Leptospira interrogans can be cultured from blood and cerebrospinal fluid during the first week of leptospirosis and from urine thereafter. Studies of in vitro sensitivity indicate that these organisms are sensitive to most antibiotics. Tetracycline and penicillin G are most often used clinically, although laboratory studies suggest that the bactericidal activity of penicillin G may be inadequate. Treponema pallidum cannot be satisfactorily cultured. It is identified by dark-field microscopy. Studies of in vivo sensitivity show that penicillin G is highly active against the syphilis pathogen. Since syphilis and gonorrhea may occur simultaneously, ceftriaxone, which is as active as penicillin G against T. pallidum but is also active against penicillinase-producing gonococci, is a logical choice for therapy. Borrelia burgdorferi has been cultured from the blood, cerebrospinal fluid, and skin of patients with
Lyme disease. In vitro studies have shown tetracycline and erythromycin to be effective against B. burgdorferi and penicillin G to be less so, although all are commonly used clinically. Ceftriaxone has also proven to be highly effective in laboratory studies and for clinical treatment.