MicrobiologyBytes

We are always being told by marketers of yogurts that the human gut contains a bustling community of different bacteria, both good and bad, and that this balance is vital to keeping you healthy. But if you target the disease-causing bacteria with medicine, what might be the collateral damage to their health-associated cousins that call the human body home? A new study just published looks into the changes that happen in the human gut when it is exposed to the widely used antibiotic, ciprofloxacin.

Ciprofloxacin is prescribed for a number of conditions, including common afflictions such as urinary tract infections. It was previously believed to cause only modest harm to the abundant beneficial bacteria of the human body. The intestinal microbiota is essential to human health, with effects on nutrition, metabolism, pathogen resistance, and other processes. Antibiotics may disrupt these interactions and cause acute disease, as well as contribute to chronic health problems, although technical challenges have hampered research on this front. Several recent studies have characterized uncultured and complex microbial communities by applying a new, massively parallel technology to obtain hundreds of thousands of sequences of a specific variable region within the small subunit rRNA gene. These shorter sequences provide an indication of diversity.

To investigate ciprofloxacin’s effect on health-associated bacteria, researchers catalogued types of bacteria present in the faeces of volunteers who were undergoing a course of treatment of ciprofloxacin. The DNA-analysis technique massively-parallel pyrosequencing was central to their approach. With this technique, the researchers examined the diversity and abundance of bacteria present in human faeces, identifying over 5,600 different bacterial species and strains. The dramatically increased detection power of this approach allowed the team to track carefully the changes in the gut’s bacterial community both during and after the course of treatment. The study found that while the patients were undergoing treatment the overall abundance of approximately 30% of the species and strains was significantly affected. The effects varied greatly between individuals, with two of the subjects showing a strong reduction in diversity. The effects didn’t stop there. Once the course of treatment had been halted, it took up to four weeks for most strains of gut bacteria to return to their pre-treatment levels. Even six months later, some types of bacteria had not managed to return to pre-treatment abundance levels. During this time of population upheaval none of the patients in the study reported signs of gut-related problems.

The bacteria present in the human gut are responsible for various aspects of host nutrition, metabolism and immune responses. This study reveals aspects of resiliency in the indigenous microbiota when subjected to perturbation, but underlines the concern that antibiotic treatment, especially when prolonged or repeated, may have long-lasting effects on overall wellbeing that could go un-noticed.

The pervasive effects of an antibiotic on the human gut microbiota, as revealed by deep 16S rRNA sequencing. PLoS Biol 6(11): e280
The human intestinal microbiota is essential to the health of the host and plays a role in nutrition, development, metabolism, pathogen resistance, and regulation of immune responses. Antibiotics may disrupt these coevolved interactions, leading to acute or chronic disease in some individuals. Our understanding of antibiotic-associated disturbance of the microbiota has been limited by the poor sensitivity, inadequate resolution, and significant cost of current research methods. The use of pyrosequencing technology to generate large numbers of 16S rDNA sequence tags circumvents these limitations and has been shown to reveal previously unexplored aspects of the ‘‘rare biosphere.’’ We investigated the distal gut bacterial communities of three healthy humans before and after treatment with ciprofloxacin, obtaining more than 7,000 full-length rRNA sequences and over 900,000 pyrosequencing reads from two hypervariable regions of the rRNA gene. A companion paper in PLoS Genetics shows that the taxonomic information obtained with these methods is concordant. Pyrosequencing of the V6 and V3 variable regions identified 3,300–5,700 taxa that collectively accounted for over 99% of the variable region sequence tags that could be obtained from these samples. Ciprofloxacin treatment influenced the abundance of about a third of the bacterial taxa in the gut, decreasing the taxonomic richness, diversity, and evenness of the community. However, the magnitude of this effect varied among individuals, and some taxa showed interindividual variation in the response to ciprofloxacin. While differences of community composition between individuals were the largest source of variability between samples, we found that two unrelated individuals shared a surprising degree of community similarity. In all three individuals, the taxonomic composition of the community closely resembled its pretreatment state by 4 weeks after the end of treatment, but several taxa failed to recover within 6 months. These pervasive effects of ciprofloxacin on community composition contrast with the reports by participants of normal intestinal function and with prior assumptions of only modest effects of ciprofloxacin on the intestinal microbiota. These observations support the hypothesis of functional redundancy in the human gut microbiota. The rapid return to the pretreatment community composition is indicative of factors promoting community resilience, the nature of which deserves future investigation.

