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Fastidiosos

Gardnerella vaginalis

Gram-variable coccobacilli

Identification & Growth

Identification

  • Clue cells on wet mount and Gram stain (Nugent score)
  • Beta-hemolytic on human blood bilayer (HBT) agar, catalase- and oxidase-negative

Growth Conditions

  • HBT agar, 35–37 °C, 5% CO2, 48 h; pinpoint colonies

Clinical Significance

  • Bacterial vaginosis; occasional UTI and puerperal infection

Intrinsic Resistance

  • No disk-diffusion breakpoints — routine susceptibility testing is not performed

Bench Alerts

  • Diagnosis rests on the Nugent score, not culture
  • Treatment is metronidazole or clindamycin; an isolated positive culture is not an indication to treat

Clinical Notes

Clinical presentations

  • Central component of bacterial vaginosis: homogeneous grey discharge, amine odour and vaginal pH above 4.5.
  • Associated with increased risk of preterm birth, postpartum endometritis and acquisition of other sexually transmitted infections.
  • Isolation from urine or blood is uncommon and requires clinical correlation before any action.

Specimens and collection

  • Lateral vaginal wall swab for microscopy; avoid endocervical collection, which does not represent the vaginal microbiota.
  • Diagnosis relies on the Nugent Gram-stain score or the Amsel criteria, not on culture alone.
  • Avoid douching, vaginal creams and intercourse in the 24–48 h before collection.

Epidemiology and at-risk populations

  • Bacterial vaginosis is the most common cause of vaginal discharge in women of reproductive age.
  • Associated factors: multiple partners, a new partner, vaginal douching and loss of peroxide-producing lactobacilli.
  • Recurrence is frequent in the first 6–12 months after treatment, requiring counselling and follow-up.

Resistance and therapeutic implications

  • Metronidazole and clindamycin, oral or topical, are the treatments recommended by STI guidelines.
  • Routine susceptibility testing is not indicated: the disease is polymicrobial and results do not guide management.
  • Biofilm formation by G. vaginalis explains part of the treatment failures and relapses.

Bench and reporting notes

  • Gram-variable pleomorphic rod; on Gram stain, clue cells are epithelial cells coated by coccobacilli with obscured borders.
  • Report the Nugent score with its interpretation (normal, intermediate, consistent with vaginosis) rather than merely listing the organism.
  • Do not report G. vaginalis as a urinary pathogen without a significant count and a compatible clinical picture.

Sources

Educational decision-support content. It does not replace laboratory validation, current guidelines or review by the responsible professional.

FAQ: Frequently Asked Questions

How to identify Gardnerella vaginalis in the lab?

Gardnerella vaginalis is identified through clue cells on wet mount and gram stain (nugent score), beta-hemolytic on human blood bilayer (hbt) agar, catalase- and oxidase-negative.

What are the intrinsic resistances of Gardnerella vaginalis?

This organism is naturally resistant to no disk-diffusion breakpoints — routine susceptibility testing is not performed. These drugs should not be reported as susceptible.

Where is Gardnerella vaginalis commonly found?

It is typically associated with bacterial vaginosis; occasional uti and puerperal infection.

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