Influence of adjunctive interferon-gamma on treatment of gentamicin- and vancomycin-resistant Enterococcus faecalis infection in mice

Post-exposure immunization against Francisella tularensis membrane proteins augments protective efficacy of gentamicin in a mouse model of pneumonic tularemia

Successful treatment of pneumonic infection with Francisella tularensis, the causative agent of tularemia, requires rapid initiation of antibiotic therapy, yet even then treatment failures may occur. Consequently, new treatments are needed to enhance the effectiveness of antimicrobial therapy for acute pneumonic tularemia. In a prior study, immunization with F. tularensis membrane protein fraction (MPF) antigens 3 days prior to challenge was reported to induce significant protection from inhalational challenge. We therefore hypothesized that MPF immunization might also be effective in enhancing infection control if combined with antibiotic therapy and administered after infection as post-exposure immunotherapy. To address this question, a 24h post-exposure treatment model of acute pulmonary Schu S4 strain of F. tularensis infection in BALB/c mice was used. Following exposure, mice were immunized with MPF and treated with low-dose gentamicin, alone or in combination and the effects on survival, bacterial burden and dissemination were assessed. We found that immunization with MPF significantly increased the effectiveness of subtherapeutic gentamicin for post-exposure treatment of pneumonic tularemia, with 100% of combination-treated mice surviving long-term. Bacterial burdens in the liver and spleen were significantly reduced in combination MPF-gentamicin treated mice at 7 days after challenge. Passively transferred antibodies against MPF antigens also increased the effectiveness of gentamicin therapy. Thus, we concluded that post-exposure immunization with MPF antigens was an effective means of enhancing conventional antimicrobial therapy for pneumonic tularemia.

Present and future therapeutic strategies for melioidosis and glanders

Burkholderia pseudomallei and Burkholderia mallei are the causative agents of melioidosis and glanders, respectively. Both Gram-negative pathogens are endemic in many parts of the world. Although natural acquisition of these pathogens is rare in the majority of countries, these bacteria have recently gained much interest because of their potential as bioterrorism agents. In modern times, their potential destructive impact on public health has escalated owing to the ability of these pathogens to cause opportunistic infections in diabetic and perhaps otherwise immunocompromised people, two growing populations worldwide. For both pathogens, severe infection in humans carries a high mortality rate, both species are recalcitrant to antibiotic therapy - B. pseudomallei more so than B. mallei - and no licensed vaccine exists for either prophylactic or therapeutic use. The potential malicious use of these organisms has accelerated the investigation of new ways to prevent and to treat the diseases. The availability of several B. pseudomallei and B. mallei genome sequences has greatly facilitated target identification and development of new therapeutics. This review provides a compilation of literature covering studies in antimelioidosis and antiglanders antimicrobial drug discovery, with a particular focus on potential novel therapeutic approaches to combat these diseases.

Immunotherapy markedly increases the effectiveness of antimicrobial therapy for treatment of Burkholderia pseudomallei infection

Burkholderia pseudomallei is a soil bacterium that is endemic in southeast Asia and northern Australia and that can cause both acutely lethal pneumonia and chronic systemic infections in humans. The effective treatment of infection with B. pseudomallei requires rapid diagnosis and prolonged treatment with high doses of antimicrobials, and even with appropriate antibiotic therapy, patient relapses are common. Thus, new approaches to the treatment of B. pseudomallei infections are needed. In the present study, we asked whether active immunotherapy with gamma interferon (IFN-gamma), a key cytokine regulating the intracellular replication of B. pseudomallei, could increase the effectiveness of conventional antimicrobial therapy for B. pseudomallei infection. Macrophage infection assays and in vivo pulmonary challenge models were used to assess the inhibitory effects of combined treatment with IFN-gamma and ceftazidime on B. pseudomallei infection. We found that treatment with even very low doses of IFN-gamma and ceftazidime elicited strong synergistic inhibition of B. pseudomallei growth within infected macrophages. In vivo, active immunotherapy markedly potentiated the effectiveness of low-dose ceftazidime therapy for the treatment of infected mice in a pulmonary challenge model of B. pseudomallei. Combined treatment was associated with a significant reduction in the bacterial burden and a significant lessening of bacterial dissemination. We concluded, therefore, that immunotherapy with either endogenous or exogenous IFN-gamma could significantly increase the effectiveness of conventional antimicrobial therapy for the treatment of acute B. pseudomallei infection.

