What causes the pH shift in bacterial vaginitis?

From the Guidelines

Bacterial vaginosis (BV) is characterized by a shift in vaginal pH from the normal acidic range (3.8-4.5) to a more alkaline environment (>4.5) due to the replacement of hydrogen peroxide-producing Lactobacillus species with anaerobic bacteria. This pH shift occurs primarily because of the replacement of hydrogen peroxide-producing Lactobacillus species with anaerobic bacteria such as Gardnerella vaginalis, Prevotella, Mobiluncus, and other anaerobes, as noted in studies such as 1 and 1. Lactobacilli normally maintain vaginal acidity by producing lactic acid and hydrogen peroxide, creating an environment inhospitable to pathogenic bacteria. When these protective bacteria decrease, anaerobic bacteria proliferate and produce enzymes and amines that raise the vaginal pH. These amines (particularly putrescine, cadaverine, and trimethylamine) are responsible for the characteristic "fishy" odor associated with BV, especially when mixed with alkaline substances like semen or menstrual blood. The elevated pH further promotes the growth of anaerobes in a self-perpetuating cycle. Factors that can trigger this microbial shift include douching, multiple sexual partners, new sexual partners, and antibiotic use that disrupts the normal vaginal flora, as discussed in 1 and 1. Understanding this pH shift is crucial for diagnosis, as testing vaginal pH is a component of Amsel's criteria used to diagnose BV clinically, highlighted in 1 and 1. Key points to consider in the diagnosis and management of BV include:

• The importance of vaginal pH in diagnosing BV
• The role of anaerobic bacteria in causing the pH shift
• The triggers for the microbial shift, such as douching and antibiotic use
• The use of Amsel's criteria for clinical diagnosis
• The need for further research on screening and treating asymptomatic BV in pregnant women, as noted in 1 and 1.

From the FDA Drug Label

Metronidazole vaginal gel is indicated in the treatment of bacterial vaginosis (formerly referred to as Haemophilus vaginitis, Gardnerella vaginitis, nonspecific vaginitis, Corynebacterium vaginitis, or anaerobic vaginosis) NOTE: For purposes of this indication, a clinical diagnosis of bacterial vaginosis is usually defined by the presence of a homogeneous vaginal discharge that (a) has a pH of greater than 4. 5, A clinical diagnosis of bacterial vaginosis was based on Amsel's criteria and defined by the presence of an abnormal homogeneous vaginal discharge that (a) has a pH of greater than 4. 5,

The pH shift in bacterial vaginosis is caused by the replacement of the normal Lactobacillus-dominated vaginal flora with a mixture of bacteria, including Gardnerella and other anaerobic bacteria, which produce volatile amines and other compounds that increase the vaginal pH.

• The normal vaginal pH is acidic, ranging from 3.8 to 4.5.
• In bacterial vaginosis, the pH is greater than 4.5.
• This pH shift is a key diagnostic criterion for bacterial vaginosis, as it is associated with the presence of clue cells and a "fishy" amine odor when mixed with a 10% KOH solution 2, 3.

From the Research

Causes of pH Shift in Bacterial Vaginitis

The pH shift in bacterial vaginitis is caused by the overgrowth of anaerobic bacteria, which replace the normal lactobacilli flora in the vagina.

• This overgrowth leads to the production of enzymes, aminopeptidases, and decarboxylases that degrade protein and convert amino acids to amines 4.
• The production of these amines contributes to the signs and symptoms associated with bacterial vaginosis, including the characteristic fishy odor and elevated vaginal pH 4, 5.
• The shift in vaginal flora from aerobic to anaerobic bacteria is a key factor in the development of bacterial vaginosis, and this shift is associated with an increase in pH 6, 7.

Role of Anaerobic Bacteria

Anaerobic bacteria, such as Bacteroides, Gardnerella vaginalis, and Mobiluncus, play a crucial role in the development of bacterial vaginosis.

• These bacteria produce polyamines, which contribute to the offensive vaginal discharge and elevated pH 5.
• The overgrowth of anaerobic bacteria is associated with a decline in lactobacilli, which are normally present in the vagina and help to maintain a healthy pH balance 4, 6.

Treatment and Prevention

Treatment of bacterial vaginosis typically involves the use of antibiotics, such as metronidazole or clindamycin, which can help to restore the normal balance of vaginal flora 4, 8.

• Alternative treatments, such as lactic acid vaginal gel, aim to restore vaginal pH and lactobacilli, and may be effective in preventing recurrence of the condition 7.