Vulvovaginal Infections

William J. Ledger, Steven S. Witkin

• Verlag: CRC Press
• Jahr: 2017
• ISBN:
  9781315360645
• Auflage: 2
• Thema: Medicina
• Thema: Teoría, práctica y referencia médicas

Vulvovaginal Infections presents new knowledge to help clinicians accurately diagnose and treat their patients and highlights for researchers remaining unsolved problems and the most promising areas for continued investigation. Clinical gynecologists will find practical advice and extensive insight into solving real-life clinical scenarios.

The book opens by presenting information on the microbiology of the vagina and vaginal immunology. It then discusses the diagnosis of vulvovaginal disease, including physical examination, screening processes, and laboratory testing.

Diagnosis is followed by covering various vulvovaginal infections including bacterial vaginosis, Candida vulvovaginitis, Trichomonas vaginalis vaginitis, genital herpes, human papillomavirus genital infections, allergic vulvovaginitis, menopausal vulvovaginitis, cytolytic vaginosis, aerobic vaginitis, and more.

For each of these conditions, the book presents information on its background, microbiology, immunology, prevention, diagnosis, and treatment. Therapy details are provided with an emphasis on nuances that can be applied to women who fail to respond to medication prescribed or who respond and then become symptomatic once treatment has ended.

This new edition discusses major advances in the characterization of endogenous microbiota that populate the genital tract in women of all ages. It also provides a more sophisticated appreciation of immune mechanisms found in the healthy female genital tract and alterations that increase both susceptibility and consequences of various infectious and noninfectious disorders. A major impetus for writing this new edition is to help the busy clinician, resident, or fellow by explaining advances in individual disorders in a manner that is relevant to their practice.

CHAPTER 1

MICROBIOLOGY OF THE VAGINA

In recent years, our knowledge of the microbiology of the vagina has undergone a profound alteration. Due to the parallel development of nonculture gene amplification techniques to amplify the bacterial gene coding for 16S ribosomal RNA and computer-generated analysis of hypervariable regions within this gene, a strikingly different and more accurate picture of the vaginal microbiome has emerged. New studies detailing the composition of the vaginal microbiome in consecutive menstrual cycles, in response to environmental changes and at different life stages, now appear frequently in the medical literature. This multitude of new data enables us to redefine what constitutes a normal, i.e., nonpathogenic, vaginal bacterial milieu and begin to more accurately evaluate and ultimately diagnose and treat individual women. However, our understanding of the mechanisms responsible for the makeup of the vaginal microbiome in individual women at different lifetime stages, and in various environments, and the triggers that induce pathological changes in bacterial composition at this site remains fragmentary. In this chapter, we will summarize the current state of knowledge of the composition of the bacterial microbiome in the lower female genital tract under different conditions and attempt to analyze the biological significance of the observations. Further analysis and interpretation of the vaginal microbiome in women with defined pathological conditions such as vulvovaginal candidiasis, bacterial vaginosis, and trichomoniasis will be found in subsequent chapters on these topics.

THE HUMAN MICROBIOME

Large multicenter and multinational government-sponsored investigations have, for the first time, begun to clearly define the intimate and mandatory relationships between the microorganisms that colonize different body sites and human physiology. It is estimated that there are 10 times more bacterial cells in our body than there are human cells, and at least 100 times more bacterial genes than human genes.¹ Our dependence on bacterial genes for the performance of biological functions necessary for our health has been clearly elucidated. Essential nutritional, immunological, and protective roles for the endogenous commensal bacterial populations in the human gastrointestinal tract are now well established. For example, fecal transplants, in which gastrointestinal bacteria from healthy individuals are provided to people with intestinal disorders, has successfully led to a reversal of pathological symptoms.² There have also been numerous attempts to alter the bacterial composition of the human vagina by the administration of purportedly “healthy” bacteria, either orally or by direct insertion into the vagina, or by altering vaginal pH with exogenous acidic preparations. Results to date have been contradictory or fragmentary due, at least in large part, to an incomplete understanding of what constitutes a normal vaginal microbiota. Before we can utilize exogenous bacteria, either natural strains or experimentally redesigned microorganisms, or other products to correct purported deficiencies and promote vaginal health, we first need to more completely understand the composition and functions of the endogenous bacteria, factors contributing to variability of the vaginal microbiome in individual women. The influence of host genetic, immune, and environmental factors on bacteria–host interactions must also be considered.

