The Birth of Pathogens: How Bacteria Become Deadly

Two new studies have revealed two very different ways bothersome bacteria strains can suddenly become deadly, evolving into difficult-to-rid pathogens that can threaten entire populations.

Gordon Dougan, a professor from the Wellcome Trust Sanger Institute (WTSI) in the UK, explained in a recent release how he and his team used the same genome sequencing technique in two very different environments to study two very different approaches bacteria can take to become a dangerous pathogen.

"We were able to define the timeframe of the origin of two completely different infectious diseases," he said, "and in future we will be able to use this approach to identify and control emerging threats."

One study, published in the Proceedings of the National Academy of Science (PNAS), describes how a strain of Salmonella enterica serovar Paratyphi A - the cause of typhoid fever - emerged in humans about 450 years ago, but since then, hasn't changed at all.

According to the study, in what is known as "genetic drift," Paratyphi A has gradually accumulated more and more mutations, allowing it to not only transfer from animals to human many centuries ago, but stay relatively hard to disrupt.

"This study is particularly timely because vaccines for Paratyphi A are currently being tested, and it is hoped that trials will start within two to three years," the WTSI proudly announced. "The research will help scientists to understand how the pathogen is moving between individuals and between populations, as well as how it is changing genetically over time."

A second study published in Nature Communications details how Group B Streptococcus (GBS) developed to become a cause of serious septicemia and shock in newborns.

In this case, it wasn't simply an unlucky genetic drift that suddenly made the bacteria more deadly, but instead human intervention.

The found that the over-use of the broad-spectrum antibiotic tetracycline "bottle-necked" potential evolutionary options for the pathogen, causing it to develop in a particularly dangerous way.

"This is possibly the earliest case of the emergence of a new disease that can be directly associated with antibiotic use," said Dougan. "GBS causes a distressing infection of sepsis and meningitis seen in new born children that can result in severe illness and death, making it one of the most serious diseases in babies."

However, now that this is understood, it can be avoided in the future.

Mark Davies, co-first author of the study explained that "by combining surveillance with the use of specific targeted antimicrobials, we can reduce the risk of a new disease emerging in the future whilst maintaining the normal protective microbial flora within us."