Eubiotic vs. dysbiotic human blood microbiota: the phenomenon of cell wall deficiency and disease-trigger potential of bacterial and fungal L-forms.

The current review provides data and focuses on blood as a niche for the presence of cell wall-deficient microbes (L-forms). The hypothesis for the existence of L-form microbiota in humans was tested by us using an innovative methodology for the isolation of L-form cultures from human blood. Criteria were conceived for the individual assessment of blood microbiota and recognition of two types of states -- "eubiotic" and "dysbiotic" blood microbiota. Cell wall-deficient microbes (CWD) that inhabit blood in healthy people are in natural balance with the host homeostasis, which corresponds to the "eubiotic" state. When interacting with a host, CWD bacteria or fungi employ a strategy distinctive for a latent lifestyle. In contrast to "eubiotic," "dysbiotic" blood microbiota manifests when the balance is disrupted and there is an excess of L-form variants of opportunistic microbes that invade from the external microbiota, i.e., from all body sites in contact with the external environment. Our case studies on people with multiple sclerosis (MS), Parkinson's disease, psoriasis, thyroid cancer, and diabetes revealed the appearance of "dysbiotic" blood microbiota that outlined the disease-trigger potential of opportunistic bacteria and fungi existing in blood as CWD variants. Blood microbiota assessment could be of diagnostic and prognostic importance for the pathological processes occurring within the body, as well as for understanding the microbial pathogenesis.

Investigation of the Relationship Between BK Virus and Human Leukocyte Antigens in Kidney Transplant Recipients.

OBJECTIVES: The main function of HLA is to present antigens to lymphocytes and to initiate specific immune responses. Autoimmune, viral, allergic, and neurologic diseases have been found to be related to HLA molecules. In renal transplant, the main target of the recipient's immune system is the HLA molecules on the surface of donor cells. HLA also plays a role in the development of an immune response to viral infections. After renal transplant, BK virus infections may occur due to immunosuppression. Here, we investigated the relationship between HLA and BK virus in renal transplant recipients. MATERIALS AND METHODS: This retrospective study investigated HLA-A, HLA-B, and HLA-DR tissue typing before renal transplant. DNA was isolated from whole blood, and tissue typing tests were performed based on polymerase chain reaction. Patients were tested for BK virus posttransplant using DNA isolated from urine and/or plasma samples. RESULTS: We found HLA-B*13 allele to be a protective factor (P < .049; odds ratio: 0.131; 95% confidence interval, 0.017-1.029) and HLA-DRB1*03 allele to be a possible risk factor (P < .029; odds ratio: 2.521; 95% confidence interval, 1.157-5.490) against BK virus. No significant relationships were found between BK virus and age, sex, donor type, and HLA mismatch. CONCLUSIONS: HLA class I molecules are known to be effective against viruses with the help of cytotoxic T cells. HLA-B*13 alleles within the HLA class I molecules were identified as protective factors against BK virus. HLA class II is associated with CD4-positive T cells that help secrete immune system cytokines, playing a role in stimulating and suppressing the immune system. We demonstrated that HLA-DRB1*03 allele could be a risk factor against BK virus. This allele may be associated with immunomodulatory cytokine secretion of the immune system.

Phase I, Dose-Escalating Study of the Safety and Pharmacokinetics of Inhaled Dry-Powder Vancomycin (AeroVanc) in Volunteers and Patients with Cystic Fibrosis: a New Approach to Therapy for Methicillin-Resistant Staphylococcus aureus.

