The bacteria produce compounds, called cephalosporinases, which inactivate and destroy certain antibiotics, such as penicillin derivatives and cepahlopsorins, protecting themselves and other beneficial bacteria that live in close proximity. However, they may also give protection from these antibiotics to harmful bacteria, such as Salmonella.
Susceptibility to antibiotics is not uniform in the hundreds of species that colonize the gut, and some of the most common bacteria, the Bacteroides, are among the most resistant.
By scanning the genome of strains of Bacterioides bacteria that live in the gut, the researchers found genes that produce an enzyme called cepahlosporinase, which specifically destroys certain antibiotics. They also showed that cephalosporinases are exported out of the bacterial cells, attached to the surface of special packages called outer membrane vesicles (OMVs).
Bacteria use OMVs to distribute compounds made inside the bacterial cells to the outside world. Among these packaged compounds are cephalosporinases that can help protect any other bacteria that are in the same environment against antibiotics such as ampicillin.
This was shown by adding the cephalosprinase-containing OMVs to cultures containing the ampicillin-susceptible gut bacteria, Bifidobacteria breve, which effectively protected them against high concentrations of antibiotics. A similar test showed that Salmonella bacteria were also protected.
The researchers now want to see whether the protection against antibiotics from gut bacteria OMVs occurs in the gut itself. If so, this would have implications for how antibiotics are used, and will improve current understanding of the growing problem of antibacterial resistance.