Enterobacteriaceae Cultural Characteristics


Enterobacteriaceae is a large and diverse family of Gram-negative bacteria that includes over 30 genera and more than 100 species. The name Enterobacteriaceae comes from the fact that many members of this family are commonly found in the intestines of animals and humans, where they are usually harmless or beneficial symbionts. However, some enterobacteria can also cause infections in various parts of the body, such as the urinary tract, respiratory tract, bloodstream, and wounds. Some of the most well-known pathogens in this family are Salmonella, Escherichia coli, Klebsiella, Shigella, Enterobacter, and Citrobacter.

Enterobacteriaceae are rod-shaped bacteria that can be motile or nonmotile. They have peritrichous flagella or fimbriae that help them attach to surfaces and hosts. They are facultative anaerobes, meaning they can grow with or without oxygen. They ferment sugars to produce acids and gases, such as lactic acid, ethanol, carbon dioxide, and hydrogen. They also reduce nitrate to nitrite, which can be detected by a colorimetric test. They do not produce cytochrome c oxidase, an enzyme involved in the electron transport chain. They are catalase-positive, meaning they can break down hydrogen peroxide into water and oxygen.

Enterobacteriaceae can be identified and classified by various biochemical tests and molecular methods. One of the most commonly used tests is the MacConkey agar, which is a selective and differential medium that inhibits the growth of Gram-positive bacteria and distinguishes between lactose-fermenting and non-lactose-fermenting enterobacteria based on the color of the colonies. Other tests include the indole test, the methyl red test, the Voges-Proskauer test, the citrate test, the urease test, and the triple sugar iron test. Molecular methods include polymerase chain reaction (PCR), DNA sequencing, and multilocus sequence typing (MLST).

Enterobacteriaceae are important for human health and disease. They play a role in maintaining the normal flora of the gut and modulating the immune system. They also produce vitamins such as vitamin K and B12 that are essential for human nutrition. However, they can also cause serious infections when they invade other tissues or organs or when they acquire antibiotic resistance genes. Some of the diseases caused by enterobacteria include gastroenteritis, typhoid fever, urinary tract infections, septicemia, pneumonia, meningitis, and plague. Some enterobacteria can also produce toxins that damage the host cells or interfere with their functions. For example, Shiga toxin produced by Shigella dysenteriae and some strains of E. coli causes bloody diarrhea and hemolytic uremic syndrome.

Enterobacteriaceae are widely distributed in nature and can be found in soil, water, plants, animals, and humans. They can also survive in various environmental conditions and adapt to different hosts. They can exchange genetic material with other bacteria through horizontal gene transfer mechanisms such as plasmids, transposons, bacteriophages, and integrons. This allows them to acquire new traits such as virulence factors and antibiotic resistance genes. Some of the most concerning enterobacteria are those that are resistant to carbapenems, a group of antibiotics that are usually reserved for treating severe infections caused by multidrug-resistant bacteria. These bacteria are called carbapenem-resistant Enterobacterales (CRE) and pose a serious threat to public health.

In this article, we will discuss the cultural characteristics of some of the most common enterobacteria that cause infections in humans. Cultural characteristics refer to the appearance and behavior of bacteria when they are grown on different types of media under specific conditions. These characteristics can help us identify and differentiate between different species or strains of enterobacteria.