Bio-Control of Salmonella in Foods Using Bacteriophages

Salmonella phage PA13076 I’m a bit of a sceptic when it comes to the idea that “phage therapy” is going to save us when the antibiotics fail. There have been enough clinical trails now to show that this cannot be true, at least in simple terms. But that’s not to say that bacteriophages don’t have their uses in controlling bacteria. Topical treatment of wounds is one interesting area, and using phages to control bacterial contamination of foods is another area worth exploring.

This paper isolates two relatively broad-spectrum Salmonella phages and tests whether they are effective in reducing contamination of chicken meat, milk and vegetables. And the answer is … somewhat effective. Phage therapy/treatment is not a magic bullet and it’s never going to be. But “more work needs to be done to determine whether phages can be used to disinfect food products“.

 

Bio-Control of Salmonella Enteritidis in Foods Using Bacteriophages. (2015) Viruses, 7, 4836-4853
Two lytic phages, vB_SenM-PA13076 (PA13076) and vB_SenM-PC2184 (PC2184), were isolated from chicken sewage and characterized with host strains Salmonella Enteritidis (SE) ATCC13076 and CVCC2184, respectively. Transmission electron microscopy revealed that they belonged to the family Myoviridae. The lytic abilities of these two phages in liquid culture showed 104 multiplicity of infection (MOI) was the best in inhibiting bacteria, with PC2184 exhibiting more activity than PA13076. The two phages exhibited broad host range within the genus Salmonella. Phage PA13076 and PC2184 had a lytic effect on 222 (71.4%) and 298 (95.8%) of the 311 epidemic Salmonella isolates, respectively. We tested the effectiveness of phage PA13076 and PC2184 as well as a cocktail combination of both in three different foods (chicken breast, pasteurized whole milk and Chinese cabbage) contaminated with SE. Samples were spiked with 1 × 104 CFU individual SE or a mixture of strains (ATCC13076 and CVCC2184), then treated with 1 × 108 PFU individual phage or a two phage cocktail, and incubated at 4 °C or 25 °C for 5 h. In general, the inhibitory effect of phage and phage cocktail was better at 4 °C than that at 25 °C, whereas the opposite result was observed in Chinese cabbage, and phage cocktail was better than either single phage. A significant reduction in bacterial numbers (1.5–4 log CFU/sample, p < 0.05) was observed in all tested foods. The two phages on the three food samples were relatively stable, especially at 4 ºC, with the phages exhibiting the greatest stability in milk. Our research shows that our phages have potential effectiveness as a bio-control agent of Salmonella in foods.

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Monkeyworld: How long have primates been infected with viruses related to HIV?

HIV Disease-causing viruses engage their hosts in ongoing arms races: positive selection for antiviral genes increases host fitness and survival, and viruses in turn select for mutations that counteract the antiviral host factors. Studying such adaptive mutations can provide insights into the distant history of host-virus interactions. A new study published of antiviral gene sequences in African monkeys suggests that lentiviruses closely related to HIV have infected primates in Africa as far back as 16 million years.

Evolutionary and Functional Analysis of Old World Primate TRIM5 Reveals the Ancient Emergence of Primate Lentiviruses and Convergent Evolution Targeting a Conserved Capsid Interface. PLoS Pathogens 20 August 2015. doi:10.1371/ journal.ppat.1005085
Old World primates in Africa are reservoir hosts for more than 40 species of simian immunodeficiency viruses (SIVs), including the sources of the human immunodeficiency viruses, HIV-1 and HIV-2. To investigate the prehistoric origins of these lentiviruses, we looked for patterns of evolution in the antiviral host gene TRIM5 that would reflect selection by lentiviruses during evolution of African primates. We identified a pattern of adaptive changes unique to the TRIM5 proteins of a subset of African monkeys that suggests that the ancestors of these viruses emerged between 11–16 million years ago, and by reconstructing and comparing the function of ancestral TRIM5 proteins with extant TRIM5 proteins, we confirmed that these adaptations confer specificity for their modern descendants, the SIVs.

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A 1,000-Year-Old Remedy For MRSA

While the antibiotic potential of some materials used in historical medicine has been demonstrated, empirical tests of entire remedies are scarce. This is an important omission, because the efficacy of “ancientbiotics” could rely on the combined activity of their various ingredients. This would lead us to underestimate their efficacy and, by extension, the scholarship of premodern doctors. It could also help us to understand why some natural compounds that show antibacterial promise in the laboratory fail to yield positive results in clinical trials.

This recent paper reconstructs a 1,000-year-old remedy which kills the bacteria it was designed to treat and have shown that this activity relies on the combined activity of several antimicrobial ingredients. The results highlight the scholarship and rational methodology of premodern medical professionals and the untapped potential of premodern remedies for yielding novel therapeutics at a time when new antibiotics are desperately needed.

