Lactobacillus parafarraginis KU495926, extracted from yogurt, hindered the growth of 14 multidrug-resistant and so-called extended spectrum beta-lactamase (ESBL) bacteria obtained from infected patients at a Washington D.C. hospital, according to Howard University biologists at the annual American Society for Microbiology meeting held in New Orleans this week (June 1-5).

ESBL bacteria make beta-lactamase enzymes, which promote resistance to certain broad-spectrum antibiotics. The researchers found that L. parafarraginis, a gram-positive microbe, produced a substance, likely a bacteriocin—a type of antimicrobial protein—that inhibited the gram-negative ESBL and multidrug-resistant pathogens. According to lead author Rachelle Allen-McFarlane, a graduate student in Broderick Eribo’s lab at Howard, this may be one of few known examples of gram-positive bacteria-derived bacteriocins inhibiting the growth of gram-negative bacteria.

Typically, bacteriocins from one particular strain are only capable of inhibiting closely related strains, Allen-McFarlane tells. Most of the time, “gram-positive kills gram-positive,” she explains. 

Though it’s rare, it is possible. “My area of interest is to identify bacteriocins from lactic acid bacteria that are capable of inhibiting multi-drug resistant and ESBL gram-negative bacteria,” she says.

To examine whether the metabolic products produced by L. parafarraginis could inhibit ESBL and drug-resistant bacteria, the researchers first demonstrated that metabolites derived from L. parafarraginis could hinder pathogenic growth in culture. Once they demonstrated this was possible, they verified their findings using flow cytometry and fluorescent microscopy. These experiments revealed that when certain pathogens, including wound-derived E. coli, were added to media containing L. parafarraginis metabolites, their growth was significantly inhibited.

Next, using PCR, the researchers identified four bacteriocin structural genes in L. parafarraginis, and as a final step, verified that this bacterium was indeed capable of producing the proteins.

In the future, Allen-McFarlane says, she hopes to identify the specific bacteriocin produced by L.parafarraginis, and demonstrate how it can inhibit such a broad range of distantly-related pathogens. 

According to Allen-McFarlane, bacteriocin-producing bacteria are currently widely used in the food industry as food additives that inhibit the growth of pathogenic organisms. But, they are not extensively applied to pharmaceuticals.

This could change. Some scientists think that bacteriocins could be the antimicrobial agents of the future, says Allen-McFarlane. “We need to start looking at [bacteriocins] because of antimicrobial resistance and the great threat that it poses to human existence.”