Magnitude of bacteremia and complement activation during Neisseria meningitidis infection: study of two co-primary cases with different clinical presentations

Neisseria meningitidis accumulate in large organs during meningococcal sepsis

Background

Neisseria meningitidis (Nm) is the cause of epidemic meningitis and fulminant meningococcal septicemia. The clinical presentations and outcome of meningococcal septic shock is closely related to the circulating levels of lipopolysaccharides (LPS) and of Neisseria meningitidis DNA (Nm DNA). We have previously explored the distribution of Nm DNA in tissues from large organs of patients dying of meningococcal septic shock and in a porcine meningococcal septic shock model.

Objective

1) To explore the feasibility of measuring LPS levels in tissues from the large organs in patients with meningococcal septic shock and in a porcine meningococcal septic shock model. 2) To evaluate the extent of contamination of non-specific LPS during the preparation of tissue samples.

Patients and methods

Plasma, serum, and fresh frozen (FF) tissue samples from the large organs of three patients with lethal meningococcal septic shock and two patients with lethal pneumococcal disease. Samples from a porcine meningococcal septic shock model were included. Frozen tissue samples were thawed, homogenized, and prepared for quantification of LPS by Pyrochrome® Limulus Amoebocyte Lysate (LAL) assay.

Results

N. meningitidis DNA and LPS was detected in FF tissue samples from large organs in all patients with meningococcal septic shock. The lungs are the organs with the highest LPS and Nm DNA concentration followed by the heart in two of the three meningococcal shock patients. Nm DNA was not detected in any plasma or tissue sample from patients with lethal pneumococcal infection. LPS was detected at a low level in all FF tissues from the two patients with lethal pneumococcal disease. The experimental porcine meningococcal septic shock model indicates that also in porcinis the highest LPS and Nm DNA concentration are detected in lungs tissue samples. The quantification analysis showed that the highest concentration of both Nm DNA and LPS are in the organs and not in the circulation of patients with lethal meningococcal septic shock. This was also shown in the experimental porcine meningococcal septic shock model.

Conclusion

Our results suggest that LPS can be quantified in mammalian tissues by using the LAL assay.

Detection and DNA quantification of Enterococcus casseliflavus in a foal with septic meningitis

CASE DESCRIPTION A 3-month-old 180-kg (396-lb) Hanoverian colt was examined because of fever, lethargy, inappetence, drooping of the left ear, and stiff neck posture. Initial treatment included empirical antimicrobial treatment and NSAIDs. CLINICAL FINDINGS Initial findings were consistent with CNS anomalies. Endoscopy revealed hyperemia, ecchymosis, and some mucopurulent exudate in the right guttural pouch. Hematologic findings were consistent with neutrophilic inflammation. On the third day of hospitalization, severe neurologic signs were observed. Computed tomography of the skull revealed a comminuted fracture of the axial aspect of the right mandibular condyle. Examination of CSF revealed turbidity, xanthochromia, and intracellular and extracellular cocci, consistent with septic meningitis. After DNA extraction from blood and CSF, sequenced products from a PCR assay for the bacterial 16S rRNA gene were 99% identical to Enterococcus casseliflavus. Microbial culture of CSF and blood samples yielded bacteria with Enterococcus spp morphology; antimicrobials were selected on the basis of susceptibility testing that identified the isolate as vancomycin resistant. A quantitative PCR assay was used to estimate Enterococcus DNA concentrations in CSF and blood. TREATMENT AND OUTCOME Treatment for E casseliflavus meningitis, including trimethoprim-sulfadiazine and ampicillin sodium administration, resulted in resolution of clinical signs. Culture of CSF and blood samples after 12 days of the targeted treatment yielded no growth. CLINICAL RELEVANCE To the authors' knowledge, this was the first report of E casseliflavus meningitis in a horse. Treatment was successful; vancomycin-resistant enterococci can be a clinical problem and may potentially be zoonotic.

Use of quantitative broad-based polymerase chain reaction for detection and identification of common bacterial pathogens in cerebrospinal fluid

BACKGROUND

Conventional laboratory diagnosis of bacterial meningitis based on microscopy followed by culture is time-consuming and has only moderate sensitivity.

OBJECTIVES

The objective was to define the limit of detection (LOD), analytic specificity, and performance characteristics of a broad-based quantitative multiprobe polymerase chain reaction (PCR) assay for rapid bacterial detection and simultaneous pathogen-specific identification in patients with suspected meningitis.

