<prompt> Chronic Burrowing ulcer is caused byMicroaerophilic streptococciPeptostreptococcusStreptococcus viridansStreptococcus pyogenes  <response>: Microaerophilic streptococci Burrowing ulcer Malenys ulcer is caused by synergistic infection of microaerophilic non hemolytic streptococci and aerobic hemolytic streptococci 