Methicillin-resistant Staphylococcus aureus (MRSA) has become a significant acute and chronic respiratory pathogen. While vancomycin is effective against MRSA, its relatively poor penetration into lung secretions and dose-limiting renal toxicity make it less effective in the respiratory setting. As inhaled administration of vancomycin would overcome these limitations, we developed a dry powder formulation suitable for inhalation (AeroVanc). Here, we report a phase I, single-dose, dose-escalating study aimed at demonstrating safety and tolerability of AeroVanc. In part I, 18 healthy subjects received a single dose of 16 mg, 32 mg, or 80 mg of AeroVanc. Two subjects also received a 250-mg dose of intravenous vancomycin. In part 2 of the study, 32 mg and 80 mg AeroVanc were administered to subjects with cystic fibrosis as single doses. There were no serious side effects. A small drop in forced expiratory volume in 1 s (FEV1) was observed in 3 subjects with cystic fibrosis, one of whom required salbutamol. Vancomycin was rapidly absorbed after inhalation. Peak and mean plasma concentrations of vancomycin were dose proportional. The average minimum concentration of vancomycin in sputum remained above the usual MIC values for MRSA for up to 24 h (minimum sputum concentration [Cmin], 32-mg dose = 3.05 µg/ml, 80-mg dose = 8.0 µg/ml). In conclusion, AeroVanc was well tolerated and achieved high levels in sputum with a mean systemic absorption of 49%, making it a potential therapeutic strategy for respiratory infection with MRSA.

Innate and Adaptive Immune Correlates of Chronic and Self-limiting EBV DNAemia in Solid-organ Transplant Recipients.

BACKGROUND: Epstein-Barr virus (EBV) DNAemia is a major risk factor for posttransplant lymphoproliferative disorder; however, immune correlates of EBV DNAemia in the transplant setting are limited. METHODS: Peripheral blood mononuclear cells were collected from 30 transplant recipients with self-limiting EBV DNAemia (SLD; n = 11) or chronic EBV DNAemia (CD; n = 19) at enrollment and 4-8 weeks later. Mass cytometry was used to characterize innate and T-cell immune correlates of EBV DNAemia. Furthermore, flow cytometry was used to measure the frequency of EBV-specific T-cell responses between groups following stimulation with an EBV-infected cell lysate. RESULTS: Unsupervised analysis of the innate compartment (CD3CD19 cells) identified 5 CD11c clusters at higher abundance in the SLD group (false discovery rate ≤ 1%). These clusters expressed CD11b, CD45RO, CD14, CD123, CD127, and CD38, among others. Unsupervised profiling of the T-cell compartment (CD3CD19) revealed 2 CD4 T-cell clusters at higher frequency among those with SLD (false discovery rate ≤ 1%), which expressed CD45RA, CCR7, CD27, CD28, and CD40L-suggestive of a naive T cell (TN). Manual biaxial gating confirmed increased frequencies of conventional dendritic cells (3.1% versus 2.1%; P = 0.023) and CD4 TN (4.4% versus 1.9%; P = 0.018) among those with SLD. Last, frequencies of interferon-γ-producing EBV-specific CD4 T cells were significantly lower in the CD group relative to those with SLD (4243 versus 250 cells/10 cells; P = 0.015). CONCLUSIONS: CD is associated with a reduction of CD11c cells, CD4 TN, and interferon-γ-producing EBV-specific CD4 T cells, suggesting an interplay between innate and adaptive immune compartments may be important for regulating EBV DNAemia.

Polymerase chain reaction blood tests for the diagnosis of invasive aspergillosis in immunocompromised people.

