Language
Country/Area
No result found
From soil to human body: What are the survival strategies and adaptive abilities of Citrobacter freundii?
Citrobacter freundii is a facultative anaerobic Gram-negative bacterium belonging to the family Enterobacteriaceae, with 13 recognized species. The bacteria are rod-shaped, typically 1–5 micrometers in length. Most C. freundii cells possess multiple flagella for locomotion, although some non-motile forms lack this feature. C. freundii is a common microorganism found in soil, but can also be found in water, sewage, food, and the intestines of animals and humans. The Citrobacter genus was discovered by Werkman and Gillen in 1932, and C. freundii was isolated and identified from soil extracts in the same year.
Cell morphology and characteristics
Exopolysaccharides from C. freundii can target hydroxyl radicals and show antioxidant activity.
The antioxidant properties of C. freundii are associated with a variety of different physical and chemical characteristics. Additionally, C. freundii has a positive impact on the treatment of some cancers, particularly in killing and curing cervical cancer. Some isolates showed toxicity towards HeLa cells, an immortal cell line derived from cervical cancer cells. C. freundii has an aggressive attachment pattern that has been found in goat cells, a property that may influence its pathogenicity to some extent; however, this does not guarantee infection.
Biofilm formation plays an important role in the infection rate of C. freundii, which exhibits different infection modes including not only attachment but also biofilm formation at room temperature. Robust biofilm attachment may also result in a tolerance reservoir of antimicrobial genes, meaning that even if attachment does not directly cause infection, the process is still building tolerance. Non-cytotoxic, multidrug-resistant C. freundii strains formed large biofilms at 25°C that resulted from aggregate attachment to epithelial cells.
Phylogeny and genome evolution
C. freundii is phylogenetically more diverse than the individual branches of E. coli and Salmonella, indicating that it is a polyphyletic genus. The phenotypic diversity of C. freundii makes its identification difficult due to its remarkable flexibility in antigenicity, pathogenicity, and cellular morphology. Nucleotide diversity is also high in C. freundii because of the deep separation between two distinct lineages within this group. Based on phylogenetic information, the divisions of these lineages are perfectly consistent with respect to geographic and host species relatedness.
Based on phylogenetic information, the divisions of these lineages are perfectly consistent with respect to geographic and host species relatedness.
Metabolic characteristics
C. freundii is able to grow on glycerol and use it as its sole carbon and energy source. The organism possesses a bacterial microcapsule that can process propylene glycol. C. freundii showed a positive methyl red reaction and a negative voltaic reaction as well as a positive catalase reaction and a negative reaction to oxidase. C. freundii is unable to hydrolyze starch, lipids, or gelatin.
C. freundii has also been investigated for tannic acid biodegradation in tannin factories, showing its potential for the removal of intermediates.
Relevance to the wider system
C. freundii is commonly found in soil microbiota and plays an important role in nitrogen cycling in the environment. C. freundii is also a nitrogen-fixing bacterium, and this process has been demonstrated in living tissue of birch trees. C. freundii is also found in the intestines of humans and other animals from various environmental sources. Although most strains are beneficial, there is significant phenotypic variation between strains, even when they share more than 99% genomic similarity. In healthy people, C. freundii interactions are generally considered non-pathogenic; however, once in the bloodstream, C. freundii can cause life-threatening infections that may progress to sepsis.
C. freundii has become a critical issue as it is increasingly found in healthcare settings. This bacteria may not only cause infections such as the urinary tract, respiratory tract and wounds, but may also lead to other complications in people with weakened immune systems. Citrobacter spp. are responsible for 3-6% of Enterobacter infections in North American healthcare settings and are among the strains most frequently associated with human infections. For human health, the main impact of C. freundii is as an opportunistic pathogen. However, as the environment changes, the phenotypes of these bacteria may also face adjustments. Of course, the factors that influence the survival and adaptation of C. freundii are also worthy of further consideration and study, which raises the question: What abilities does this bacterium have to ensure its survival and reproduction in a changing environment?
