L-PHASE infections of the blood, which are not detected by routine culture, may cause treatment failures in septicemia. Two examples are presented in which septicemia became increasingly severe during antibiotic therapy, although routine blood cultures were repeatedly negative. This apparent inconsistency was explained by the presence of L forms in blood cultures prepared simultaneously but with a defined medium.
Using the special medium, L growth was demonstrated in 18 hours in contrast to the five- to seven-day growth period formerly required for L growth from septicemias. This technique offers the practical advantage that sensitivity tests may be read at the end of two days and followed by specific therapy for L-phase infections.
It is now known that infection with the L phase of bacteria occurs commonly in man, and furthermore, that the L form can occur spontaneously without induction by antibiotics, although penicillin has greatly increased its incidence.
MATTMAN LH, MATTMAN PE. L Forms of Streptococcus Fecalis in Septicemia. Arch Intern Med. 1965;115(3):315-321. doi:10.1001/archinte.1965.03860150059011