A Rare Case of Fungal Rhinosinusitis Caused by Scedosporium apiopermum.

Fungal rhinosinusitis (FRS) is inflammation of the paranasal sinus mucosa due to fungal infections, which can be invasive or non-invasive. The occurrence of a sphenoid mucocele with a fungal ball is rare. We report a case of sphenoid sinus mucocele with a fungal ball caused by Scedosporium apiopermum in a 32-year-old female who presented to the Emergency Department with persistent headache not relieved on medications. The radiological images showed a mucocele with clival osteomyelitis. Urgent endoscopic examination and debridement was undertaken which demonstrated a mucocele with fungal ball. Microbiological examination confirmed it to be Scedosporium apiopermum.

Mycobacterium kansasii osteomyelitis - a masquerading disease.

INTRODUCTION: Non-tuberculous mycobacteria (NTM) are environmental bacteria capable of causing an opportunistic myriad of infections. Mycobacterium kansasii, one such NTM, is responsible for causing pulmonary disease in immunocompromised patients. Rare extrapulmonary manifestations such as lymphadenitis, osteoarticular manifestations, and skin and soft tissue infections are also observed. CASE PRESENTATION: Here, we report an unusual case of sternoclavicular joint and elbow joint infection with M. kansasii in a relatively immunocompetent patient. Histopathology did not show classic granulomas and mycobacterial infection was not initially considered as a possibility. However repeat biopsies were sent for mycobacterial cultures which then grew M. kansasii. CONCLUSION: Diagnosis of M. kansasii in such cases can be difficult and culture-positive results may not necessarily imply positive diagnosis as they can be environmental contaminants. Furthermore, M. kansasii can cause infections without the characteristic granuloma formation, which can further complicate tissue diagnosis. This underlines the importance of ensuring that tissue samples obtained are cultured for mycobacteria.

A Nonribosomal Peptide Synthase Gene Driving Virulence in Mycobacterium tuberculosis.

Nonribosomal peptide synthases produce short peptides in a manner that is distinct from classical mRNA-dependent ribosome-mediated translation. The Mycobacterium tuberculosis genome harbors a nonribosomal peptide synthase gene, nrp, which is part of a gene cluster proposed to be involved in the biosynthesis of isonitrile lipopeptides. Orthologous clusters are found in other slow-growing pathogenic mycobacteria and actinomycetes. To probe the role of the nrp gene in infection, we generated an nrp deletion mutant in M. tuberculosis H37Rv and tested its virulence in immunocompetent (C57BL/6) mice. The nrp mutant strain displayed lower initial growth rates in the lungs and a defective dissemination to the spleens of infected mice. Mice infected with the mutant strain also survived for twice as long as those infected with wild-type M. tuberculosis and, remarkably, showed subdued pathology, despite similar bacterial loads at later stages of infection. The differences in the course of infection between wild-type and nrp mutant strains were accompanied by distinct dynamics of the immune response. Most strikingly, the nrp mutant was highly attenuated in immunodeficient (SCID-, recombination activating 2 [RAG2]-, and gamma interferon [IFN-γ]-deficient) mice, suggesting that macrophages control the nrp mutant more efficiently than they control the wild-type strain. However, in the presence of IFN-γ, both strains were equally controlled. We propose that the nrp gene and its associated cluster are drivers of virulence during the early stages of infection.IMPORTANCE Over 10 million people developed tuberculosis (TB) in 2016, and over 1.8 million individuals succumbed to the disease. These numbers make TB the ninth leading cause of death worldwide and the leading cause from a single infectious agent. Therefore, finding novel therapeutic targets in Mycobacterium tuberculosis, the pathogen that causes most cases of human TB, is critical. In this study, we reveal a novel virulence factor in M. tuberculosis, the nrp gene. The lack of nrp highly attenuates the course of M. tuberculosis infection in the mouse model, which is particularly relevant in immune-deficient hosts. This is very relevant as TB is particularly incident in immune-suppressed individuals, such as HIV patients.

Identification of a Desaturase Involved in Mycolic Acid Biosynthesis in Mycobacterium smegmatis.

