The extended-spectrum β-lactamase (ESBL) CTX-M-55, a CTX-M-15 variant distinguished by an amino-acid substitution (Ala77Val), has enhanced enzymatic activity due to higher structural stability. In Korea, CTX-M-55 remains insufficiently characterized, particularly in the context of urinary tract infections (UTIs). We identified CTX-M-55 among uropathogenic Escherichia coli isolates and compared its microbiological characteristics with those of CTX-M-15. In total, 247 E. coli isolates were collected from patients with acute pyelonephritis at Hanyang University Seoul Hospital, an 860-bed tertiary-care hospital, between July 2019 and December 2021. ESBL production was confirmed using a double-disk synergy test, and minimum inhibitory concentrations (MICs) were determined. Resistance genes were detected using PCR, and CTX-M-15 sequences were analyzed. Among 38 isolates detected using PCR, eight were confirmed as CTX-M-55 using further sequence analysis. CTXM-55 showed (P > 0.05) a trend toward increased resistance to aztreonam, cefotaxime, ceftazidime, and cefepime, while showing decreased resistance to amoxicillin/clavulanate and piperacillin/tazobactam. CTX-M-55 had higher MIC 50 values than CTX-M-15 for ceftazidime ( > 16 vs. 8 µg/mL), cefepime (32 vs. 1 µg/mL), and piperacillin/tazobactam (0.5 vs.0.25 µg/mL). Virulence factors and coexisting resistance genes did not significantly differ.Our findings suggest that, given its increased resistance to ceftazidime and cefepime, CTXM-55 should be considered when treating UTIs in Korea.

This study was done to characterize distribution of Rickettsia spp. in ticks in the northwestern and southwestern provinces in the Republic of Korea. A total of 2,814 ticks were collected between May and September 2009. After pooling, 284 tick DNA samples were screened for a gene of Rickettsia-specific 17-kDa protein using nested PCR (nPCR), and produced 88 nPCR positive samples. Of these positives, 75% contained 190-kDa outer membrane protein gene (ompA), 50% 120-kDa outer membrane protein gene (ompB), and 64.7% gene D (sca4). The nPCR products of ompA, ompB, and sca4 genes revealed close relatedness to Rickettsia japonica, R. heilongjiangensis, and R. monacensis. Most Rickettsia species were detected in Haemaphysalis longicornis. This tick was found a dominant vector of rickettsiae in the study regions in the Republic of Korea.
DNA ; Genes, vif ; Membrane Proteins ; Polymerase Chain Reaction ; Republic of Korea ; Rickettsia ; Ticks