A delivery vehicle for introducing a polynucleotide into an antibiotic-resistant microorganism, wherein the delivery vehicle is selected from the group consisting of a plasmid (such as a conjugative plasmid or other plasmid replicon), a nucleotide vector, linear double-stranded DNA, a non-virulent bacteriophage and a lysogenic bacteriophage, and comprises a recombinant polynucleotide for inactivation of DNA carrying at least one antibiotic resistance gene encoding an enzyme which confers antibiotic resistance to a microrganism, wherein the recombinant polynucleotide comprises a clustered regularly interspaced short palindromic repeat (CRISPR) array nucleic acid sequence having or transcribing multiple RNA guide molecules, wherein each RNA guide molecule: (i) is transcribed from its own promoter sequence; (ii) mediates the binding of a CRISPR associated (Cas) DNA-binding polypeptide or its functional equivalent or its modified version thereof to the at least one antibiotic resistance gene(s); and (iii) has a spacer sequence sufficiently complementary to a target DNA sequence of the at least one antibiotic resistance gene for the at least one antibiotic resistance gene to be targeted and inactivated in the presence of a CRISPR associated (Cas) DNA-binding polypeptide or a functional equivalent or a modified version thereof, and wherein: either the Cas DNA-binding polypeptide or a functional equivalent or a modified version thereof is a modified Cas DNA-binding polypeptide which creates a deletion and reseals the target DNA sequence to inactivate the at least one antibiotic resistance gene to prevent double-strand break -induced killing of the microorganism, such that the microorganism becomes sensitised to an antibiotic, or the Cas DNA-binding polypeptide or a functional equivalent or a modified version thereof creates a DSB in the target DNA sequence to inactivate the at least one antibiotic resistance gene, and the delivery vehicle further comprises a nucleotide sequence encoding a gene product which prevents direct killing of the microorganism due to the generation of the DSB in the at least one antibiotic resistance gene, such that the microorganism becomes sensitised to an antibiotic. (i) is transcribed from its own promoter sequence; (ii) mediates the binding of a CRISPR associated (Cas) DNA-binding polypeptide or its functional equivalent or its modified version thereof to the at least one antibiotic resistance gene(s); and (iii) has a spacer sequence sufficiently complementary to a target DNA sequence of the at least one antibiotic resistance gene for the at least one antibiotic resistance gene to be targeted and inactivated in the presence of a CRISPR associated (Cas) DNA-binding polypeptide or a functional equivalent or a modified version thereof, and wherein: either the Cas DNA-binding polypeptide or a functional equivalent or a modified version thereof is a modified Cas DNA-binding polypeptide which creates a deletion and reseals the target DNA sequence to inactivate the at least one antibiotic resistance gene to prevent double-strand break -induced killing of the microorganism, such that the microorganism becomes sensitised to an antibiotic, or the Cas DNA-binding polypeptide or a functional equivalent or a modified version thereof creates a DSB in the target DNA sequence to inactivate the at least one antibiotic resistance gene, and the delivery vehicle further comprises a nucleotide sequence encoding a gene product which prevents direct killing of the microorganism due to the generation of the DSB in the at least one antibiotic resistance gene, such that the microorganism becomes sensitised to an antibiotic. either the Cas DNA-binding polypeptide or a functional equivalent or a modified version thereof is a modified Cas DNA-binding polypeptide which creates a deletion and reseals the target DNA sequence to inactivate the at least one antibiotic resistance gene to prevent double-strand break -induced killing of the microorganism, such that the microorganism becomes sensitised to an antibiotic, or the Cas DNA-binding polypeptide or a functional equivalent or a modified version thereof creates a DSB in the target DNA sequence to inactivate the at least one antibiotic resistance gene, and the delivery vehicle further comprises a nucleotide sequence encoding a gene product which prevents direct killing of the microorganism due to the generation of the DSB in the at least one antibiotic resistance gene, such that the microorganism becomes sensitised to an antibiotic.