Phialophora parasitica, an emerging pathogen

Monoconidial cultures derived from 12 clinical and environmental isolates of Phialophora parasitica were compared with respect to morphologic and physiologic characteristics and response to antifungal agents. No yeast cells were seen in 1- and 3-week-old slide culture preparations. Also, not all of the distinguishing characteristics of this species were displayed by all isolates on all media examined. Although the isolates grew on Sabouraud agar with chloramphenicol and cycloheximide, some inhibition was observed. All cultures were strongly urease-positive and hydrolyzed casein and starch; most decomposed tyrosine but not gelatin. All but one environmental isolate grew well at both 23 and 37 degrees C, but none grew at 40 degrees C. In the sensitivity testing the isolates did not vary much in their response to each drug, although some anomalies were observed. Amphotericin B and miconazole had minimum inhibitory concentrations in the low sensitivity range (2.0-8.0 and 2.5-10 micrograms m-1 respectively), for most isolates, and most isolates were resistant to both 5-fluorocytosine and ketoconazole. Limited observations were made on three other Phialophora species which might be confused with P. parasitica.     

Laribacter hongkongensis: an emerging pathogen of infectious diarrhea

Laribacter hongkongensis is relatively a new name in the list of bacterial pathogens for gastroenteritis and travelers’ diarrhea. Addition of another name increases burden on the enteric infections as a whole. L. hongkongensis belongs to Neisseriaceae family of β subclass Proteobacteria. L. hongkongensis was initially isolated in Hong Kong from blood and empyema of an alcoholic cirrhotic patient in 2001, followed by reports from Korea and China, representing a total of 38 articles in PubMed until April 2013. As of now, there is no report from Indian subcontinent where infectious diarrhea is very much prevalent and a major burden. This review provides information about the microbiological characteristics, consideration of an emerging pathogen, relative pathogenicity, genome and proteome content, resistance toward multiple antibiotics, adaptability to different stress, and other features since its time of discovery. Investigation for this bacterium may avoid misidentification as other microbial flora. Further studies like the geographical distribution, type of infection, disease burden, pathogenicity, or genomic exploration of this bacterium will be useful in characterizing them properly. This bacterium may possibly be the emerging threat to public health.     

Edwardsiella tarda - virulence mechanisms of an emerging gastroenteritis pathogen

Human Edwardsiella tarda infections often manifest as gastroenteritis, but can become systemic and potentially lethal. E. tarda uses virulence factors that include type III and type VI secretion systems, quorum sensing, two-component systems, and exoenzymes to gain entry into and survive within the host. Better understanding of interactions between these factors will lead to the development of novel antimicrobials against E. tarda and other enterics.     

Human infection with Photorhabdus asymbiotica: an emerging bacterial pathogen

The three currently recognised Photorhabdus species are bioluminescent bacteria that are pathogenic to insects. P. luminescens and P. temperata form a symbiotic relationship with nematodes that infect insects. P. asymbiotica, on the other hand, has only been isolated from human clinical specimens from the USA and Australia. The bacterium has been associated with locally invasive soft tissue and disseminated bacteraemic infections. An invertebrate vector for P. asymbiotica has not yet been identified.     

BK polyomavirus: emerging pathogen

BK polyomavirus (BKPyV) is a small double-stranded DNA virus that is an emerging pathogen in immunocompromised individuals. BKPyV is widespread in the general population, but primarily causes disease when immune suppression leads to reactivation of latent virus. Polyomavirus-associated nephropathy and hemorrhagic cystitis in renal and bone marrow transplant patients, respectively, are the most common diseases associated with BKPyV reactivation and lytic infection. In this review, we discuss the clinical relevance, effects on the host, virus life cycle, and current treatment protocols.     

Cryptococcus gattii: an emerging fungal pathogen infecting humans and animals

Infectious fungi are among a broad group of microbial pathogens that has and continues to emerge concomitantly due to the global AIDS pandemic as well as an overall increase of patients with compromised immune systems. In addition, many pathogens have been emerging and re-emerging, causing disease in both individuals who have an identifiable immune defect and those who do not. The fungal pathogen Cryptococcus gattii can infect individuals with and without an identifiable immune defect, with a broad geographic range including both endemic areas and emerging outbreak regions. Infections in patients and animals can be severe and often fatal if untreated. We review the molecular epidemiology, population structure, clinical manifestations, and ecological niche of this emerging pathogen.     

Mutation rate dynamics reflect ecological change in an emerging zoonotic pathogen

Mutation rates vary both within and between bacterial species, and understanding what drives this variation is essential for understanding the evolutionary dynamics of bacterial populations. In this study, we investigate two factors that are predicted to influence the mutation rate: ecology and genome size. We conducted mutation accumulation experiments on eight strains of the emerging zoonotic pathogen Streptococcus suis. Natural variation within this species allows us to compare tonsil carriage and invasive disease isolates, from both more and less pathogenic populations, with a wide range of genome sizes. We find that invasive disease isolates have repeatedly evolved mutation rates that are higher than those of closely related carriage isolates, regardless of variation in genome size. Independent of this variation in overall rate, we also observe a stronger bias towards G/C to A/T mutations in isolates from more pathogenic populations, whose genomes tend to be smaller and more AT-rich. Our results suggest that ecology is a stronger correlate of mutation rate than genome size over these timescales, and that transitions to invasive disease are consistently accompanied by rapid increases in mutation rate. These results shed light on the impact that ecology can have on the adaptive potential of bacterial pathogens.     