BACKGROUND: This is an update of the original review published in the Cochrane Database of Systematic Reviews Issue 10, 2015.Invasive aspergillosis (IA) is the most common life-threatening opportunistic invasive mould infection in immunocompromised people. Early diagnosis of IA and prompt administration of appropriate antifungal treatment are critical to the survival of people with IA. Antifungal drugs can be given as prophylaxis or empirical therapy, instigated on the basis of a diagnostic strategy (the pre-emptive approach) or for treating established disease. Consequently, there is an urgent need for research into both new diagnostic tools and drug treatment strategies. Increasingly, newer methods such as polymerase chain reaction (PCR) to detect fungal nucleic acids are being investigated. OBJECTIVES: To provide an overall summary of the diagnostic accuracy of PCR-based tests on blood specimens for the diagnosis of IA in immunocompromised people. SEARCH METHODS: We searched MEDLINE (1946 to June 2015) and Embase (1980 to June 2015). We also searched LILACS, DARE, Health Technology Assessment, Web of Science and Scopus to June 2015. We checked the reference lists of all the studies identified by the above methods and contacted relevant authors and researchers in the field. For this review update we updated electronic searches of the Cochrane Central Register of Controlled Trials (CENTRAL; 2018, Issue 3) in the Cochrane Library; MEDLINE via Ovid (June 2015 to March week 2 2018); and Embase via Ovid (June 2015 to 2018 week 12). SELECTION CRITERIA: We included studies that: i) compared the results of blood PCR tests with the reference standard published by the European Organisation for Research and Treatment of Cancer/Mycoses Study Group (EORTC/MSG); ii) reported data on false-positive, true-positive, false-negative and true-negative results of the diagnostic tests under investigation separately; and iii) evaluated the test(s) prospectively in cohorts of people from a relevant clinical population, defined as a group of individuals at high risk for invasive aspergillosis. Case-control and retrospective studies were excluded from the analysis. DATA COLLECTION AND ANALYSIS: Authors independently assessed quality and extracted data. For PCR assays, we evaluated the requirement for either one or two consecutive samples to be positive for diagnostic accuracy. We investigated heterogeneity by subgroup analyses. We plotted estimates of sensitivity and specificity from each study in receiver operating characteristics (ROC) space and constructed forest plots for visual examination of variation in test accuracy. We performed meta-analyses using the bivariate model to produce summary estimates of sensitivity and specificity. MAIN RESULTS: We included 29 primary studies (18 from the original review and 11 from this update), corresponding to 34 data sets, published between 2000 and 2018 in the meta-analyses, with a mean prevalence of proven or probable IA of 16.3 (median prevalence 11.1% , range 2.5% to 57.1%). Most patients had received chemotherapy for haematological malignancy or had undergone hematopoietic stem cell transplantation. Several PCR techniques were used among the included studies. The sensitivity and specificity of PCR for the diagnosis of IA varied according to the interpretative criteria used to define a test as positive. The summary estimates of sensitivity and specificity were 79.2% (95% confidence interval (CI) 71.0 to 85.5) and 79.6% (95% CI 69.9 to 86.6) for a single positive test result, and 59.6% (95% CI 40.7 to 76.0) and 95.1% (95% CI 87.0 to 98.2) for two consecutive positive test results. AUTHORS' CONCLUSIONS: PCR shows moderate diagnostic accuracy when used as screening tests for IA in high-risk patient groups. Importantly the sensitivity of the test confers a high negative predictive value (NPV) such that a negative test allows the diagnosis to be excluded. Consecutive positives show good specificity in diagnosis of IA and could be used to trigger radiological and other investigations or for pre-emptive therapy in the absence of specific radiological signs when the clinical suspicion of infection is high. When a single PCR positive test is used as the diagnostic criterion for IA in a population of 100 people with a disease prevalence of 16.3% (overall mean prevalence), three people with IA would be missed (sensitivity 79.2%, 20.8% false negatives), and 17 people would be unnecessarily treated or referred for further tests (specificity of 79.6%, 21.4% false positives). If we use the two positive test requirement in a population with the same disease prevalence, it would mean that nine IA people would be missed (sensitivity 59.6%, 40.4% false negatives) and four people would be unnecessarily treated or referred for further tests (specificity of 95.1%, 4.9% false positives). Like galactomannan, PCR has good NPV for excluding disease, but the low prevalence of disease limits the ability to rule in a diagnosis. As these biomarkers detect different markers of disease, combining them is likely to prove more useful.

[Pancytopenia of unknown origin in a 52-year-old patient]. / Unklare Panzytopenie bei einem 52-jährigen Patienten.

