A small puncture wound on a woman s arm has become swollen, hot to the touch, and intensely painful. There is tissue necrosis, but it is not gassy, and under the microscope Gram-positive cocci in chains are present. Which of the following microbes is likely to be responsible?   Pseudomonas aeruginosa   Streptococcus pyogenes     Staphylococcus aureus       Clostridium perfringens      Sporothrix schenckii