Sodium azide (NaN3) was evaluated as inhibitor of microbial growth and activity in marine sediment resuspensions by monitoring the abundance of free-living and sessile bacteria using both flow cytometry and qPCR methods. Results show that 50mM of NaN3 strongly inhibits bacterial growth under natural and enriched resource conditions. •NaN3 efficiency on planktonic and sessile microorganisms depends on concentration and resource availability.•Under natural resource conditions 50mM NaN3 inhibits microbial growth and activity.•Under enhanced resource condition 5mM NaN3 only reduced microbial growth and activity.•Under enhanced resource condition 50mM NaN3 inhibited the growth of sessile bacteria for 11days.•Faint planktonic growth persisted with enhanced resource conditions and 50mM NaN3.