A 52-year-old patient developed pancytopenia of unknown origin 1.5 years after allogeneic stem cell transplantation. The bone marrow aspirate showed visceral leishmaniasis (VL). Although VL is distributed world-wide, the incidence in patients after allogeneic stem cell transplantation is rare.

Combination of sepsis biomarkers may indicate an invasive fungal infection in haematological patients.

Background: Invasive fungal infections are a major threat to a large cohort of immunocompromised patients, including patients with chemotherapy-associated neutropenia. Early differential diagnosis with bacterial infections is often complicated, which leads to a delay in empirical antifungal therapy and increases risk for adverse outcome. Accessibility and performance of specific fungal antigen and PCR-tests are still limited, while sepsis biomarkers are more broadly used in most settings currently. Methods: Haematological patients hospitalized to receive chemotherapy with proven or probable invasive fungal infection or microbiologically proven bacterial bloodstream infection were included in the study. C-reactive protein was assessed daily during the profound neutropenia period, while procalcitonin or presepsin were measured during the first 48 hours after the onset of febrile episode. Results: There were totally 64 patients included in the study, 53 with bacterial bloodstream infections and 11 with invasive fungal infections. Combination of CRP >120 with PCT <1.25 or presepsin <170 was shown to be a possible combined biomarker for invasive fungal infections in immunocompromised patients, with areas under the ROC-curves: 0.962 (95% CI 0.868 to 0.995) for PCT-based combination and 0.907 (95% CI 0.692 to 0.990) for presepsin-based combination.

Torque Teno Virus Is Associated With the State of Immune Suppression Early After Liver Transplantation.

The development of noninvasive biomarkers that reflect the state of immunosuppression (IS) remains an unmet need in liver transplantation (LT). Torque Teno virus (TTV) is a highly prevalent, nonpathogenic DNA virus whose plasma levels may be associated with the immune status of the host. The aim of this study was to assess the role of TTV as a biomarker of IS in LT recipients. TTV DNA in plasma was quantified by real-time polymerase chain reaction at different time points during the first year after transplant in a prospectively followed cohort of 63 de novo LT recipients, and any correlation between TTV DNA and biopsy-proven acute cellular rejection (ACR) and opportunistic infections was then evaluated. In addition, TTV DNA was studied in 10 longterm LT recipients in monotherapy with tacrolimus, 10 tolerant recipients, and 10 healthy controls. TTV was detected in the plasma of all patients. Among the 63 LT recipients, 20 episodes of ACR were diagnosed, and there were 28 opportunistic infections, 26 of them being cytomegalovirus (CMV) infections. TTV viremia was significantly lower during ACR (4.41 versus 5.95 log10 copies/mL; P = 0.002) and significantly higher during CMV infections (5.79 versus 6.59 log10 copies/mL; P = 0.009). The area under the receiver operating characteristic curve of TTV viral load for the diagnosis of moderate ACR was 0.869, with a sensitivity and negative predictive value of 100%, respectively, for a cutoff point of 4.75 log10 copies/mL. There were no statistically significant differences in TTV DNA in either longterm or tolerant patients and healthy controls. In conclusion, plasma TTV DNA levels are associated with immune-related events after LT and could constitute a potential biomarker of the state of IS during the first months after transplant.

Visceral leishmaniasis in hematopoietic cell transplantation: Case report and review of the literature.

