Enterobacteriales are a large and varied order of bacteria. Found in numerous environments, they are defined by specific cellular traits. These microbes are gram-negative, rod-shaped, and facultative anaerobes, allowing them to survive with or without oxygen. This adaptability contributes to their widespread presence in ecological niches from soil and water to animal intestines.
Common Members of the Enterobacteriales Order
Within the Enterobacteriales order, several genera are widely recognized for their impact on human health. Escherichia is one of the most well-known, with Escherichia coli (E. coli) being its most famous species. Most strains of E. coli are harmless and live in the intestines of people and animals, but some can cause illness.
Another prominent member is the genus Salmonella. Bacteria in this group are commonly associated with foodborne illnesses and are often transmitted through contaminated food products. These bacteria are a frequent cause of infections globally, making them a focus of public health efforts.
The genus Klebsiella includes bacteria found in the natural environment, like soil and water. They are also known for their role in healthcare-associated infections. Klebsiella pneumoniae, for instance, can cause serious infections in hospital settings. These bacteria possess a capsule, a protective outer layer that helps them evade the body’s defenses.
Yersinia is a genus that contains several species capable of causing human disease, most notably Yersinia pestis, the bacterium responsible for plague. While plague is now rare, other species like Yersinia enterocolitica can cause a gastrointestinal condition known as yersiniosis.
Role in Human Health and the Environment
Many members of the Enterobacteriales order are commensal organisms, living in or on another organism without causing harm. A significant population resides in the gastrointestinal tracts of humans and other animals as part of the gut microbiota. In this environment, they contribute to health by aiding digestion and synthesizing certain vitamins.
These bacteria are not confined to animal intestines; they are also ubiquitous in the natural world. They can be found in soil, on decaying vegetation, and in various water sources. In these habitats, they participate in nutrient cycling by helping break down dead organic material.
Most Enterobacteriales are mesophilic, preferring moderate temperatures, which explains their prevalence in environments inhabited by humans and animals. This adaptability allows them to transition between different hosts and environmental reservoirs.
Infections Caused by Enterobacteriales
While many Enterobacteriales are harmless, some can cause a wide range of infections when they move from their usual locations or when a person’s immune system is compromised.
Gastrointestinal Infections
The most common diseases from pathogenic Enterobacteriales are gastrointestinal. Bacteria like certain strains of E. coli and Salmonella cause gastroenteritis. Symptoms include diarrhea, abdominal cramps, and vomiting. These infections are acquired through consuming contaminated food or water.
Urinary Tract Infections
Enterobacteriales are a leading cause of urinary tract infections (UTIs). E. coli is the most frequent culprit, as the bacteria travel from the gut to the urinary tract, where they can multiply and cause inflammation. UTIs can affect the bladder (cystitis) or ascend to the kidneys (pyelonephritis).
Respiratory Infections
Some members of this order also cause respiratory infections, such as pneumonia. Klebsiella pneumoniae is a notable example, associated with hospital-acquired pneumonia. This infection is particularly dangerous for individuals who are already hospitalized or have underlying health conditions.
Systemic Infections
In some cases, Enterobacteriales can enter the bloodstream, leading to bacteremia. If the body’s response to this bloodstream infection becomes overwhelming, it can trigger sepsis, a life-threatening condition. Sepsis involves widespread inflammation that can lead to tissue damage and organ failure. Genera like Escherichia, Klebsiella, and Enterobacter are frequently implicated in cases of bacteremia and sepsis.
Antibiotic Resistance Concerns
A growing challenge in treating these infections is antibiotic resistance. Many species have developed mechanisms to withstand antibiotics, making infections difficult to manage. This resistance is acquired through genetic mutations or by obtaining resistance genes from other bacteria. The use of antibiotics in medicine and agriculture has contributed to the spread of these resistant strains.
Of particular concern is the emergence of multidrug-resistant organisms (MDROs). Within this order, a group known as Carbapenem-resistant Enterobacteriaceae (CRE) poses a significant public health threat. Carbapenems are powerful antibiotics reserved for serious infections. When bacteria become resistant to them, treatment options become severely limited.
The primary mechanism for this resistance is producing enzymes called carbapenemases, which break down carbapenem antibiotics. One common type is Klebsiella pneumoniae carbapenemase (KPC). The presence of CRE in healthcare facilities is problematic, as they can cause outbreaks of infections that are difficult to treat, leading to higher mortality rates.