MicrobiologyBytes

Researchers have developed a single vaccine which protects against both rabies and Ebola virus. These two viruses are related to each other, but do not cross-react serologically. By inserting elements of the Ebola virus GP protein into an existing rabies virus vaccine, a single bivalent vaccine was produced. Although it works in the laboratory, the new vaccine – or something similar based on this first attempt – need to be tested in primates and eventually in humans.

Apart from people, Ebola virus is thought to have eradicated thousands of gorillas, prompting the World Conservation Union to raise their status to “critically endangered” in 2007, the first time a mammal has become critically endangered as a direct result of disease. Vaccination could help prevent future deaths.

Inactivated or Live-Attenuated Bivalent Vaccines that Confer Protection against Rabies and Ebola Viruses. J Virol. Aug 17 2011
The search for a safe and efficacious vaccine for Ebola virus continues as no current vaccine candidate is nearing licensure. We have developed (a) replication-competent, (b) replication-deficient, and (c) chemically inactivated rabies virus (RABV) vaccines expressing Zaire ebolavirus (ZEBOV) glycoprotein (GP) using a reverse genetics system based on the SAD B19 RABV wildlife vaccine. ZEBOV GP is efficiently expressed by these vaccine candidates and is incorporated into virions. The vaccine candidates were avirulent after inoculation of adult mice, and viruses with a deletion in the RABV glycoprotein have greatly reduced neurovirulence after intracerebral inoculation in suckling mice. Immunization with live or inactivated RABV vaccines expressing ZEBOV GP induced humoral immunity against each virus and conferred protection from both lethal RABV and EBOV challenge in mice. The bivalent RABV/ZEBOV vaccines described here have several distinct advantages that may speed the development of inactivated vaccines for use in humans and potentially live or inactivated vaccines for endemic nonhuman primates at risk of EBOV infection.

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Many years ago in microbiology practical classes, we used to encourage students to smear bright red Serratia marcescens bacteria all over their hands so we could demonstrate principles of epidemiology and the spread of infection. At the time, this was believed to be a harmless marine bacterium, but we stopped when it gradually realised that this bug is not as harmless as we used to think. S. marcescens has been in the news recently as the cause of the highly contagious white pox disease which kills corals, but it has a wide host range that includes plants, insects and nematodes, and it is also an opportunistic pathogen of mammals including humans. A new paper in PLoS ONE reveals the way in which this bacterium invades human cells.

Serratia marcescens Is Able to Survive and Proliferate in Autophagic-Like Vacuoles inside Non-Phagocytic Cells. 2011 PLoS ONE 6(8): e24054. doi:10.1371/journal.pone.0024054
Serratia marcescens is an opportunistic human pathogen that represents a growing problem for public health, particularly in hospitalized or immunocompromised patients. However, little is known about factors and mechanisms that contribute to S. marcescens pathogenesis within its host. In this work, we explore the invasion process of this opportunistic pathogen to epithelial cells. We demonstrate that once internalized, Serratia is able not only to persist but also to multiply inside a large membrane-bound compartment. This structure displays autophagic-like features, acquiring LC3 and Rab7, markers described to be recruited throughout the progression of antibacterial autophagy. The majority of the autophagic-like vacuoles in which Serratia resides and proliferates are non-acidic and have no degradative properties, indicating that the bacteria are capable to either delay or prevent fusion with lysosomal compartments, altering the expected progression of autophagosome maturation. In addition, our results demonstrate that Serratia triggers a non-canonical autophagic process before internalization. These findings reveal that S. marcescens is able to manipulate the autophagic traffic, generating a suitable niche for survival and proliferation inside the host cell.

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In my time as a microbiology student, the nitrogen cycle was a staple of introductory microbiology classes (as it still is), and we all learned that nitrification, the process of converting harmful ammonia into less toxic nitrate was carried out by Nitrosomonas and Nitrobacter and that kept our goldfish alive.

Whaddya know? 30 years later I find out that … like many of the things we thought we knew back then … that was wrong.

Aquarium Nitrification Revisited: Thaumarchaeota Are the Dominant Ammonia Oxidizers in Freshwater Aquarium Biofilters. 2011 PLoS ONE 6(8): e23281. doi:10.1371/journal.pone.0023281
Ammonia-oxidizing archaea (AOA) outnumber ammonia-oxidizing bacteria (AOB) in many terrestrial and aquatic environments. Although nitrification is the primary function of aquarium biofilters, very few studies have investigated the microorganisms responsible for this process in aquaria. This study used quantitative real-time PCR (qPCR) to quantify the ammonia monooxygenase (amoA) and 16S rRNA genes of Bacteria and Thaumarchaeota in freshwater aquarium biofilters, in addition to assessing the diversity of AOA amoA genes by denaturing gradient gel electrophoresis (DGGE) and clone libraries. AOA were numerically dominant in 23 of 27 freshwater biofilters, and in 12 of these biofilters AOA contributed all detectable amoA genes. Eight saltwater aquaria and two commercial aquarium nitrifier supplements were included for comparison. Both thaumarchaeal and bacterial amoA genes were detected in all saltwater samples, with AOA genes outnumbering AOB genes in five of eight biofilters. Bacterial amoA genes were abundant in both supplements, but thaumarchaeal amoA and 16S rRNA genes could not be detected. For freshwater aquaria, the proportion of amoA genes from AOA relative to AOB was inversely correlated with ammonium concentration. DGGE of AOA amoA genes revealed variable diversity across samples, with nonmetric multidimensional scaling (NMDS) indicating separation of freshwater and saltwater fingerprints. Composite clone libraries of AOA amoA genes revealed distinct freshwater and saltwater clusters, as well as mixed clusters containing both freshwater and saltwater amoA gene sequences. These results reveal insight into commonplace residential biofilters and suggest that aquarium biofilters may represent valuable biofilm microcosms for future studies of AOA ecology.

