Pathogen Factors
Pathogenesis and epidemiology of NSTIs caused by E. coli are not
well studied in comparison to uropathogenic E. coli . There are
two methods to genetically classify E. coli . The conventional
method for classification of E. coli is by phylogenetic group.
Recently, however, another classification method for E. coli has
been developed. The MLST method characterises isolates of bacterial
species using the sequences of internal fragments of 7 house-keeping
genes. In this case, the causative E. coli strain was ST127 in
MLST and virulent phylogenetic group B2. Recently, ST127 was recognised
as a pathogen in urinary tract infection (9,10). This strain was also
reported as a pathogen in necrotising enterocolitis in preterm infants
(11) and in bloodstream infections (12). What is notable about this
strain is that, despite having high antibiotic sensitivity, it possesses
many pathogenic genes. However, the pathogenesis of the ST127 strain in
the setting of skin infection has yet to be studied.
In this case, it was also possible to identify the genes of the
pathogen. Virulence factors such as adhesion, toxins, iron acquisition
and invasion were analysed. The virulence patterns of the strains from
the skin and soft tissue infection in this patient were similar on
whole-genome analysis to strains from uropathogenic infection and sepsis
(13); however, the available epidemiologic data with a large number ofE. coli strains was insufficient. The virulence factors suspected
of having an association with skin and soft tissue infection were
cytotoxic necrotising factor 1 and hemolysin (4,14). These toxins were
both positive in this patient, and were reported in other cases to
trigger inflammation during infection (15,16) as a result of
interactions with neutrophils and monocyte-derived dendritic cells. The
patient in this case had a weakened immune system caused by liver
cirrhosis, which may have altered the appropriate immune response to
interaction with these toxins.