Laser Scatterometer Distinguishes Wild Type, Mutant Bacteria

A laser scatterometer tool has been demonstrated to quickly and noninvasively detect harmful bacteria, including mutant listeria varieties, within 24 hours. It holds promise for the identification of mutant bacteria, and could be used to identify mutant bacteria from natural settings such as from contaminated food.

The method — dubbed BARDOT for bacterial rapid detection using optical scattering technology — could be quicker than conventional methods for studying microbial pathogenesis, a labor-intensive process involving the development, growth and genetic analysis of mutant bacteria strains.

BARDOT scans bacteria colonies looking for patterns unique to each bacterium. When the light penetrates a bacteria colony, it produces a scatter pattern that can be matched against a library of known bacteria patterns to identify a match. The system can identify bacteria such as salmonella, listeria, bacillus, vibrio and E. coli within 24 hours.

Now researchers from Purdue University have shown that BARDOT can pinpoint small genetic mutations in listeria.

"This is a versatile microbiology tool, and we wanted to see if we can use it for mutant strains," said professor Arun Bhunia said. "This is a really powerful tool to help researchers find those mutant strains much easier on a petri plate. You can avoid the laborious techniques required to screen or detect these mutant strains."

Mutant bacteria can be used to understand the biology of pathogens and how to combat dangerous outbreaks in food. The laser system enables visual comparison of the scatter patterns of wild type bacteria with those of mutant bacteria, for example, those that have had a gene deleted. The reverse was also true; by restoring the deleted gene, the BARDOT system recognized the bacteria as a regular wild type of strain.

The researchers reported that among the biophysical parameters examined, the colony height and optical density did not reveal any discernible differences between the mutant and wild type strains, meaning BARDOT could be used to screen and enumerate mutant strains separately from the wild type based on differential colony scatter patterns.

The research was published in Applied and Environmental Microbiology (doi: 10.1128/aem.04129-15).