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The Batwa Pygmies, also known as Twa, are believed to be the original inhabitants of the equatorial forests of the Great Lakes region of Central Africa. They live in southwestern Uganda, northern and southern Rwanda and in many areas of the Kivu province of the Democratic Republic of the Congo (DRC). An interersting feature of the Batwa is that they differ significantly from neighboring Bantu agriculturalists in having fewer caries lesions and reduced tooth loss. Differences in diet and lifestyle provide the most likely explanation for the greater prevalence of caries lesions and tooth loss among the Bantu than among the Batwa. The Batwa have less access to highly cariogenic, refined carbohydrates than do the Bantu. In addition, because of their hunter-gatherer lifestyle, the diet of the Batwa tends to be higher in animal protein than that of the Bantu, and this would also contribute to a lower caries rate.

It is also possible that the oral microbiome of the Batwa may either influence, or be influenced by, the lower prevalence of caries.To investigate this further, researchers analyzed the saliva microbiome diversity of the Batwa in comparison with agricultural groups from similar enviroments in Africa, in order to address the following questions:

1. How different is the Batwa saliva microbiome from that of African agriculturalists
2. Is the low level of dental caries in the Batwa associated with particular microbial taxa?

High Diversity of the Saliva Microbiome in Batwa Pygmies. 2011 PLoS ONE 6(8): e23352. doi:10.1371/journal.pone.0023352
We describe the saliva microbiome diversity in Batwa Pygmies, a former hunter-gatherer group from Uganda, using next-generation sequencing of partial 16S rRNA sequences. Microbial community diversity in the Batwa is significantly higher than in agricultural groups from Sierra Leone and the Democratic Republic of Congo. We found 40 microbial genera in the Batwa, which have previously not been described in the human oral cavity. The distinctive composition of the salvia microbiome of the Batwa may have been influenced by their recent different lifestyle and diet.

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Sudan is a large country with a diverse population and history of civil conflict. Poverty levels are high with a gross national income per capita of less than two thousand dollars. The country has a high burden of tuberculosis (TB) with an estimated 50,000 incident cases during 2009, when the estimated prevalence was 209 cases per 100,000 of the population. Few studies have been undertaken on TB in Sudan and the prevalence of drug resistant disease is not known.

In this study Mycobacterium tuberculosis isolates from 235 patients attending three treatment centers in Sudan were screened for susceptibility to isoniazid, rifampicin, ethambutol and streptomycin by the proportion method on Lowenstein Jensen media. 232 isolates were also genotyped by spoligotyping. Demographic details of patients were recorded using a structured questionnaire. Statistical analyses were conducted to examine the associations between drug resistance with risk ratios computed for a set of risk factors (gender, age, case status – new or relapse, geographic origin of the patient, spoligotype, number of people per room, marital status and type of housing).

Multi drug-resistant tuberculosis (MDR-TB), being resistance to at least rifampicin and isoniazid, was found in 5% of new cases and 24% of previously treated patients. Drug resistance was associated with previous treatment with risk ratios of 3.51 for resistance to any drug and 5.23 for MDR-TB. Resistance was also associated with the geographic region of origin of the patient, being most frequently observed in patients from the Northern region and least in the Eastern region with risk ratios of 7.43 and 14.09 for resistance to any drug and MDR-TB.

“We conclude that emergence of drug resistant tuberculosis has the potential to be a serious public health problem in Sudan and that strengthened tuberculosis control and improved monitoring of therapy is needed. Further surveillance is required to fully ascertain the extent of the problem.”

Tuberculosis in Sudan: a study of Mycobacterium tuberculosis strain genotype and susceptibility to anti-tuberculosis drugs. BMC Infectious Diseases 11:219 2011

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Synthesis of subgenomic (SG) messenger RNAs (mRNAs) by (+)strand RNA viruses allows the differential expression of specific virus genes, both quantitatively and temporally. SG RNAs have the following properties:

• They are made in infected cells but do not interfere with the normal course of virus replication
• The SG RNA sequences are shorter than their cognate genomic RNAs
• Their sequences are usually co-terminal with the 3′ genomic sequence but sometimes are co-terminal with the 5′ sequences. Yet other viruses make SG RNAs which contain a 5′ co-terminal leader joined to a 3′ co-terminal sequence
• Typically, whether a messenger SG RNA contains only one ORF, or multiple ORFs, with some rare exceptions, only the 5′ ORF is translated. Although most SG RNAs function as messengers and are translated, other SG RNAs, generally those with 5′ co-terminal sequences, have other functions.

