The invention encompasses compositions, kits and methods for modifying bacteria, preferably naturally occurring bacteria, in situ. These can be used to treat, prevent or cure microbiome-associated diseases or disorders by modulating the molecules expressed and/or secreted by bacterial populations of the microbiome in a specific manner. The genomic modifications can modify the interactions between part or all of these populations and the host in a way that decreases their deleterious potential on host health. The compositions, kits and methods of the invention do not result in the direct death of these populations or a direct significant inhibition of their growth. The invention further includes methods for screening for genetic modifications in the bacteria, for determining the efficiency of vectors at inducing these genetic mutations, and for determining the effects of these mutations on bacterial growth.