carry bacterial symbionts, insect‐associated nematodes do not alter the beetles' native bacterial communities, nor do their microbiomes differ according to nematode or beetle host species. The conservation of Diplogastrid nematodes associations with Melolonthinae beetles and sulphate‐reducing bacteria suggests a possible link between beetle–bacterial communities and their associated nematodes. Our results establish a starting point towards understanding the dynamic interactions between soil macroinvertebrates and their microbiota in a highly accessible urban environment.     

Cryptococcal meningitis with malaria

Cryptococcal meningitis is an uncommon infection globally, including Nigeria. This systemic fungal infection often is associated with immunodeficiency. The most common causes of meningitis in Nigeria in the 2–3 year age group are the malaria parasites and bacteria. The concomittant infections ofCryptococcal neoformans andPlasmodium falciparum are uncommon. We present here the report of a case of fatal cryptococcal meningitis with malaria infection in a 2 year old child from Nigeria (one of the malaria endemic regions of the world). This case emphasizes the importance of doing a combination of fungal and bacterial cultures as well as looking for malarial parasites in the determination of etiological agents of meningitis in any hospital in Africa. We suggest that cerebrospinal fluid from meningitis cases must be cultured using Sabouraud dextrose agar and any growth on the agar must be examined using Indian ink.     

Bacterial Cytolysin during Meningitis Disrupts the Regulation of Glutamate in the Brain,Leading to Synaptic Damage

Streptococcus pneumoniae (pneumococcal) meningitis is a common bacterial infection of the brain. The cholesterol-dependent cytolysin pneumolysin represents a key factor, determining the neuropathogenic potential of the pneumococci. Here, we demonstrate selective synaptic loss within the superficial layers of the frontal neocortex of post-mortem brain samples from individuals with pneumococcal meningitis. A similar effect was observed in mice with pneumococcal meningitis only when the bacteria expressed the pore-forming cholesterol-dependent cytolysin pneumolysin. Exposure of acute mouse brain slices to only pore-competent pneumolysin at disease-relevant, non-lytic concentrations caused permanent dendritic swelling, dendritic spine elimination and synaptic loss. The NMDA glutamate receptor antagonists MK801 and D-AP5 reduced this pathology. Pneumolysin increased glutamate levels within the mouse brain slices. In mouse astrocytes, pneumolysin initiated the release of glutamate in a calcium-dependent manner. We propose that pneumolysin plays a significant synapto- and dendritotoxic role in pneumococcal meningitis by initiating glutamate release from astrocytes, leading to subsequent glutamate-dependent synaptic damage. We outline for the first time the occurrence of synaptic pathology in pneumococcal meningitis and demonstrate that a bacterial cytolysin can dysregulate the control of glutamate in the brain, inducing excitotoxic damage.     

Activation of brain endothelium by pneumococcal neuraminidase NanA promotes bacterial internalization

Streptococcus pneumoniae (SPN), the leading cause of meningitis in children and adults worldwide, is associated with an overwhelming host inflammatory response and subsequent brain injury. Here we examine the global response of the blood–brain barrier to SPN infection and the role of neuraminidase A (NanA), an SPN surface anchored protein recently described to promote central nervous system tropism. Microarray analysis of human brain microvascular endothelial cells (hBMEC) during infection with SPN or an isogenic NanA‐deficient (ΔnanA) mutant revealed differentially activated genes, including neutrophil chemoattractants IL‐8, CXCL‐1, CXCL‐2. Studies using bacterial mutants, purified recombinant NanA proteins and in vivo neutrophil chemotaxis assays indicated that pneumococcal NanA is necessary and sufficient to activate host chemokine expression and neutrophil recruitment during infection. Chemokine induction was mapped to the NanA N‐terminal lectin‐binding domain with a limited contribution of the sialidase catalytic activity, and was not dependent on the invasive capability of the organism. Furthermore, pretreatment of hBMEC with recombinant NanA protein significantly increased bacterial invasion, suggesting that NanA‐mediated activation of hBMEC is a prerequisite for efficient SPN invasion. These findings were corroborated in an acute murine infection model where we observed less inflammatory infiltrate and decreased chemokine expression following infection with the ΔnanA mutant.     

Quercetin protects rats from catheter‐related Staphylococcus aureus infections by inhibiting coagulase activity

Coagulase (Coa) activity is essential for the virulence of Staphylococcus aureus (S aureus), one of the most important pathogenic bacteria leading to catheter‐related bloodstream infections (CRBSI). We have demonstrated that the mutation of coagulase improved outcomes in disease models of S aureus CRBSI, suggesting that targeting Coa may represent a novel antiinfective strategy for CRBSI. Here, we found that quercetin, a natural compound that does not affect S aureus viability, could inhibit Coa activity. Chemical biological analysis revealed that the direct engagement of quercetin with the active site (residues Tyr187, Leu221 and His228) of Coa inhibited its activity. Furthermore, treatment with quercetin reduced the retention of bacteria on catheter surfaces, decreased the bacterial load in the kidneys and alleviated kidney abscesses in vivo. These data suggest that antiinfective therapy targeting Coa with quercetin may represent a novel strategy and provide a new leading compound with which to combat bacterial infections.     

