Cell-wall-deficient bacteria

Abstract

Authors' reply Sir—The definitions for the various terms to describe cell-wall-deficient organisms are not universally agreeable: “There is no uniformity of terminology for cell wall altered microbes, with lack of agreement even among authorities”.1Mattman LH Cell wall deficient forms: stealth pathogens. 3rd edn. CRC Press LLC, Boca Raton, FL, USA2001Google Scholar The two commonly used terms, L-form and spheroplasts, refer only to pleomorphic variants of bacteria or fungi with altered cell walls, which may or may not require hypertonic media, and may or may not revert to the normal forms. The term cell-wall-deficient is, however, widely used, and we deliberately chose to use this term since it is more encompassing than L-form, protoplast, and spheroplast. Despite the ambiguity of the definitions of terms on cell-wall-deficient bacteria, we noted two concrete and inarguable findings. First, the cell-wall-deficient form must have multiplied in the blood-culture broth in the absence of antibiotics. Without bacterial multiplication, the bloodculture system could not detect the presence of bacteria. However, cell-walldeficient forms could not have been recovered from patients as the normal form and induced in the blood-culture bottles in vitro by antibiotics because the small amount of residual antibiotics present in the inoculated blood would be absorbed by the blood-culture resin. Furthermore, in any blood-culture bottle that was positive for cell-walldeficient form, we inoculated 20 μL broth on a lawn of Staphylococcus aureus (NCTC 6571) to look for residual antibiotic effect. No zone of inhibition was noted on any inoculated plate (data not shown). Second, the cell-wall-deficient form must have reverted after subculturing, since the colony morphologies of these subcultures on routine agar plates, the growth rate, antibiotic susceptibility, and the gram-stain appearance are all identical to vegetative cells with normal cell walls. As for the possibility that lysis of leucocytes and erythrocytes might contribute to the increased recovery of bacteria, the erythrocytes were crenated rather than lysed in the hypertonic broth (as our figure showed). Cell-wall-deficient forms have on rare occasions been implicated in various infections, such as central nervous system infections, urinary tract infections, and infective endocarditis.2Fernandes PB Panos C Wall-less microbial isolate from a human renal biopsy.J Clin Microbiol. 1977; 5: 106-107PubMed Google Scholar, 3Calderon E Albuerne A Gonzalez S Winkler L Cell wall deficient bacteria (L form) in meningitis.Rev Latinoam Microbiol. 1971; 13: 95-100PubMed Google Scholar, 4Neu HC Goldreyer B Isolation of protoplasts in a case of enterococcal endocarditis.Am J Med. 1968; 45: 784-788Summary Full Text PDF PubMed Scopus (15) Google Scholar Most of these infections occur de novo. The role of these micro-organisms in infections in immunocompromised hosts has not been systematically studied. Since antibiotics remain one of the most successful ways to induce cellwall-deficient forms in vitro, and immunocompromised patients, such as bone marrow transplant recipients, receive the most intensive antibiotic treatment, the role of this group of organisms in susceptible patients really needs to be looked at more closely. Cell-wall-deficient bacteriaPatrick Woo and colleagues (March 3, 2001)1 report on the isolation of cell-wall-deficient bacteria from the blood cultures of febrile neutropenic bone-marrow transplant recipients. Specific antibiotics, especially those acting on the bacterial cell wall and at sub-minimum inhibitory concentrations, will result in morphological variants. We have shown, for example, that Bacillus licheniformis, B subtilis, and Pseudomonas aeruginosa, produce L-forms, protoplasts, or cell-wall-damaged bacteria in the presence of various antibiotics including β-lactams and the quinolones. Full-Text PDF Cell-wall-deficient bacteriaP C Woo and colleagues1 describe how cell-wall-deficient bacteria can be induced in vitro and in vivo by antibiotics that act on the cell walls, and that these organisms, having fragile structures, are rarely cultivated by conventional blood-culture system. Their discussion was quite interesting, but, in light of our experience, we have some comments on the interpretation of their results. Full-Text PDF