Discussion
VAIs constitute a risk factor for infection in patients undergoing
hemodialysis. The pattern of microbes responsible for infection varies
substantially among different types of access (25). Pooled data show
that S. epidermidis accounts for most CVC-related infections,
whereas S. aureus is more common in AVF- and AVG-related
infections. In our study, staphylococcal species accounted for 58.67%
of VAIs, with S. aureus being the most commonly implicated
species, followed by CoNS and S. argenteus . In the 150 isolates
collected from patients with VAIs, S. aureus was the predominant
pathogen in AVG- and TCC-related infections, with a rate of 37/79
(46.84%) and 22/71 (30.99%), respectively. S. argenteus ,
another in SAC species, was also more predominant in AVG-related
infections than in TCC-related infections. Notably, the nine S.
epidermidis isolates were mainly collected from AVG-related infections
(6/9); this finding is not consistent with those reported by a previous
study (26), which indicated that improving sterilization management
procedures during hemodialysis may reduce the number of skin clones such
as S. epidermidis on TCCs. Regarding representative Gram-negative
bacteria in VAIs, P. aeruginosa and BCC predominantly caused TCC
infections; in particular, BCC caused only TCC infections.
In patients undergoing hemodialysis, S. aureus infection is
common, especially MRSA infection, the incidence of which was reported
to be higher than that observed in the general population by 100-fold
(27). In our study, MRSA and MSSA infections accounted for 62.71% and
37.29% of S. aureus VAIs, respectively, with ST45, ST59, and
ST239 being the predominant clones. Compared with our previous study,(4)
the present study revealed that ST45, ST59, and ST239 were common in
other diseases or surgical infections, indicating that these are major
clones in our institution and warrant more attention. Notably, we also
found the S. aureus ST239—an emerging multidrug-resistant MRSA
clone worldwide that generally carries an SCCmec type III
element—in methicillin-sensitive strains without mecA .
Furthermore, a novel nonpigmented staphylococcal lineage that cannot be
distinguished from S. aureus using routine microbiological
identification methods is now formally classified as S.
argenteus ; it was initially described as part of the distinct S.
aureus CC (CC75) that is prevalent in aboriginal communities in the
Northern Territory of Australia (28). S. argenteus comprising
several CCs with many STs, especially ST2250, is the most commonly
reported lineage with an extensive geographic distribution, including
France, Belgium, Thailand, Taiwan, Japan, and China, indicating a global
spread (29-35). The widespread S. argenteus has been isolated
from both humans and animals. In our institution, ST2250 was the primary
and only methicillin-sensitive ST revealed in VAIs, a finding that is
consistent with those for previously reported S.
argenteus -infected bacteremia cases in Taiwan (33).
The BCC is a group of opportunistic pathogens comprising at least 20
different species that commonly cause infections in immunocompromised
patients, particularly those with cystic fibrosis (CF). B.
contaminans was first identified from a contaminated Sargasso Sea DNA
sample (36) and is increasingly associated with CF. However, other
hospitalized non-CF patients have been reported to be affected byB. contaminans and B. cepacia infections. Nevertheless,B. contaminans has been found to be a contaminant in manufactured
products, including pharmaceuticals and disinfectants (37, 38). In our
institution, we obtained all BCC isolates from infected TCCs in
hemodialysis patients with VAI; this suggests that the repeated use of
mechanical device detergent and hemodialyzer reprocessing may cause
contamination and that BCC species can survive in a harsh environment.
In this 5-year study, we collected 150 isolates from hemodialysis
patients with VAIs and analyzed the isolates on the basis of the year of
isolation (i.e., study period interval). Although the number of isolates
from infected accesses was relatively low in the interval 2015–2018,
the incidence of S. aureus , S. argenteus , and BCC
infections increased by approximately 10% (i.e., 45.76%, 13.56%, and
13.56%, respectively). By contrast, CoNS and P. aeruginosainfections decreased by nearly 3%–5%. Previous studies have not
addressed the spread or transmission of S. argenteus in the
hospital environment (39). Nevertheless, the growing trend of S.
argenteus in VAIs indicates the potential and importance of this novel,
difficult-to-delimit species in healthcare-associated infections.
Therefore, infection prevention and control measures that can be applied
for S. aureus can be adopted for S. argenteus .