Who observed a mold growing in an unwashed culture plate while working on Staphylococcus bacterium?

Alexander Fleming

The individual who noticed the development of mold on an unclean culture plate while conducting research on Staphylococcus bacteria was: (b) Alexander Fleming.

Explanation: Alexander Fleming, a Scottish bacteriologist, made this significant observation in 1928. While working with Staphylococcus bacteria, he accidentally left a culture plate uncovered, allowing airborne mold spores to contaminate the culture. Upon returning to his laboratory, Fleming noticed that the area surrounding the mold colonies remained clear of bacterial growth. This observation led him to identify the mold as Penicillium and to discover its inhibitory effect on the growth of bacteria. Fleming's discovery of the antibiotic properties of Penicillium marked the beginning of the era of antibiotics and revolutionized medical treatment.