Objectives: Young children could act as important carriers of cefotaxime-resistant Enterobacteriaceae. However, most studies on these bacteria have focused on hospitalized adults. Therefore, we determined the prevalence and characteristics of ESBL-, plasmid-determined AmpC-type β-lactamase (PABL)- and carbapenemase-producing diarrhoeagenic Escherichia coli isolates mainly from infants and children in the south-west region of Korea over a 10 year period. Methods: Non-duplicate E. coli clinical isolates were recovered from diarrhoeagenic patient specimens at 12 hospitals in Gwangju, Korea, between January 2007 and December 2016. Antimicrobial susceptibilities and molecular features of ESBL- and carbapenemase-producing isolates were determined. Results: A total of 1047 pathogenic E. coli isolates were collected and 58 cefotaxime-resistant E. coli isolates (5.5%) were identified. The prevalence and types of β-lactamase genes increased steadily from 5.7% in 2007 to 11.6% in 2016 with some fluctuations. CTX-M-14 (53.4%) was the predominant CTX-M genotype. PFGE revealed high genetic heterogeneities among diarrhoeagenic E. coli isolates, suggesting horizontal transfer of antibiotic resistance genes, which was also proved by conjugation assay. Conclusions: Progressive increases in carriage rates and the number of β-lactamase types, and the possibility of community outbreaks of these food-borne bacteria in young children, may pose tangible public health threats.

Hard ticks are known vectors of various pathogens, including the severe fever with thrombocytopenia syndrome virus, Rickettsia spp., Coxiella burnetii, Borrelia spp., Anaplasma phagocytophilum, and Ehrlichia spp. This study aims to investigate the distribution and prevalence of tick-borne pathogens in southwestern Korea from 2019 to 2022. A total of 13,280 ticks were collected during the study period, with H. longicornis accounting for 86.1% of the collected ticks. H. flava, I. nipponensis and A. testudinarium comprised 9.4%, 3.6%, and 0.8% of the ticks, respectively. Among 983 pools tested, Rickettsia spp. (216 pools, 1.6% MIR) were the most prevalent pathogens across all tick species, with R. japonica and R. monacensis frequently detected in I. nipponensis and Haemaphysalis spp., respectively. Borrelia spp. (28 pools, 0.2% MIR) were predominantly detected in I. nipponensis (27 pools, 13.8% MIR, P < 0.001). Co-infections, mainly involving Rickettsia monacensis and Borrelia afzelii, were detected in I. nipponensis. Notably, this study identified R. monacensis for the first time in A. testudinarium in South Korea. These findings offer valuable insights into the tick population and associated pathogens in the region, underscoring the importance of tick-borne disease surveillance and prevention measures.

This study evaluated the long-term impact of rotavirus vaccination on prevalence, seasonality, and genotype distribution in Gwangju, Korea for 13 seasons. Rotavirus was identified using ELISA and then sequenced for G and P genotypes by Reverse Transcription Polymerase Chain Reactions for diarrhoeagenic patient specimens from local hospitals between January 2008 and August2020. Of 26,902 fecal samples, 2919 samples (10.9%) were ELISA positive. The prevalence declined from 16.3% in pre-vaccine era to 5.4% in post-vaccine era. In the pre-vaccine period, G1P[8] was the most common genotype, followed by G2P[4], G3P[8], and G9P[8], etc. In the transitional period, the proportion of G2P[4] became the dominant genotype and G1P[8] was still commonly identified. In contrast, the novel genotype G8P[8] was predominant in the post-vaccine period. Meanwhile, G2P[4] and G8P[8] were major genotypes in both Rotarix and RotaTeq groups. The substantial decline of G1P[8] prevalence, reemergence of G1P[8], G3P[8], and G2P[4] rotavirus strains, and surge of the rare G8P[8] after vaccine introduction were interesting points to note. The continuous surveillance on the genotypes of RV will be needed to understand rotavirus epidemiology and their evolutionary patterns, as caution is required when interpreting temporal changes in RV genotype dynamic.

Non-typhoid Salmonella infection is a major agent of food-borne outbreaks as well as individual cases worldwide. However, few studies on drug-resistant Salmonella strains, especially those recovered from young children, are available. Therefore, we determined the prevalence and characteristics of cephalosporin-resistant Salmonella isolates in the south-west region of Korea over a five-year period. Non-duplicate Salmonella clinical isolates were recovered from diarrhoeagenic patient specimens at 12 hospitals in Gwangju, Korea between January 2014 and December 2018. Antimicrobial susceptibility testing and molecular features of cephalosporin-resistant isolates were determined. A total of 652 Salmonella isolates were collected and 48 cefotaxime-resistant Salmonella isolates (7.4%), that belonged to nine Salmonella serovars, were identified. These were S. Enteritidis, S. Typhimurium, S. I 4,[5],12:i:-, S. Virchow, S. Agona, S. Bareilly, S. Infantis, S. Newport, and S. Schleissheim. The prevalence rate increased from 5.3% in 2014 to 10.3% in 2018. S. Virchow (44.4%) showed significantly high resistant rate compared to the other serovars. PGFE genotyping revealed high genetic homogeneities among each Salmonella serovars, suggesting clonal dissemination of cephalosporin-resistant strains. Progressive increases in carriage rates and the possibility of community outbreaks by cephalosporin-resistant Salmonella in young children may pose tangible public health threats.