Study finds plasmids can accelerate evolution of antibiotic resistance
A study published Monday in Nature Ecology and Evolution suggests plasmids may play more of a role in spreading and facilitating antibiotic resistance than previously thought.
Plasmids, which are mobile pieces of DNA, have long been known to spread resistance by facilitating the horizontal transfer of antibiotic-resistant genes between bacteria. An example of how plasmids work is found in MCR-1, a colistin-resistance gene that was identified in Escherichia coli bacteria in China and has since been found in more than 30 countries. But what is less clear is the role that plasmids play as catalysts in gene evolution.
To explore that question, researchers from the University of Oxford used a novel experimental model to determine whether bacteria carrying antibiotic resistance genes on plasmids have evolutionary advantages over bacteria that have resistance genes on chromosomes. The model involved creating strains of E Coli with a beta-lactamase gene on either the chromosome or a multi-copy plasmid, then exposing the strains to increasing concentrations of the antibiotic ceftazidime.
What the researchers found was that beyond facilitating horizontal gene transfer, the plasmid accelerated the development of ceftazidime resistance in the E coli strains by facilitating the evolution of novel variants of the gene, increasing the rate of appearance of those variants, and then amplifying the effects through greater gene expression.
"Our paper demonstrates that plasmids can also act as evolutionary catalysts that accelerate the evolution of new forms of resistance," senior author Craig MacLean, PhD, an associate professor in the department of zoology at Oxford, said in a university press release. "This occurs because bacteria usually carry more than one copy of a plasmid, which allows resistance genes carried by plasmids to rapidly evolve new functions—in this case, the ability to degrade an antibiotic. Additionally, plasmids automatically amplify the number of copies of these new and improved resistance genes."
MacLean and his colleagues say their findings have general implications for the "evolution of antibiotic resistance, adaptation and innovation in bacteria," and argue that they highlight the importance of developing new drugs that can block plasmid replication.
Nov 7 Nature Ecology and Evolution study
Nov 8 University of Oxford press release
Camel exposure cited in latest Saudi MERS case
Saudi Arabia's ministry of health (MOH) today announced a new MERS-CoV case, involving a 53-year-old man who had contact with camels before he became ill.
The patient, a Saudi citizen from Kharj in the central part of the country, experienced Middle East respiratory coronavirus (MERS-CoV) symptoms and is hospitalized in stable condition.
The new case, part of a small but steady stream of MERS-CoV infections, lifts Saudi Arabia's MERS total to 1,476 cases, 616 of them fatal. Eight people are still being treated. Saudi Arabia, where the virus was first detected in humans in 2012, has the world's highest number of cases.
Nov 9 Saudi MOH statement
Canadian lab worker monitored after potential Ebola exposure
A Canadian researcher working with pigs that were experimentally infected with Ebola virus may have been exposed to the virus because of a split seam in his protective suit, which he noticed during decontamination, the Associated Press (AP) reported yesterday.
The man works at Canada's National Centre for Foreign Animal Disease in Winnipeg. John Copps, DVM, the lab's director, told the AP that the man was working in a biosafety level 4 (BSL 4) lab at the time. The incident occurred 2 days ago.
Officials said the man was offered an Ebola vaccine, but due to privacy concerns they didn't say if he received it. He is in isolation and will be monitored for 21 days by local health officials.
Copps said the risk is considered low to the employee, his coworkers, and the community.
Nov 8 AP story
Cholera vaccine campaign launches in Haiti
A large team assembled by Haiti's health ministry yesterday launched a campaign to immunize people against cholera in areas hit hardest by Hurricane Matthew in October, the Pan American Health Organization (PAHO) said today in a press release.
The goal is to vaccinate about 800,000 people in Sud and Grand'Anse departments, the two most affected areas, which are located in southwestern Haiti. The campaign is expected to last until Nov 14.
Workers will target people age 1 and older in 16 communes, and experts project that a single dose of the vaccine could prevent 60% to 70% of severe cholera infections. Researchers have recently reported that a single dose of cholera vaccine, rather than the recommended two doses given 2 weeks apart, could help prevent infection and offer some degree of herd protection while stretching limited vaccine supplies.
The World Health Organization (WHO) and PAHO put together a team of epidemiologists and immunization experts to provide technical support, the GAVI Alliance provided the vaccines, and the International Medical Corps, UNICEF, and other partners took other steps, such as preserving the cold chain for storing the vaccine and providing logistical support.
Jean Luc Poncelet, MD, PhD, Haiti's WHO/PAHO representative, said in the statement that vaccination is meant to complement other preventive measures. "Each person must be a leader of change: daily chlorination of water in the house, drinking potable water, rehydration if there is diarrhea, and seeking treatment. To avoid deaths, there are health services that are working and available."
Haiti has experienced a surge in cholera cases following the hurricane. In late October the United Nations Office for the Coordination of Humanitarian Affairs said since early October Haiti has reported 3,423 suspected cases, 1,065 in Sud department and 752 in Grand'Anse.
Nov 9 PAHO press release
Oct 28 CIDRAP News story "Worsening cholera in Haiti, Yemen prompts stepped-up response"
Oct 18 CIDRAP News scan "Promising results noted in single-dose cholera vaccine field trial"
5.6 million Afghan children to be vaccinated against polio
The WHO, alongside Afghanistan's Ministry of Public Health and UNICEF, announced the launch of a massive polio vaccine campaign targeting 5.6 million children under the age of 5 in Afghanistan. The campaign began on Nov 7 and will continue through the end of the week.
Afghanistan's political turmoil and mountainous terrain have made vaccination a challenge, and the current campaign is fueled by a final push to reach children in Kunar, Paktika, Helmand, and Kandahar provinces, as well as Kabul. Afghanistan, Pakistan, and Nigeria are the last three polio-endemic countries in the world. So far this year, 12 cases of wild polio virus have been reported in the four of the targeted Afghan provinces.
According to the WHO, the vaccine drive will be carried out by 25,000 volunteers. The polio vaccine is halal, and last week Islamic leaders urged parents in Afghanistan to vaccinate their children, emphasizing that the vaccine is safe and effective, even for newborns, the agency said.
Nov 7 WHO statement