Successful treatment of methicillin-resistant Staphylococcus aureus osteomyelitis with combination therapy using linezolid and rifampicin under therapeutic drug monitoring.

Linezolid is an effective antibiotic against most gram-positive bacteria including drug-resistant strains such as methicillin-resistant Staphylococcus aureus. Although linezolid therapy is known to result in thrombocytopenia, dosage adjustment or therapeutic drug monitoring of linezolid is not generally necessary. In this report, however, we describe the case of a 79-year-old woman with recurrent methicillin-resistant S. aureus osteomyelitis that was successfully treated via surgery and combination therapy using linezolid and rifampicin under therapeutic drug monitoring for maintaining an appropriate serum linezolid concentration. The patient underwent surgery for the removal of the artificial left knee joint and placement of vancomycin-impregnated bone cement beads against methicillin-resistant S. aureus after total left knee implant arthroplasty for osteoarthritis. We also initiated linezolid administration at a conventional dose of 600 mg/h at 12-h intervals, but reduced it to 300 mg/h at 12-h intervals on day 9 because of a decrease in platelet count and an increase in serum linezolid trough concentration. However, when the infection exacerbated, we again increased the linezolid dose to 600 mg/h at 12-h intervals and performed combination therapy with rifampicin, considering their synergistic effects and the control of serum linezolid trough concentration via drug interaction. Methicillin-resistant S. aureus infection improved without reducing the dose of or discontinuing linezolid. The findings in the present case suggest that therapeutic drug monitoring could be useful for ensuring the therapeutic efficacy and safety of combination therapy even in patients with osteomyelitis who require long-term antibiotic administration.

Treatment of mediastinitis due to methicillin-resistant Staphylococcus aureus in a renal dysfunction patient undergoing adjustments to the linezolid dose.

This study is the first case report of the treatment of methicillin-resistant Staphylococcus aureus (MRSA) mediastinitis using therapeutic drug monitoring of the serum and wound exudate concentrations of linezolid in a renal dysfunction patient. In the present study, the serum trough concentration of linezolid was maintained between 2 and 7 µg/mL. Therapeutic drug monitoring dosage adjustments may be especially useful in patients with renal dysfunction and severe MRSA infection.

Clinical significance of methicillin-resistant coagulase-negative staphylococci obtained from sterile specimens.

Distinguishing true coagulase-negative staphylococci bacteremia from contamination remains a challenge. We conducted a retrospective analysis of 183 patients with methicillin-resistant coagulase-negative staphylococci (MR-CoNS)-positive and methicillin-resistant Staphylococcus aureus-positive cultures obtained from sterile sites such as blood, synovial fluid, ascitic fluid, and cerebrospinal fluid. Of the 209 MR-CoNS isolates, 83 (39.7%) were considered infection associated, and 126 (60.3%) were considered contamination. MR-CoNS isolates cultured from synovial fluid were more likely to be infection associated (P = 0.009). The median interval from insertion of a central venous catheter to onset of infection tended to be longer in MR-CoNS infection cases than in methicillin-resistant S. aureus infection cases (41 days versus 14 days, P = 0.055). In conclusion, our results suggest that the proportion of cases of true MR-CoNS infection may be higher than previously reported.

Engineering HIV-1-resistant T-cells from short-hairpin RNA-expressing hematopoietic stem/progenitor cells in humanized BLT mice.

