Andreas Wellmer

Rifampin Reduces Early Mortality in Experimental Streptococcus pneumoniae Meningitis

Compared with beta-lactam antibiotics, rifampin releases smaller quantities of proinflammatory cell wall products from Streptococcus pneumoniae in vitro. Mice infected intracerebrally with S. pneumoniae were treated subcutaneously with 2-mg doses of rifampin or ceftriaxone (n=43 each) every 12 h for 3 days and then observed for another 3 days. Rifampin reduced overall mortality from 49% to 26% (P=.04). Kaplan-Meyer analysis revealed a substantial reduction of mortality during the first 24 h in mice receiving rifampin (difference in survival time: P=.007). Eight h after receiving a single 2-mg dose of rifampin or ceftriaxone, rifampin-treated mice had lower serum and cerebrospinal fluid concentrations of lipoteichoic and teichoic acids than did ceftriaxone-treated mice (median serum level: <0.5 vs. 27.0 ng/mL, P=.02; median cerebrospinal fluid level of pooled specimens: 97.5 vs. 206.0 ng/mL). Thus, the use of rifampin appears promising for reducing the release of proinflammatory bacterial components and decreasing early mortality in bacterial meningitis.

Decreased Virulence of a Pneumolysin-Deficient Strain of Streptococcus pneumoniae in Murine Meningitis

ABSTRACT Pneumolysin, neuraminidases A and B, and hyaluronidase are virulence factors of Streptococcus pneumoniae that appear to be involved in the pathogenesis of meningitis. In a murine model of meningitis after intracerebral infection using mutants of S. pneumoniae D39, only mice infected with a pneumolysin-deficient strain were healthier at 32 and 36 h, had lower bacterial titers in blood at 36 h, and survived longer than the D39 parent strain. Cerebellar and spleen bacterial titers, meningeal inflammation, and neuronal damage scores remained uninfluenced by the lack of any of the virulence factors.

Spatial memory and learning deficits after experimental pneumococcal meningitis in mice

Survivors of bacterial meningitis frequently suffer from long-term sequelae, particularly from learning and memory deficits. For this reason, spatial memory and learning was studied in a mouse model of ceftriaxone-treated Streptococcus pneumoniae meningitis. Persistent deficits of spatial learning despite normal motor function were observed in mice infected with 10(4) colony-forming units (CFU) in 25 microl of saline into the right forebrain in comparison to mice treated with an equal amount of saline. Survivors of meningitis performed significantly worse in memorizing a hidden platform in a Morris water maze. After 2 weeks, the difference between post-meningitis and control mice diminished. Yet, when the platform was moved after 180 days, learning of the new location was still strongly impaired in mice surviving meningitis.

Rifampin Reduces Production of Reactive Oxygen Species of Cerebrospinal Fluid Phagocytes and Hippocampal Neuronal Apoptosis in Experimental Streptococcus pneumoniae Meningitis

Bacterial compounds induce the production of reactive oxygen species (ROS) in meningitis. Rifampin releases smaller quantities of proinflammatory compounds from Streptococcus pneumoniae than do beta-lactam antibiotics. Therefore, rabbits infected intracisternally with S. pneumoniae were treated intravenously either with rifampin 5 mg/kg/h or ceftriaxone 10 mg/kg/h (n=9 each). Before initiation of antibiotic treatment, a strong positive correlation between ROS production of cerebrospinal fluid (CSF) phagocyte populations and bacterial CSF titers was observed (granulocytes: rs=.90, P<.0001; monocytes: rs=.81, P<.0001). CSF leukocytes from rifampin-treated rabbits produced less ROS (monocytes at 2 h after initiation of treatment: P=.045; at 5 h: P=.014; granulocytes at 5 h: P=.036) than did leukocytes from animals receiving ceftriaxone. The CSF malondialdehyde concentrations and the density of apoptotic neurons in the dentate gyrus were lower in rifampin- than in ceftriaxone-treated animals (P=.002 and.005). The use of rifampin to reduce the release of ROS and to decrease secondary brain injury appears promising.

