So, should we be worried about Shewanella?

The marine environment is largely considered an uncommon reservoir for the acquisition of human-related pathogens. In fact, only a small number of bacterial species are usually associated with the infection of humans, the most notable obviously being in the Vibrio genus. However, recently, strains of the genus Shewanella are increasingly being implicated as a growing cause of maritime-associated disease. A study by J. M. Janda therefore attempts to corroborate information on the genus, in order to examine both its pathogenicity, and its mechanisms for infection.

The Shewanella genus itself has grown in size from a single type species in 1980 to more than 60 accepted or proposed species.  And, with this increased understanding of the genus’ taxonomy, has come the realisation that there is a great deal of diversity within the Shewanella. For instance, some species have been implicated as sources of bioremediation while others have been posited as future sources of microbial fuel cells. While this indicates a potential benefit of Shewanella, there are, on the other hand, some major pathogenic species in the genus that have the capability to cause human disease.

The understanding of Shewanella species as disease-causing agents has been revolutionised by the use of 16S sRNA sequencing. In fact, until the early 1990s it was thought that only one species of the genus, S. putrefaciens, was causing disease in humans. However, molecular techniques have now revealed that a large proportion of the strains causing human infection actually belong to S. algae. In addition to this, there have been reports of S.baliotis causing necrotisingfasciitis similar to cases of V. vulnificus. There have also been incidences where S. xiamenensis has been implicated in health care-associated peripancreatic infection. More recently, Shewanella has even been implicated as having a potential role in gastrointenstinal disease.

Human infection of Shewanella is directly, or indirectly, associated with contact with the marine ecosystem and its inhabitants due to the ubiquitous nature of the genus in the marine environment. In fact, the most common cause of infection is bacterial introduction through abraded urfaces. This can include a number of things such as penetration by a sea urchin spine, swimming in the ocean or occupational exposure from fishing and crabbing, among others.

Of course, the real question is; should this be a cause for concern? And the answer is, no, not for now. However, it is important to use modern molecular techniques to further the research the genus. Techniques like 16s rRNA sequencing may be key in monitoring the pathogenicity of the genus as well as aiding its identification as a causative agent of human disease. By expanding on current knowledge of the genus it should be possible to not only minimise its threat as a disease factor, but also maximise its potential as a human rescource.

Janda, J. M. (2014). Shewanella: a Marine Pathogen as an Emerging Cause of Human Disease. Clinical Microbiology. 36 (4), 25-29.