Visceral leishmaniasis has been recognized as an opportunistic infection affecting people with cellular-immunity impairment, including hematopoietic cell transplantation (HCT) recipients. We describe the case of a young Italian man with Hodgkin lymphoma, who developed visceral leishmaniasis after multiple lines of chemotherapy and allogenic HCT. Literature review of visceral leishmaniasis in HCT recipients was also performed. Eleven patients (median age 50 years, 9 male) developed visceral leishmaniasis after allogenic (n = 9) and autologous (n = 2) HCT. Most of them presented with fever and pancytopenia. Bone marrow examination was the main diagnostic technique; liposomal amphotericin B was the treatment of choice. Four out of eight patients (for whom data are available) experienced visceral leishmaniasis relapse. Visceral leishmaniasis in HCT recipients is a rare event that should be suspected in patients with persistent fever, pancytopenia and possible exposure to Leishmania spp., remembering that - as well as South-East Asia, East Africa and South America - it is endemic in several European regions.

Mediastinitis superinfected by Achromobacter xylosoxidans. A case report.

We describe an extremely rare case of mediastinitis superinfected by emerging Achromobacter xylosoxidans. After mitral and aortic valves replacement, the patient first developed a Staphylococcus aureus mediastinitis, and five days after starting adapted antibiotic therapy, superficial pus analysis revealed the presence of Achromobacter xylosoxidans. This superinfection was considered superficial and focus was made on Staphylococcus aureus mediastinitis. Three weeks later, no more Staphylococcus aureus was found in pus samples and the sepsis seemed under control. Unfortunately, blood cultures were again positive for Achromobacter xylosoxidans three weeks later and the patient died from septic shock.

Specific Immunity to Cytomegalovirus in Pediatric Cardiac Transplantation.

BACKGROUND: Cytomegalovirus (CMV) infection is implicated in endothelial dysfunction and graft damage after pediatric heart transplantation. CMV-specific immune responses are thought to be necessary for CMV viral control but there is little data in pediatric heart transplantation. METHODS: We studied 28 consecutive pediatric heart transplant recipients for 1 year posttransplant. CMV T-cell expressing IFN-γ, TNF-α, and IL-2 in response to ex vivo stimulation with CMV lysates or peptides were measured. Circulating cytokines were measured in plasma. Generalized Additive Models were applied to the data to model changes of cell population dynamics over time. RESULTS: CMV-specific T cell-mediated responses were impaired in the first 8 weeks posttransplant. During this period, 25% of patients had CMV viremia, of which those with VLs of 10 000 or more CMV deoxyribonucleic acid copies/mL were given ganciclovir. In this group, the frequency of CD4+ and CD8+ T cells producing IFN-γ and the CD8+CD57+ granzyme B+ T-cell population increased at 12 to 24 weeks and remained elevated for the duration of the study. CONCLUSIONS: We have shown that CMV viremia is associated with CMV-specific immune responses and increased CD8+CD57+ granzyme B+ cells at 1 year posttransplant; however, early responses were not predictive of impending CMV viremia. It remains to be seen if the early CMV immune response detected is associated with endothelial and allograft damage, in light of previous studies demonstrating increased vasculopathy in pediatric patients with CMV viremia.

Cortisol level as risk factor for malignant hematologic pathology in children exposed to ionizing radiation after Chornobyl accident. / STAN ERYTROÏDNOÏ, GRANULOTsYTARNOÏ TA TROMBOTsYTARNOÏ LANOK GEMOPOEZU NA ETAPAKh KhIMIOTERAPIÏ U DITEY̆ Z GOSTRYMY LIMFOBLASTNYMY LEY̆KEMIIaMY, IaKI ZAZNALY VPLYVU IONIZUIuChOGO VYPROMINIuVANNIa VNASLIDOK AVARIÏ NA ChAES.

