Enterobacter aerogenes is a type of bacterium that often garners attention due to its widespread presence in various environments. This bacterium is a common inhabitant of many natural settings and can also be found in association with humans.
Understanding Enterobacter aerogenes
Enterobacter aerogenes is classified as a Gram-negative bacterium, meaning it does not retain the crystal violet stain used in the Gram staining procedure. It is a facultative anaerobe, indicating its ability to grow both in the presence and absence of oxygen. This bacterium is also rod-shaped, a common morphology among many bacterial species. Enterobacter aerogenes belongs to the family Enterobacteriaceae, a large group of bacteria that includes many well-known species.
This bacterium exhibits a versatile nature, allowing it to adapt and thrive in diverse conditions and habitats. This adaptability is characteristic of many members within the Enterobacteriaceae family.
What Enterobacter aerogenes Looks Like Under the Microscope
When observed through a light microscope, Enterobacter aerogenes displays a distinct rod-shaped morphology, also known as bacillus. These individual cells typically measure approximately 0.6 to 1.0 micrometers (µm) in diameter and range from 1.2 to 3.0 µm in length. This size range is characteristic of many Gram-negative rods, requiring high magnification to discern their details.
Upon Gram staining, Enterobacter aerogenes cells appear pink or red, confirming their Gram-negative status. This coloration results from the bacterium’s thin peptidoglycan layer in its cell wall, which does not retain the primary crystal violet stain. Instead, the counterstain, safranin, stains the decolorized cells pink. These bacteria are commonly observed as single cells, in pairs, or occasionally forming short chains.
Enterobacter aerogenes is also typically motile, meaning it can move independently. This motility is facilitated by peritrichous flagella, which are numerous hair-like appendages distributed over the entire surface of the bacterial cell. The presence of these flagella allows the bacterium to propel itself through liquid environments.
Laboratory Identification of Enterobacter aerogenes
Beyond its microscopic appearance, definitive identification of Enterobacter aerogenes in a laboratory setting involves culturing and biochemical testing. When grown on selective and differential agar plates, such as MacConkey agar or Eosin Methylene Blue (EMB) agar, Enterobacter aerogenes produces distinctive colonies. On MacConkey agar, it typically forms pink colonies due to its ability to ferment lactose, producing acid that lowers the pH and causes the neutral red indicator to turn pink. On EMB agar, it can produce dark-centered colonies with a metallic green sheen, another indicator of strong lactose fermentation.
A series of biochemical tests further differentiates Enterobacter aerogenes from other similar bacteria. The IMViC tests, which include Indole, Methyl Red, Voges-Proskauer, and Citrate utilization tests, are frequently employed. Enterobacter aerogenes typically tests negative for Indole and Methyl Red, and positive for Voges-Proskauer and Citrate. Additional tests, such as sugar fermentation profiles, help to create a unique biochemical fingerprint for the bacterium.
Microscopic examination, particularly Gram staining and morphology assessment, serves as a crucial initial step. While it provides valuable preliminary information, it is not sufficient for a definitive diagnosis. The combination of characteristic colony morphology on various media and specific biochemical reactions is necessary for accurate identification. In complex cases or for rapid confirmation, molecular methods like Polymerase Chain Reaction (PCR) can be utilized to detect specific genetic sequences unique to Enterobacter aerogenes.
Where Enterobacter aerogenes is Encountered
Enterobacter aerogenes is widely distributed in natural environments, making it a ubiquitous bacterium. It can be readily found in water, soil, and sewage systems. This bacterium also frequently colonizes various food products, demonstrating its adaptability to different substrates. Its presence in these diverse habitats highlights its role as an environmental microorganism.
In humans, Enterobacter aerogenes commonly resides in the gastrointestinal tract as a commensal organism, meaning it can live there without typically causing harm. However, under certain conditions, it can act as an opportunistic pathogen. This means it primarily causes infections in individuals who are immunocompromised or those in healthcare settings. Infections commonly associated with Enterobacter aerogenes include urinary tract infections, respiratory tract infections, and wound infections.