Clostridium tetani is the bacterium responsible for causing tetanus, a potentially fatal disease that affects the nervous system. It is a spore-forming bacterium and can survive in harsh conditions. The irregular shape of the bacteria is due to the formation of spores, which can make the cells appear swollen or bulging.
The other options provided do not fit the description of an irregular, gram-positive rod. Lactobacillus acidophilus is a gram-positive rod-shaped bacterium, but it is not irregular. Streptococcus pyogenes and Staphylococcus aureus are both gram-positive cocci, not rods. Mycobacterium tuberculosis is a slender, rod-shaped bacterium, but it is not irregular and is actually classified as acid-fast rather than gram-positive.