Related:

• Resistance to Widely-Used Antibiotics among Inhabitants of Remote South American Villages
• Probiotics – weapons in the war against gut pathogens
• Breast is Best?
• Probiotics – friendly bacteria?

The first-ever European Antibiotic Awareness Day will take place across Europe on 18 November 2008. European Antibiotic Awareness Day will be an annually recurring event that will raise awareness about the risks associated with inappropriate use of antibiotics and how to take antibiotics responsibly. European Antibiotic Awareness Day will set focus specifically on the need for everybody to stop any unnecessary use of antibiotics.
European Antibiotic Awareness Day is a European health initiative in close collaboration with the World Health Organization, as well as many other relevant representative stakeholder groups such as health professionals and scientists. All public authorities, healthcare professionals, child care professionals and social workers as well as private organisations, families and individuals are encouraged to take part in the initiative and to launch their own activities or discussions on responsible use of antibiotics on European Antibiotic Awareness Day.

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Aspergillosis is a group of lung diseases caused by infection with Aspergillus, a fungus (mold) that grows on decaying plant matter. Because Aspergillus is widespread in the environment, people often breathe in its spores. For most people, this is not a problem – their immune system rapidly kills the fungal spores. However, people with asthma or cystic fibrosis sometimes develop allergic bronchopulmonary aspergillosis, a condition in which the spores trigger an allergic reaction in the lungs that causes coughing, wheezing. and breathlessness. Other people can develop an aspergilloma – a fungus ball that grows in cavities in the lung caused by other illnesses such as tuberculosis. However, the most serious form of aspergillosis is invasive aspergillosis. This pneumonia-like infection, which is fatal if left untreated, affects people who have a weakened immune system (for example, people with leukemia) and can spread from the lungs into the heart, brain, and other parts of the body. Aspergillosis is usually treated with triazole drugs, which inhibit an enzyme that the fungus needs to make its cell membranes; this enzyme is encoded by a gene called cyp51A. Voriconazole is the first-line therapy for aspergillosis but itraconazole and posaconazole are also sometimes used and ravuconazole is in clinical development.

About half of patients with invasive aspergillosis recover if they are given triazoles. Worryingly, however, strains of Aspergillus fumigatus (the type of Aspergillus usually involved in invasive aspergillosis) with resistance to several triazoles have recently been isolated from some patients in The Netherlands. If multi-azole resistant strains of A. fumigatus become common, they could have a serious impact on the management of invasive aspergillosis. However, noone knows what proportion of A. fumigatus strains isolated from patients with aspergillosis are resistant to several azole drugs. That is, no-one knows the “prevalence” of multi-azole resistance. In a new study, researchers investigated the prevalence and development of azole resistance in A. fumigatus.

Since 1994, all fungal isolates from patients at the Radboud University Nijmegen Medical Center in the Netherlands have been stored. The researchers’ search of this collection yielded 1,908 A. fumigatus isolates that had been collected from 1,219 patients over a 14-year period. Of these, the isolates from 32 patients grew in the presence of itraconazole. All the itraconazole-resistant isolates (which also had increased resistance to voriconazole, ravuconazole, and posaconazole) were collected after 1999; the annual prevalence of itraconazole-resistant isolates ranged from 1.7% to 6%. The researchers then sequenced the cyp51A gene in each resistant isolate. Thirty had a genetic alteration represented as TR/L98H. This “dominant resistance mechanism” consisted of a single amino acid change in the cyp51A gene and an alteration in the gene’s promoter region (the region that controls how much protein is made from a gene). The researchers also analyzed A. fumigatus isolates from patients admitted to 28 other hospitals in the Netherlands. Itraconazole resistance was present in isolates from 13 patients (out of 101 patients) from nine hospitals; the TR/L98H genetic alteration was present in 69% of the itraconazole-resistant isolates. Finally, itraconazole resistance was present in six isolates from four other countries (out of 317 isolates from six countries); only one Norwegian isolate had the TR/L98H genetic alteration.