METHODS

A PCR algorithm consisting of initial broad-based detection of Eubacteriales by a universal probe, followed by pathogen identification using either pathogen-specific probes or Gram-typing probes, was employed to detect pathogens. The 16S rRNA gene, which contains both conserved and variable regions, was chosen as the target. Pathogen-specific probes were designed for Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae, Staphylococcus epidermidis, Staphylococcus aureus, Escherichia coli, and Listeria monocytogenes. Gram-positive and -negative typing probes were designed based on conserved regions across all eubacteria. The LOD and time to detection were assessed by dilutional mocked-up samples. A total of 108 convenience cerebrospinal fluid (CSF) clinical samples obtained from the Johns Hopkins Hospital (JHH) microbiology laboratory were tested, and results were compared with hospital microbiologic culture reports.

RESULTS

The LOD of the assay ranged from 10(1) to 10(2) colony-forming units (CFU)/mL. Pathogen-specific probes showed no cross-reactivity with other organisms. Time to detection was 3 hours. In clinical specimens, the universal probe correctly detected 16 of 22 culture-positive clinical specimens (sensitivity = 72.7%; 95% confidence interval [CI] = 49.8% to 89.3%), which were all correctly characterized by either pathogen-specific or Gram-typing probes. Adjusted sensitivity after removing probable microbiologic laboratory contaminants was 88.9% (95% CI = 65.3% to 98.6%). The universal probe was negative for 86 of 86 culture-negative specimens.

CONCLUSIONS

A broad-based multiprobe PCR assay demonstrated strong analytic performance characteristics. Findings from a pilot clinical study showed promise in translation to human subjects, supporting potential utility of the assay as an adjunct to traditional diagnostics for early identification of bacterial meningitis.

Functional significance of factor H binding to Neisseria meningitidis

Neisseria meningitidis is an important cause of septicemia and meningitis. To cause disease, the bacterium must successfully survive in the bloodstream where it has to avoid being killed by host innate immune mechanisms, particularly the complement system. A number of pathogenic microbes bind factor H (fH), the negative regulator of the alternative pathway of complement activation, to promote their survival in vivo. In this study, we show that N. meningitidis binds fH to its surface. Binding to serogroups A, B, and C N. meningitidis strains was detected by FACS and Far Western blot analysis, and occurred in the absence of other serum factors such as C3b. Unlike Neisseria gonorrhoeae, binding of fH to N. meningitidis was independent of sialic acid on the bacterium, either as a component of its LPS or its capsule. Characterization of the major fH binding partner demonstrated that it is a 33-kDa protein; examination of insertion mutants showed that porins A and B, outer membrane porins expressed by N. meningitidis, do not contribute significantly to fH binding. We examined the physiological consequences of fH bound to the bacterial surface. We found that fH retains its activity as a cofactor of factor I when bound to the bacterium and contributes to the ability of N. meningitidis to avoid complement-mediated killing in the presence of human serum. Therefore, the recruitment of fH provides another mechanism by which this important human pathogen evades host innate immunity.

Use of robotized DNA isolation and real-time PCR to quantify and identify close correlation between levels of Neisseria meningitidis DNA and lipopolysaccharides in plasma and cerebrospinal fluid from patients with systemic meningococcal disease

The present study, using robotized DNA isolation and quantitative PCR based on the Neisseria meningitidis-specific capsular transport A gene, demonstrates the ease, rapidity, specificity, and sensitivity of quantifying neisserial DNA in plasma (n = 65) and cerebrospinal fluid (CSF) (n = 12) from patients with systemic meningococcal disease. We found a close correlation between the levels of neisserial DNA and lipopolysaccharides in plasma (r = 0.905) and in CSF (r = 0.964). The median concentration of neisserial DNA in plasma in 23 patients with persistent shock was 2 x 10(7) copies/ml, versus <10(3) copies/ml in 42 nonshock patients. Furthermore, quantitative PCR made possible estimates of the total number of meningococci in plasma, as opposed to conventional blood cultures, suggesting about 1,000 dead meningococci for every viable bacterium. Finally, with logistic regression analyses, neisserial DNA may predict a patient's disease severity and outcome at hospital admission. The number of meningococci in plasma and CSF appears to be the main determinant of the lipopolysaccharide levels, clinical presentation, and outcome.

Meningococcal bacterial DNA load at presentation correlates with disease severity

AIMS

To determine bacterial loads in meningococcal disease (MCD), their relation with disease severity, and the factors which determine bacterial load.

METHODS

Meningococcal DNA quantification was performed by the Taqman PCR method on admission and sequential blood samples from patients with MCD. Disease severity was assessed using the Glasgow Septicaemia Prognostic Score (GMSPS, range 0-15, severe disease > or =8).

