Serratia

The germ is named after the Italian physicist Serafina Serrati.

Serratia refers to a genus of gram-negative rod-shaped bacteria, in the order Enterobacterales and the family Yersiniaceae. Members of the family Serratia are peritrichous flagellated and thus motile, they are (except for a few subspecies - Cho GS et al.2020) sporeless and grow facultatively anaerobic. Serratia produce deoxyribonuclease as a special biochemical reaction behavior.

The genus includes several species, some of which have also been found in humans. Other Serratia species act as plant pathogens (Kim HJ et al. 2021). The most important species in human medicine are:

• Serratia marescens
• Serratia liquefaciens
• Serratia rubideae
• Serratia fonticola

Human infections with Serratia spp. are generally limited to Serratia marcescens and the Serratia liquefaciens complex. There are few data on infections caused by the remaining Serratia spp. as they are rarely isolated from clinical specimens (Karkey A et al. 2018).

Serratia species are present worldwide (Karkey A et al. 2018). They are found in water, soil and also in food (Wang J et al. 2019). Serratia species preferentially colonize the intestinal flora in humans.

Virulence factors: Serratia marcescens forms a pore-forming toxin with haemolysin. This family of toxins has nothing in common with the pore-forming toxins of the E. coli type (RTX toxins), the alpha toxin of Staphylococcus aureus or the thiol-activated toxin of group A beta-hemolytic streptococci (streptolysin O). The S. marcescens haemolysin proteins ShlB and ShlA, have protein sequence homologues in Proteus mirabilis, Haemophilus ducreyi, Yersinia pestis, Yersinia enterocolitica and others (Hertle R 2005) .

Infections with Serratia, Klebsiella and Enterobacter are often acquired nosocomially and occur mainly in patients with impaired immunocompetence. Thus, pathogens of the genus Serratia are also frequently a problem in intensive care units or in children's hospitals. Serratia can cause a variety of infections, including bacteremia, postoperative wound infections, intravascular catheter infections, and infections of the respiratory (pneumonia) or urinary tract (cystitis, pyelonephritis). Serratia, particularly S. marcescens, has a greater affinity for urinary tract infections. However, the pathogens are also found in sepsis, endocarditis, meningitis, wound infections, and osteomyelitis. The pathogen is particularly feared during endoprosthetic surgery.

Diagnosis is made by culture (testing of metabolic activity with a coloured series; Malti-TOF mass spectrometry) of blood and/or other infected tissue. Sensitivity testing is also performed. Multiple H and O antigens may be useful for strain typing in hospital infections to identify transmission pathways.

As bacterial pathogens, Serratia are treated with antibiotics. The therapy of infections with Serratia is problematic, as the bacterium is resistant to many antibiotics, e.g. to numerous cephalosporins. Among others, aminoglycosides are used, especially amikacin. However, efficient antibiotic therapy is only possible after successful germ isolation and preparation of an antibiogram.

Serratia marcescens is also known as Bacterium prodigiosum, host fungus or miracle bacillus. Most important representative of the Serratia, special feature is the red pigmentation.

1. Cho GS et al.(2020) Serratia nevei sp. nov. and Serratia bockelmannii sp. nov., isolated from fresh produce in Germany and reclassification of Serratia marcescens subsp. sakuensis Ajithkumar et al. 2003 as a later heterotypic synonym of Serratia marcescens subsp. marcescens. Syst Appl Microbiol. 43:126055.
2. Grimont PA et al.(1978) The genus Serratia. Annu Rev Microbiol 32:221-248.
3. Hertle R (2005) The family of Serratia type pore forming toxins. Curr Protein Pept Sci 6: 313-325.
4. Karkey A et al. (2018) Outbreaks of Serratia marcescens and Serratia rubidaea bacteremia in a central Kathmandu hospital following the 2015 earthquakes. Trans R Soc Trop Med Hyg 112: 467-472.
5. Kim HJ et al. (2021) Complete Genome Resource of Serratia plymuthica C-1 that Causes Root Rot Disease in Korean Ginseng. Plant Dis 105:202-204.
6. Wang J et al. (2019) Serratia microhaemolytica sp. nov. isolated from an artificial lake in Southern China. Antonie Van Leeuwenhoek 112:1447-1456.