Citrobacter koseri is a species of gram-negative bacteria from the Enterobacteriaceae family. This rod-shaped microorganism is a facultative anaerobe, meaning it can survive with or without oxygen. It is found widely in the natural environment, such as in soil and water, and is also a normal inhabitant of the human gastrointestinal tract. C. koseri exists as a harmless part of the gut microbiome.
This bacterium can act as an opportunistic pathogen, causing infections. It primarily poses a risk to individuals with weakened or developing immune systems. Its ability to cause disease in vulnerable populations makes it a subject of clinical interest. Most infections linked to C. koseri are acquired in healthcare settings.
Infections Caused by Citrobacter koseri
The most severe infections associated with Citrobacter koseri occur in infants, specifically neonates. It is a significant cause of neonatal meningitis, an inflammation of the membranes surrounding the brain and spinal cord. This condition is particularly dangerous in newborns, often leading to the formation of brain abscesses, which are collections of pus that can cause destructive and permanent damage to developing brain tissue. The presence of these abscesses complicates the infection and worsens the prognosis.
Symptoms of neonatal meningitis are often subtle and non-specific, which can delay diagnosis. Parents and caregivers may notice fever, persistent irritability, lethargy or excessive sleepiness, and poor feeding. As the infection progresses, more alarming symptoms such as seizures can occur. Even with treatment, a significant percentage of survivors experience long-term neurological problems, including developmental delays, epilepsy, and hydrocephalus, a condition involving excess fluid in the brain.
While it is most notorious for its impact on infants, C. koseri can also cause infections in other vulnerable groups. In adults, the bacterium is associated with a range of other illnesses. These include urinary tract infections (UTIs), bloodstream infections (sepsis), and respiratory infections like pneumonia. It can also cause infections in wounds or surgical sites, typically in a hospital setting.
Transmission and Vulnerable Populations
There are multiple pathways for transmission, but infections are most common in specific, controlled environments. The spread of the bacterium is a major concern within healthcare facilities, especially in units that care for newborns.
Transmission can occur vertically, from mother to infant during childbirth, if the mother carries the bacterium as part of her gut flora. More commonly, transmission is horizontal, spreading from person to person. This is a particular risk in hospital nurseries or neonatal intensive care units (NICUs), where the bacterium can be passed from the hands of healthcare workers or other caregivers to the infant. Contaminated medical equipment can also serve as a source of transmission in these settings.
Neonates, especially those born prematurely, are the population most at risk for severe infection. Other vulnerable groups include the elderly and people with compromised immune systems.
Diagnosis and Treatment
Confirming an infection with Citrobacter koseri requires laboratory analysis. Healthcare professionals will first collect a sample from the suspected site of infection. Depending on the symptoms, this could be a sample of blood for a suspected bloodstream infection, urine for a UTI, or cerebrospinal fluid (CSF) for suspected meningitis. The CSF is obtained through a lumbar puncture, also known as a spinal tap.
Once collected, the sample is sent to a laboratory where it is cultured. This process involves placing the sample in a special medium that encourages any bacteria present to grow. If C. koseri is the cause, it will multiply in the culture, allowing technicians to identify it through microscopic examination and biochemical tests.
Treatment for C. koseri infections relies on antibiotics. However, a significant challenge in managing these infections is the bacterium’s potential for antibiotic resistance. Some strains of C. koseri are naturally resistant to certain common antibiotics, and others have acquired resistance to multiple drugs. Because of this, treatment cannot follow a one-size-fits-all approach.
After the bacteria are cultured, laboratories perform antibiotic susceptibility testing. This test exposes the specific strain of C. koseri from the patient to a panel of different antibiotics to see which ones are effective at killing it or stopping its growth. The results guide physicians in selecting the most appropriate and effective antibiotic medication for the individual patient.
Prevention Strategies
Preventing the spread of Citrobacter koseri is heavily focused on practices within healthcare environments, where the most vulnerable patients are cared for. The most important prevention measure is rigorous infection control, starting with strict hand hygiene protocols. All hospital staff, parents, and visitors in neonatal units must meticulously wash their hands or use alcohol-based hand sanitizer before and after handling infants.
Beyond handwashing, other institutional practices are needed to control transmission. This includes the thorough cleaning and sterilization of all medical equipment, from incubators and ventilators to feeding supplies. In the event of an outbreak in a nursery or NICU, a strategy known as cohorting may be implemented. This involves grouping infected infants together with dedicated nursing staff to prevent further spread to uninfected babies.
In the wider community, prevention aligns with general good hygiene practices. Since the bacterium can be found in the gut, proper handwashing after using the restroom and before preparing or eating food is important. While community-acquired C. koseri infections are rare, these standard hygiene measures reduce the overall risk of transmitting this and many other types of bacteria.