Complex sentence: Penicillin is the most common antibiotic used in treatment of "S. suis" infection; in cases with cardiac involvement (endocarditis), gentamicin should also be given for synergistic effect.
Split into simpler sentences: Penicillin is the most common antibiotic used in treatment of "S. suis" infection. In cases with cardiac involvement (endocarditis), gentamicin should also be given for synergistic effect.