Ramularia collo-cygni: the biology of an emerging pathogen of barley.

Ramularia collo-cygni is now recognized as an important pathogen of barley in Northern Europe and New Zealand. It induces necrotic spotting and premature leaf senescence, leading to loss of green leaf area in crops, and can result in substantial yield losses. The fungus produces a number of anthraquinone toxins called rubellins, which act as host nonspecific toxins with photodynamic activity. These toxins induce lipid peroxidation and are possibly the cause of the chlorosis and necrosis observed in leaves infected with R. collo-cygni. The fact that the fungus can remain latent in barley plants until flowering, coupled with its very slow growth in vitro, makes it difficult to detect in crops. As a result, the epidemiology of this pathogen remains poorly understood. However, the recent development of rapid and reliable PCR methods for specific detection of R. collo-cygni offers the prospect of increased understanding of its epidemiology and improved disease control.     

Phylogenetic concordance analysis shows an emerging pathogen is novel and endemic

Distinguishing whether pathogens are novel or endemic is critical for controlling emerging infectious diseases, an increasing threat to wildlife and human health. To test the endemic vs. novel pathogen hypothesis, we present a unique analysis of intraspecific host-pathogen phylogenetic concordance of tiger salamanders and an emerging Ranavirus throughout Western North America. There is significant non-concordance of host and virus gene trees, suggesting pathogen novelty. However, non-concordance has likely resulted from virus introductions by human movement of infected salamanders. When human-associated viral introductions are excluded, host and virus gene trees are identical, strongly supporting coevolution and endemism. A laboratory experiment showed an introduced virus strain is significantly more virulent than endemic strains, likely due to artificial selection for high virulence. Thus, our analysis of intraspecific phylogenetic concordance revealed that human introduction of viruses is the mechanism underlying tree non-concordance and possibly disease emergence via artificial selection.     

Partitioning the net effect of host diversity on an emerging amphibian pathogen

The ‘dilution effect’ (DE) hypothesis predicts that diverse host communities will show reduced disease. The underlying causes of pathogen dilution are complex, because they involve non-additive (driven by host interactions and differential habitat use) and additive (controlled by host species composition) mechanisms. Here, we used measures of complementarity and selection traditionally employed in the field of biodiversity–ecosystem function (BEF) to quantify the net effect of host diversity on disease dynamics of the amphibian-killing fungus Batrachochytrium dendrobatidis (Bd). Complementarity occurs when average infection load in diverse host assemblages departs from that of each component species in uniform populations. Selection measures the disproportionate impact of a particular species in diverse assemblages compared with its performance in uniform populations, and therefore has strong additive and non-additive properties. We experimentally infected tropical amphibian species of varying life histories, in single- and multi-host treatments, and measured individual Bd infection loads. Host diversity reduced Bd infection in amphibians through a mechanism analogous to complementarity (sensu BEF), potentially by reducing shared habitat use and transmission among hosts. Additionally, the selection component indicated that one particular terrestrial species showed reduced infection loads in diverse assemblages at the expense of neighbouring aquatic hosts becoming heavily infected. By partitioning components of diversity, our findings underscore the importance of additive and non-additive mechanisms underlying the DE.     

Enzymatic characterization of isocitrate dehydrogenase from an emerging zoonotic pathogen Streptococcus suis

Streptococcus suis, a Gram-positive coccus, is an emerging zoonotic pathogen for both humans and pigs, but little is known about the properties of its metabolic enzymes. Isocitrate dehydrogenase (IDH) is a key regulatory enzyme in the citric acid cycle that catalyzes the oxidative decarboxylation of isocitrate yielding α-ketoglutarate and NAD(P)H. Here, we report the overexpression and enzymatic characterization of IDH from S. suis Serotype 2 Chinese highly virulent strain 05ZYH33 (SsIDH). The molecular weight of SsIDH was estimated to be 74 kDa by gel filtration chromatography, suggesting a homodimeric structure. Additionally, SsIDH was divalent cation-dependent and Mg²⁺ was found to be the most effective cation. The optimal pH of SsIDH was 7.0 (Mn²⁺) and 8.5 (Mg²⁺), and the maximum activity was around 30 °C (Mn²⁺) and 50 °C (Mg²⁺), respectively. Heat inactivation studies showed that SsIDH retained 50% activity after 20 min of incubation at 49 °C. Sequence comparison revealed that SsIDH had a significantly homologous identity to bacterial homodimeric IDHs. The recombinant SsIDH displayed a 117-fold (k_cat/K_m) preference for NAD⁺ over NADP⁺ with Mg²⁺, and a 80-fold greater specificity for NAD⁺ than NADP⁺ with Mn²⁺. Therefore, SsIDH has remarkably high coenzyme preference toward NAD⁺. This current work is expected to shed light on the functions of metabolic enzymes in S. suis and provide useful information for SsIDH to be considered as a possible candidate for serological diagnostics and detection of S. suis infection.     