Down-regulation of the HIV-1 coreceptor CCR5 holds significant potential for long-term protection against HIV-1 in patients. Using the humanized bone marrow/liver/thymus (hu-BLT) mouse model which allows investigation of human hematopoietic stem/progenitor cell (HSPC) transplant and immune system reconstitution as well as HIV-1 infection, we previously demonstrated stable inhibition of CCR5 expression in systemic lymphoid tissues via transplantation of HSPCs genetically modified by lentiviral vector transduction to express short hairpin RNA (shRNA). However, CCR5 down-regulation will not be effective against existing CXCR4-tropic HIV-1 and emergence of resistant viral strains. As such, combination approaches targeting additional steps in the virus lifecycle are required. We screened a panel of previously published shRNAs targeting highly conserved regions and identified a potent shRNA targeting the R-region of the HIV-1 long terminal repeat (LTR). Here, we report that human CD4(+) T-cells derived from transplanted HSPC engineered to co-express shRNAs targeting CCR5 and HIV-1 LTR are resistant to CCR5- and CXCR4- tropic HIV-1-mediated depletion in vivo. Transduction with the combination vector suppressed CXCR4- and CCR5- tropic viral replication in cell lines and peripheral blood mononuclear cells in vitro. No obvious cytotoxicity or interferon response was observed. Transplantation of combination vector-transduced HSPC into hu-BLT mice resulted in efficient engraftment and subsequent stable gene marking and CCR5 down-regulation in human CD4(+) T-cells within peripheral blood and systemic lymphoid tissues, including gut-associated lymphoid tissue, a major site of robust viral replication, for over twelve weeks. CXCR4- and CCR5- tropic HIV-1 infection was effectively inhibited in hu-BLT mouse spleen-derived human CD4(+) T-cells ex vivo. Furthermore, levels of gene-marked CD4(+) T-cells in peripheral blood increased despite systemic infection with either CXCR4- or CCR5- tropic HIV-1 in vivo. These results demonstrate that transplantation of HSPCs engineered with our combination shRNA vector may be a potential therapy against HIV disease.

Sequence-based spa typing as a rapid screening method for the areal and nosocomial outbreaks of MRSA.

Methicillin-resistant Staphylococcus aureus (MRSA) is the leading cause of nosocomial infection and MRSA outbreaks have become a major problem. Therefore, the rapid and accurate typing of MRSA isolates is important for epidemiological surveys and nosocomial infection control. Pulsed-field gel electrophoresis (PFGE) is considered as the gold standard technique for MRSA typing, because of its high discriminatory power, but its procedure is rather complicated and time-consuming. The spa gene encodes a cell wall component of Staphylococcus aureus protein A, and exhibits polymorphism. Sequencing the spa gene is expected superior to PFGE in speed and data interpretation. In the present study, we evaluated whether spa typing of MRSA is useful for nosocomial outbreak analysis and epidemiological investigations. We analyzed 19 nosocomial outbreak isolates from 4 separate hospitals and 26 isolates from outpatients of Toyama University Hospital. Either PFGE or spa typing revealed a single nosocomial strain that appears unique to each hospital. Indeed, spa typing confirmed the four different strains, but PFGE demonstrated only 3 strains. With the total 45 isolates, PFGE showed 16 different patterns and spa typing showed 12 patterns. Moreover, we were able to analyze the spa gene in about 2 days, from sampling to obtaining the results, whereas it took about 7 days with PFGE. In conclusion, sequence-based spa typing shows comparable sensitivities to PFGE, and is a rapid and easy handling method. The sequence-based spa typing can be used as the rapid screening test when MRSA outbreak is suspected in areas and hospitals.

[Generalized tetanus with intractable autonomic cardiovascular instability in an aged woman].

Tetanus is characterized by tetanic convulsions related to the actions of tetanospasmin produced by Clostridium tetani. Another important characteristic of tetanus is the instability of the cardiovascular system related to sympathetic hyperactivity in the autonomic nervous system, and it may be an important prognostic factor. We report a patient with tetanus in whose unstable circulatory kinetics made circulation management difficult. A 77-year-old woman who injured in a fall, 11 days after trismus appeared and 3 day after convulsion appeared. It was not severe case in the acuity classification. However, repeated generalized convulsions and autonomic imbalance involving the cardiovascular system were observed clinically, suggesting a severe case. Because of the unstable circulatory kinetics, the patient was carefully managed was performed in the intensive care unit (ICU), and she improved. ICU management may be essential for treating severe tetanus with cardiovascular complications. Acquired immunity is not achieved after the onset of tetanus, and since elderly people, in particular, as in our own caset, are easily injured when they fall, we recommend vaccination.