Opinion: Looking for non-culturable strains

Traditional culture methods may not spot certain potentially harmful organisms, so there is a clear need for alternative strategies

Susan Birks
Deputy Editor

When stressed, some bacteria have the ability to take on a state of low metabolic activity and low growth, but once in more favourable conditions they can resuscitate. Such organisms pose particular problems for microbiologists as they are often non-culturable using traditional semi solid growth media and at certain pH or incubation temperatures, making them difficult to spot.

As more is known about these viable but non-culturable (VBNC) organisms, it is becoming apparent that different testing strategies are required to detect or quantify their presence. IDEXX looks at strategies for detecting VBNC such as Legionella in water systems.

Another study highlighting the fact that traditional culture methods are limited and often provide a biased look at which microbes are present comes in the form of a paper published on 11 March, in the journal Applied and Environmental Microbiology, written by Maria J. Soto-Girón, et al. It describes the microbial communities found in shower hoses at a major US hospital. The study documented bacteria found using cutting-edge metagenomic techniques that cannot be detected using traditional culture-based microbiology assays.

The microbiome study found an abundant population of bacteria that the researchers believe are novel ‘mycobacterium-like’ species not described previously, while the traditional culture-based methods identified organisms affiliated with Proteobacteria – such as members of the genera Sphingomonas, Blastomonas and Porphyrobacter – as the most abundant.

Clearly traditional culture methods have a huge role to play in bacteria detection but they will not pick up everything and need to be tailored to find specific microbes. Metagenomics, meanwhile, gives a more complete and quantitative picture of which micro-organisms are there and how abundant they are, but comes at a much higher cost. Future work is needed to cover the middle ground and provide more cost-effective strategies.

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