Bacteremia of Gardnerella vaginalis after endometrial ablation

Gardnerella and vaginal health: the truth is out there

The human vagina is a dynamic ecosystem in which homeostasis depends on mutually beneficial interactions between the host and their microorganisms. However, the vaginal ecosystem can be thrown off balance by a wide variety of factors. Bacterial vaginosis (BV) is the most common vaginal infection in women of childbearing age but its etiology is not yet fully understood, with different controversial theories being raised over the years. What is generally accepted is that BV is often characterized by a shift in the composition of the normal vaginal microbiota, from a Lactobacillus species dominated microbiota to a mixture of anaerobic and facultative anaerobic bacteria. During BV, a polymicrobial biofilm develops in the vaginal microenvironment, being mainly composed of Gardnerella species. The interactions between vaginal microorganisms are thought to play a pivotal role in the shift from health to disease and might also increase the risk of sexually transmitted infections acquisition. Here, we review the current knowledge regarding the specific interactions that occur in the vaginal niche and discuss mechanisms by which these interactions might be mediated. Furthermore, we discuss the importance of novel strategies to fight chronic vaginal infections.

Cholesterol-Dependent Cytolysins Produced by Vaginal Bacteria: Certainties and Controversies

Bacterial vaginosis (BV) is a vaginal anaerobic dysbiosis that affects women of reproductive age worldwide. BV is microbiologically characterized by the depletion of vaginal lactobacilli and the overgrowth of anaerobic bacterial species. Accumulated evidence suggests that Gardnerella spp. have a pivotal role among BV-associated bacteria in the initiation and development of BV. However, Gardnerella spp. often colonize healthy women. Lactobacillus iners is considered as a prevalent constituent of healthy vaginal microbiota, and is abundant in BV. Gardnerella spp. and L. iners secrete the toxins vaginolysin (VLY) and inerolysin (INY), which have structural and activity features attributed to cholesterol-dependent cytolysins (CDCs). CDCs are produced by many pathogenic bacteria as virulence factors that participate in various stages of disease progression by forming lytic and non-lytic pores in cell membranes or via pore-independent pathways. VLY is expressed in the majority of Gardnerella spp. isolates; less is known about the prevalence of the gene that encodes INY. INY is a classical CDC; membrane cholesterol acts a receptor for INY. VLY uses human CD59 as its receptor, although cholesterol remains indispensable for VLY pore-forming activity. INY-induced damage of artificial membranes is directly dependent on cholesterol concentration in the bilayer, whereas VLY-induced damage occurs with high levels of membrane cholesterol (>40 mol%). VLY primarily forms membrane-embedded complete rings in the synthetic bilayer, whereas INY forms arciform structures with smaller pore sizes. VLY activity is high at elevated pH, which is characteristic of BV, whereas INY activity is high at more acidic pH, which is specific for a healthy vagina. Increased VLY levels in vaginal mucosa in vivo were associated with clinical indicators of BV. However, experimental evidence is lacking for the specific roles of VLY and INY in BV. The interplay between vaginal bacterial species affects the expression of the gene encoding VLY, thereby modulating the virulence of Gardnerella spp. This review discusses the current evidence for VLY and INY cytolysins, including their structures and activities, factors affecting their expression, and their potential impacts on the progression of anaerobic dysbiosis.

Gram-Positive Uropathogens, Polymicrobial Urinary Tract Infection, and the Emerging Microbiota of the Urinary Tract

Gram-positive bacteria are a common cause of urinary-tract infection (UTI), particularly among individuals who are elderly, pregnant, or who have other risk factors for UTI. Here we review the epidemiology, virulence mechanisms, and host response to the most frequently isolated Gram-positive uropathogens: Staphylococcus saprophyticus, Enterococcus faecalis, and Streptococcus agalactiae. We also review several emerging, rare, misclassified, and otherwise underreported Gram-positive pathogens of the urinary tract including Aerococcus, Corynebacterium, Actinobaculum, and Gardnerella. The literature strongly suggests that urologic diseases involving Gram-positive bacteria may be easily overlooked due to limited culture-based assays typically utilized for urine in hospital microbiology laboratories. Some UTIs are polymicrobial in nature, often involving one or more Gram-positive bacteria. We herein review the risk factors and recent evidence for mechanisms of bacterial synergy in experimental models of polymicrobial UTI. Recent experimental data has demonstrated that, despite being cleared quickly from the bladder, some Gram-positive bacteria can impact pathogenic outcomes of co-infecting organisms. When taken together, the available evidence argues that Gram-positive bacteria are important uropathogens in their own right, but that some can be easily overlooked because they are missed by routine diagnostic methods. Finally, a growing body of evidence demonstrates that a surprising variety of fastidious Gram-positive bacteria may either reside in or be regularly exposed to the urinary tract and further suggests that their presence is widespread among women, as well as men. Experimental studies in this area are needed; however, there is a growing appreciation that the composition of bacteria found in the bladder could be a potentially important determinant in urologic disease, including susceptibility to UTI.

