Understanding Mobiluncus in Bacterial Vaginosis

Mobiluncus are gram-variable anaerobic bacterial species found in the human vagina and bowel. Two species identified are connected with BV in women: Mobiluncus curtisii and Mobiluncus mulieris.

Mobiluncus have been found in other parts of the body, including breast and umbilical abscesses, the placenta, blood cultures, pelvic inflammatory disease, and in those who had a preterm delivery.

It isn’t clear which specific symptoms are attributable to Mobiluncus in the vagina.

How Mobiluncus spp. operate

Mobiluncus are known to develop biofilms, are very mobile, and are very capable attachers to vaginal epithelial cells.

Mobiluncus attach to glucose or mannose (present in vaginal epithelial cells), but if those sugars are not present, Mobiluncus can use adhesins. Adhesins are special adhesive excretions that allow attachment to vaginal epithelial cells. This attachment is toxic to the cell.

Mobiluncus spp. have an association with Gardnerella vaginalis and some strains are antibiotic-resistant, particularly to the typical bacterial vaginosis (BV) treatment of metronidazole.

Mobiluncus are difficult to culture, making PCR testing important when ruling bacteria out during BV treatments.

Mobiluncus are proving somewhat complex to define. There isn’t a lot of information on the exact nature of these bacteria, or their role in vulvovaginal health or disease.

Mobiluncus spp. and BV

Mobiluncus may be found in up to 82 per cent of women with BV, but positive PCR test results of this bacteria in women without BV range from 0-38 per cent.

The fact Mobiluncus may be resistant to antibiotics is not discussed by many doctors who treat BV, with metronidazole continuing to be prescribed regardless – most strains and species of bacteria are never sought out.

Misprescribing in this way contributes to the unacceptably high failure rate of antibiotics in treating BV.

Proper testing is of paramount importance when dealing with suspected BV to determine precisely which bacteria are present prior to treatment. Ask for PCR testing to detect.

Women with what’s known as ‘complicated vaginal flora’ have higher levels of Mobiluncus and are more likely to have recurrent bacterial vaginosis.

M. curtisii and M. mulieris are highly specific to BV. M. curtisii is the most likely to be involved in BV, and is known to be resistant to metronidazole – the most commonly prescribed antibiotic for BV.

The presence of M. curtisii and the recurrence of BV at 65-70 days post-antibiotic-treatment are associated.

Recurrent BV could be due to the inability of metronidazole to clear this bacteria from the vagina but is also likely to include the inability of metronidazole to penetrate biofilms.

Treating Mobiluncus

Standard medical treatment of Mobiluncus is antibiotics. Metronidazole may not be very effective against Mobiluncus (but three times daily for seven days may have a favourable effect), with clindamycin seeing a better success rate.

Research into BV and Mobiluncus curtisii

A study at a sexual health clinic in the United States took vaginal swabs of 100 women symptomatic for BV, treating the BV with antibiotics.

All study participants took metronidazole for seven days or 14 days, plus or minus azithromycin. Study subjects were checked at day 21, 35-40, and 65-70 after the start of the study.

If a subject had a recurrence of symptomatic BV, they were discontinued from the study, however, if BV was asymptomatic and present, they were kept in the study.

Vaginal swabs and polymerase chain reaction (PCR) tests were performed at baseline and at each follow-up visit. The participants in the study had M. curtisii present at baseline (detected by PCR) with three follow-up visits.

Recurrence of BV at 65-70 days was defined as a Nugent score of 7-10 regardless of symptoms.

Persistence of M. curtisii was defined as the organism being present at baseline and at at least one of the follow-up visits.

Persistence of M. curtisii at baseline and at least one other visit was significantly associated with a recurrence of BV.

Almost 68 per cent of the women with persistent M. curtisii had a recurrence of BV compared with 11 per cent of women who had no evidence of M. curtisii by PCR after the baseline treatment visit.

The way that M. curtisii shows up in the PCR testing was of note, since the organism either didn’t show up in visits two and three (after treatment), but visit four, or the organism was present in all tests.

The former may indicate reinfection, while the latter may indicate a lack of clearance, however, they could both mean a lack of clearance.

Sexual transmissibility between partners was not addressed in this study, but we know that BV can be sexually transmitted.

Mobiluncus spp. historically

Mobiluncus spp. were recognised in vaginal fluids as early as 1895 and was first isolated in 1913. Mobiluncus includes 22 individual strains.

Another name for Mobiluncus, due to a coincidental co-discovery, is Falcivibrio. Mobiluncus spp. has been likened to other bacterial families, Actinomycetales and Bacteroidaceae.

Determining the Gram stain was initially problematic, with results positive for both gram-negative and gram-positive, leaving researchers with gram-variable as the final answer.

References

Forsum, U. The biology of Mobiluncus. Venereology, Vol. 14, No. 4, 2001: 169-73.
Costello, J., Blaize, J., L’Amoreaux, W., & McCoy, E. (2007). Ultrastructure of the Pathogenic Bacteria Mobiluncus mulieris. Microscopy and Microanalysis, 13(S02), 336-337.
De Boer JM, Plantema FH. Ultrastructure of the in situ adherence of Mobiluncus to vaginal epithelial cells. Can J Microbiol. 1988 Jun;34(6):757-66.
A. Menolascina, B. Nieves*, Z. Calderas, and C.L. Sanoja, Adherence and Cytotoxicity Capacity of Mobiluncus Strains Isolated from Patients with Bacterial Vaginosis, Anaerobe (1999) 5, 487±489 Article No. anae.1999.0295
MELTZER MC, DESMOND RA, SCHWEBKE JR. Association of Mobiluncus curtisii With Recurrence of Bacterial Vaginosis. Sexually transmitted diseases. 2008;35(6):611-613. doi:10.1097/OLQ.0b013e318167b105.
Nygaard OG1, Csángó PA, Jagars G. Bacterial vaginosis associated with Mobiluncus species in general practice. Tidsskr Nor Laegeforen. 1991 Mar 10;111(7):845-7.
Nyirjesy P, McIntosh MJ, Steinmetz JI, Schumacher RJ, Joffrion JL. The effects of intravaginal clindamycin and metronidazole therapy on vaginal mobiluncus morphotypes in patients with bacterial vaginosis. Sex Transm Dis. 2007 Apr;34(4):197-202.