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The Many Faces of Enterococcus spp.—Commensal, Probiotic and Opportunistic Pathogen

As commensals, enterococci colonize the digestive system and participate in the modulation of the immune system in humans and animals. For many years reference enterococcal strains have been used as probiotic food additives or have been recommended as supplements for the treatment of intestinal dysbiosis and other conditions. The use of Enterococcus strains as probiotics has recently become controversial due to the ease of acquiring different virulence factors and resistance to various classes of antibiotics. Enterococci are also seen as opportunistic pathogens. This problem is especially relevant in hospital environments, where enterococcal outbreaks often occur.

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Articles of Interest

Controversial Aspects Displayed by Enterococci: Probiotics or Pathogens?

However, following the emergence of antibiotic-resistant (AMR) enterococci and particularly of the vancomycin-resistant enterococci (VRE), these microorganisms have turned from generally recognized as safe (GRAS) for human consumption to significant pathogens threatening human health and thriving in the hospital environment.

Enterococcal Infection—Treatment and Antibiotic Resistance

Enterococci are commensals of the gastrointestinal (GI) tract of humans and animals, and, in the absence of antibiotics, establish a symbiotic relationship with the human microbiota. In normal circumstances, enterococci are found in low numbers in the colon, as compared with other members of the gut flora (such as anaerobes) (Murray, 2000). The “natural” balance in the microbiota becomes altered by the presence of antibiotics; the administration of cephalosporins and metronidazole, which are often used as part of an empiric regimen in critically ill patients, kills many Gram-negative and anaerobic bacteria in the intestine, but enterococci tend to survive

Enterococci and Their Interactions with the Intestinal Microbiome

The Enterococcus genus comprises over 50 species that live as commensal bacteria in the gastrointestinal (GI) tracts of insects, birds, reptiles, and mammals. Named “entero” to emphasize their intestinal habitat, Enterococcus faecalis and Enterococcus faecium were first isolated in the early 1900s and are the most abundant species of this genus found in the human fecal microbiota. In the past 3 decades, enterococci have developed increased resistance to several classes of antibiotics and emerged as a prevalent causative agent of health care-related infections. In U.S. hospitals, antibiotic use has increased the transmission of multidrug-resistant enterococci.

Enterococci, from Harmless Bacteria to a Pathogen

Enterococci are gastrointestinal commensals whose hardiness allowed them to colonize very diverse environments, including soils, water, food, and feed. This ability to overcome adverse conditions makes enterococci problematic once they colonize hospital niches. Together with the malleability of their genomes, the capacity to acquire and disseminate determinants of antibiotic resistance has contributed to converting what was once just another opportunistic pathogen into a first-class clinical problem.

Enterococci: Between Emerging Pathogens and Potential Probiotics

Enterococci are ubiquitous microorganisms that could be found everywhere; in water, plant, soil, foods, and gastrointestinal tract of humans and animals. They were previously used as starters in food fermentation due to their biotechnological traits (enzymatic and proteolytic activities) or protective cultures in food biopreservation due to their produced antimicrobial bacteriocins called enterocins or as probiotics, live cells with different beneficial characteristics such as stimulation of immunity, anti-inflammatory activity, hypocholesterolemic effect, and prevention/treatment of some diseases. However, in the last years, the use of enterococci in foods or as probiotics caused an important debate because of their opportunistic pathogenicity implicated in several nosocomial infections due to virulence factors and antibiotic resistance, particularly the emergence of vancomycin-resistant enterococci.

Enterococcus (E. Faecalis & E. Faecium)

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Enterococcus spp. as a Producer and Target of Bacteriocins: A Double-Edged Sword in the Antimicrobial Resistance Crisis Context

Enterococcus spp. are one of the most frequent producers of bacteriocins (enterocins), which provides them with an advantage to compete in their natural environment, which is the gut of humans and many animals. The enterocins' activity against microorganisms from different phylogenetic groups has raised interest in Enterococcus spp. in different contexts throughout the last decades, especially in the food industry. Nevertheless, some species can also cause opportunistic life-threatening infections and are frequently multidrug-resistant (MDR). Vancomycin-resistant Enterococcus (VRE), in particular, are an ongoing global challenge given the lack of therapeutic options.

The Enterococcus: a Model of Adaptability to Its Environment

The genus Enterococcus comprises a ubiquitous group of Gram-positive bacteria that are of great relevance to human health for their role as major causative agents of health care-associated infections. The enterococci are resilient and versatile species able to survive under harsh conditions, making them well adapted to the health care environment.

The Genus Enterococcus: Between Probiotic Potential and Safety Concerns—An Update

A considerable number of strains belonging to different species of Enterococcus are highly competitive due to their resistance to wide range of pH and temperature. Their competitiveness is also owed to their ability to produce bacteriocins recognized for their wide-range effectiveness on pathogenic and spoilage bacteria. Enterococcal bacteriocins have attracted great research interest as natural antimicrobial agents in the food industry, and as a potential drug candidate for replacing antibiotics in order to treat multiple drugs resistance pathogens. However, the prevalence of virulence factors and antibiotic-resistance genes and the ability to cause disease could compromise their application in food, human and animal health.

The life and times of the Enterococcus

It appears likely that we will soon be faced with increasing numbers of enterococci for which there is no adequate therapy. Enterococci are important human pathogens that are increasingly resistant to antimicrobial agents. These organisms were previously considered part of the genus Streptococcus but have recently been reclassified into their own genus, called Enterococcus. Enterococcus faecalis and E. faecium... They are now the third most common organism seen in nosocomial infections.

The rise of the Enterococcus: beyond vancomycin resistance

Enterococci are some of the most versatile organisms found to infect hospitalized patients. The epidemiology of enterococcal infections has evolved since the emergence of these pathogens and has seen the rise of Enterococcus faecium as a nosocomial pathogen with serious clinical implications. The effect of antibiotics on the microbiota of the gastrointestinal tract and subsequent alterations in the regulation of the gut immune system can favour colonization by multidrug-resistant enterococci.

Resources

Infectious Disease Advisor

Enterococcus, a gram-positive bacteria with relatively low virulence, was first described by Thiercelin in 1899 following its discovery in the human gastrointestinal tract and further detailed by MacCallum and Hastings in a case of infective endocarditis. Enterococci are early colonizers in the infant gut. Although 2 species — Enterococcus faecalis and Enterococcus faecium — are abundant in feces, the organism typically accounts for less than 1% of the population of normal microbiota.

StatPearls

Enterococci are Gram-positive facultative anaerobic cocci in short and medium chains, which cause difficult-to-treat infections in the nosocomial setting. They are a common cause of UTIs, bacteremia, and infective endocarditis and rarely cause intra-abdominal infections and meningitis. They have intrinsic resistance to some antibiotics and acquire and transfer resistance to other bacteria via mobile genetic elements.