Johnson C C, Wexler H M, Becker S, Garcia M, Finegold S M
Medical Service, Veterans Administration Wadsworth Medical Center, Los Angeles, California 90073.
Antimicrob Agents Chemother. 1989 Mar;33(3):369-72. doi: 10.1128/AAC.33.3.369.
The activity of antimicrobial agents against Fusobacterium species has been reported as variable in the literature. For some strains, the inconsistency arises from difficulty in determining the endpoint of growth in agar dilution susceptibility tests. Certain strains persist as a subtle haze beyond the levels of antibiotic that permit conventional colonial growth. We have determined by light and electron microscopy that this haze represents the colonial growth of cell-wall-defective (CWD) variants of the parent Fusobacterium. The CWD forms could be propagated indefinitely in hypertonic medium containing the antibiotic inducing agent. However, when the antibiotic was eliminated, the organisms would revert to their native morphology. Formation of CWD variants was observed in the presence of cell-wall-active drugs (e.g., beta-lactam agents) but not with drugs that work by a different mechanism (e.g., clindamycin or chloramphenicol). Fourteen of 22 F. varium strains, 8 of 11 F. mortiferum strains, 2 of 10 F. gonidiaformans strains, and 1 of 4 of F. necrophorum strains could be induced to a CWD form in vitro in the usual agar dilution susceptibility test. Although the clinical significance of CWD variants of Fusobacterium is unknown, they may be a source of confusion in interpreting agar dilution susceptibility tests.
抗菌药物对梭杆菌属细菌的活性在文献中报道不一。对于一些菌株，在琼脂稀释药敏试验中确定生长终点存在困难，导致结果不一致。某些菌株在抗生素水平超过允许传统菌落生长的情况下仍持续呈现细微的浑浊。我们通过光学显微镜和电子显微镜确定，这种浑浊代表亲本梭杆菌细胞壁缺陷（CWD）变体的菌落生长。CWD形式可在含有抗生素诱导剂的高渗培养基中无限繁殖。然而，当去除抗生素后，这些微生物会恢复其原始形态。在存在细胞壁活性药物（如β-内酰胺类药物）时观察到CWD变体的形成，但在通过不同机制起作用的药物（如克林霉素或氯霉素）存在时未观察到。在常规琼脂稀释药敏试验中，22株多变梭杆菌中有14株、11株死亡梭杆菌中有8株、10株产子梭杆菌中有2株以及4株坏死梭杆菌中有1株可在体外诱导形成CWD形式。虽然梭杆菌CWD变体的临床意义尚不清楚，但它们可能是解释琼脂稀释药敏试验结果时造成混淆的一个原因。
