BackgroundStaphylococcus aureus (S. aureus) is a major nosocomial pathogen that causes a variety of infections and toxicoses. In recent years, the percentage of rifampicin-resistant S. aureus has increased rapidly in China. The aims of this study were to analyze 1) the level of rifampicin resistance in S. aureus and its correlation with mutations in the rpoB gene, and 2) the molecular characterization of rifampicin-resistant S. aureus isolates.Results88 rifampicin-resistant S. aureus isolates were collected for this study. Of the 88 isolates, 83 (94.3%) were high-level rifampicin resistant (MIC≥8 mg/L) while the remaining 5 isolates (5.7%) had a low-level resistance to rifampicin (MIC, 2 to 4 mg/L). Four amino acid substitutions were found in the 88 isolates, which were 481His/Asn (95.5%), 466Leu/Ser (87.5%), 477Ala/Asp (6.8%) and 486Ser/Leu (4.5%) respectively. All mutations were found to be present in cluster I of the rpoB gene. The low-level resistant isolates were found to have only one mutation, while the high-level resistant isolates had at least two or more mutations. The most common multiple mutations were 481His/Asn+466Leu/Ser(92.8%,77/83). The other multiple mutations found were 481His/Asn+477Ala/Asp (6.0%,5/83), and 481His/Asn+466Leu/Ser+477Ala/Asp (1.2%,1/83). Out of 28 high-level rifampicin-resistant S. aureus isolates, three molecular types were found, namely, ST239-MRSA-III-spa t030 (25/28, 89.3%), ST239-MRSA-III-spa t021 (2/28, 7.1%), and ST239-MRSA-III-spa t045 (1/28, 3.6%).ConclusionsRifampicin resistance in S. aureus was closely associated with mutations in the rpoB gene. High-level rifampicin-resistant S. aureus is one of the most important features in Anhui Provincial Hospital, and high-level rifampicin resistance in S. aureus is associated with multiple mutations of rpoB gene. The prevalence of high-level rifampicin-resistant S. aureus in Anhui may be associated with the spread of the ST239-MRSA III-spa t030 clone.

Background: Streptococcus suis is a zoonotic pathogen that can cause severe infections such as meningitis and septicemia in both swine and humans. Rapid and accurate identification of the causative agent is very important for guiding clinical choices in administering countermeasures. Case Report: Here, we report a case of fatal S. suis infection in a patient who worked as a butcher in China. The 59-year-old man, who had previously undergone splenectomy, injured his finger while processing pork and developed severe sepsis. While blood cultures were negative following antibiotic treatment, S. suis was determined to be the causative agent by metagenomic next-generation sequencing (mNGS) and Sanger sequencing. Conclusion: Identification of etiological agents using techniques such as blood culture prior to antibiotic treatment is very important. mNGS may represent a useful method for diagnosis of infectious diseases, especially post-antibiotic treatment.

Acquisition of vancomycin resistance in Staphylococcus aureus is often accompanied by a reduction in virulence, but the mechanisms underlying this change remain unclear. The present study was undertaken to investigate this process in a clinical heterogeneous vancomycin-intermediate S. aureus (hVISA) strain, 10827; an hVISA reference strain, Mu3; and a VISA reference strain, Mu50, along with their respective series of vancomycin-induced resistant strains. In these strains, increasing MICs of vancomycin were associated with increased expression of the vancomycin resistance-associated regulator gene (vraR) and decreased expression of virulence genes (hla, hlb, and coa) and virulence-regulated genes (RNAIII, agrA, and saeR). These results suggested that VraR might have a direct or indirect effect on virulence in S. aureus. In electrophoretic mobility shift assays, VraR did not bind to promoter sequences of hla, hlb, and coa genes, but it did bind to the agr promoter region. In DNase I footprinting assays, VraR protected a 15-nucleotide (nt) sequence in the intergenic region between the agr P2 and P3 promoters. These results indicated that when S. aureus is subject to induction by vancomycin, expression of vraR is upregulated, and VraR binding inhibits the function of the Agr quorum-sensing system, causing reductions in the virulence of VISA/hVISA strains. Our results suggested that VraR in S. aureus is involved not only in the regulation of vancomycin resistance but also in the regulation of virulence.

Purpose: To evaluate the administration regimen of ceftazidime/avibactam (CZA) for bloodstream infections caused by Enterobacteriaceae and Pseudomonas aeruginosa. Methods: The minimal inhibitory concentrations (MICs) of CZA against Enterobacteriaceae and P. aeruginosa isolated from blood cultures at member hospitals in BRICS (Blood Bacterial Resistant Investigation Collaborative System) in 2019 were determined by broth micro-dilution methodology. A 10,000-patient Monte Carlo simulation (MCS) was used to calculate the probability of target attainment (PTA) and cumulative fraction of response (CFR) for different CZA dosage regimens to evaluate their efficacies and optimize the best initial dosage regimen. Results: Altogether, 6487 Enterobacteriaceae and P. aeruginosa strains were isolated from the blood cultures. The overall CZA resistance rate was 2.31%, of which the Enterobacteriaceae and P. aeruginosa rates were 1.57% and 14.29%, respectively. The MCS showed that the greater the MIC value, the worse the therapeutic effect. When the CZA MIC was ≤8 mg/L, the standard dose (2.5g iv q8h) achieved 90% PTA in the subset of patients with creatinine clearance (CrCl) values from 51 to 120 mL/min. Although the high-dose regimen (3.75g iv q8h) achieved 90% PTA in patients with CrCl values from 121 to 190 mL/min, implementing the low-dose regimen (1.25g iv q8h) was also effective for patients in the 51-89 mL/min CrCl range. Generally, the high-dose regimen (3.75g iv q8h) reached 90% CFR against all of the strains. Conversely, in patients with CrCl values of 121-190 mL/min, the standard dose (2.5g iv q8h) failed to reach 90% CFR against some Enterobacteriaceae members and P. aeruginosa. When the dose was reduced to the low-dose regimen (1.25g iv q8h), no patients reached 90% CFR against some Enterobacteriaceae members and P. aeruginosa. Conclusion: CZA has good antibacterial activity against Enterobacteriaceae and P. aeruginosa in bloodstream infections. Clinicians could make individualized treatment regimens in accordance with the sensitivity of the strains and the level of renal function in their patients to best predict the drug-related clinical responses.