The present invention relates to the field of therapeutics and, more in particular, to pharmaceutical compositions for the prevention and/or treatment of bacterial infections and antibacterial-induced dysfunctions. The compositions of the present invention demonstrate high species-specificity in inhibiting the growth of a small number of bacterial species, and most importantly are effective also against multi drug resistant (MDR) clinical isolate species. Interestingly, one of those combinations pairs a non- antibiotic drug, vanillin, with an antibiotic drug, spectinomycin, to demonstrate a surprisingly strong inhibitory effect on the growth of clinically relevant Gram-negative pathogenic and multi-drug resistant E. coli isolates. A second set of compounds combines the polymyxin colistin with loperamide, a rifamycin, or a macrolide. Importantly, this invention relates to combinations that enable narrow-spectrum antibacterial therapies, constituting a major effort of current and future drug development efforts in order to prevent major side effects of antibacterial strategies. This invention also relates to pharmaceutical combinations useful to prevent an adverse effect on the gut microbiome, induced by the use of antibacterial compounds.