In vivo efficacy of cefotaxime and amoxicillin against penicillin-susceptible, penicillin-resistant and penicillin-cephalosporin-resistant strains of Streptococcus pneumoniae in a mouse pneumonia model

Objective: To compare cefotaxime (CTX) to amoxicillin (AMO) (usually considered the definitive therapy for penicillinsusceptible Streptococcus pneumoniae infections) in an immunocompromised mouse pneumonia model.
Methods: Three S. pneumoniae clinical isolates were used: two serotype 19 strains, a penicillin-susceptible (P^s) strain (penicillin MIC = 0.03 μ/mL) and a highly penicillin-resistant (P^r) strain (penicillin MIC = 4 μ/mL), and one serotype 23F strain, a penicillin-cephalosporin-resistant (CFTR) strain (CTX MIC = 4 μ/mL).
Results: CTX activity in this mouse model of pneumonia induced by the highly penicillin-resistant strain of S. pneumoniae was lower than expected from its low MIC against this organism. Furthermore, AMO had greater efficacy than CTX against a CFTR S. pneumoniae strain.
Conclusion: Our data suggest that there is no major difference in the in vivo efficacy of the two agents, cefotaxime and amoxicillin, against penicillin-resistant and penicillin-cephalosporin-resistant S. pneumoniae.     

Analysis of the pathological lesions of the lung in a mouse model of cutaneous infection with Streptococcus pyogenes

Invasive diseases such as toxic shock syndrome caused by Streptococcus pyogenes (S. pyogenes) are re‐emerging infectious diseases. The mechanism of pathogenesis is not completely understood although the virulence of this organism has been analyzed using animal model systems, particularly using mice. The analysis of the progression of infection, however, is difficult. Computed tomography (CT) scanning is an extremely powerful technique that we applied to the mouse model of cutaneous infection with S. pyogenes. Two or three days after subcutaneous administration of bacteria, high density reticular areas were detected in the lung by CT. Histopathological examination of the lung was performed to examine the results of CT. Increased numbers of cytokeratin‐positive epithelial cells, probably alveolar type II epithelial cells, were detected but no remarkable increase of inflammatory cell infiltrates was observed. Our results show that the pathological lesions of the lung in this model, wherein relatively few numbers of neutrophils were in the alveoli, are well correlated with the lung of a part of streptococcal toxic shock syndrome patients. Therefore, CT may be useful in assessing the progression of S. pyogenes infection, particularly in the pathological lesions of the lung in this model.     

Influenza A virus induction of oxidative stress and MMP-9 is associated with severe lung pathology in a mouse model

Infection by different strains of influenza virus presents different pictures. Whether the pathogenicity of influenza virus is defined by the ability of the virus to induce differential immunopathlogical responses in the lungs still remains unclear. We compared the immunopathological response induced by influenza virus A/WSN/33 (H1N1) and that by A/Panama-like (H3N2) virus in C57BL/6 mice. WSN virus, in contrast to Panama-like virus, induced high mortality and severe lung pathology accompanied by massive Gr-1⁺ and CD11b⁺ cell infiltration and high levels of CXCL6/GCP-2, CCL2/MCP-1 and TIMP-1 production. Infection by WSN virus but not by Panama-like virus induced up-regulation of the active and latent forms of MMP-9 in the lungs and MMP-2/9 inhibitor partially reduced WSN virus-induced lung pathology. Both Gr-1⁺ and CD11b⁺ cells in WSN virus-infected lungs produced reactive oxygen and nitrogen species (ROS/RNS). While wild type mice infected by WSN virus had severe lung pathology and the presence of oxidized phospholipids and numerous MMP-9⁺ cells in the lungs, ncf1 deficiency ablated their expression and manifested less lung pathology. Employing a pulmonary mouse model we demonstrated in this study that infection by virulent influenza virus is characterized by a heavy cellular infiltration, severe lung pathology which is accompanied by oxidative stress and MMP-9 production.     