BIRTH TO PUBERTY

The prevalent dogma is that the female upper genital tract is sterile and that the newborn baby first becomes colonized with bacteria following disruption of the maternal–fetal membranes and/or during passage through the vagina. This is probably a simplistic and inaccurate view, at least for many pregnancies. Nonpregnant women may be positive for bacteria in their endometrium,³ and bacteria have been recovered from almost 25% of placentas that were obtained from women who were delivered by cesarean section in the absence of labor.⁴ Bacteria, as well as viruses, have been consistently identified in amniotic fluid during the midtrimester (reviewed in Reference ⁵). In any event, the baby certainly becomes infected with the mother’s vaginal bacteria during delivery, and the female infant’s vagina is similar to the bacterial composition of her mother. In babies born by cesarean section to women who were not in labor, the baby’s vaginal microbiota more closely resembles the mother’s skin bacteria.⁶ In both cases, however, under the influence of the mother’s estrogen, lactic acid–producing bacteria such as Lactobacillus species colonize the vagina from the gastrointestinal tract and predominate. Estrogen promotes glycogen deposition on vaginal epithelial cells. This is degraded by host alpha-amylase and the products efficiently utilized by Lactobacilli for anaerobic glycolysis. The end product, lactic acid, renders the vagina acidic and retards or prevents the growth of other bacteria. When the mother’s estrogen is no longer present, the vaginal pH increases toward neutrality, the female baby’s vagina loses its lactobacillus population and, instead, becomes dominated by enteric and skin bacteria as well as by Candida albicans and genital mycoplasmas.⁷ At puberty, under the influence of rising estrogen levels and renewed glycogen deposition on epithelial cells, the bacterial composition of the vagina reverts back to one dominated by lactic acid–producing bacteria.

REPRODUCTIVE AGE WOMEN

It has become abundantly clear that the vaginal bacterial population in apparently healthy reproductive age women can be quite diverse as well as changeable within one menstrual cycle or between different cycles.⁸,⁹ This has made the definition of what constitutes a normal vaginal microbiota quite difficult to pinpoint and, at the very least, clearly highlights the inaccuracy of making a clinical diagnosis on the basis of analyzing only a single vaginal sample. The following discussion highlights the predominant findings from vaginal samples obtained from women in the United States and Western Europe. Variations in predominant Lactobacillus species as well as the detection of unique bacterial genera at different frequencies might be expected in the analysis of comparable samples from women in other parts of the world and depending on economic status and cultural norms.¹⁰ The diversity of microorganisms most commonly present in the vagina of healthy reproductive age women is delineated in Table 1.1.

Approximately 80% of healthy reproductive age women appear to be predominantly colonized in their vagina by one or a combination of four Lactobacillus species: L. crispatus, L. iners, L.gasseri, and L. jensenii. Other lactobacillus species are also occasionally detected but are rarely predominant. In about 20% of healthy women, Lactobacilli are either present in low numbers or are undetectable, and the predominant bacterial genera may be one or a combination of facultative and anaerobic bacteria: Gardnerella vaginalis, Atopobium vaginae, Streptococcus, Prevotella, Sneathia, Mobiluncus, and other biotypes. The proportion of instances in which one Lactobacillus species or bacterial genera was dominant varied with the specific population being evaluated. It is important to emphasize that other bacteria, such as Atopobium, Megasphaera, and Leptotrichia, are also lactic acid producers and, thus, an acidic vaginal pH can be maintained in the absence of Lactobacilli. The absence of a vaginal microbiota dominated by Lactobacilli is more common in Hispanic or African-American women than in women of European or Asian origin.¹¹ As a consequence of this, the mean vaginal pH of healthy Hispanic or African-American women is elevated compared to that of White or Asian women.

Studies evaluating the vaginal microbiota during different stages of the menstrual cycle have yielded highly variable results. In some women, the vaginal microbiota was stable throughout the cycle and even during menstruation, while in other women, large variations were observed at different time points. It must be emphasized that regardless of whether or not alterations in the vaginal microbiota were observed, all subjects remained in good health. Therefore, the apparent stability or instability of a woman’s bacterial population is not predictive of vaginal health. The most frequent changes in composition of the vaginal microbiota in the majority of women were observed during menstruation and following sexual intercourse. These changes were temporary. It should be noted that the microbiome of the human ejaculate has been characterized in a recent study, and there were more bacteria than there were spermatozoa in a semen sample. It has been suggested that the vaginal and seminal microbiome of sex partners may be related.¹² Factors influencing the composition of the vaginal microbiota are shown in Table 1.2.

Table 1.1 Microorganisms most frequently detected in the vagina of healthy reproductive age women

Microorganism	Species
Lactobacilli	L.crispatus, L. iners, L. gasseri, L. jensenii
Cocci	Staphylococcus aureus, group B and D streptococci, peptococci, peptostreptococci
Bacilli	Gardnerella vaginalis, Escherichia coli, Bacteroides spp., Prevotella spp., diphtheroids, propionibacteria, Clostridia spp., fusobacteria
Mycoplasmas	Mycoplasma hominis, Ureaplasma urealyticum, Ureaplasma parvum
Yeast	Candida albicans
Viruses	Human papillomavirus

Table 1.2 Factors influencing the composition of the vaginal microbiota

Factor	Effect
Estrogen	Promotes dominance of Lacto...