O-Mi Lee

Salmonella enterica subsp. enterica serovar Gallinarum biovar Gallinarum (SG) causes fowl typhoid, an important poultry disease, but the genetic diversity and phylogenetic relationships among Korean SG isolates remain insufficiently investigated. We analyzed 26 Korean SG isolates collected between 2002 and 2026 and compared them with 57 publicly available SG genomes from other countries using whole-genome sequencing. Using a cutoff of 100 core-genome single-nucleotide polymorphisms, 83 isolates were classified into eight clusters and ten singletons, with all Korean isolates assigned to the same cluster. Five sequence types (ST78, ST331, ST13540, ST14504, ST14529) were identified. ST78 was predominant, whereas ST14504 and ST14529 were identified exclusively among Korean isolates. Bayesian phylogenetic analysis estimated the time to the most recent common ancestor of the Korean isolates to be approximately 1990. Genomic analyses revealed differences in Salmonella pathogenicity islands, virulence genes, plasmid replicons, antimicrobial resistance genes, and quinolone resistance-determining region mutations. A resistance profile comprising aac(3)-VIa, aadA1, sul1, and qacEΔ1 was observed exclusively in 12 Korean isolates; of these, eleven harbored only the IncFII(S) plasmid replicon, and IncX1 was also detected in one isolate, together with bla_TEM-1B and tet(A). These findings provide valuable genomic and epidemiological insights into SG and may contribute to improved control of fowl typhoid.

Fowl typhoid, caused by Salmonella Gallinarum (SG), remains an important poultry disease. We characterized 136 SG isolates, one per farm, from diagnostic submissions of diseased chickens to the national veterinary laboratory in South Korea from 2002 to 2026, comparing two periods (2002–2010 and 2011–2026). Antimicrobial susceptibility was determined by broth microdilution, the spvB polyproline linker (PPL; the region joining the two functional domains of the SpvB virulence factor) was sequenced, and genetic relatedness was assessed by XbaI–pulsed-field gel electrophoresis (PFGE). Resistance to nalidixic acid was most frequent (93.4%), followed by streptomycin (83.1%) and ciprofloxacin (71.3%). Resistance to ampicillin, tetracycline, and nalidixic acid was less frequent in 2011–2026 (false discovery rate-adjusted p < 0.05), and these associations persisted after adjustment for chicken type. Multidrug resistance was detected in 52.2% of isolates, without significant change between periods. However, 13 of the 34 multidrug-resistant isolates from 2002–2010 were resistant to four or more antimicrobial classes, whereas all 37 from 2011–2026 were resistant to exactly three classes. Five PPL lengths of 13–21 prolines were identified, and their distribution differed between periods (p = 0.016). Isolates carrying ≥17 prolines were more frequent in 2011–2026 than in 2002–2010 (p < 0.01). PFGE yielded 61 pulsotypes in 27 clusters, with two dominant clusters detected across years and chicken types. These findings indicate that the PFGE-defined SG population showed temporal phenotypic changes within Korean poultry flocks, underscoring the need for continued surveillance of resistance and genotype.

Biomineralization, a well-known natural phenomenon associated with various microbial species, is being studied to protect and strengthen building materials such as concrete. We characterized Rhodococcus erythreus S26, a novel urease-producing bacterium exhibiting CaCO₃-forming activity, and investigated its ability in repairing concrete cracks for the development of environment-friendly sealants. Strain S26 grown in solid medium formed spherical and polygonal CaCO₃ crystals. The S26 cells grown in a urea-containing liquid medium caused culture fluid alkalinization and increased CaCO₃ levels, indicating that ureolysis was responsible for CaCO₃ formation. Urease activity and CaCO₃ formation increased with incubation time, reaching a maximum of 2054 U/min/mL and 3.83 g/L, respectively, at day four. The maximum CaCO₃ formation was achieved when calcium lactate was used as the calcium source, followed by calcium gluconate. Although cell growth was observed after the induction period at pH 10.5, strain S26 could grow at a wide range of pH 4–10.5, showing its high alkali tolerance. FESEM showed rhombohedral crystals of 20–60 µm in size. EDX analysis indicated the presence of calcium, carbon, and oxygen in the crystals. XRD confirmed these crystals as CaCO₃ containing calcite and vaterite. Furthermore, R. erythreus S26 successfully repaired the artificially induced large cracks of 0.4–0.6 mm width.