Characterization and risk assessment of novel SXT/R391 integrative and conjugative elements with multidrug resistance in Proteus mirabilis isolated from China, 2018-2020.

Proteus mirabilis can transfer transposons, insertion sequences, and gene cassettes to the chromosomes of other hosts through SXT/R391 integrative and conjugative elements (ICEs), significantly increasing the possibility of antibiotic resistance gene (ARG) evolution and expanding the risk of ARGs transmission among bacteria. A total of 103 strains of P. mirabilis were isolated from 25 farms in China from 2018 to 2020. The positive detection rate of SXT/R391 ICEs was 25.2% (26/103). All SXT/R391 ICEs positive P. mirabilis exhibited a high level of overall drug resistance. Conjugation experiments showed that all 26 SXT/R391 ICEs could efficiently transfer to Escherichia coli EC600 with a frequency of 2.0 × 10-7 to 6.0 × 10-5. The acquired ARGs, genetic structures, homology relationships, and conservation sequences of 26 (19 different subtypes) SXT/R391 ICEs were investigated by high-throughput sequencing, whole-genome typing, and phylogenetic tree construction. ICEPmiChnHBRJC2 carries erm (42), which have never been found within an SXT/R391 ICE in P. mirabilis, and ICEPmiChnSC1111 carries 19 ARGs, including clinically important cfr, blaCTX-M-65, and aac(6')-Ib-cr, making it the ICE with the most ARGs reported to date. Through genetic stability, growth curve, and competition experiments, it was found that the transconjugant of ICEPmiChnSCNNC12 did not have a significant fitness cost on the recipient bacterium EC600 and may have a higher risk of transmission and dissemination. Although the transconjugant of ICEPmiChnSCSZC20 had a relatively obvious fitness cost on EC600, long-term resistance selection pressure may improve bacterial fitness through compensatory adaptation, providing scientific evidence for risk assessment of horizontal transfer and dissemination of SXT/R391 ICEs in P. mirabilis.IMPORTANCEThe spread of antibiotic resistance genes (ARGs) is a major public health concern. The study investigated the prevalence and genetic diversity of integrative and conjugative elements (ICEs) in Proteus mirabilis, which can transfer ARGs to other hosts. The study found that all of the P. mirabilis strains carrying ICEs exhibited a high level of drug resistance and a higher risk of transmission and dissemination of ARGs. The analysis of novel multidrug-resistant ICEs highlighted the potential for the evolution and spread of novel resistance mechanisms. These findings emphasize the importance of monitoring the spread of ICEs carrying ARGs and the urgent need for effective strategies to combat antibiotic resistance. Understanding the genetic diversity and potential for transmission of ARGs among bacteria is crucial for developing targeted interventions to mitigate the threat of antibiotic resistance.

Detection of transferable oxazolidinone resistance determinants in Enterococcus faecalis and Enterococcus faecium of swine origin in Sichuan Province, China.

OBJECTIVES: The aim of this study was to detect transferable oxazolidinone resistance determinants (cfr, optrA and poxtA) in Enterococcus faecalis and Enterococcus faecium isolates of swine origin in Sichuan Province, China. METHODS: A total of 158 enterococcal isolates (93 E. faecalis and 65 E. faecium) isolated from 25 large-scale swine farms (2016-2017) were screened for the presence of cfr, optrA and poxtA by PCR. The genetic environments of cfr, optrA and poxtA were characterised by whole-genome sequencing. Transfer of oxazolidinone resistance determinants was determined by conjugation or electrotransformation experiments. RESULTS: The transferable oxazolidinone resistance determinants cfr, optrA and poxtA were detected in zero, six and one enterococcal isolates, respectively. The poxtA gene in one E. faecalis isolate was located on a 37 990-bp plasmid that co-harboured fexB, cat, tet(L) and tet(M) and could be conjugated to E. faecalis JH2-2. One E. faecalis isolate harboured two different OptrA variants, including one variant with a single substitution (Q219H) that has not been reported previously. Two optrA-carrying plasmids, pC25-1 (45 581bp) and pC54 (64 500bp), shared a 40 494-bp identical region containing the genetic context IS1216E-fexA-optrA-erm(A)-IS1216E that could be electrotransformed into Staphylococcus aureus. Four different chromosomal optrA gene clusters were found in five strains, in which optrA was associated with Tn554 or Tn558 inserted into the radC gene. CONCLUSION: This study highlights the fact that mobile genetic elements, such as plasmids, IS1216E, Tn554 and Tn558, may facilitate the horizontal transmission of optrA and poxtA genes.

Electrical properties and behaviors of cuprous oxide cubes under high pressure.

An accurate in situ electrical resistivity measurement of cuprous oxide cubes has been conducted in a diamond anvil cell at room temperature with pressures up to 25 GPa. The abnormal electrical resistivity variation found at 0.7-2.2 GPa is attributed to the phase transformation from a cubic to a tetragonal structure. Three other discontinuous changes in the electrical resistivity are observed around 8.5, 10.3, and 21.6 GPa, corresponding to the phase transitions from tetragonal to pseudocubic to hexagonal to another hexagonal phase, respectively. The first-principles calculations illustrate that the electrical resistivity decrease of the tetragonal phase is not related to band-gap shrinkage but related to a higher quantity of electrons excited from strain-induced states increasing in band gap with increasing pressure. The results indicate that the Cu(2)O cubes begin to crush at about 15 GPa and completely transform into nanocrystalline at 25 GPa.