OBJECTIVE: Determination of serum cortisol level in the initial period of acute leukemia in children, who exposed to ion izing radiation and other factors of Chornobyl accident, depending on their age and prognosis of disease. MATERIALS AND METHODS: The study involved 283 children residents of Kyiv, Zhytomyr and Chernihiv regions. There were 90 acute leukemia patients(AL) (ALL - 56, AML - 34), and 193 people of comparison group with anemia, leukemoid reactions and lymphadenopathy. We analyzed the type of comorbid somatic pathology, diseases in the genealogy, hematological parameters, cortisol levels in blood serum and irradiation doses in all children. In patients with AL expected median survival was calculated. RESULTS: In 28.9 % of AL children the initial cortisol content was below 200 nmol/l, in 7.8 % - higher than 500 nmol/l (in the comparison group 10.4 % and 17.1 % respectively). Among AL patients with cortisol levels below 200 nmol/l were significantly less amount of persons with chronic bacterial infections and persistent viral infections (CMV, EBV) and in the genealogy of these children allergic reactions, endocrine pathology diagnosed more often compared with patients, whose hormone levels was higher than 200 nmol/l (p < 0.05). Distribution of children from control group by gradations of cortisol, age groups, defined somatic pathology and diseases in genealogy had no difference. It is shown, that lower initial blood serum cortisol level in ALL children correlates to a greater probability of relapse (Rs = -0,67). In patients with AML a direct correlation between cortisol level and median survival was detected (Rs = 0,79). Children radiation doses were ranging from 0.08 mSv to 14.9 mSv, and there were slightly higher among residents of Zhytomyr region (8.4 ± 1.2 mSv) compared to other regions. However, these doses did not affect blood serum cortisol levels in children and the course of AL. CONCLUSIONS: These data suggest the need for correction and individualization of corticosteroid doses for optimization of AL patients treatment. Children, who have lower than normative serum cortisol levels are at increased risk of hema tologic pathology and they need for hematologic monitoring.

Persistent anemia in a kidney transplant recipient with parvovirus B19 infection.

Anemia after kidney transplant is not uncommon. This paper reports a case of unexplained anemia in a kidney transplant recipient that persisted for more than two months, and that did not respond to recombinant human erythropoietin treatment but was successfully treated after diagnosing Parvovirus B19 (ParvoV B19) infection. A middle-aged male underwent living-unrelated kidney transplantation from Pakistan in April 2015. He was on triple immuno-suppression therapy consisting of prednisolone, tacrolimus, and mycophenolate mofetil. He presented with anemia which persisted for more than two months that did not improve with Darbepoetin alpha and required blood transfusions. A bone marrow biopsy demonstrated pure erythroid hypoplasia and occasional giant pronormoblasts characteristic of a ParvoV B19 infection. The serum was highly positive for ParvoV B19 DNA polymerase chain reaction. The anemia resolved completely three weeks after the administration of intravenous immunoglobulin. ParvoV B19 infection should be considered in the differential diagnosis of kidney transplant recipients who present with anemia associated with a low reticulocyte count.

Seroprevalence of cytomegalovirus in donors & opportunistic viral infections in liver transplant recipients.

BACKGROUND & OBJECTIVES: Opportunistic virus infections are common in liver transplant (LT) recipients. There is a risk of developing infection with cytomegalovirus (CMV) and herpes-related viruses such as herpes simplex virus-1 and 2 (HSV-1 & 2), Epstein-Barr virus (EBV) and Varicella Zoster virus (VZV), reactivation of infection and recurrent infection. This study was conducted to determine CMV seropositivity in donors and its influence on LT recipients and seropositivity of CMV, HSV-1 and 2, EB viral capsid antigen (EBVCA) and VZV in LT recipients and their reactivation. METHODS: Pre-transplant data for IgG and IgM for CMV (and donor), HSV-1 and -2, EB viral capsid antigen (VCA) and VZV were available for 153 recipients. All recipients were on ganciclovir or valganciclovir prophylaxis for three months after LT. For reactivation rates, findings of post-transplant CMV quantitative reverse transcription polymerase chain reaction (CMV qRT-PCR) assay were associated with pre-transplant serological profile. RESULTS: Of the 153 LT recipients, 131 were men (85.6%). The median age of LT was 46 yr (range 9 months-71 yr). Overall exposure to CMV was 71.8 per cent followed by EB VCA (61.4%) and VZV (49.6%). Susceptibility to both HSV-1 and -2 was high across all decades (P<0.001). Seropositivity of CMV in donor was 90.9 per cent (100 out of 110). Post-transplant CMV qRT- PCR was positive in 17 (26.6%; 3 in recipient negative) of 64 samples tested. qRT-PCR assay was positive in one out of four (25%) tested for HSV-1 and nine out of 19 (47.4%) tested for EBV. Two recipients tested for HSV-2 and one for VZV were negative. There were three deaths in recipients (D+ R+) who were also positive for CMV qRT PCR. There was one death due to HSV-1 pneumonia. One patient with EBV reactivation developed post-transplant lymphoproliferative disorder two years after transplant. INTERPRETATION & CONCLUSIONS: Transplant recipient were at highest risk of acquiring HSV-1 and -2 more so for HSV-2. CMV exposure in transplant recipients and donors were very high and at greatest risk for recipient reactivation rate. Despite this, death related to CMV reactivation was low.

