The pathogenMycobacterium marinum, a faster growing close relative ofMycobacterium tuberculosis, has a single rRNA operon per genome

Asap1 Affects the Susceptibility of Zebrafish to Mycobacterium by Regulating Macrophage Migration

The ADP ribosylation factor (ARF) GTPase activation protein ASAP1 possesses multiple biological functions, including regulation of cytoskeletal dynamics, small GTP-binding protein receptor recycling, and intracellular vesicle trafficking. Recently, ASAP1 polymorphisms have been reported to be associated with human susceptibility to tuberculosis (TB) according to a large-scale genome-wide association study (GWAS); ASAP1 expression affects dendritic cell migration, which may be involved in TB predisposition. However, it remains unclear whether ASAP1 affects TB in vivo. To address this issue, we used zebrafish as a model system to examine the effects of Asap1 against Mycobacterium marinum, an organism closely related to Mycobacterium tuberculosis. Two zebrafish asap1 homologs (asap1a and asap1b) were identified and characterized. By morpholino knockdown of asap1a and asap1b as a whole, we found that the asap1 morphants showed a higher mycobacterial load than the controls, which was almost rescued by injecting asap1 mRNA that confers resistance to mycobacterial infection. These Asap1-depleted zebrafish also exhibited decreased macrophage migration in response to tail injury or upon infection with M. marinum in the hindbrain ventricle, which was also proved in THP1-derived macrophages of knockdown ASAP1. Together, these findings represent a new perspective on the role of Asap1 in resistance to mycobacterial infection.

Mycobacterium marinum

Mycobacterium marinum is a well-known pathogenic mycobacterium for skin and soft tissue infections and is associated with fishes and water. Among nontuberculous mycobacteria (NTM), it is the leading cause of extrarespiratory human infections worldwide. In addition, there is a specific scientific interest in M. marinum because of its genetic relatedness to Mycobacterium tuberculosis and because experimental infection of M. marinum in fishes mimics tuberculosis pathogenesis. Microbiological characteristics include the fact that it grows in 7 to 14 days with photochromogenic colonies and is difficult to differentiate from Mycobacterium ulcerans and other mycolactone-producing NTM on a molecular basis. The diagnosis is highly suspected by the mode of infection, which is related to the hobby of fishkeeping, professional handling of marine shells, or swimming in nonchlorinated pools. Clinics distinguished skin and soft tissue lesions (typically sporotrichoid or subacute hand nodules) and lesions disseminated to joint and bone, often related with the local use of corticosteroids. In clinical microbiology, microscopy and culture are often negative because growth requires low temperature (30°C) and several weeks to succeed in primary cultivation. The treatment is not standardized, and no randomized control trials have been done. Therapy is a combination of surgery and antimicrobial agents such as cyclines and rifampin, with successful outcome in most of the skin diseases but less frequently in deep tissue infections. Prevention can be useful with hand protection recommendations for professionals and all persons manipulating fishes or fish tank water and use of alcohol disinfection after contact.

Histologic and molecular characterization of Edwardsiella piscicida infection in largemouth bass (Micropterus salmoides)

The genus Edwardsiella is composed of a diverse group of facultative anaerobic, gram-negative bacteria that can produce disease in a wide variety of hosts, including birds, reptiles, mammals, and fish. Our report describes the isolation and identification of Edwardsiella piscicida associated with chronic mortality events in 2 separate captive largemouth bass ( Micropterus salmoides) populations in New York and Florida. Wet-mount biopsies of skin mucus, gill, kidney, and spleen from several affected largemouth bass contained significant numbers of motile bacteria. Histologic examination revealed multifocal areas of necrosis scattered throughout the heart, liver, anterior kidney, posterior kidney, and spleen. Many of the necrotic foci were encapsulated or replaced by discrete granulomas and associated with colonies of gram-negative bacteria. Initial phenotypic and matrix-assisted laser desorption ionization–time of flight mass spectrometric analysis against existing spectral databases of recovered isolates identified these bacteria as Edwardsiella tarda. Subsequent molecular analysis using repetitive sequence mediated and species-specific PCR, as well as 16S rRNA, rpoB, and gyrB sequences, classified these isolates as E. piscicida. As a newly designated taxon, E. piscicida should be considered as a differential for multiorgan necrosis and granulomas in largemouth bass.