Subgenomic messenger RNAs: mastering regulation of (+)-strand RNA virus life cycle. Virology. 2011 412(2):245-255
Many (+)-strand RNA viruses use subgenomic (SG) RNAs as messengers for protein expression, or to regulate their viral life cycle. Three different mechanisms have been described for the synthesis of SG RNAs. The first mechanism involves internal initiation on a (-)-strand RNA template and requires an internal SGP promoter. The second mechanism makes a prematurely terminated (-)-strand RNA which is used as template to make the SG RNA. The third mechanism uses discontinuous RNA synthesis while making the (-)-strand RNA templates. Most SG RNAs are translated into structural proteins or proteins related to pathogenesis: however other SG RNAs regulate the transition between translation and replication, function as riboregulators of replication or translation, or support RNA-RNA recombination. In this review we discuss these functions of SG RNAs and how they influence viral replication, translation and recombination.

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The complement system is a major component of innate immunity and consists of both soluble factors and cell surface receptors that interact to sense and respond to invading pathogens. The complement system links the innate and adaptive immune responses by a variety of mechanisms including enhancing humoral immunity, regulating antibody effector mechanisms, and modulating T cell function. In addition to these roles in normal host immune responses, the complement system has pathogenic roles in a variety of ischemic, inflammatory, and autoimmune diseases.

The complement system is a critical determinant of the outcome of infection by a variety of different viruses. Our understanding of the mechanisms by which complement protects from virus-induced disease has improved dramatically. Research in this area will not only continue to contribute to our knowledge of viral pathogenesis, but will continue to provide insight into the regulation of immune responses, and lead to improved therapeutic and vaccine approaches for both viral and non-viral pathogens. Perhaps less well understood are the mechanisms by which complement functions as a pathogenic effector in some virus-induced diseases. Further progress towards identifying the signals and pathways that lead to complement activation, which are not understood for many viruses, particularly in vivo, and a deeper understanding of the impact of complement activation on host immune responses to viral infection may shed light. Continued investigation of the role of complement in viral pathogenesis will provide important insights into virus–host interactions and strategies to prevent or treat virus-induced disease.

Complement and viral pathogenesis. Virology. 2011 411(2): 362-373
The complement system functions as an immune surveillance system that rapidly responds to infection. Activation of the complement system by specific recognition pathways triggers a protease cascade, generating cleavage products that function to eliminate pathogens, regulate inflammatory responses, and shape adaptive immune responses. However, when dysregulated, these powerful functions can become destructive and the complement system has been implicated as a pathogenic effector in numerous diseases, including infectious diseases. This review highlights recent discoveries that have identified critical roles for the complement system in the pathogenesis of viral infection.

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The HTLV-1 Tax protein both activates viral replication and is involved in HTLV-1-mediated transformation of T lymphocytes. The transforming properties of Tax include altering the expression of select cellular genes via activation of cellular pathways and perturbation of both cell cycle control mechanisms and apoptotic signals. The recent discovery that Tax undergoes a hierarchical sequence of posttranslational modifications that control its intracellular localization provides provocative insights into the mechanisms regulating Tax transcriptional and transforming activities.

Move or Die: the Fate of the Tax Oncoprotein of HTLV-1. (2011) Viruses 3(6): 829-857 doi:10.3390/v3060829

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A myriad of factors favor the emergence and re-emergence of arthropod-borne viruses (arboviruses), including migration, climate change, intensified livestock production, an increasing volume of international trade and transportation, and changes to ecosystems (e.g., deforestation and loss of biodiversity). Consequently, arboviruses are distributed worldwide and represent over 30% of all emerging infectious diseases identified in the past decade. Although some arboviral infections go undetected or are associated with mild, flu-like symptoms, many are important human and veterinary pathogens causing serious illnesses such as arthritis, gastroenteritis, encephalitis and hemorrhagic fever and devastating economic loss as a consequence of lost productivity and high mortality rates among livestock. One of the most consistent molecular features of emerging arboviruses, in addition to their near exclusive use of RNA genomes, is the inclusion of viral, non-structural proteins that act as interferon antagonists. In this review, we describe these interferon antagonists and common strategies that arboviruses use to counter the host innate immune response. In addition, we discuss the complex interplay between host factors and viral determinants that are associated with virus emergence and re-emergence, and identify potential targets for vaccine and anti-viral therapies.

The Role of Interferon Antagonist, Non-Structural Proteins in the Pathogenesis and Emergence of Arboviruses. (2011) Viruses 3(6): 629-658; doi:10.3390/v3060629

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