Mycolic acids are unique long chain fatty acids found in the cell walls of mycobacteria including the tubercle bacillus, Mycobacterium tuberculosis. The introduction of double bonds in mycolic acids remains poorly understood, however, genes encoding two potential aerobic desaturases have been proposed to be involved in this process. Here we show that one of these genes, desA1, is essential for growth of the saprophytic Mycobacterium smegmatis. Depletion of desA1 in a M. smegmatis conditional mutant led to reduction of mycolic acid biosynthesis and loss of viability. The DesA1-depleted cells exhibited two other phenotypes: using 14[C]-labelling, we detected the accumulation of minor mycolic acid-related species that migrated faster in a silver TLC plate. Spiral Time of Flight Mass Spectroscopic analysis suggested the presence of species with sizes corresponding to what were likely monoenoic derivatives of α-mycolic acids. Additionally, conditional depletion led to the presence of free fatty acyl species of lengths ~C26-C48 in the lysing cells. Cell viability could be rescued in the conditional mutant by Mycobacterium tuberculosis desA1, highlighting the potential of desA1 as a new drug target in pathogenic mycobacteria.

MmpL genes are associated with mycolic acid metabolism in mycobacteria and corynebacteria.

Mycolic acids are vital components of the cell wall of the tubercle bacillus Mycobacterium tuberculosis and are required for viability and virulence. While mycolic acid biosynthesis is studied extensively, components involved in mycolate transport remain unidentified. We investigated the role of large membrane proteins encoded by mmpL genes in mycolic acid transport in mycobacteria and the related corynebacteria. MmpL3 was found to be essential in mycobacteria and conditional depletion of MmpL3 in Mycobacterium smegmatis resulted in loss of cell wall mycolylation, and of the cell wall-associated glycolipid, trehalose dimycolate. In parallel, an accumulation of trehalose monomycolate (TMM) was observed, suggesting that mycolic acids were transported as TMM. In contrast to mycobacteria, we found redundancy in the role of two mmpL genes, in Corynebacterium glutamicum; a complete loss of trehalose-associated and cell wall bound corynomycolates was observed in an NCgl0228-NCgl2769 double mutant, but not in individual single mutants. Our studies highlight the role of mmpL genes in mycolic acid metabolism and identify potential new targets for anti-TB drug development.

Two polyketide-synthase-associated acyltransferases are required for sulfolipid biosynthesis in Mycobacterium tuberculosis.

The methyl-branched fatty acyl components of sulfolipid-I (SL-I), a major glycolipid of the human pathogen Mycobacterium tuberculosis, are synthesized by the polyketide synthase Pks2. Rv3824c (papA1), located downstream of pks2, encodes a protein that belongs to a subfamily of acyltransferases associated with mycobacterial polyketide synthases [polyketide synthase-associated proteins (PAPs)]. The presence of a conserved acyltransferase motif (HX(3)DX(14)Y) suggested a role for PapA1 in acylation of sulfated trehalose to form SL-I. Targeted deletion of the H37Rv papA1 resulted in loss of SL-I, demonstrating its role in mycobacterial sulfolipid biosynthesis. Furthermore, SL-I synthesis was restored in the mutant strain following complementation with papA1, but not with mutant alleles of papA1 containing alterations of key residues in the acyltransferase motif, confirming that PapA1 was an acyltransferase. While other M. tuberculosis pks clusters are associated with a single PAP-encoding gene, it was demonstrated that another open reading frame, Rv3820c (papA2), located 5.8 kb downstream of papA1 is also an acyltransferase gene involved in SL-I biosynthesis: deletion of papA2 abolished SL-I production. The absence of any partially acylated intermediates in either null mutant indicated that both PapA1 and PapA2 were required for all acylation steps of SL-I assembly.

Deletion of kasB in Mycobacterium tuberculosis causes loss of acid-fastness and subclinical latent tuberculosis in immunocompetent mice.

Mycobacterium tuberculosis, the causative agent of tuberculosis, has two distinguishing characteristics: its ability to stain acid-fast and its ability to cause long-term latent infections in humans. Although this distinctive staining characteristic has often been attributed to its lipid-rich cell wall, the specific dye-retaining components were not known. Here we report that targeted deletion of kasB, one of two M. tuberculosis genes encoding distinct beta-ketoacyl- acyl carrier protein synthases involved in mycolic acid synthesis, results in loss of acid-fast staining. Biochemical and structural analyses revealed that the DeltakasB mutant strain synthesized mycolates with shorter chain lengths. An additional and unexpected outcome of kasB deletion was the loss of ketomycolic acid trans-cyclopropanation and a drastic reduction in methoxymycolic acid trans-cyclopropanation, activities usually associated with the trans-cyclopropane synthase CmaA2. Although deletion of kasB also markedly altered the colony morphology and abolished classic serpentine growth (cording), the most profound effect of kasB deletion was the ability of the mutant strain to persist in infected immunocompetent mice for up to 600 days without causing disease or mortality. This long-term persistence of DeltakasB represents a model for studying latent M. tuberculosis infections and suggests that this attenuated strain may represent a valuable vaccine candidate against tuberculosis.