Search

Long-term administration of certain macrolides is efficacious in patients with persistent pulmonary Pseudomonas aeruginosa infection, despite how limited the clinically achievable concentrations are, being far below their MICs. An increase in the sub-MIC of macrolide exposure-dependent sensitivity to nitrosative stress is a typical characteristic of P. aeruginosa . However, a few P. aeruginosa clinical isolates do not respond to sub-MIC of macrolide treatment. Therefore, we examined the effects of sub-MIC of erythromycin (EM) on the sensitivity to nitrosative stress together with an efflux pump inhibitor (EPI) phenylalanine arginyl β-naphthylamide (PAβN). The sensitivity to nitrosative stress increased, suggesting that the efflux pump was involved in inhibiting the sub-MIC of macrolide effect. Analysis using efflux pump-mutant P. aeruginosa revealed that MexAB-OprM, MexXY-OprM, and MexCD-OprJ are factors in reducing the sub-MIC of macrolide effect. Since macrolides interfere with quorum sensing (QS), we demonstrated that the QS-interfering agent furanone C-30 (C-30) producing greater sensitivity to nitric oxide (NO) stress than EM. The effect of C-30 was decreased by overproduction of MexAB-OprM. To investigate whether the increase in the QS-interfering agent exposure-dependent sensitivity to nitrosative stress is characteristic of P. aeruginosa clinical isolates, we examined the viability of P. aeruginosa treated with NO. Although treatment with EM could reduce cell viability, a high variability in EM effects was observed. Conversely, C-30 was highly effective at reducing cell viability. Treatment with both C-30 and PAβN was sufficiently effective against the remaining isolates. Therefore, the combination of a QS-interfering agent and an EPI could be effective in treating P. aeruginosa infections.

A Gram-stain-negative, spiral bacterium (PAGU 1991 T ) was isolated from the blood of a patient with diffuse large B-cell lymphoma. Phylogenetic analysis based on 16S rRNA gene sequences showed that the isolate was very closely related to Helicobacter equorum LMG 23362 T (99.1 % similarity), originally isolated from a faecal sample from a healthy horse. PAGU 1991 T was also very closely related to PAGU 1750 in our strain library (=CCUG 41437) with 99.7 % similarity. Additional phylogenetic analyses based on the 23S rRNA gene sequence and GyrA amino acid sequence further supported the close relationship between the two human isolates (PAGU 1991 T and PAGU 1750) and the horse strain. However, a phylogenetic analysis based on 16S rRNA showed that the two human isolates formed a lineage that was distinct from the horse strain (less than 99.2 % similarity). In silico whole-genome comparisons based on digital DNA-DNA hybridization, average nucleotide identity based on blast and orthologous average nucleotide identity using usearch between the two human isolates and the type strain of H. equorum showed values of less than 52.40, 93.47, and 93.50 %, respectively, whereas those between the two human isolates were 75.8, 97.2, and 97.2 %, respectively. These data clearly demonstrated that the two human isolates formed a single species, distinct from H. equorum . Morphologically, the human isolates could be distinguished by the type of flagella; the human isolates showed a bipolar sheathed flagellum, whereas that of H. equorum was monopolar. Biochemically, the human isolate was characterized by growth at 42 °C under microaerobic conditions and nitrate reduction unability. We conclude that the two human isolates, obtained from geographically and temporally distinct sources, were a novel species, for which we propose the name Helicobacter kumamotonensis sp. nov., with the type strain PAGU 1991 T (=GTC 16810 T =CCUG 75774 T ).