Activity of LY333328 in experimental meningitis caused by a Streptococcus pneumoniae strain susceptible to penicillin

ABSTRACT In a rabbit model of Streptococcus pneumoniaemeningitis single doses of 10 and 2.5 mg of the glycopeptide LY333328 per kg of body weight reduced bacterial titers in cerebrospinal fluid (CSF) almost as rapidly as ceftriaxone at 10 mg/kg/h (changes in log CFU, −0.29 ± 0.21 and −0.26 ± 0.22 versus −0.34 ± 0.15/ml/h). A dose of 1 mg/kg was bacteriostatic (change in log CFU, 0.01 ± 0.11/ml/h). In two animals receiving LY333328 at a dose of 40 mg/kg the bacterial titers were reduced by 0.54 and 0.51 log CFU/ml/h. The penetration of CSF by LY333328 was 1 to 5%. The concentrations of lipoteichoic and teichoic acids in CSF and neuronal damage were similar in ceftriaxone- and LY333328-treated animals.

Ly-6G+CCR2− Myeloid Cells Rather Than Ly-6ChighCCR2+ Monocytes Are Required for the Control of Bacterial Infection in the Central Nervous System

Myeloid cell recruitment is a characteristic feature of bacterial meningitis. However, the cellular mechanisms important for the control of Streptococcus pneumoniae infection remain largely undefined. Previous pharmacological or genetic studies broadly depleted many myeloid cell types within the meninges, which did not allow defining the function of specific myeloid subsets. Herein we show that besides CD11b+Ly-6G+CCR2− granulocytes, also CD11b+Ly-6ChighCCR2+ but not Ly-6ClowCCR2− monocytes were recruited in high numbers to the brain as early as 12 h after bacterial challenge. Surprisingly, CD11b+Ly-6ChighCCR2+ inflammatory monocytes modulated local CXCL2 and IL-1β production within the meninges but did not provide protection against bacterial infection. Consistent with these results, CCR2 deficiency strongly impaired monocyte recruitment to the infected brains but was redundant for disease pathogenesis. In contrast, specific depletion of polymorphonuclear granulocytes caused elevated local bacterial titer within the brains, led to an aggravated clinical course, and enhanced mortality. These findings demonstrate that Ly-6ChighCCR2+ inflammatory monocytes play a redundant role for the host defense during bacterial meningitis and that predominantly CD11b+Ly-6G+CCR2− myeloid cells are involved in the restriction of the extracellular bacteria.

Gemifloxacin Is Effective in Experimental Pneumococcal Meningitis

ABSTRACT In a rabbit model of Streptococcus pneumoniaemeningitis, 5 mg of gemifloxacin mesylate (SB-265805) per kg/h reduced the bacterial titers in cerebrospinal fluid (CSF) almost as rapidly as 10 mg of ceftriaxone per kg/h (Δlog CFU/ml/h ± standard deviation [SD], −0.25 ± 0.09 versus −0.38 ± 0.11; serum and CSF concentrations of gemifloxacin were 2.1 ± 1.4 mg/liter and 0.59 ± 0.38 mg/liter, respectively, at 24 h). Coadministration of 1 mg of dexamethasone per kg did not affect gemifloxacin serum and CSF levels (2.7 ± 1.4 mg/liter and 0.75 ± 0.34 mg/liter, respectively, at 24 h) or activity (Δlog CFU/ml/h ± SD, −0.26 ± 0.11).

Transcriptional regulation of caspases in experimental pneumococcal meningitis.