Gardnerella vaginalis bacteremia associated with severe acute encephalopathy in a young female patient

Gardnerella vaginalis is a facultative anaerobic bacterium that inhabits the genitourinary tract of both healthy women and those with bacterial vaginosis. We report a case of G. vaginalis bacteremia associated with severe toxic encephalopathy in a young woman. Anaerobic blood cultures yielded pure growth of small gram-variable rods later identified as G. vaginalis by both rapid biochemical tests and 16S rRNA gene sequencing. The patient recovered after treatment with amoxicillin-clavulanate according to the in vitro susceptibility testing. The complete genome of G. vaginalis isolate from blood cultures was determined. In vitro G. vaginalis isolate produced elevated amounts of a pore-forming toxin vaginolysin compared to control G. vaginalis isolates. We hypothesize that this toxin, if produced in high amounts in blood, is able to disrupt the blood-brain barrier and exert a toxic activity on brain cells.

Transient microbiota exposures activate dormant Escherichia coli infection in the bladder and drive severe outcomes of recurrent disease

Pathogens often inhabit the body asymptomatically, emerging to cause disease in response to unknown triggers. In the bladder, latent intracellular Escherichia coli reservoirs are regarded as likely origins of recurrent urinary tract infection (rUTI), a problem affecting millions of women worldwide. However, clinically plausible triggers that activate these reservoirs are unknown. Clinical studies suggest that the composition of a woman’s vaginal microbiota influences her susceptibility to rUTI, but the mechanisms behind these associations are unclear. Several lines of evidence suggest that the urinary tract is routinely exposed to vaginal bacteria, including Gardnerella vaginalis, a dominant member of the vaginal microbiota in some women. Using a mouse model, we show that bladder exposure to G. vaginalis triggers E. coli egress from latent bladder reservoirs and enhances the potential for life-threatening outcomes of the resulting E. coli rUTI. Transient G. vaginalis exposures were sufficient to cause bladder epithelial apoptosis and exfoliation and interleukin-1-receptor-mediated kidney injury, which persisted after G. vaginalis clearance from the urinary tract. These results support a broader view of UTI pathogenesis in which disease can be driven by short-lived but powerful urinary tract exposures to vaginal bacteria that are themselves not “uropathogenic” in the classic sense. This “covert pathogenesis” paradigm may apply to other latent infections, (e.g., tuberculosis), or for diseases currently defined as noninfectious because routine culture fails to detect microbes of recognized significance.

Millions of women suffer from recurrent urinary tract infections (rUTI) and the only treatment option is prophylactic antibiotics, which contributes to antibiotic resistance. In experimental models, Escherichia coli, the dominant UTI pathogen, establishes reservoirs inside the bladder lining; it is believed that some cases of rUTI in women may be due to these reservoirs awakening in response to triggers that are still unknown. Here we present a new mouse model that demonstrates the first clinically plausible trigger of rUTI arising from these reservoirs. Specifically, we show that bladder exposure to Gardnerella vaginalis, a common member of the vaginal microbial community, can drive the emergence of E. coli from bladder reservoirs. Furthermore, upon its exposure to the urinary tract, this vaginal organism caused severe kidney damage and other complications, suggesting that carriage of particular vaginal bacteria could also impact a woman’s risk for kidney infection. Bladder exposure to G. vaginalis is likely to occur during sexual activity in many women. Taken together, these data provide the first explanation for why certain characteristics of the vaginal microbiota have been linked with rUTI. Finally, our findings suggest that targeting specific members of the vaginal community may be an effective strategy for treating rUTI.