These findings indicate that azole resistance is emerging in A. fumigatus and may already be more prevalent than generally thought. Given the dominance of the TR/L98H genetic alteration in the azole-resistant clinical isolates, the researchers suggest that A. fumigatus isolates harboring this alteration might be present and spreading in the environment rather than being selected for during azole treatment of patients. Why azole resistance should develop in A. fumigatus in the environment is unclear but might be caused by the use of azole-containing fungicides. Further studies are now urgently needed to find out if this is the case, to measure the international prevalence and spread of A. fumigatus isolates harboring the TR/L98H genetic alteration, and, most importantly, to develop alternative treatments for patients with azole-resistant aspergillosis.

Emergence of azole resistance in Aspergillus fumigatus and spread of a single resistance mechanism. 2008 PLoS Med 5(11): e219
Resistance to triazoles was recently reported in Aspergillus fumigatus isolates cultured from patients with invasive aspergillosis. The prevalence of azole resistance in A. fumigatus is unknown. We investigated the prevalence and spread of azole resistance using our culture collection that contained A. fumigatus isolates collected between 1994 and 2007. We investigated the prevalence of itraconazole (ITZ) resistance in 1,912 clinical A. fumigatus isolates collected from 1,219 patients in our University Medical Centre over a 14-y period. The spread of resistance was investigated by analyzing 147 A. fumigatus isolates from 101 patients, from 28 other medical centres in The Netherlands and 317 isolates from six other countries. The isolates were characterized using phenotypic and molecular methods. The electronic patient files were used to determine the underlying conditions of the patients and the presence of invasive aspergillosis. ITZ-resistant isolates were found in 32 of 1,219 patients. All cases were observed after 1999 with an annual prevalence of 1.7% to 6%. The ITZ-resistant isolates also showed elevated minimum inhibitory concentrations of voriconazole, ravuconazole, and posaconazole. A substitution of leucine 98 for histidine in the cyp51A gene, together with two copies of a 34-bp sequence in tandem in the gene promoter was found to be the dominant resistance mechanism. Microsatellite analysis indicated that the ITZ-resistant isolates were genetically distinct but clustered. The ITZ-sensitive isolates were not more likely to be responsible for invasive aspergillosis than the ITZ-resistant isolates. ITZ resistance was found in isolates from 13 patients (12.8%) from nine other medical centres in The Netherlands, of which 69% harboured the TR/L98H substitution, and in six isolates originating from four other countries. Azole resistance has emerged in A. fumigatus and might be more prevalent than currently acknowledged. The presence of a dominant resistance mechanism in clinical isolates suggests that isolates with this mechanism are spreading in our environment.

Related:

• All About Fungi: Part 1
• Fungal Infections
• Gamma interferon and fungal infections

Penicillins and synthetic beta-lactam antibiotics have dramatically transformed health care and quality of life in the 80 years since Alexander Fleming’s discovery of Penicillium. Large-scale production of beta-lactam antibiotics is the result of sustained industrial strain improvement, representing numerous rounds of mutagenesis and selection. Penicillin titers and productivities have increased by at least three orders of magnitude in the past 60 years, representing an unprecedented success in industrial strain improvement.

Current industrial Penicillium strains are derived from a single natural isolate of P. chrysogenum obtained during WWII from an infected cantaloupe. Biochemical and genetic analysis of industrial strains led to the identification of several important mutations in high-producing strains, including amplification of penicillin biosynthesis genes. However, much of the molecular basis for improved productivity remains to be elucidated. A detailed understanding of the molecular biology of P. chrysogenum is not only relevant for natural penicillins, but by applying genetic engineering approaches, it has become possible to extend the range of fermentation products to include beta-lactam derivatives that could previously only be produced by chemical modification.

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To gain more insight into penicillin synthesis, researchers have recently sequenced the 32.19 Mbp genome of P. chrysogenum and identified numerous genes responsible for key steps in penicillin production (Genome sequencing and analysis of the filamentous fungus Penicillium chrysogenum. Nature Biotechnology, 28 September 2008). DNA microarrays were used to compare the transcriptomes of the sequenced strain and a penicillinG high-producing strain. Transcription of genes involved in biosynthesis of valine, cysteine and alpha-aminoadipic acid – precursors for penicillin biosynthesis – as well as of genes encoding microbody proteins, was increased in the high-producing strain. Some gene products were shown to directly control beta-lactam output. Many key cellular transport processes involving penicillins and intermediates still remain to be characterized at the molecular level. Genes predicted to encode transporters were strongly overrepresented among the genes transcriptionally upregulated under conditions that stimulate penicillinG production, illustrating potential for future genomics-driven metabolic engineering.

