Gene study helps explain Legionnaires' probe complications

April 08, 2015

Genetic research helps to explain why tracing the source of an outbreak of Legionnaires' disease that claimed four lives has proven to be more complicated than scientists hoped.

A DNA study of bacteria samples taken from patients infected during the 2012 outbreak in Edinburgh shows that it was caused by several subtypes of the bacteria.

The unexpected discovery means that tracing the source of this - and any future outbreaks - will be challenging, researchers say.

There were 92 confirmed or suspected cases during the outbreak in 2012 in addition to the four deaths.

In a bid to prove where the infection came from, attempts had been made to grow samples of Legionella - the bacteria that causes Legionnaires' disease - from water samples taken from the suspected source. Legionella is difficult to grow in the laboratory and attempts to do so during the Edinburgh investigation proved unsuccessful.

As an alternative approach, scientists led by the University of Edinburgh's Roslin Institute looked at the entire genetic code of bacteria samples taken from patients.

The team worked with colleagues from the University's Centre for Immunity, Infection and Evolution, the Royal Infirmary of Edinburgh and the Scottish Microbiology Reference Laboratories, NHS Greater Glasgow and Clyde.

They identified four subtypes of the bacteria that had probably existed at the source for many months before the outbreak, the scientists say.

The subtypes varied in their genes, which made some more likely to cause life-threatening symptoms of infection. Some patients were infected with more than one subtype.

These findings suggest that the severity of disease may be influenced by the bacteria itself, as well as known factors such as lung disease and smoking that make patients more susceptible to infection.

Legionella usually lives in water and is found in rivers, lakes and reservoirs in low numbers. Problems arise when the bacteria gets into purpose-built water systems in urban areas, such as cooling towers, air-conditioning units and spa pools. If the temperature rises and water starts to evaporate, the bacteria can be carried through the air and infect people in the surrounding area.

Strict health and safety laws governing the control and maintenance of water systems help to minimise the risk of disease outbreaks.

Professor Ross Fitzgerald, who led the study at The Roslin Institute, said: "Genetic analysis is a powerful tool to help us track outbreaks of infectious diseases. Unfortunately, our findings suggest that it may be very challenging to prove conclusively where the Edinburgh outbreak came from, which will make it difficult for investigators to prosecute those responsible."

Dr Paul McAdam, who was also involved in the study at The Roslin Institute, said: "If the observed genetic diversity of bacteria associated with the Edinburgh outbreak turns out to be typical of other outbreaks, the discovery could mean that the source of future infections will be equally difficult to trace."
-end-
Genetic sequencing of the samples was performed by Edinburgh Genomics, the University of Edinburgh's major DNA sequencing facility. The research is published in the journal Genome Biology.

The Roslin Institute receives strategic funding from the Biotechnology and Biological Sciences Research Council.

University of Edinburgh

Related Bacteria Articles from Brightsurf:

Siblings can also differ from one another in bacteria
A research team from the University of Tübingen and the German Center for Infection Research (DZIF) is investigating how pathogens influence the immune response of their host with genetic variation.

How bacteria fertilize soya
Soya and clover have their very own fertiliser factories in their roots, where bacteria manufacture ammonium, which is crucial for plant growth.

Bacteria might help other bacteria to tolerate antibiotics better
A new paper by the Dynamical Systems Biology lab at UPF shows that the response by bacteria to antibiotics may depend on other species of bacteria they live with, in such a way that some bacteria may make others more tolerant to antibiotics.

Two-faced bacteria
The gut microbiome, which is a collection of numerous beneficial bacteria species, is key to our overall well-being and good health.

Microcensus in bacteria
Bacillus subtilis can determine proportions of different groups within a mixed population.

Right beneath the skin we all have the same bacteria
In the dermis skin layer, the same bacteria are found across age and gender.

Bacteria must be 'stressed out' to divide
Bacterial cell division is controlled by both enzymatic activity and mechanical forces, which work together to control its timing and location, a new study from EPFL finds.

How bees live with bacteria
More than 90 percent of all bee species are not organized in colonies, but fight their way through life alone.

The bacteria building your baby
Australian researchers have laid to rest a longstanding controversy: is the womb sterile?

Hopping bacteria
Scientists have long known that key models of bacterial movement in real-world conditions are flawed.

Read More: Bacteria News and Bacteria Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.