Final answer:
John Tyndall is credited with demonstrating the presence of heat-resistant microbes which later, through the work of Robert Koch, were identified as endospores - durable forms of bacteria that can survive extreme conditions.
Step-by-step explanation:
John Tyndall demonstrated the presence of heat-resistant microbes. Robert Koch determined these to be endospores.
The discovery of heat-resistant microbes was made by John Tyndall, who found that certain microorganisms could survive at high temperatures that would normally kill other types. This observation eventually led to the identification of endospores, which are tough, protective structures created by some bacteria such as Bacillus and Clostridium genera. It was Robert Koch who recognized these resistant forms as endospores, a crucial discovery at the time for the field of microbiology.
His research clarified why sterilization methods sometimes failed to kill all bacteria and established that these endospores could withstand boiling temperatures and are actually dormant, hardy forms of bacteria. Koch's work, together with his postulates, contributed significantly to the development of germ theory and modern bacteriology. With his keen investigation and scientific rigor, he laid down the groundwork that has greatly impacted our understanding of infectious diseases and the necessity for thorough sterilization to prevent the spread of pathogens.