Access to the full range of genomics techniques will be invaluable for further innovation in antibiotics production. Despite the massive improvements already achieved in classical strain improvement, further improvement of penicillin production remains a distinct possibility.

Related:

• All About Fungi: Part 1 | Part 2
• Penicillin: Triumph and Tragedy
• Peptidoglycan – the strength and weakness of bacteria

Tuberculosis, caused by the bacterium Mycobacterium tuberculosis, kills over 2 million people each year. It is estimated that approximately one-third of the world population is infected with M. tuberculosis, though the majority will never develop active disease. Almost 1 in 20 cases of tuberculosis worldwide is resistant to multiple drugs (known as multidrug-resistant TB or MDR-TB).

Tuberculosis can be a difficult disease to diagnose, mainly due to the difficulty in culturing this slow-growing organism in the laboratory. It takes 4–12 weeks for a laboratory culture to be clearly positive. While microscopy and culture are still the major backbone for laboratory diagnosis of tuberculosis, rapid diagnosis still relies on a medical evaluation including a medical history, a chest X-ray and a physical examination, and may also include a tuberculin skin test or serological tests. These methods are used in rich countries but are probably not available in much of the developing world where the majority of tuberculosis carriers live.

New TB tests are being developed that offer the hope of offering cheaper, faster and more accurate TB testing. The majority of new molecular tests use polymerase chain reaction (PCR)-based detection of nucleic acids, including both DNA and RNA, which are specific to M. tuberculosis, or mutations in mycobacterial genes which are associated with resistance to anti-tuberculosis drugs such as isoniazid and rifampicin. Other new diagnostic tests use PCR or antibody assays to detect the release of interferon-gamma in response to mycobacterial infection. Recently, microarray techniques have been employed extensively for the detection of drug resistance-related mutations.

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While genetic assays are useful for rapid detection of drug resistance compared to the time taken by culture-based methods, not all drug-resistant isolates have mutations in the “hot spots” of genes commonly associated with drug resistance. Another drawback of some tests is their inability to detect minor populations of drug-resistant organisms in cultures from clinical samples. In defining drug resistance, the presence of 1–10% of drug-resistant organisms in culture can make it functionally drug resistant. However, routine nucleic acid hybridization assays require about 15–20% of a drug-resistant strain in a culture to qualify as a mutant isolate.

Interferon-gamma tests have been quite successful in detecting latent TB infection in areas with concurrent vaccination programs, since these tests do not get “confused” by the presence of an immunogen. Currently, two types of test for the detection of interferon-gamma production by T lymphocytes are available, ELISA and ELISPOT. These tests seem to reflect the degree of exposure to M. tuberculosis in household contacts of TB patients and occupational contact in TB hospitals. The major obstacles in implementing interferon-gamma tests include their high costs, requirement of highly trained personnel and fresh blood samples, all formidable obstacles in most areas with high TB prevalance.

Mycobacterium tuberculosis has no significant animal or environmental reservoirs and shows limited genetic diversity. In spite of this, TB continues to be a widespread and devastating disease. The need for new faster-acting diagnostic tests and better drugs is clear.

Tuberculosis: diagnostics. Tuberculosis (Edinb). 2007 87 Suppl 1: S14-7 doi:10.1016/j.tube.2007.05.001

Related:

• Tuberculosis – is the white plague winning?
• How can we overcome the barriers to treating drug-resistant TB?
• The Influence of Host and Bacterial Genotype on the Development of Tuberculosis

Few bacteria are loners – more often they grow in crowds and squat on surfaces where they form a community. These so-called biofilms develop on any surface that bacteria can attach themselves to. The dilemma we face is that neither disinfectants and antibiotics, nor phagocytes (cells which typically destroy microorganisms) and our immune system can destroy these biofilms. This is a particular problem in hospitals if these bacteria form a community on a catheter or implant where they could potentially cause a serious infection. Scientists in Germany have just identified one of the fundamental mechanisms used by the bacteria in biofilms to protect themselves against the attacking phagocytes – the discovery that biofilm bacteria use chemical weapons to defend themselves.