Pass the garlic.

A 1,000-Year-Old Antimicrobial Remedy with Antistaphylococcal Activity. (2015) mBio 6(4): e01129-15. doi: 10.1128/mBio.01129-15
Plant-derived compounds and other natural substances are a rich potential source of compounds that kill or attenuate pathogens that are resistant to current antibiotics. Medieval societies used a range of these natural substances to treat conditions clearly recognizable to the modern eye as microbial infections, and there has been much debate over the likely efficacy of these treatments. Our interdisciplinary team, comprising researchers from both sciences and humanities, identified and reconstructed a potential remedy for Staphylococcus aureus infection from a 10th century Anglo-Saxon leechbook. The remedy repeatedly killed established S. aureus biofilms in an in vitro model of soft tissue infection and killed methicillin-resistant S. aureus (MRSA) in a mouse chronic wound model. While the remedy contained several ingredients that are individually known to have some antibacterial activity, full efficacy required the combined action of several ingredients, highlighting the scholarship of premodern doctors and the potential of ancient texts as a source of new antimicrobial agents.

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SV40 – not finished yet

SV40 translocation Every year I treat the students on my virology course to a lengthy diatribe about how important SV40 has been to understanding so many different aspects of virology. How can such a small virus have made such a big impact? 55 years after its discovery, SV40 continues to surpise and illuminate us.

How non-enveloped viruses penetrate a host membrane to enter cells and cause disease remains enigmatic. To infect cells, the non-enveloped SV40 must transport itself across the ER membrane to reach the cytosol. A new study reveals some of the details of how it achieves that. Cellular Hsp105-powered disaggregation machinery pulls SV40 into the cytosol, most likely by uncoating the ER membrane-penetrating virus. Because this disaggregation machinery is thought to clear cellular aggregated proteins, the authors propose that the force generated by this machinery can also be hijacked by this non-enveloped virus to propel its entry into the host.

 

A Non-enveloped Virus Hijacks Host Disaggregation Machinery to Translocate across the Endoplasmic Reticulum Membrane. (2015) PLoS Pathog 11(8): e1005086. doi: 10.1371/journal.ppat.1005086
Mammalian cytosolic Hsp110 family, in concert with the Hsc70:J-protein complex, functions as a disaggregation machinery to rectify protein misfolding problems. Here we uncover a novel role of this machinery in driving membrane translocation during viral entry. The non-enveloped virus SV40 penetrates the endoplasmic reticulum (ER) membrane to reach the cytosol, a critical infection step. Combining biochemical, cell-based, and imaging approaches, we find that the Hsp110 family member Hsp105 associates with the ER membrane J-protein B14. Here Hsp105 cooperates with Hsc70 and extracts the membrane-penetrating SV40 into the cytosol, potentially by disassembling the membrane-embedded virus. Hence the energy provided by the Hsc70-dependent Hsp105 disaggregation machinery can be harnessed to catalyze a membrane translocation event.

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Virus-resistant pigs

FMDV In 2001, an epidemic of foot and mouth disease in the UK resulted in the destruction of over six million livestock, restrictions on international trade, and economic costs in excess of £3 billion. Foot and mouth disease is most common in developing areas of the world, such as parts of Asia, Africa and the Middle East, and an outbreak of the disease in animals raised as food resources in such areas can have a devastating effect on economic growth. Research just published reports the results of experiments on genetically engineered pigs that could have broad implications for the control of the disease.

The virus that causes foot and mouth disease (FMD) comes in seven types, each of which requires a specific vaccine for immunization. The Chinese team focused on a protein called VP1 that is variable across all different FMD viruses. VP1 is part of the virus capsid, a three-dimensional array of proteins that is involved in receptor binding and entry into host cells. The researchers looked for the small RNA that was best able to stop the replication of the FMD virus. They then integrated the gene coding for this small RNA into the genome of single pig cells. FMD virus was almost completely inhibited from growing and dividing inside the cells derived from transgenic pigs.

This work is a proof of concept for the use of RNA interference technology to produce transgenic livestock with increased resistance to virus infection. Although this technology could potentially increase food security, it also faces major challenges since, to date, neither the Food and Drug Administration in the United States nor the European Food Safety Authority have approved genetically engineered animals for human consumption. A global consensus on the regulation of genetically engineered organisms has not been reached and each country adopts policy at a national level. However, the governments in a number of countries – including Argentina, Brazil and China – view transgenic products as a way to resolve food security issues. Such countries have simpler protocols for the approval of transgenic products, which might allow transgenic animals to be approved for human consumption.

