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MBL, WOODS HOLE, MA—More than 600 different kinds of bacteria live in the human mouth, but only a handful can be identified at any one time using conventional microscopy. That has left researchers and clinicians in the dark about where the rest may be, and how they may be interacting. 

Yet with a new imaging technique developed at the ǧ����Ƶ, up to 120 different kinds of bacteria in human dental plaque can be detected in a single field of view.

“Until now, it has been routine to label and identify only a handful of different microbes in any sample. We have broken through that technical barrier,” says Alex Valm, a doctoral candidate in the Brown-MBL Graduate Program in Biological and Environmental Science, who led the research effort along with MBL President and Director Gary Borisy.

The new technique allows researchers to study the bacterial interactions in plaque that may lead to diseases such as periodontitis. It may also help elucidate the structure of other biofilms (aggregates of microbes) in the body that cause health problems, such as cystic fibrosis and antibiotic-resistant infections.

“One of the central tenets of biology is form fits function. So if we want to understand the function of these complex microbial communities in our body, such as dental plaque, we need to know their structure at the micron scale,” Valm says.

Called CLASI-FISH, the imaging technique combines a traditional method for attaching fluorescent probes to specific DNA sequences (fluorescence in situ hybridization, or FISH) with a novel way increase the number of probes that can be used and to “unmix” the signals the probes put out (combinatorial labeling and spectral imaging, or CLASI).

Valm’s research was featured last week at the  in Denver.

On December 14 at noon in Candle House 104/105, Valm will present his Ph.D. thesis defense, “Systems-level analysis of multicellular microbial community structure.”

In addition to Borisy and Valm, contributors to the CLASI research are ǧ����Ƶ scientists Jessica Mark Welch, Mitchell Sogin, and Rudolf Oldenbourg; Brown-MBL graduate student Yuko Hasegawa; MBL microscopy support coordinator Louis Kerr; Chris Reiken of Carl Zeiss, Inc, and bacterial geneticist Floyd E. Dewhirst of the Forsyth Institute in Cambridge, Mass.

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