Final answer:
Louis Pasteur is credited with disproving the theory of spontaneous generation by demonstrating that bacterial growth in nutrient broths was due to contamination by airborne microbes, supporting the theory that 'life only comes from life'.
Step-by-step explanation:
The individual credited for demonstrating that emergent bacterial growth in nutrient broths was due to contamination by pre-existing cells rather than spontaneous generation is Louis Pasteur. Pasteur conducted controlled experiments, including the famous swan-neck flask experiment, which showed that sterilized broths would remain free of microbial growth unless they were exposed to the air, implying that microbes in the air were responsible for the growth seen in unsterilized broths. His work played a critical role in disproving the theory of spontaneous generation, which proposed that life could arise from non-living matter, and instead supported the alternative theory that 'life only comes from life'.