Complete genome sequence of Rickettsia heilongjiangensis, an emerging tick-transmitted human pathogen

Rickettsia heilongjiangensis is an emerging tick-transmitted human pathogen causing far-Eastern spotted fever. Here we report the complete sequence and the main features of the genome of R. heilongjiangensis (strain 054).     

Genome sequence of Diplorickettsia massiliensis, an emerging Ixodes ricinus-associated human pathogen

Diplorickettsia massiliensis is a gammaproteobacterium in the order Legionellales and an agent of tick-borne infection. We sequenced the genome from strain 20B, isolated from an Ixodes ricinus tick. The genome consists of a 1,727,973-bp chromosome but no plasmid and includes 2,269 protein-coding genes and 42 RNA genes, including 3 rRNA genes.     

Anthropogenic signature in the incidence and distribution of an emerging pathogen of poplars

The introduction and establishment of non-native plant pathogens into new areas can result in severe outbreaks. Septoria leaf spot and canker caused by Sphaerulina musiva is one of the most damaging poplar diseases in northeastern and north-central North America. Stem and branch cankers can be devastating on susceptible trees, leading to tree death and reduced biomass in commercial plantations. In the Pacific Northwest region of North America, the first report of the disease was made in 2006 in the Fraser Valley of British Columbia (BC), Canada. To investigate the incidence and distribution of S. musiva from its point of introduction into BC, five plantations of Populus trichocarpa (black cottonwood), 500 P. trichocarpa trees from natural populations, and 23 plantations of hybrid poplars were surveyed by using real-time PCR assays targeting S. musiva and its native sister species, S. populicola. Our survey suggests a strong anthropogenic signature to the emergence of the non-native S. musiva. Detection frequency of S. musiva was high in hybrid poplar plantations (116 trees infected, 54.2 % of the sampled trees), while detection of the native S. populicola was limited to 13.1 % (22 trees infected). By contrast, in natural stands of P. trichocarpa, less than 2 % of the trees were positive for S. musiva (7 trees) while ~75 % were positive for S. populicola (433 trees). All the S. musiva detections in natural stands of the native P. trichocarpa were from trees located in the vicinity (<2.5 km) of hybrid poplar plantations. Identification of the genotypes found in the hybrid poplar plantations revealed that they are in majority F1 progeny from P. trichocarpa × P. deltoides (T × D) (82 %) and P. nigra × P. maximowiczii (N × M) (7.8 %) crosses, which are generally susceptible (intermediate level of susceptibility between the two parental species) to the canker disease. Our results suggest that the emergence of S. musiva in BC is related to the planting of susceptible hybrid poplars. Even if the disease has not yet established itself in natural poplar populations outside of the Fraser Valley, infected plantations could act as a reservoir that could promote its spread into nearby native P. trichocarpa populations.     

Identification and characterization of an RTX toxin in the emerging pathogen Kingella kingae

Kingella kingae is an emerging bacterial pathogen that is increasingly recognized as the causative agent of a variety of pediatric diseases, including septic arthritis and osteomyelitis. The pathogenesis of K. kingae disease is believed to begin with colonization of the upper respiratory tract. In the present study, we examined interactions between K. kingae and cultured respiratory epithelial cells and observed potent cytotoxicity, detected by both microscopy and lactic acid dehydrogenase (LDH) release assays. Experiments with synovial and macrophage cell lines revealed cytotoxicity for these cell types as well. Using mariner mutagenesis and a screen for loss of cytotoxicity, a genetic locus encoding an RTX toxin system was identified. Disruption of the K. kingae RTX locus resulted in a loss of cytotoxicity for respiratory epithelial, synovial, and macrophage cell lines. DNA sequence analysis demonstrated that the RTX locus is flanked by insertion elements and has a reduced G+C content compared to that of the whole genome. Two relatively less invasive Kingella species, K. oralis and K. denitrificans, were found to be noncytotoxic and to lack the RTX region, as determined by LDH release assays and Southern blotting. We concluded that K. kingae expresses an RTX toxin that has wide cellular specificity and was likely acquired horizontally. The possible roles for this toxin in the pathogenesis of K. kingae disease include breaching of the epithelial barrier and destruction of target tissues, such as synovium (joint lining).     

Modelling genitourinary defects in mice: an emerging genetic and developmental system

The rising incidence of genitourinary (GU) defects among newborns establishes the need and opportunity to focus research efforts on the amelioration of this growing public-health concern. Sadly, our inability to explain the causes of GU defects can be directly attributed to our lack of understanding of GU gene function. Recently, mouse models have been used to provide new insights into the mechanisms that underlie congenital GU malformations.