In Vitro Inhibition of Klebsiella pneumoniae by Lactobacillus delbrueckii Subsp delbrueckii LDD01 (DSM 22106): An Innovative Strategy to Possibly Counteract Such Infections in Humans?

Goals:To determine the in vitro antimicrobial activity of selected Lactobacillus strains isolated from the feces of healthy humans against Klebsiella pneumoniae.Background:Klebsiella is ubiquitous in nature and may colonize the skin, the pharynx, or the gastrointestinal tract of humans. Despite the widespread use of antibiotic molecules with a broad spectrum in hospitalized patients, an increased overall load of klebsiellae as well as the subsequent development of multidrug-resistant strains able to synthesize extended-spectrum beta-lactamase have been registered. These strains are particularly virulent, express capsular-type K55, and have a considerable ability to propagate.Study:The 4 strains Lactobacillus paracasei LPC01 (CNCM I-1390), Lactobacillus rhamnosus LR04 (DSM 16605), Bifidobacterium longum B2274 (DSM 24707), and Lactobacillus delbrueckii subsp. delbrueckii LDD01 (DSM 22106) were tested. The analysis was performed using both a disc-diffusion assay and the broth-dilution procedure, also including an evaluation of the supernatants obtained from a fresh broth culture of each bacterium.Results:L. delbrueckii subsp. delbrueckii LDD01 demonstrated the best inhibitory results among all the tested strains. The antibacterial activity of the supernatant was retained even after treatment with -amylase and neutralization with NaOH 1N, thus suggesting the protein structure of the inhibitory molecule. In contrast, it was completely lost after treatment with proteinase K.Conclusions:Overall results suggest that the inhibitory effect of L. delbrueckii subsp. delbrueckii LDD01 should be attributed to the production of a bacteriocin. This strain may be prospectively useful for strengthening probiotic formulations and possibly counteract infections by K. pneumoniae in humans.