Detection of Bacteria in Phagocyte-Smears from Septicemia-Suspected Blood by In Situ Hybridization Using Biotinylated Probes

We report herein the detection of intracellular bacteria in phagocyte-smears obtained from septicemia-suspected blood samples by in situ hybridization. This was obtained by using nick-translated biotin-11-dUTP-labeled DNA probes and streptavidin-alkaline phosphatase conjugates for visualization of the hybridized signals. The probes were made from random genomic DNA clones of bacteria which are frequently the causative agents of bacteremia, such as Staphylococcus spp., Pseudomonas aeruginosa, Enterococcus faecalis, Escherichia coli, Klebsiella spp. and Enterobacter spp. When our in situ hybridization method was compared with conventional culture protocols for the ability to detect bacteria from the blood of patients suspected of having septicemia, 30 positive results were obtained in 50 specimens by in situ hybridization methods. In contrast, only 7 positive results were obtained by blood cultures. Thus, even if bacteria cannot be detected by conventional blood cultures and histology, our in situ hybridization method allows for direct observation of bacterial foci in circulating phagocytes and identification of the bacteria. Our investigations suggest that in septicemia, circulating polymorphonuclear neutrophils carry some surviving bacteria as well as metabolized bacterial DNA and RNA for a considerable period of time. Thus, our in situ hybridization method using the phagocyte-smears have diagnostic value for detecting most bacteria which cause septicemia.     

Development of hematogenous pneumococcal meningitis in adult mice: the role of TNF-alpha

Bacterial penetration across the blood-brain barrier (BBB) into the central nervous system is the first step in development of meningitis. The role of tumor necrosis factor-alpha (TNF-alpha) in the penetration process was examined with peripheral infection of Streptococcus pneumoniae type 6. After intraperitoneal infection of S. pneumoniae type 6, the BBB opening was increased continuously from 6 h and the mice died of septic shock within 36 h due to bacterial overgrowth. The bacteria crossed the BBB and began to deposit in brain at 6 h post infection. There was strong staining of TNF-alpha on blood vessels of brain from 6 h to 24 h post infection. Anti-TNF-alpha antibody blocked both the BBB opening and the entrance of circulatory S. pneumoniae type 6 into brain, indicating that TNF-alpha played an important role in controlling the opening of BBB. Furthermore, an adult murine model of hematogenous pneumococcal meningitis was developed that is based on opening of the BBB by TNF-alpha and controlling the degree of bacteremia by cefazolin antibiotic. In conclusion, hematogenous meningitis developed as TNF-alpha initiated BBB opening, peripheral bacteria entered into the brain and formed bacterial emboli, and then progressed to meningitis.     

Host tissues as microhabitats for Wolbachia and quantitative insights into the bacterial community in terrestrial isopods

Animal–bacterial symbioses are highly dynamic in terms of multipartite interactions, both between the host and its symbionts as well as between the different bacteria constituting the symbiotic community. These interactions will be reflected by the titres of the individual bacterial taxa, for example via host regulation of bacterial loads or competition for resources between symbionts. Moreover, different host tissues represent heterogeneous microhabitats for bacteria, meaning that host‐associated bacteria might establish tissue‐specific bacterial communities. Wolbachia are widespread endosymbiotic bacteria, infecting a large number of arthropods and filarial nematodes. However, relatively little is known regarding direct interactions between Wolbachia and other bacteria. This study represents the first quantitative investigation of tissue‐specific Wolbachia–microbiota interactions in the terrestrial isopod Armadillidium vulgare. To this end, we obtained a more complete picture of the Wolbachia distribution patterns across all major host tissues, integrating all three feminizing Wolbachia strains (wVulM, wVulC, wVulP) identified to date in this host. Interestingly, the different Wolbachia strains exhibited strain‐specific tissue distribution patterns, with wVulM reaching lower titres in most tissues. These patterns were consistent across different host genetic backgrounds and might reflect different co‐evolutionary histories between the Wolbachia strains and A. vulgare. Moreover, Wolbachia‐infected females carried higher total bacterial loads in several, but not all, tissues, irrespective of the Wolbachia strain. Taken together, this quantitative approach indicates that Wolbachia is part of a potentially more diverse bacterial community, as exemplified by the presence of highly abundant bacterial taxa in the midgut caeca of several A. vulgare populations.