Apoptosis and necrosis in brain account for neurological sequelae in survivors of bacterial meningitis. In meningitis, several mechanisms may trigger death pathways leading to activation of transcription factors regulating caspases mRNA synthesis. Therefore, we used a multiprobe RNA protection assay (RPA) to examine the expression of 9 caspase‐mRNA in the course of experimental Streptococcus pneumoniae meningitis in mouse brain. Caspase‐6, ‐7 and ‐11 mRNA were elevated 6 hours after infection. 12 hours after infection caspases‐1, ‐2, ‐8 and ‐12 mRNA rose. Caspase‐14 mRNA was elevated 18 h and caspase‐3 mRNA 24 h after infection. In situ hybridization detected caspases‐3, ‐8, ‐11 and ‐12 mRNA in neurons of the hippocampal formation and neocortex. Development of sepsis was paralleled by increased transcription of caspases mRNA in the spleen.

Protein synthesis inhibiting clindamycin improves outcome in a mouse model of Staphylococcus aureus sepsis compared with the cell wall active ceftriaxone.

Objective The release of proinflammatory components from bacteria depends on the mode of action of the antibacterial therapy used. We studied whether this influences mortality in experimental sepsis. Design In a lethal murine model of Staphylococcus aureus sepsis, animals were randomly assigned to receive the protein synthesis inhibitor clindamycin (CLI) or the &bgr;-lactam ceftriaxone (CRO). Setting Therapy was introduced subcutaneously 5 hrs after intraperitoneal injection of 10 colony forming units of S. aureus American Type Culture Collection 29213 and was continued every 8 hrs for 3 days. Measurements and Results Survival was higher in mice receiving CLI (29/50 animals [58%]) than in mice receiving CRO (16/50 animals [32%];p = .015). Mice treated with CRO died earlier than mice receiving CLI (p = .002). Eight hours after the first antibiotic dose, the motor performance of mice receiving CRO had deteriorated more than it did for mice receiving CLI (p = .009). Higher levels of tumor necrosis factor-&agr; were measured in serum (p = .027) and peritoneal fluid (p = .001) of CRO-treated mice. In vitro, CLI released smaller amounts of staphylococcal enterotoxin A than CRO. Conclusions Antibiotic treatment of Gram-positive sepsis with a protein synthesis inhibitor decreases morbidity and mortality compared with a bacteriolytic compound. This may be caused by a reduction of the concentrations of proinflammatory/toxic bacterial components and cytokines.

Experimental Pneumococcal Meningitis: Impaired Clearance of Bacteria from the Blood Due to Increased Apoptosis in the Spleen in Bcl-2-Deficient Mice

ABSTRACT Necrotic and apoptotic neuronal cell death can be found in pneumococcal meningitis. We investigated the role of Bcl-2 as an antiapoptotic gene product in pneumococcal meningitis using Bcl-2 knockout (Bcl-2−/−) mice. By using a model of pneumococcal meningitis induced by intracerebral infection, Bcl-2-deficient mice and control littermates were assessed by clinical score and a tight rope test at 0, 12, 24, 32, and 36 h after infection. Then mice were sacrificed, the bacterial titers in blood, spleen, and cerebellar homogenates were determined, and the brain and spleen were evaluated histologically. The Bcl-2-deficient mice developed more severe clinical illness, and there were significant differences in the clinical score at 24, 32, and 36 h and in the tight rope test at 12 and 32 h. The bacterial titers in the blood were greater in Bcl-2-deficient mice than in the controls (7.46 ± 1.93 log CFU/ml versus 5.16 ± 0.96 log CFU/ml [mean ± standard deviation]; P < 0.01). Neuronal damage was most prominent in the hippocampal formation, but there were no significant differences between groups. In situ tailing revealed only a few apoptotic neurons in the brain. In the spleen, however, there were significantly more apoptotic leukocytes in Bcl-2-deficient mice than in controls (5,148 ± 3,406 leukocytes/mm2 versus 1,070 ± 395 leukocytes/mm2; P < 0.005). Bcl-2 appears to counteract sepsis-induced apoptosis of splenic lymphocytes, thereby enhancing clearance of bacteria from the blood.