What Is Rahnella and How Does It Affect Humans?

Rahnella is a genus of bacteria belonging to the Enterobacteriaceae family. These microorganisms are characterized as Gram-negative, rod-shaped, and facultatively anaerobic, which means they can survive in environments with or without oxygen. The genus was first described in 1976 and officially named in honor of the German-American microbiologist Otto Rahn.

The species within this genus, such as Rahnella aquatilis, are distinguished by specific biochemical traits. For instance, they are motile at cooler temperatures around 22-25°C but become nonmotile at human body temperature (36-37°C). While they grow well under standard laboratory conditions, their identification can be challenging as they share many similarities with other bacteria in the Enterobacteriaceae family.

Natural Habitats of Rahnella

The name of the most common species, Rahnella aquatilis, hints at its primary habitat, as it is frequently isolated from freshwater sources like rivers and lakes, as well as from soil. It is considered a ubiquitous environmental organism, thriving in these natural settings. Its ability to grow at colder temperatures, even as low as 4°C, is an adaptation to living in such environments.

Beyond water and soil, Rahnella has also been found in association with plants and trees. For example, it has been isolated from the inner bark of oak trees and the sap of maple trees. Some strains have even been discovered in more extreme locations, such as sediment in the Antarctic peninsula.

Rahnella Infections in Humans

While widespread in the environment, Rahnella is an infrequent cause of human illness. It is an opportunistic pathogen, meaning it causes infections in individuals with weakened immune systems. Populations most susceptible include those with underlying diseases, patients receiving immune-suppressing treatments, young children, and individuals with indwelling medical devices. The first clinical isolate reported to the Centers for Disease Control and Prevention came from a burn wound in 1985.

The types of infections depend on how the bacteria enter the body and can include bloodstream infections (bacteremia), urinary tract infections, wound infections, and respiratory infections. The symptoms of a Rahnella infection are not specific and align with the general signs of the type of infection it causes. For instance, a bloodstream infection might lead to fever and chills, while a urinary tract infection could cause urinary-specific symptoms. Because these infections are rare, the presence of Rahnella is often an unexpected finding during laboratory analysis.

Diagnosis and Treatment of Rahnella

Identifying a Rahnella infection begins with collecting a sample from the patient, such as blood, urine, or a swab from a wound. The sample is then cultured in a laboratory to grow the bacteria. Once bacterial colonies are present, technicians perform a series of biochemical tests to determine their characteristics.

Because Rahnella can be biochemically similar to other bacteria, it may be misidentified by automated systems. More advanced methods like 16S rRNA gene sequencing or mass spectrometry can be used for a definitive identification.

Treatment for infections caused by Rahnella involves antibiotics. An important step in the diagnostic process is antibiotic susceptibility testing. This test exposes the specific bacterial isolate to various antibiotics to see which ones are effective at inhibiting its growth. This is important because some isolates can be resistant to certain drugs like ampicillin.

The prognosis for a patient with a Rahnella infection is good, provided that the infection is correctly identified and treated with appropriate antibiotics. The patient’s underlying health status also plays a significant role in their recovery. With proper medical care, most individuals recover without long-term consequences.