Physiology of mycobacteria

Mycobacterium tuberculosis is a prototrophic, metabolically flexible bacterium that has achieved a spread in the human population that is unmatched by any other bacterial pathogen. The success of M. tuberculosis as a pathogen can be attributed to its extraordinary stealth and capacity to adapt to environmental changes throughout the course of infection. These changes include: nutrient deprivation, hypoxia, various exogenous stress conditions and, in the case of the pathogenic species, the intraphagosomal environment. Knowledge of the physiology of M. tuberculosis during this process has been limited by the slow growth of the bacterium in the laboratory and other technical problems such as cell aggregation. Advances in genomics and molecular methods to analyze the M. tuberculosis genome have revealed that adaptive changes are mediated by complex regulatory networks and signals, resulting in temporal gene expression coupled to metabolic and energetic changes. An important goal for bacterial physiologists will be to elucidate the physiology of M. tuberculosis during the transition between the diverse conditions encountered by M. tuberculosis. This review covers the growth of the mycobacterial cell and how environmental stimuli are sensed by this bacterium. Adaptation to different environments is described from the viewpoint of nutrient acquisition, energy generation, and regulation. To gain quantitative understanding of mycobacterial physiology will require a systems biology approach and recent efforts in this area are discussed.

Synchronous replication initiation in novel Mycobacterium tuberculosis dnaA cold-sensitive mutants

The genetic aspects of oriC replication initiation in Mycobacterium tuberculosis are largely unknown. A two-step genetic screen was utilized for isolating M. tuberculosis dnaA cold-sensitive (cos) mutants. First, a resident plasmid expressing functional dnaA integrated at the attB locus in dnaA null background was exchanged with an incoming plasmid bearing a mutagenized dnaA gene. Next, the mutants that were defective for growth at 30 degrees C, a non-permissive temperature, but resumed growth and DNA synthesis when shifted to 37 degrees C, a permissive temperature, were subsequently selected. Nucleotide sequencing analysis located mutations to different regions of the dnaA gene. Modulation of the growth temperatures led to synchronized DNA synthesis. The dnaA expression under synchronized DNA replication conditions continued to increase during the replication period, but decreased thereafter reflecting autoregulation. The dnaAcos mutants at 30 degrees C were elongated suggesting that they may possibly be blocked during the cell division. The DnaA115 protein is defective in its ability to interact with ATP at 30 degrees C, but not at 37 degrees C. Our results suggest that the optimal cell cycle progression and replication initiation in M. tuberculosis requires that the dnaA promoter remains active during the replication period and that the DnaA protein is able to interact with ATP.

Mycobacterium marinum: ubiquitous agent of waterborne granulomatous skin infections

Mycobacterium marinum is a waterborne mycobacterium that commonly infects fish and amphibians worldwide. Infection in humans occurs occasionally, in most cases as a granulomatous infection localized in the skin, typically following minor trauma on the hands. For this reason, infection is especially common among aquarium keepers. Such local infection may-though infrequently-spread to tendon sheaths or joints. Disseminated disease, which is rare, can occur in immunosuppressed patients. In order to obtain a definitive diagnosis, culture and histopathological examination of biopsies from skin or other tissues are recommended. Infections sometimes heal spontaneously, but drug treatment is usually necessary for several months in order to cure the infection. Doxycycline or clarithromycin is used most commonly, although in severe cases, a combination of rifampicin and ethambutol is recommended.

Das langsame Wachstum von Mykobakterien

A characteristic feature of mycobacteria is their slow growth rate, which in addition strongly varies in different species of the genus. All highly pathogenic species such as M. tuberculosis and M. leprae causing tuberculosis and leprosy, respectively, belong to the slow growing mycobacteria, while the apathogenic and opportunistic species are members of the fast growing mycobacteria. This suggests that the question be posed whether there is causality between mycobacterial growth rate and virulence. We discuss possible reasons for the slow and variable growth rates of mycobacteria and the current state of knowledge concerning the significance of slow growth for mycobacterial pathogenicity.

Estimation of ribosomal RNA operon (rrn) copy number in Acinetobacter isolates and potential of patterns of rrn operon-containing fragments for typing strains of members of this genus

The copy number of the rrn operon in 70 strains of Acinetobacter including the type strains of almost all the genomic species with validated names was estimated after digestion of their genomic DNA by the restriction enzymes BglII and PstI, and Southern blotting. Copy number estimates varied between and among species, with between 3 and 7 rrn operon copies detected. Copy number estimates obtained from the same strain with the two enzymes sometimes varied. BglII generated RFLP patterns of the rrn containing fragments obtained from Southern blots after agarose gel electrophoresis were examined for their value in identifying Acinetobacter isolates. This method was very reproducible with the same fragment pattern always generated from the same isolate on repeated analysis. Often multiple strains of the same genomic species gave identical or very similar patterns (e.g. Acinetobacter baylyi), clustering closest together on the dendrogram generated after numerical analysis of these patterns. However, with some, like BG5 and BG8, the patterns derived from the different strains, some of which had been placed in this genomic species from DNA:DNA hybridization data, varied considerably to each other and to the type strain. Little similarity was seen when relationships between these strains based on these patterns were compared to those using DNA:DNA hybridization data. Often these patterns could be used to question earlier identification of strains using phenotypic characters. Thus, strain AB82 thought to belong to genomic species 5 gave an identical pattern to A. bouvetii(T) (DSM 14964). In some cases this pattern analysis suggested that novel species of Acinetobacter might exist among the strains examined.