Until now, scientists have been unable to understand the root of the biofilm problem – the inability of phagocytes to destroy these biofilms. The researchers investigated this problem by modelling the problem on marine bacteria. Marine bacteria face constant threats in their habitat from environmental phagocytes (amoebae) which behave in a similar way in the sea as do immune cells in our body (i.e. they seek out, and feed on, bacteria). As long as bacteria are swimming freely and separately in the water, they are easy pickings for these predators. However, if they become attached to a surface and socialize with other bacteria, the amoebae can no longer successfully attack them. The surprising thing was that the amoebae attacking the biofilms were de-activated or even killed. The bacteria are clearly not just building a fortress, they are also fighting back. The bacteria utilise chemical weapons to achieve this. A widespread and highly effective molecule used by marine bacteria is the pigment violacein. Once the defence system is ready, the biofilm shimmers a soft purple colour. If the attackers consume just a single cell of the biofilm – and the pigment they contain – this paralyses the attackers momentarily and the violacein triggers a suicide mechanism in the amoebae. Biofilms may no longer be seen just as a problem; they may also be a source of new bioactive agents. When organized in biofilms, bacteria produce highly effective substances which individual bacteria alone cannot produce. And the scientists hope to use these molecules to combat a specific group of pathogens, human parasites that cause devastating infections such as sleeping illness and malaria. Amoeba are ancient relatives of these pathogens and thus biofilm-derived weapons may provide an excellent basis for the design of new parasiticidal drugs.

Marine Biofilm Bacteria Evade Eukaryotic Predation by Targeted Chemical Defense. 2008 PLoS ONE 3(7): e2744
Many plants and animals are defended from predation or herbivory by inhibitory secondary metabolites, which in the marine environment are very common among sessile organisms. Among bacteria, where there is the greatest metabolic potential, little is known about chemical defenses against bacterivorous consumers. An emerging hypothesis is that sessile bacterial communities organized as biofilms serve as bacterial refuge from predation. By testing growth and survival of two common bacterivorous nanoflagellates, we find evidence that chemically mediated resistance against protozoan predators is common among biofilm populations in a diverse set of marine bacteria. Using bioassay-guided chemical and genetic analysis, we identified one of the most effective antiprotozoal compounds as violacein, an alkaloid that we demonstrate is produced predominately within biofilm cells. Nanomolar concentrations of violacein inhibit protozoan feeding by inducing a conserved eukaryotic cell death program. Such biofilm-specific chemical defenses could contribute to the successful persistence of biofilm bacteria in various environments and provide the ecological and evolutionary context for a number of eukaryote-targeting bacterial metabolites.

Related:

• Early bacterial adhesion dynamics
• Communication, cooperation, competition and cheating – bacteria are just like us
• Enzyme helps bacteria beat body by building biofilm
• Bacteria hedge their bets

Resistance to ciprofloxacin, a member of one of the most commonly used groups of antibiotics in the world, has been discovered by a team of Canadian researchers among people in remote South American villages who are believed to have never taken this medication. The researchers found high levels of ciprofloxacin resistance in Escherichia coli in Amerindians from the Guyanese rainforest. These individuals are reported as never having received treatment with ciprofloxacin or related fluoroquinolone antibiotics. The Amerindians had however received frequent treatment for malaria (which is a eukaryotic parasite and not a bacterium) with chloroquine. Chloroquine is used widely around the world to combat malaria, and it also is a close chemical cousin of the fluoroquinolones. Fluoroquinolones began widespread use in the late 1980s and now are among the most commonly used antibiotics in North America and Europe. Because the bacteria carried by the Guyanese Amerindians were resistant to ciprofloxacin, the researchers suggest that it is possible that exposure to chloroquine may make the bacteria that people carry in their intestines resistant to fluoroquinolones – a theory that, if corroborated by further research, could have important public health implications in developing countries and in the developed world. They also found resistance in many other species of bacteria – including Salmonella – that are found in rectal swabs. This means that chloroquine use for malaria may make the fluoroquinolones less effective for many common tropical diseases such as typhoid fever, diarrheal illnesses, and possibly also tuberculosis and pneumonia in the developing world.