Bacterial strain PAGU 2197 T , which was isolated from soil collected from the bottom of a pond in Japan, is characterized in this study. Cells of strain PAGU 2197 T were aerobic, Gram-negative, short rod-shaped, non-motile, flexirubin-producing, oxidase-positive, catalase-positive and lecithinase-negative. A phylogenetic study based on 16S rRNA gene sequences and multilocus sequence analysis ( gyrB , rpoB and rpoD ) indicated that strain PAGU 2197 T belongs to the genus Chryseobacterium and is a member of an independent lineage including Chryseobacterium tructae CCUG 60111 T (sequence similarity, 95.9 %), Chryseobacterium lactis CCUG 60566 T (93.4 %) and Chryseobacterium viscerum CCUG 60103 T (91.6 %). The average nucleotide identity values were 80.83-85.04 %. Because average nucleotide identity values of 95-96 % exceed the 70 % DNA-DNA hybridization cutoff value for species discrimination, strain PAGU 2197 T represents a novel species in the genus Chryseobacterium . The genome of strain PAGU 2197 T was 4 967 738 bp with a G+C content of 35.5 mol%. The sole respiratory quinone of strain PAGU 2197 T was MK-6; the major cellular fatty acids were iso-C 15 : 0 , iso-C 17 : 0 3OH, summed feature 3 (C 16 : 1  ω 7 c and/or C 16 : 1  ω 6 c ) and summed feature 9 (iso-C 17 : 1  ω 9 c and/or C 16 : 0 10-methyl); and the major polar lipids were phosphoglycolipids and phosphatidylethanolamine. These results indicate that strain PAGU 2197 T should be classified as representing a novel species in the genus Chryseobacterium , for which the name Chryseobacterium lecithinasegens sp. nov. is proposed, with strain PAGU 2197 T (=NBRC 114264 T =CCUG 75150 T ) as the type strain.

Introduction . Streptococcus dysgalactiae subsp. equisimilis (SDSE) is a β-hemolytic streptococcus that causes severe invasive streptococcal infections, especially in the elderly and people with underlying diseases. SDSE strains are primarily characterized by Lancefield group G or C antigens. Hypothesis/Gap Statement. We have previously reported the prevalence of Lancefield group A SDSE (GA-SDSE) strains in Japan and have analysed the draft genome sequences of these strains. As GA-SDSE is a rare type of SDSE, only one complete genome has been sequenced to date. Aim. The present study is focused on genetic characteristics of GA-SDSE strains. In order to examine molecular characteristics, we also tested growth inhibition of other streptococci by GA-SDSE. Methodology. We determined the complete genome sequences of three GA-SDSE strains by two new generation sequencing systems (short-read and long-read sequencing data). Using the sequences, we also conducted a comparative analysis of GA-SDSE and group C/G SDSE strains. In addition, we tested multiplex and quantitative PCRs targeting the GA-SDSE, group G SDSE, and S. pyogenes . Results. We found a group-specific conserved region in GA-SDSE strains that is composed of genes encoding predicted anti-bacteriocin and streptococcal lantibiotic (Sal) proteins. Multiplex and quantitative PCRs targeting the GA-SDSE-specific region were able to distinguish between GA-SDSE, other SDSE, and S. pyogenes strains. The growth of GA-SDSE was suppressed in the presence of group G SDSE, indicating a possible explanation for the low frequency of isolation of GA-SDSE. Conclusion. The comparative genome analysis shows that the genome of GA-SDSE has a distinct arrangement, enabling the differentiation between S. pyogenes , GA-SDSE, and other SDSE strains using our PCR methods.

Introduction. Little is known about the epidemiology of Enterobacter cloacae strains producing a carbapenemase or metallo-beta-lactamase in Vietnamese hospitals. Aim. This study analysed E. cloacae strains resistant to imipenem or meropenem that had been isolated from patients admitted to one of the largest hospitals in Vietnam in 2014-2017. Methodology. Eighteen Vietnamese (VN) strains were subjected to whole-genome sequencing and their sequences compared with those of 17 E. cloacae strains carrying a carbapenemase or metallo-beta-lactamase in the database (db strains). Results. Although the distribution of virulence factors did not differ significantly between VN and db strains, all 18 VN isolates harboured blaNDM-1 , phylogenetic analysis revealed a high clonality of the VN strains. Bayesian phylogenetic analysis suggested that the VN strains speciated relatively recently. Conclusions. Several prevalent clones of carbapenem-resistant E. cloacae have circulated within Vietnamese hospitals. Adequate measures are needed to prevent their further spread.