Pseudozyma and other non-Candida opportunistic yeast bloodstream infections in a large stem cell transplant center.

Non-Candida opportunistic yeasts are emerging causes of bloodstream infection (BSI) in immunocompromised hosts. However, their clinical presentation, management, and outcomes in stem cell transplant (SCT) recipients are not well described. We report the first case to our knowledge of Pseudozyma BSI in a SCT recipient. He had evidence of cutaneous involvement, which has not been previously described in the literature. He became infected while neutropenic and receiving empiric micafungin, which is notable because Pseudozyma is reported to be resistant to echinocandins. He was successfully treated with the sequential use of liposomal amphotericin B and voriconazole. A review of the literature revealed nine reported instances of Pseudozyma fungemia. We performed a retrospective review of 3557 SCT recipients at our institution from January 2000 to June 2015 and identified four additional cases of non-Candida yeast BSIs. These include two with Cryptococcus, one with Trichosporon, and one with Saccharomyces. Pseudozyma and other non-Candida yeasts are emerging pathogens that can cause severe and disseminated infections in SCT recipients and other immunocompromised hosts. Clinicians should have a high degree of suspicion for echinocandin-resistant yeasts, if patients develop breakthrough yeast BSIs while receiving echinocandin therapy.

A Mouse Model of Post-Stroke Pneumonia Induced by Intra-Tracheal Inoculation with Streptococcus pneumoniae.

BACKGROUND: Stroke-induced immunodeficiency increases the risk of infectious complications, which adversely affects neurological outcome. Among those, pneumonia affects as many as one third of stroke patients and is the main contributor to mortality in the post-acute phase of stroke. Experimental findings on post-stroke susceptibility to spontaneous pneumonia in mice are contradictory. Here, we established a mouse model inducing standardized bacterial pneumonia and characterized the impaired pulmonary cellular and humoral immune responses after experimental stroke. METHODS: Bacterial pneumonia was induced by intra-tracheal inoculation with Streptococcus pneumoniae at different time points after transient middle cerebral artery occlusion (MCAO). Bacterial counts in lungs and blood, histological changes, and cytokine production in the lungs were assessed. Furthermore, we investigated the effect of pneumonia on stroke outcome. RESULTS: Intra-tracheal inoculation resulted in reproducible pneumonia and bacteraemia, and demonstrated post-stroke susceptibility to streptococcal pneumonia developing with a delay of at least 24 h after MCAO. Higher bacterial counts in mice infected 3 days after stroke induction correlated with reduced neutrophil and macrophage infiltration in the lungs and lower levels of pro-inflammatory cytokines in the broncho-alveolar lavage compared to sham-operated animals. Pneumonia increased mortality without affecting brain-infiltrating leukocytes. CONCLUSIONS: In this standardized mouse model of post-stroke pneumonia, we describe attenuated leukocyte infiltration and cytokine production in response to bacterial infection in the lungs that has a profound effect on outcome.