Citrobacter freundii complex is a group of bacteria that warrants attention. While often an unassuming resident in various environments, certain conditions can transform these bacteria into agents of concern for human health.
Understanding Citrobacter freundii Complex
The Citrobacter freundii complex refers to a group of closely related, rod-shaped bacteria classified as Gram-negative within the Enterobacteriaceae family. These bacteria are facultative anaerobes, meaning they can survive and grow both with and without oxygen. They typically measure between 1 to 5 micrometers in length and many possess flagella, allowing them to move.
This complex includes several species, such as Citrobacter freundii, Citrobacter youngae, Citrobacter braakii, Citrobacter werkmanii, and Citrobacter gillenii. While often found as a harmless part of the gut microbiome in humans and animals, they are considered opportunistic pathogens. This means they can cause infections when an individual’s immune system is weakened or when the bacteria enter parts of the body where they do not normally reside.
Sources and Transmission
Citrobacter freundii complex bacteria are widespread in nature, commonly inhabiting soil, water, and sewage. They are also found in the intestinal tracts of both humans and various animals.
Transmission to humans can occur through several pathways. Ingestion of contaminated food or water is a common route. Direct contact, especially in healthcare settings, also contributes to their spread, as does poor hygiene.
Health Concerns
While generally harmless in the healthy human gut, Citrobacter freundii complex can cause a range of infections, particularly in individuals with compromised immune systems, newborns, the elderly, or those with underlying medical conditions like diabetes or cancer. These bacteria are frequently associated with healthcare-associated infections. They can infect various sites within the body, leading to different clinical manifestations.
Common sites of infection include the urinary tract, where they can cause urinary tract infections with symptoms such as burning during urination, frequent urges to urinate, and foul-smelling urine. They can also lead to respiratory tract infections like pneumonia, wound infections, and bloodstream infections, which may manifest as fever and chills. In newborns, especially premature infants, Citrobacter freundii complex can cause severe conditions such as meningitis, an infection of the membranes surrounding the brain and spinal cord, and sepsis, a life-threatening systemic response to infection. Invasive infections can have a high mortality rate, ranging from 33% to 48%.
Diagnosis and Treatment
Diagnosing infections caused by the Citrobacter freundii complex typically involves laboratory culture of samples from the affected site. This may include blood, urine, sputum, or wound swabs. These culture-based methods, along with biochemical identification, help identify the specific bacterial strain. Advanced molecular techniques, such as 16S rRNA sequencing, can also be used for precise species differentiation.
Treatment primarily relies on antibiotic therapy. However, a significant challenge in treating Citrobacter freundii complex infections is the increasing prevalence of antibiotic resistance. Some strains have developed resistance to multiple classes of antibiotics, including ampicillin, cephalosporins, and even carbapenems, which are often considered last-resort antibiotics for severe infections. This resistance is often mediated by genetic elements that can transfer between bacteria. Due to this, susceptibility testing is routinely performed on isolated strains to determine which antibiotics will be most effective. This guides clinicians in selecting appropriate treatment, sometimes requiring higher-strength antibiotics. General prevention strategies, such as maintaining good hand hygiene and proper sterilization of medical devices, are important, especially in healthcare settings, to minimize the spread of these bacteria.