Mucormycosis: an emerging disease?

ABSTRACTMucormycosis is the third invasive mycosis in order of importance after candidiasis and aspergillosis and is caused by fungi of the class Zygomycetes. The most important species in order of frequency is Rhizopus arrhizus (oryzae). Identification of the agents responsible for mucormycosis is based on macroscopic and microscopic morphological criteria, carbohydrate assimilation and the maximum temperature compatible with its growth. The incidence of mucormycosis is approximately 1.7 cases per 1000 000 inhabitants per year, and the main risk-factors for the development of mucormycosis are ketoacidosis (diabetic or other), iatrogenic immunosuppression, use of corticosteroids or deferoxamine, disruption of mucocutaneous barriers by catheters and other devices, and exposure to bandages contaminated by these fungi. Mucorales invade deep tissues via inhalation of airborne spores, percutaneous inoculation or ingestion. They colonise a high number of patients but do not cause invasion. Mucormycosis most commonly manifests in the sinuses (39%), lungs (24%), skin (19%), brain (9%), and gastrointestinal tract (7%), in the form of disseminated disease (6%), and in other sites (6%). Clinical diagnosis of mucormycosis is difficult, and is often made at a late stage of the disease or post-mortem. Confirmation of the clinical form requires the combination of symptoms compatible with histological invasion of tissues. The probable diagnosis of mucormycosis requires the combination of various clinical data and the isolation in culture of the fungus from clinical samples. Treatment of mucormycosis requires a rapid diagnosis, correction of predisposing factors, surgical resection, debridement and appropriate antifungal therapy. Liposomal amphotericin B is the therapy of choice for this condition. Itraconazole is considered to be inappropriate and there is evidence of its failure in patients suffering from mucormycosis. Voriconazole is not active in vitro against Mucorales, and failed when used in vivo. Posaconazole and ravuconazole have good activity in vitro. The overall rate of mortality of mucormycosis is approximately 40%

The unexpected essentiality of glnA2in Mycobacterium smegmatisIs salvaged by overexpression of the global nitrogen regulator glnR, but not by L-, D-or iso-glutamine

Nitrogen metabolism plays a central role in the physiology of microorganisms, and Glutamine Synthetase (GS) genes are present in virtually all bacteria. In M. Tuberculosis, four GS genes are present, but only glnA1 is essential, whereas glnA2 was shown to be non-essential for in-vitro as well as in-vivo growth and pathogenesis, and is postulated to be involved in D-glutamine and iso-glutamine synthesis. Whilst investigating the activity of an antimicrobial compound in M. Smegmatis, we found a spontaneous temperature-sensitive mutant in glnA2 (I133F), and used it to investigate the role of glnA2 in M. Smegmatis. We deleted the native glnA2 and replaced it with a mutated allele. This re-created the temperature sensitivity-as after 3-4 seemingly normal division cycles, glnA2 became essential for growth. This essentiality could not be salvaged by neither L, D-nor iso-glutamine, suggesting an additional role of glnA2 in M. Smegmatis over its role in M. Tuberculosis. We also found that overexpression of the global nitrogen regulator glnR enabled bypassing the essentiality of glnA2, allowing the creation of a complete deletion mutant. The discrepancy between the importance of glnA2 in Mtb and M. Smegmatis stresses the caution in which results in one are extrapolated to the other

Characterization of Mycobacterium smegmatis Expressing the Mycobacterium tuberculosis Fatty Acid Synthase I (fas1) Gene

Unlike most other bacteria, mycobacteria make fatty acids with the multidomain enzyme eukaryote-like fatty acid synthase I (FASI). Previous studies have demonstrated that the tuberculosis drug pyrazinamide and 5-chloro-pyrazinamide target FASI activity. Biochemical studies have revealed that in addition to C(16:0), Mycobacterium tuberculosis FASI synthesizes C(26:0) fatty acid, while the Mycobacterium smegmatis enzyme makes C(24:0) fatty acid. In order to express M. tuberculosis FASI in a rapidly growing Mycobacterium and to characterize the M. tuberculosis FASI in vivo, we constructed an M. smegmatis Δfas1 strain which contained the M. tuberculosis fas1 homologue. The M. smegmatis Δfas1 (attB::M. tuberculosis fas1) strain grew more slowly than the parental M. smegmatis strain and was more susceptible to 5-chloro-pyrazinamide. Surprisingly, while the M. smegmatis Δfas1 (attB::M. tuberculosis fas1) strain produced C(26:0), it predominantly produced C(24:0). These results suggest that the fatty acid elongation that produces C(24:0) or C(26:0) in vivo is due to a complex interaction among FASI, FabH, and FASII and possibly other systems and is not solely due to FASI elongation, as previously suggested by in vitro studies

Pyrazinoic Acid and Its n-Propyl Ester Inhibit Fatty Acid Synthase Type I in Replicating Tubercle Bacilli

The activity of different analogs of pyrazinamide on Mycobacterium tuberculosis fatty acid synthase type I (FASI) in replicating bacilli was studied. Palmitic acid biosynthesis was diminished by 96% in bacilli treated with n-propyl pyrazinoate, 94% in bacilli treated with 5-chloro-pyrazinamide, and 97% in bacilli treated with pyrazinoic acid, the pharmacologically active agent of pyrazinamide. We conclude that the minimal structure of pyrazine ring with an acyl group is sufficient for FASI inhibition and antimycobacterial activity

Endocarditis Caused by Extended-Spectrum-β-Lactamase-Producing Klebsiella pneumoniae: Emergence of Resistance to Ciprofloxacin and Piperacillin-Tazobactam during Treatment despite Initial Susceptibility

Three episodes of bacteremia occurred in the course of prosthetic valve endocarditis caused by an extended-spectrum-β-lactamase (ESBL)-producing Klebsiella pneumoniae strain. The second isolate developed resistance to ciprofloxacin and the third isolate to piperacillin-tazobactam (PIP-TZ) following sequential therapy with each agent. The first isolate was resistant to PIP-TZ only at high inocula, the second isolate acquired increased transcription of the acrA gene, and the third isolate became resistant to PIP-TZ due to loss of β-lactamase inhibition by TZ. We question if and how PIP-TZ susceptibility should be reported for ESBL-producing Enterobacteriaceae