The bitter legal tussle between 3M and investors and lawyers involved with a failed acquisition took an unusual turn on Thursday.

First, a bit of background.

The $27 billion Maplewood-based conglomerate was sued in the United Kingdom by a group of investors called Porton Capital Inc. and a subsidiary of the British Defense Ministry. They claimed 3M failed to aggressively market their homegrown technology, called BacLite, which detects potentially deadly superbugs in hospitals.

The initial pricetag in the deal was $16 million with potential earn out-payments of up to $69 million.

A few years later, 3M shut the business down, saying the BacLite technology was a bust.

Last May, Porton representatives, including Washington lawyer Lanny J. Davis, former special counsel to President Clinton, and Twin Cities attorney, Robert Hopper, held a press conference in Minneapolis to discuss the issue. Porton also launched a website, organized demonstrations and issued several news releases protesting 3M’s decision to shelf BacLite. They called on the Food and Drug Administration to investigate the matter.

In short, they said a potentially life-saving technology was unceremoniously ditched by 3M.

3M responded in June by filing a federal lawsuit, first in New York, then later refiled in the District of Columbia, against Porton CEO Harvey Boulter and Davis. The complaint alleges they engaged in defamation, conspiracy and blackmail in an effort to extract millions from the company. They also alleged that Porton’s public relations campaign was intended to embarrass Sir George Buckley, 3M’s British-born CEO, who was recently knighted by Queen Elizabeth.

On Thursday, Davis filed an “anti-SLAPP” motion in the District of Columbia suit, claiming the company has attempted to thwart his right to speak on “an important public health matter by filing a tactical lawsuit” against him.

SLAPP is short for “strategic lawsuit against public participation” — that is, a suit intended to censor, intimidate and silence critics by burdening them with huge legal costs, at least until they give up the fight.

In a statement, 3M lawyer William A. Brewer III said, “Our client views this as another desperate attempt to deflect from the merits of the lawsuit it filed against Mr. Davis. Needless to say, we understand completely why Mr. Davis will make any and all attempts to avoid having his conduct and that of his clients scrutinized. We think that this, together with the other actions he has made, will be unavailing.”

Janet Moore covers medical technology for the Star Tribune.