Neutrophils are essential for rapid clearance of Enterococcus faecium in mice

A progressive increase in infections with multiresistant Enterococcus faecium has been reported, especially in cancer patients and neutropenic patients. Despite its increasing importance as a nosocomial pathogen, knowledge of the pathogenesis of E. faecium infections is highly limited. In this study, we investigated the role of neutrophils during peritonitis with subsequent bacteremia caused by E. faecium. Therefore, we depleted neutrophils by intraperitoneal injections of monoclonal antibody RB6-8C5. Mice were followed for 5 days, and the enterococcal outgrowth and inflammatory response were compared between neutropenic mice and immunoglobulin G-injected control mice. Neutropenic mice demonstrated a severe delay in enterococcal clearance from all cultured organs (peritoneal fluid, blood, and lung and liver tissue). In particular, neutropenic mice remained bacteremic for up to 3 days, whereas all nonneutropenic mice had cleared the bacteria from circulation by 2 days. Furthermore, neutropenic mice displayed elevated peritoneal cytokine and chemokine levels 1 day after the infection and attracted fewer macrophages into the peritoneal cavity. In the circulation, a prolonged elevation of tumor necrosis factor alpha, interleukin-6, and the acute-phase proteins serum amyloid A and complement 3 were measured in neutropenic mice. In conclusion, attraction of neutrophils to the primary site of E. faecium infection is important for a rapid clearance of this bacterium, thereby attenuating a systemic inflammatory response.

Intranasal interleukin-12 treatment promotes antimicrobial clearance and survival in pulmonary Francisella tularensis subsp. novicida infection

Francisella tularensis is a highly virulent facultative intracellular bacterium and is considered a potential biological warfare agent. Inhalation tularemia can lead to the development of bronchopneumonia, which is frequently fatal without medical intervention. Treatment strategies that directly target the respiratory mucosa may extend the efficacy of therapy, particularly for the medical management of acute aerosol exposure. To this end, we describe an intranasal (i.n.) strategy for the treatment of pulmonary Francisella infection in mice that uses a combinatorial approach with the conventional antibiotic gentamicin and interleukin 12 (IL-12). The i.n. administration of IL-12 alone promoted bacterial clearance and extended the time to death but did not prevent mortality against lethal pulmonary challenge with Francisella tularensis subsp. novicida. However, i.n. treatment with gentamicin and IL-12 therapeutically at 8 and 24 h after challenge markedly enhanced the rate of survival (70 to 100%) against pulmonary infection compared to the rates of survival for animals treated with antibiotic alone (17%) or IL-12 alone (0%). A delay in combinatorial therapy over a span of 4 days progressively decreased the efficacy of this treatment regimen. This combinatorial treatment was shown to be highly dependent upon the induction of endogenous gamma interferon and may also involve the activation of natural killer cells. Together, these findings suggest that IL-12 may be a potent adjunct for chemotherapy to enhance drug effectiveness against pulmonary Francisella infection.

Combinatorial immunotherapies for infectious diseases

Combating pathogenic organisms by combinatorial approaches involving appropriate immune response molecules and antimicrobial drugs represents a progessively more apparent and successful therapeutic paradigm for the treatment of acute and chronic persistent infectious diseases. This review explores areas of current innovation and provides an update of the present state of knowledge concerning combination of chemotherapy with several immune-based interventions in infections. In the future, a better understanding of microbial immune modulation and evasion may continue to open new avenues of inquiry and carefully targeted application of adjunctive immunotherapies.

Effects of adjunctive treatment with combined cytokines in a neutropenic mouse model of multidrug-resistant Enterococcus faecalis septicemia

STUDY OBJECTIVE

To examine whether the antienterococcal efficacy of a regimen of gentamicin plus vancomycin combined with granulocyte colony-stimulating factor (G-CSF) is enhanced by concurrent therapy with interferon-gamma (IFN-gamma).

SETTING

Hospital laboratory.

INTERVENTION

Mice rendered neutropenic by cyclophosphamide were intraperitoneally inoculated with a gentamicin- and vancomycin-resistant Enterococcus faecalis isolate.

MEASUREMENTS AND MAIN RESULTS

Infected animals were randomized into treatment groups that received G-CSF alone or in combination with various dosages of IFN-gamma. Additional groups of animals received vancomycin; G-CSF, G-CSF plus vancomycin, IFN-gamma, and G-CSF; or vancomycin with both cytokines. Addition of IFN-gamma to G-CSF regimen resulted in no significant change (p>0.05) in survival, compared with treatment with G-CSF alone. Also, the antienterococcal efficacy of antibiotic plus G-CSF was not modified by coadministration of IFN-gamma.

CONCLUSION

This study suggests that adjunctive application of combined cytokines may not be more beneficial than only G-CSF in combination with an antibiotic to treat multidrug-resistant enterococcal infection.

Phagocytosis and killing of intracellular pathogens: interaction between cytokines and antibiotics

Phagocytosis and bacterial killing are the primary functions of macrophages. Among the mechanisms involved in the phagocytic process, cytokines, especially those of T-helper 1 profile, appear to influence considerably the internalization and the intracellular fate of the pathogen within the macrophage. In particular, the evidence for a cooperation of cytokines with antibiotics in intracellular infection could provide new therapeutic approaches to intracellular infectious diseases in the future.