Enterobacteriaceae represents a large and diverse family of bacteria found widely across various environments. These microorganisms inhabit diverse niches, including soil, water, plants, and the intestines of humans and animals. Their ubiquitous presence and varied interactions make understanding this group important.
What Are Enterobacteriaceae?
Enterobacteriaceae are Gram-negative, rod-shaped bacteria. They do not retain the crystal violet stain due to their cell wall structure, appearing as elongated cylinders.
A defining characteristic is their metabolic flexibility; they are facultative anaerobes. This means they can grow with or without oxygen. All members of Enterobacteriaceae ferment glucose, a key test for identification.
Common Examples and Their Habitats
Several Enterobacteriaceae members are frequently encountered. Escherichia coli is a prevalent inhabitant of the lower intestines of warm-blooded animals, including humans. While many strains are harmless commensals, some can cause intestinal and extraintestinal infections.
Salmonella species are primarily found in the intestines of birds, reptiles, and mammals. These bacteria are often transmitted through contaminated food and water. Klebsiella species, particularly Klebsiella pneumoniae, are commonly found in the normal flora of the mouth, skin, and intestines. They can also exist in soil and water environments.
Shigella species are human pathogens, typically found in the intestinal tracts of humans and other primates. They are known for causing severe diarrheal diseases. Proteus species are widely distributed in the environment, including soil, water, and decaying organic matter, and are also part of the normal gut flora in humans and animals.
Yersinia species are found in various animal reservoirs, with Yersinia pestis causing plague, often found in rodents and their fleas. Yersinia enterocolitica and Yersinia pseudotuberculosis are associated with gastrointestinal infections in humans, found in pigs, other animals, and environmental sources like water.
Impact on Human Health
Enterobacteriaceae play a dual role in human health, acting as both beneficial residents and pathogens. Many Escherichia coli strains are integral components of the normal human gut microbiota. These beneficial bacteria contribute to digestion by breaking down complex carbohydrates and synthesize vitamins K and some B vitamins. Their presence also helps prevent colonization by harmful microbes.
Despite these beneficial roles, numerous Enterobacteriaceae species are opportunistic pathogens or primary invaders. They are a leading cause of urinary tract infections (UTIs), with E. coli being responsible for a large percentage of these cases. Foodborne illnesses are frequently caused by Salmonella and pathogenic E. coli strains, leading to symptoms like diarrhea, vomiting, and abdominal cramps.
These bacteria can also cause more severe infections, especially in vulnerable individuals or when they spread. This includes pneumonia, particularly in hospitalized patients or those with weakened immune systems, often caused by Klebsiella species. Furthermore, they can lead to bloodstream infections, which are serious. The ability of some strains to acquire antibiotic resistance genes complicates clinical management.
Prevention and Management
Preventing Enterobacteriaceae infections involves sound hygiene practices and ensuring food and water safety. Regular and thorough handwashing with soap and water reduces the spread of these bacteria, especially after using the restroom and before handling food. Proper food handling and preparation are also important to prevent foodborne illnesses.
This includes cooking meats to appropriate internal temperatures and avoiding cross-contamination between raw and cooked foods. Ensuring access to clean, treated drinking water is another fundamental public health measure to prevent waterborne infections. When severe infections occur, medical professionals typically treat them with antibiotics. The specific antibiotic chosen depends on the bacteria’s type and its susceptibility to various drugs.