Foot and mouth disease: Virus-resistant pigs might help to stem next outbreak. (2015) eLife 4: e09790. doi: 10.7554/eLife.09790

Transgenic shRNA pigs reduce susceptibility to foot and mouth disease virus infection. (2015) eLife 4: e06951. doi: 10.7554/eLife.06951

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Microbial Genomics

Microbial Genomics Microbial Genomics is a new fully open access, online-only journal from the Society for General Microbiology. Increasingly I try only to link to open access journals from MicrobiologyBytes, but I don’t write much about microbial genomics – why is that? Well for one thing it’s not really my area of expertise, but more importantly, the increasingly impenetrable jargon genomics papers are writen in would not be helpful to the sort of general audience who read MicrobiologyBytes. So while I welcome the open access nature of Microbial Genomics … there’s a problem.

What’s missing from the new journal is the sort of expnatory overview good journals are now providing, such as the Author Summary in PLoS Pathogens, or the Significance paragraph in PNAS. The Impact Statements in Microbial Genomics are good, but not quite the same thing. Microbial Genomics may rely on science bloggers to translate its research ghettospeak into language the oublic can understand, but to me, it’s an opportunity missed.

(Of course, I do know how much researchers hate writing these things ;-)

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Repeated infection with malaria makes mosquitoes more dangerous

Mosquito In malaria-endemic regions, humans are often infected repeatedly with the Plasmodium parasite, and the consequences of such multiple infections are under intense study. In contrast, little is known about possible co-infection and its consequences in the Anopheles mosquitoes that transmit the disease. A new study reports that not only can individual mosquitoes accumulate infections from multiple blood feeds, but also that an existing malaria infection makes mosquitoes more susceptible to a second infection, and that infections reach higher densities when another strain is already present.

The researchers set up cages of female Anopheles mosquitoes and allowed them at defined times to feed on mice infected with two different Plasmodium strains. They found that mosquitoes can accumulate mixed strain malaria infections after feeding on multiple hosts, and found that parasites have a greater chance of establishing a secondary infection if another Plasmodium strain is already present in a mosquito. Moreover, the presence of the primary infection facilitated replication of the secondary infection while the first infection developed as normal. This resulted in doubly infected mosquitoes having substantially higher parasite loads. The large parasite numbers do not appear to kill the insects, and as it is expected that mosquitoes carrying more parasites are more likely to transmit malaria to vertebrates, mosquitoes taking multiple infective bites might disproportionally contribute to malaria transmission. This in turn would increase rates of mixed infections in vertebrate (including human) hosts, with implications for the evolution of parasite virulence and the spread of drug-resistant strains.

 

Existing Infection Facilitates Establishment and Density of Malaria Parasites in Their Mosquito Vector. (2015) PLoS Pathog 11(7): e1005003. doi: 10.1371/journal.ppat.1005003
Very little is known about how vector-borne pathogens interact within their vector and how this impacts transmission. Here we show that mosquitoes can accumulate mixed strain malaria infections after feeding on multiple hosts. We found that parasites have a greater chance of establishing and reach higher densities if another strain is already present in a mosquito. Mixed infections contained more parasites but these larger populations did not have a detectable impact on vector survival. Together these results suggest that mosquitoes taking multiple infective bites may disproportionally contribute to malaria transmission. This will increase rates of mixed infections in vertebrate hosts, with implications for the evolution of parasite virulence and the spread of drug-resistant strains. Moreover, control measures that reduce parasite prevalence in vertebrate hosts will reduce the likelihood of mosquitoes taking multiple infective feeds, and thus disproportionally reduce transmission. More generally, our study shows that the types of strain interactions detected in vertebrate hosts cannot necessarily be extrapolated to vectors.

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All Good Things

Woodlouse Some observant microbiologists have noticed that microbiologybytes.com is no more. That doesn’t mean that MicrobiologyBytes is going away, only that this is its home now. The content now called MicrobiologyBytes has moved “home” (URL) four times since I created it in the mid 1990’s. It will probably move home again in the future – it’s already set up base camps in Twitter, Facebook, Tumblr and Google+, none of which existed when the idea was created. The Internet has changed a great deal since the grandaddy of MicrobiologyBytes was born in ’95. The Internet will continue to change in future, and MicrobiologyBytes will change with it.

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Why poliovirus replication has been studied for more than 50 years

A 21st Century Perspective of Poliovirus Replication

It’s very rare to find a long term prospective on any science topic being published in scientific journals. There are few authors who are capable of writing them well and little credit for doing so in a world obsessed with novelty. That makes this short article in PLoS Pathogens all the more valuable and all the more worth while reading.

A 21st Century Perspective of Poliovirus Replication. (2015) PLoS Pathog 11(6): e1004825. doi: 10.1371/journal.ppat.1004825

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