Lacticaseibacillus rhamnosus CRL 2244 secreted metabolites display killing and antibiotic synergistic activity against multi-drug resistant pathogens

Abstract

A growing increase in the number of serious infections caused by multidrug resistant bacteria(MDR) is challenging our society. Despite efforts to discover novel therapeutic options,few antibiotics targeting MDR have been approved by the Food and Drug Administration(FDA). Lactic acid bacteria have emerged as a promising therapeutic alternative due to theirdemonstrated ability to combat MDR pathogens in vitro. Our previous co-culture studiesshowed Lacticaseibacillus rhamnosus CRL 2244 as having a potent killing effect againstcarbapenem-resistant Acinetobacter baumannii (CRAB) strains. Here we report that cellfreeconditioned media (CFCM) samples obtained from Lcb. rhamnosus CRL 2244 culturesincubated at different times display antimicrobial activity against 43 different pathogens,including CRAB, methicillin-resistant Staphylococcus aureus (MRSA) and carbapenemaseKlebsiella pneumoniae (KPC)-positive strains. Furthermore, transwell and ultrafiltrationanalyses together with physical and chemical/biochemical tests showed that Lcb. rhamnosusCRL 2244 secretes a <3 kDa metabolite(s) whose antimicrobial activity is not significantlyimpaired by mild changes in pH, temperature and various enzymatic treatments.Furthermore, sensitivity and time-kill assays showed that the bactericidal activity of the Lcb.rhamnosus CRL 2244 metabolite(s) enhances the activity of some current FDA approvedantibiotics. We hypothesize that this observation could be due to the effects of Lcb. rhamnosusCRL 2244 metabolite(s) on cell morphology and the enhanced transcriptional expression of genes coding for the phenylacetate (PAA) and histidine catabolic Hut pathways,metal acquisition and biofilm formation, all of which are associated with bacterial virulence.Interestingly, the extracellular presence of Lcb. rhamnosus CRL 2244 induced thetranscription of the gene coding for the CidA/LgrA protein, which is involved in programmedcell death in some bacteria. Overall, the findings presented in this report underscore thepromising potential of the compound(s) released by Lcb. rhamnosus CRL2244 as an alternativeand/or complementary option to treat infections caused by A. baumannii as well asother MDR bacterial pathogens.