RESULTS

Median admission bacterial load was 1.6 x 10(6) DNA copies/ml of blood (range 2.2 x 10(4) to 1.6 x 10(8)). Bacterial load was significantly higher in patients with severe (8.4 x 10(6)) compared to milder disease (1.1 x 10(6), p = 0.018). This difference was greater in septicaemic patients (median 1.6 x 10(7) versus 9.2 x 10(5), p < 0.001). Bacterial loads were significantly higher in patients that died (p = 0.017). Admission bacterial load was independent of the duration of clinical symptoms prior to admission, with no difference between the duration of symptoms in mild or severe cases (median, 10.5 and 11 hours respectively). Bacterial loads were independent of DNA elimination rates following treatment.

CONCLUSION

Patients with MCD have higher bacterial loads than previously determined with quantitative culture methods. Admission bacterial load is significantly higher in patients with severe disease (GMSPS > or =8) and maximum load is highest in those who die. Bacterial load is independent of the duration of clinical symptoms or the decline in DNA load.

Gram-negative bacteria induce proinflammatory cytokine production by monocytes in the absence of lipopolysaccharide (LPS)

Tumour necrosis factor-alpha (TNF-alpha), IL-1alpha and IL-6 production by human monocytes in response to a clinical strain of the Gram-negative encapsulated bacteria Neisseria meningitidis and an isogenic lpxA- strain deficient in LPS was investigated. Wild-type N. meningitidis at concentrations between 105 and 108 organisms/ml and purified LPS induced proinflammatory cytokine production. High levels of these cytokines were also produced in response to the lpxA- strain at 107 and 108 organisms/ml. The specific LPS antagonist bactericidal/permeability-increasing protein (rBPI21) inhibited cytokine production induced by LPS and wild-type bacteria at 105 organisms/ml but not at higher concentrations, and not by LPS-deficient bacteria at any concentration. These data show that proinflammatory cytokine production by monocytes in response to N. meningitidis does not require the presence of LPS. Therapeutic strategies designed to block LPS alone may not therefore be sufficient for interrupting the inflammatory response in severe meningococcal disease.

Complement deficiency states and meningococcal disease

Analysis of complement deficiency states has supported the role of complement in host defense and elucidated diseases associated with defective complement function. Although neisserial infection plays a prominent role in these deficiency states, examination of individuals with late complement component deficiency (LCCD) reveals a particular propensity for recurrent meningococcal disease and provides important clues to the role of complement in neisserial infections. In response to meningococcal disease, LCCD individuals produce significantly greater amounts of antilipooligosaccharide (LOS) antibody which can kill group B meningococcus in a complement-sufficient in vitro system. Further studies of antibody cross-reactivity to other meningococci has led to a clearer understanding of its epitopic specificity. Nevertheless, epidemiologic evidence is consistent with the relative absence of protective immunity in LCCD persons following an episode of infection and supported by quantitation of antibody to capsular polysaccharide. However, compared to anti-LOS antibodies, anticapsular antibodies can offer immune protection to LCCD individuals via complement-dependent opsonophagocytosis--the only form of complement-mediated killing available to these persons. Thus vaccination of LCCD persons with capsular antigens is considered an important means of protecting these high-risk individuals against meningococcal disease.

Infectious diseases associated with complement deficiencies

The complement system consists of both plasma and membrane proteins. The former influence the inflammatory response, immune modulation, and host defense. The latter are complement receptors, which mediate the cellular effects of complement activation, and regulatory proteins, which protect host cells from complement-mediated injury. Complement activation occurs via either the classical or the alternative pathway, which converge at the level of C3 and share a sequence of terminal components. Four aspects of the complement cascade are critical to its function and regulation: (i) activation of the classical pathway, (ii) activation of the alternative pathway, (iii) C3 convertase formation and C3 deposition, and (iv) membrane attack complex assembly and insertion. In general, mechanisms evolved by pathogenic microbes to resist the effects of complement are targeted to these four steps. Because individual complement proteins subserve unique functional activities and are activated in a sequential manner, complement deficiency states are associated with predictable defects in complement-dependent functions. These deficiency states can be grouped by which of the above four mechanisms they disrupt. They are distinguished by unique epidemiologic, clinical, and microbiologic features and are most prevalent in patients with certain rheumatologic and infectious diseases. Ethnic background and the incidence of infection are important cofactors determining this prevalence. Although complement undoubtedly plays a role in host defense against many microbial pathogens, it appears most important in protection against encapsulated bacteria, especially Neisseria meningitidis but also Streptococcus pneumoniae, Haemophilus influenzae, and, to a lesser extent, Neisseria gonorrhoeae. The availability of effective polysaccharide vaccines and antibiotics provides an immunologic and chemotherapeutic rationale for preventing and treating infection in patients with these deficiencies.