Plans are being considered by major global health-promotion organizations to launch a campaign of widespread use in Africa and South America of a new anti-malarial treatment regimen called Artemesinin combination therapy (ACT). ACT usually includes quinoline drugs similar to chloroquine. These drugs are closely related to both chloroquine and fluoroquinolones. The researchers plan to carry out further studies to identify whether some quinolines may be less likely to induce quinolone resistance than others, and thus may be safer for malaria control programs. Dr Mike Silverman and 19 other volunteer health care professionals traveled by airplane from Bartica, a town that serves as the gateway to the interior of the Guyanese rainforest, to a handful of remote villages as part of annual humanitarian medical missions between 2002 and 2005. They took rectal swabs from 535 people in Bartica and the remote villages. They also asked the local inhabitants about whether they had ever been exposed to chloroquine or fluoroquinolones, and took water samples. They took the samples home and analyzed them. The team found that 5.4% of the rectal-swab samples contained ciprofloxacin-resistant Escherichia coli, with a 4.8% resistance rate among the remote-village samples. This is a very high rate – particularly when compared to the 4% rate found in a recent study of ciprofloxacin resistance in American intensive care units where fluroquinolones are very intensively used. It is also particularly remarkable because fluoroquinolones had never been available in these communities.

The ciprofloxacin-resistant E. coli samples were also all found to be highly resistant to chloroquine, and to have characteristics that would confer resistance to all fluoroquinolones including the newer drugs levofloxacin and moxifloxacin. Furthermore, the team found that one of the water samples they took in 2004 contained ciprofloxacin-resistant E. coli and another contained a small amount of chloroquine, probably from human waste contamination. Because of a widespread malaria outbreak in rural Guyana in late 2002, 30% of the villagers tested by the Canadian team in 2003 said they had been given chloroquine within the past six months, and in 2005 86% said they had used chloroquine within the past two years. The rates of chloroquine use may in fact have been much higher the investigators believe. This is because patient reports are not always reliable, and because of the very extensive treatment with chloroquine during the late-2002 malaria epidemic. The data also showed that community-wide fluoroquinolone resistance rose dramatically shortly after the malaria outbreak, further suggesting a link between chloroquine use for malaria and bacterial resistance to fluoroquinolones. Together, these data suggest that we must focus our efforts on prevention of malaria using mosquito-control measures such as bednets and by developing vaccines. For the short term, however, we still will have no choice but to use these lifesaving antimalarial drugs. However we need to investigate which of the antimalarials can be used in the future with the least impact on bacterial drug resistance.

Antimalarial Therapy Selection for Quinolone Resistance among Escherichia coli in the Absence of Quinolone Exposure, in Tropical South America. PLoS ONE 3(7): e2727
Bacterial resistance to antibiotics is thought to develop only in the presence of antibiotic pressure. Here we show evidence to suggest that fluoroquinolone resistance in Escherichia coli has developed in the absence of fluoroquinolone use. Over 4 years, outreach clinic attendees in one moderately remote and five very remote villages in rural Guyana were surveyed for the presence of rectal carriage of ciprofloxacin-resistant Gram-negative bacilli (GNB). Drinking water was tested for the presence of resistant GNB by culture, and the presence of antibacterial agents and chloroquine by HPLC. The development of ciprofloxacin resistance in E. coli was examined after serial exposure to chloroquine. Patient and laboratory isolates of E. coli resistant to ciprofloxacin were assessed by PCR-sequencing for quinolone-resistance-determining-region (QRDR) mutations. In the very remote villages, 4.8% of patients carried ciprofloxacin-resistant E. coli with QRDR mutations despite no local availability of quinolones. However, there had been extensive local use of chloroquine, with higher prevalence of resistance seen in the villages shortly after a Plasmodium vivax epidemic (p 0.01). Antibacterial agents were not found in the drinking water, but chloroquine was demonstrated to be present. Chloroquine was found to inhibit the growth of E. coli in vitro. Replica plating demonstrated that 2-step QRDR mutations could be induced in E. coli in response to chloroquine. In these remote communities, the heavy use of chloroquine to treat malaria likely selected for ciprofloxacin resistance in E. coli. This may be an important public health problem in malarious areas.

