Efficacy of ciprofloxacin and moxifloxacin against Nocardia brasiliensis in vitro and in an experimental model of actinomycetoma in BALB/c mice

Mycetoma medical therapy

Medical treatment of mycetoma depends on its fungal or bacterial etiology. Clinically, these entities share similar features that can confuse diagnosis, causing a lack of therapeutic response due to inappropriate treatment. This review evaluates the response to available antimicrobial agents in actinomycetoma and the current status of antifungal drugs for treatment of eumycetoma.

Global burden of human mycetoma: a systematic review and meta-analysis

Mycetoma is a chronic infectious disease of the subcutaneous tissue with a high morbidity. This disease has been reported from countries between 30°N and 15°S since 1840 but the exact burden of disease is not known. It is currently unknown what the incidence, prevalence and the number of reported cases per year per country is. In order to estimate what the global burden of mycetoma is, a meta-analysis was performed. In total 50 studies were included, which resulted in a total of 8763 mycetoma cases. Most cases were found in men between 11 and 40 years of age. The foot was most commonly affected. Most cases were reported from Mexico, Sudan and India. Madurella mycetomatis was the most prevalent causative agent world-wide, followed by Actinomadura madurae, Streptomyces somaliensis, Actinomadura pelletieri, Nocardia brasiliensis and Nocardia asteroides. Although this study represents a first indication of the global burden on mycetoma, the actual burden is probably much higher. In this study only cases reported to literature could be used and most of these cases were found by searching archives from a single hospital in a single city of that country. By erecting (inter)national surveillance programs a more accurate estimation of the global burden on mycetoma can be obtained.

Nocardia brasiliensis cell wall lipids modulate macrophage and dendritic responses that favor development of experimental actinomycetoma in BALB/c mice

Nocardia brasiliensis is a Gram-positive facultative intracellular bacterium frequently isolated from human actinomycetoma. However, the pathogenesis of this infection remains unknown. Here, we used a model of bacterial delipidation with benzine to investigate the role of N. brasiliensis cell wall-associated lipids in experimental actinomycetoma. Delipidation of N. brasiliensis with benzine resulted in complete abolition of actinomycetoma without affecting bacterial viability. Chemical analyses revealed that trehalose dimycolate and an unidentified hydrophobic compound were the principal compounds extracted from N. brasiliensis with benzine. By electron microscopy, the extracted lipids were found to be located in the outermost membrane layer of the N. brasiliensis cell wall. They also appeared to confer acid-fastness. In vitro, the extractable lipids from the N. brasiliensis cell wall induced the production of the proinflammatory cytokines interleukin-1β (IL-1β), IL-6, and CCL-2 in macrophages. The N. brasiliensis cell wall extractable lipids inhibited important macrophage microbicidal effects, such as tumor necrosis factor alpha (TNF-α) and nitric oxide (NO) production, phagocytosis, bacterial killing, and major histocompatibility complex class II (MHC-II) expression in response to gamma interferon (IFN-γ). In dendritic cells (DCs), N. brasiliensis cell wall-associated extractable lipids suppressed MHC-II, CD80, and CD40 expression while inducing tumor growth factor β (TGF-β) production. Immunization with delipidated N. brasiliensis induced partial protection preventing actinomycetoma. These findings suggest that N. brasiliensis cell wall-associated lipids are important for actinomycetoma development by inducing inflammation and modulating the responses of macrophages and DCs to N. brasiliensis.

In vitro and in vivo intracellular killing effects of tigecycline against clinical nontyphoid Salmonella isolates using ceftriaxone as a comparator

Salmonella is an important, worldwide food-borne pathogen. Resistance to fluoroquinolones and cephalosporins has been increasingly reported, and new therapeutic agents are desperately needed. In this study, we evaluated the in vitro antimicrobial susceptibility of clinical nontyphoidal Salmonella isolates to tigecycline. Antibacterial activity of tigecycline, ceftriaxone, and ciprofloxacin were investigated by time-kill studies and the murine peritonitis model. The MIC₅₀/MIC₉₀ values of tigecycline, ceftriaxone, and ciprofloxacin against 76 Salmonella isolates were 0.25/0.5, 1/8, and 0.125/0.5 μg/ml, respectively. The intracellular inhibitory activity of tigecycline at 0.5 μg/ml (1 × MIC) against Salmonella isolates in human peripheral blood mononuclear cells was sustained for 24 h. In a mouse peritonitis model, tigecycline reduced the extracellular and intracellular bacterial counts from 10⁷ CFU/ml and 10⁵ CFU/ml, respectively, to an undetectable level within 96 h. The results were similar to those obtained with ceftriaxone. The survival rate of mice exposed to tigecycline after being infected by an inoculum of 1 × 10⁵ CFU was 80%, and that of mice exposed to ceftriaxone was 100%. When the inoculum was increased to 1.3 × 10⁶ CFU, the survival rate of mice treated by tigecycline was 20%, and that of mice exposed to ceftriaxone was 0% (P = 0.2). When a ceftriaxone- and ciprofloxacin-resistant but tigecycline-susceptible isolate was tested, mice treated by tigecycline had a higher survival rate than those treated by ceftriaxone (15/20 [75%] versus 6/20 [30%]; P = 0.011). Our results suggest that tigecycline is at least as effective as ceftriaxone for murine Salmonella infections and warrants further clinical investigations to delineate its potential against human Salmonella infections.

In vitro activity of ACH-702, a new isothiazoloquinolone, against Nocardia brasiliensis compared with econazole and the carbapenems imipenem and meropenem alone or in combination with clavulanic acid

The in vitro activities of ACH-702 and other antimicrobials against 30 Nocardia brasiliensis isolates were tested. The MIC(50) (MIC for 50% of the strains tested) and MIC(90) values of ACH-702 were 0.125 and 0.5 microg/ml. The same values for econazole were 2 and 4 microg/ml. The MIC(50) and MIC(90) values of imipenem and meropenem were 64 and >64 microg/ml and 2 and 8 microg/ml, respectively; the addition of clavulanic acid to the carbapenems had no effect.