Abstract
Ceftriaxone-resistant Enterobacterales remain a public health threat; contemporary data investigating their molecular epidemiology are limited. Five hundred consecutive ceftriaxone-resistant (MIC ≥ 4 µg/mL) Enterobacterales bloodstream isolates were collected between 2018 and 2022 from three Maryland hospitals. Broth microdilution confirmed antibiotic susceptibilities. Whole-genome sequencing identified extended-spectrum β-lactamase (ESBL) and
genes both in bacterial chromosomes (c-
) and on plasmids (p-
). Mutations in promoter or attenuator regions of the
c-
gene (i.e.,
gene) with the potential to result in
derepression were investigated. The presence of ESBL or
genes was confirmed in 497 (99.4%) isolates. Two hundred seventy-nine (55.8%) isolates had both ESBL and
genes. ESBL families were identified among 398 (80%) patients:
(
= 370),
(
= 17),
(
= 14), and
(
= 5). Ceftriaxone-resistant Enterobacterales species carrying ESBL genes included the following:
(67%),
(24%),
(4%),
(2%),
complex (2%),
(1%),
(<1%), and
(<1%). c-
genes were identified in 374 (75%) of the 500 isolates. Only 7% of
isolates with mutations in the promoter or attenuator region of the c-
gene exhibited resistance to cefoxitin, a proxy for increased AmpC production. Two p-
genes were confirmed in 25 (5%) of the 500 isolates:
(72%) and
(28%; confined to
[92%] and
[8%]). Until comprehensive β-lactamase molecular testing is available, the species-specific prevalence of ESBL and
genes in ceftriaxone-resistant Enterobacterales should be considered to promote effective albeit judicious antibiotic prescribing. Mutations in promoter or attenuator regions of the
c-
gene do not appear to contribute significantly to increased AmpC production in this species.