Cell Wall Characteristics of Mobiluncus Species

Abstract

The three type strains and a reference strain of Mobiluncus examined in this study had a gram-positive type of cell walls. All four strains were susceptible to vancomycin and resistant to colistin, and the overall susceptibility patterns with other antimicrobial agents were consistent with those of gram-positive microorganisms. Strains of Mobiluncus mulieris were lysed by 3% potassium hydroxide, and strains of Mobiluncus curtisii were not. However, all of the strains examined had intermediate levels of Limulus amebocyte-lysate reactivity that was not lipopolysaccharide associated. Lipopolysaccharide was not detected when whole-cell lysates were digested with proteinase K, separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and silver stained. In addition, 2-keto-3-deoxyoctulosonic acid and heptose were not detected by gas chromatography of 0-methyloxime acetate derivatives of whole-cell carbohydrates. Saponification and gas chromatography of whole-cell fatty acids showed that none of the four strains examined had detectable levels of hydroxylated fatty acids. Hydroxylated fatty acids or aldehyde fatty acids were not detected in acid hydrolysates of crude cell membrane preparations. (1,4,17,27,30,35,37,39,41,45,48), although the taxonomic position of members of this genus is still unresolved (15,43).The genus Mobiluncus has been tentatively assigned to the family Bacteroidaceae (43), which includes obligately anaerobic straight, curved, or helical gram-negative and gram-positive rod-shaped bacteria (18). The Gram reactions of strains of Mobiluncus are typically gram negative or variable (15, 43), although electron micrographs show that structurally these organisms have gram-positive cell walls (41, 43) and lack an outer membrane. Likewise, anaerobic curved rod-shaped organisms belonging to the genera Butyrivibrio, Lachnospira, and Acetivibrio (B), which are also members of the family Bacteruidaceae, stain gram negative but are structurally gram positive. Among anaerobic curved rods consistent with Mobiluncus, fatty acid aldehydes (presumably from plasmologens) have been detected, while hydroxlated fatty acids (found predominately in gram-negative bacteria) have not been found (39). Mobiluncus species are resistant to some antimicrobial agents which traditionally inhibit gram-negative microorganisms and are susceptible to some antimicrobial agents which inhibit gram-positive microorganisms (1,8,15,42,43,44). Limulus amebocyte lysate (LAL) reactivity, an indicator of gram-negative endotoxin, has also been reported (29).In this study, we compared characteristics of the type * Corresponding author.strains and a reference strain of Mobiluncus since previous reports have included organisms of undetermined taxonomic position which resemble members of this genus. We examined four strains of Mobiluncus for the following characteristics which are indicative of cell wall type: cell lysis, lipopolysaccharide (LPS), endotoxin reactivity, fatty acid content, antimicrobial agent susceptibility, and carbohyd...

Susceptibility of Mobiluncus species to 23 antimicrobial agents and 15 other compounds

“…appears to be heterogeneous. Results may vary with the method used since the same two strains of M. mulieris tested by Carlone et al (2), which had MICS of 16 and 32 jig/ml, had MICs in the range <0.2 to 6.25 ,ug/ml in the present study.…”

“…All studies that differentiated M. curtisii (short curved rods) from M. mulieris (long curved rods) found that most or all strains of the former were resistant to metronidazole (2,4,9,10,12). There is no such consensus regarding M. mulieris.…”

“…MICs We are aware of six prior reports containing Mobiluncus susceptibility patterns (2,4,5,9,10,12). It should be noted that both strains of M. curtisii and one of the two strains of M. mulieris tested by Carlone et al (2) were tested by Spiegel et al (10) and that all four strains were tested in the present study. Only one of six studies that tested beta-lactam antibiotics found them inactive against Mobiluncus spp.…”

“…Although their role in BV is not yet understood, reports of their presence in up to 50% of women with (10) and only 0 to 5% without (10,12) BV have provoked a great deal of interest in these organisms. Several researchers have also reported that most or all strains of short curved rods (M. curtisii) (2,4,9,10,12) and some strains of long curved rods (M. mulieris) (2,4,10,12) are resistant to metronidazole, the drug of choice for treating BV. One could speculate that the presence of metronidazoleresistant Mobiluncus spp.…”

“…Several reseachers have published susceptibility patterns, but recommended methods have rarely been used (5). When methods have been modified, quality control has only rarely been included (2).…”