Evaluation of a virus derived from MDCK cells infected persistently with influenza A virus as a potential live-attenuated vaccine candidate in the mouse model

A temperature-sensitive mutant virus unable to replicate at 38 degrees C was recovered from passage 189 (IVpi-189) of Madin-Darby canine kidney cells infected persistently with influenza A. Immunofluorescent staining of the IVpi-189 virus-infected cells revealed disrupted transport of the matrix (M) 1 protein into the nucleus at non-permissive temperatures, resulting in retention of the nucleoprotein (NP) in the nucleus. Upon comparison with the parental influenza A E61-24-P15 strain used to establish persistent infection, amino acid exchanges were found in the M1 protein of IVpi-189 virus; arginine to glutamine at position 72 and threonine to alanine at position 139. When mice were inoculated intranasally with IVpi-189 virus, virus growth in the lungs was restrained and terminated rapidly. Prior intranasal inoculation with only a small dose of IVpi-189 virus induced humoral and cellular immune responses and protected mice against subsequent virulent virus challenge. These results indicate that IVpi-189 virus, an avirulent temperature-sensitive mutant, is a promising candidate for use as a live-attenuated vaccine.     

The Tim-3/galectin-9 pathway involves in the homeostasis of hepatic Tregs in a mouse model of concanavalin A-induced hepatitis

T cell immunoglobulin- and mucin-domain-containing molecule-3 (Tim-3) is a negative regulator of interferon (IFN)-γ-secreting CD4⁺ Th1 cells and plays a key role in autoimmune diseases. Here, we report that galectin-9 expression was increased in hepatic CD4⁺CD25⁺ T cells in a mouse model of concanavalin A (Con A)-induced hepatitis. Moreover, Tim-3 showed increased levels in CD4⁺CD25⁺ Foxp3⁺ regulatory T cells (Tregs). Further analyses showed that blocking the Tim-3/galectin-9 pathway resulted in the suppression of Tregs in vitro, thereby significantly increasing interferon (IFN)-γ production from hepatic Teffs. Moreover, blockade of Tim-3 in vivo with an anti-Tim-3 antibody exacerbated the acute hepatitis, possibly by increased IFN-γ production. Furthermore, we found that in vitro activation of CD4⁺CD25⁻ T cells with the T cell receptor (TCR) plus interleukin 2 (IL-2) up-regulated Tim-3 expression. And the induced Tim-3 interacted with galectin-9 to induce CD4⁺ T cell apoptosis which could be partly reversed by blocking Tim-3 signaling. Our results suggested that the Tim-3/galectin-9 pathway plays a critical role in the homeostasis of hepatic Tregs through the elimination induction in Teffs and the inhibition of IFN-γ release, which contributes to the pathogenesis of liver damage and constitutes at least part of the mechanism underlying the induction of hepatitis by Con A.     

Generation and characterization of new monoclonal antibodies against swine origin 2009 influenza A (H1N1) virus and evaluation of their prophylactic and therapeutic efficacy in a mouse model

In 2009, a swine-origin influenza A virus – A(H1N1)pdm09 – emerged and has became a pandemic strain circulating worldwide. The hemagglutinin (HA) of influenza virus is a potential target for the development of anti-viral therapeutic agents. Here, we generated mAbs by immunization of baculovirus-insect expressing trimeric recombinant HA of the A(H1N1)pdm09 strain. Results indicated that the mAbs recognized two novel neutralizing and protective epitopes-“STAS” and “FRSK” which located near Cb and Ca1 antigenic regions respectively and were conserved in almost 2009–2016 influenza H1N1 stains. The mAb 12E11 demonstrated higher protective efficacy than mAb 8B10 in mice challenge assay. Both mAb pretreatments significantly reduced virus titers and pro-inflammatory cytokines in mice lung postinfection (p < 0.01), and showed prophylactic and therapeutic efficacies even 48 h postinfection (p < 0.05). Combination therapy using the mAbs with oseltamivir pre- and post-treatment showed synergistic therapeutic effect in mice model (p < 0.01). Further investigation for clinical application in humans is warranted.