Almost 1 in 20 cases of tuberculosis worldwide is resistant to multiple drugs (known as multidrug-resistant TB or MDR-TB) and the World Health Organization has called for a massive scale up in public health efforts to tackle these cases. A group of MDR-TB experts has outlined its recommendations on conducting research that would help in the scale up. MDR-TB can be effectively treated using second-line TB drugs, though these drugs are more expensive, less potent, and less well tolerated than first-line drugs. Fewer than 2% of all patients with MDR-TB are receiving appropriate second-line treatment. The WHO has therefore called for a dramatic scale up of MDR-TB treatment as a routine component of TB control, setting a target of treating 1.6 million patients with MDR-TB by 2015. Pilot projects of MDR-TB management (known as programmatic management of drug-resistant TB or PMDT) in five low income settings showed treatment success rates of 59%-83%. The new agenda identifies the most important barriers to scaling up the treatment of MDR-TB and prioritizes the research questions to be addressed to overcome these barriers. The research priorities include new and improved tools for testing patients to see if they have drug-resistant TB clinical trials of simplified and shorter second-line treatments for MDR-TB new and improved strategies for diagnosis of drug-resistant TB, for helping patients complete the whole course of drug treatment, and for controlling the spread of the infection understanding geographic variations in the occurrence of drug resistance clinical trials to test whether giving TB drugs to people who came into contact with patients with drug-resistant TB prevents them from developing resistant TB. With increasing recognition of drug-resistant TB worldwide, the time has come to move PMDT in resource-limited settings beyond the limited, pilot project phase.

Scaling up programmatic management of drug-resistant tuberculosis: A prioritized research agenda. 2008 PLoS Med 5(7): e150
Summary:
The World Health Organization calls for massive scale-up of programmatic management of drug-resistant tuberculosis in resource-limited settings. Several technical and operational barriers impede the achievement of this scale-up. A research agenda, developed by the Stop TB Partnership, identifies the most important barriers and prioritizes the research questions to be addressed in order to overcome these barriers. Research priorities include:

• new and improved tools for drug resistance testing
• clinical trials of simplified and shorter second-line treatment regimens
• new and improved strategies for diagnosis of drug-resistant tuberculosis, treatment adherence, and infection control
• understanding of the geographic variations in occurrence of drug resistance
• clinical trials of prophylactic treatment of contacts of patients with drug-resistant tuberculosis

Related:

• Tuberculosis – is the white plague winning?
• Extreme drug resistant tuberculosis (XDR-TB)
• Extreme drug resistant tuberculosis (XDR-TB) update
• World Tuberculosis Day: new drugs for an old foe

Lantibiotics are gene-encoded, ribosomally synthesized derived peptides that have attracted widespread scientific attention in recent years not only as promising safe and natural food additives but also as potential chemotherapeutic agents. The original, and most intensively studied lantibiotic, nisin, has a long record of safe use, is US Food and Drug Administration (FDA) approved and is one of only a few bacteriocins to have been applied commercially. It has antibacterial activity against many Gram-positive bacteria including food-borne pathogens such as staphylococci, bacilli, clostridia and mycobacteria. Nisin is also active against the bacteria responsible for bovine mastitis, an inflammation of the udder that is both persistent and costly to treat, and for this reason has been incorporated into a number of commercial products that are used as an alternative treatment to antibiotics.

Nisin is the prototype of the lantibiotic group of antimicrobial peptides. It exhibits broad spectrum inhibition of Gram-positive bacteria including important food pathogens and clinically relevant antibiotic-resistant bacteria. Significantly, the gene-encoded nature of nisin means that it can be subjected to gene-based bioengineering to generate novel derivatives. Here, we take advantage of this to generate the largest bank of randomly mutated nisin derivatives reported to date, with the ultimate aim of identifying variants with enhanced bioactivity. This approach led to the identification of a nisin-producing strain with enhanced bioactivity against the mastitic pathogen Streptococcus agalactiae resulting from an amino acid change in the hinge region of the peptide. Prompted by this discovery, site-directed and site-saturation mutagenesis of the hinge region residues was employed, resulting in the identification of additional derivatives with enhanced bioactivity and specific activity against Gram-positive pathogens including Listeria monocytogenes and/or Staphylococcus aureus. The identification of these derivatives represents a major step forward in the bioengineering of nisin, and lantibiotics in general, and confirms that peptide engineering can deliver derivatives with enhanced antimicrobial activity against specific problematic spoilage and pathogenic microbes or against Gram-positive bacteria in general.

The generation of nisin variants with enhanced activity against specific Gram-positive pathogens
Molecular Microbiology 27 May 2008

Related:

• Bacteriocins
• A new web-accessible database for bacteriocin characterization