Detection of the classical G2576U mutation in linezolid resistant Staphylococcus aureus along with isolation of linezolid resistant Enterococcus faecium from a patient on short-term linezolid therapy: First report from India

Purpose: Linezolid is an effective drug against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE). We describe the emergence of linezolid resistance in MRSA and VRE from India. Material and Methods: One MRSA and two VRE strains were isolated from a patient on linezolid therapy of one week duration. All three isolates were resistant to linezolid with minimal inhibitory concentrations (MIC) ≥4 mg/L. The 746-bp region flanking the possible G2576U mutation on the corresponding DNA from the 23S rRNA was amplified by polymerase chain reaction (PCR) and amplicons were sequenced for all the three isolates. Conjugation experiments using the linezolid resistant MRSA (LRMRSA) and linezolid resistant VRE (LRVRE) isolates as donors and wild strains of corresponding genera as recipients were performed. Results: The MRSA isolate had the classical G2576U mutation. High quality value scores in the sequencing software validated the mutation. Conjugation studies did not indicate presence of transferable resistance for linezolid. Sequencing did not indicate presence of any mutation in the two LRVRE isolates. Conclusions: This is the first report from India citing resistance in Staphylococcus and Enterococcus against Linezolid.     

Resistance to linezolid in Staphylococcus aureus before its release

Resistance to antibiotics is a global problem in geriatric centres. OBJECTIVE: The aim of this study was to determine the frequency of the resistance to linezolid in Staphylococcus aureus strains before its release in a geriatric centre. METHOD: From 03-01-01 to 03-04-30 linezolid was included in the panel of antibiotics tested in S. aureus strains. The susceptibilities were estimated by the disk diffusion test in routine clinical microbiology practice. RESULTS: A total of 213 strains of S. aureus was analysed. All of them were susceptible to the following antibiotics: linezolid, cotrimoxazol, fosfomycin, and glycopeptides. The meticillin-resistant S. aureus (MRSA) represented 67.1% (60.3-73.3) strains. The resistance to pefloxacin, tobramycin and erythromycin concerned 92.3% (86.3-95.9), 73.4% (65.3-80.3) and 31.5% (24.1-39.8) of MRSA strains respectively. The MRSA strains were less resistant to the following antimicrobial drugs: gentamicin 7.0% (3.6-12.8), fusidic acid 2.1% (0.5-6.5) and rifampicin 1.4% (0.2-5.5). The resistance concerning at the same time gentamicin, pefloxacin and fucidic acid represented 2.1% (0.5-6.5) of SARM strains, rifampicin was not interested. CONCLUSION: Linezolid was effective in vitro in S. aureus strains regardless their susceptibilities in meticillin. According to its effectiveness in vivo, linezolid may be of use for the treatment of infections due to MRSA. However, there has been two reports of resistance of MRSA in clinical infections. The use of linezolid has to follow the instructions and it should be carefully monitored.     

Sepsis due to linezolid resistant Staphylococcus cohnii and Staphylococcus kloosii: first reports of linezolid resistance in coagulase negative staphylococci from India

Linezolid, a viable alternative to vancomycin against methicillin resistant staphylococcal isolates, has been in use for a decade around the globe. However, resistance against staphylococci remains extremely rare and unreported from most of the Asian countries. Herein, we report two cases of linezolid resistant, coagulase negative staphylococcal sepsis for the first time from India. The first case was an 18-year-old burn patient, who, after a major graft surgery, landed in sepsis, and linezolid resistant Staphylococcus cohnii with an minimum inhibitory concentration (MIC) of >256 μg/ml by both broth microdilution and Etest, was isolated from multiple blood cultures. The second patient was a 60-year-old male with an intracranial bleed and sepsis, from whose blood cultures, linezolid resistant Staphylococcus kloosii was repeatedly isolated. Linezolid MIC was >32 μg/ml by broth microdilution and >16 μg/ml by Etest.     

Enhanced activity of linezolid against Staphylococcus aureus in cerebrospinal fluid

Linezolid is considered for treatment of central nervous system (CNS) infections caused by multidrug-resistant Gram-positive bacteria. Therefore, the influence of cerebrospinal fluid (CSF) on the antimicrobial activity of linezolid was evaluated in vitro. Time-kill curves were conducted in CSF and Mueller-Hinton broth (MHB) using Staphylococcus aureus (ATCC 29213) and Staphylococcus epidermidis (ATCC 12228) strains. In CSF lower linezolid concentrations were needed against S. aureus (1× MIC) and S. epidermidis (0.5× MIC) to achieve bacteriostasis than in MHB (4× MIC for both strains). Good activity of linezolid in CSF supports performance of clinical trials evaluating its potential for treatment of CNS infections.     

Predictive score of haematological toxicity in patients treated with linezolid

Objective

The aims of our study were to determine the factors associated with developing haematological toxicity (HT) in patients taking linezolid (LZD), to develop a predictive model of HT in these patients, and to evaluate factors associated with 30-day mortality.

Methods

This was an observational retrospective cohort study of patients treated for at least 5 days with LDZ in 2015. Demographic, clinical and analytical data were collected. Development of HT was defined as a 25% platelet count decrease between the basal count and the 1-week lab test.

Results

Five hundred forty-nine patients were finally included, mean age was 73.3 (SD 15.4) years, and 303 (55.2%) were men. One hundred seventy-five (30.1%) patients achieved HT criteria during treatment with LZD and 41 (7.5%) died. The final model included the presence of cerebrovascular disease (2 points), moderate or severe liver disease (2 points), renal failure (2 points) and basal platelet count less than 90,000/mm3 (8 points). This new model showed an AUC of 0.711 (IC 95% 0.664–0.757; p?<?0.001) to predict the development of HT. The probability of HT based on this classification was 6.2, 29.9 and 76.5% for low (0–4 points), intermediate (5–10 points) and high risk (>10 points), respectively. The independent variables associated with 30-day mortality were metastatic solid tumor, lymphoma, age >75 years and HT.

Conclusion

This score could help in the identification of patients with high risk for HT and assess the use of an antibiotic other than LZD, an important issue considering its relation with 30-day mortality observed in our study.

     

Treatment of meningitis due to methicillin-resistant Staphylococcus epidermidis with linezolid

Methicillin-resistant Staphylococcus epidermidis (MRSE) can cause nosocomial meningitis in the presence of prosthetic devices. Vancomycin is the treatment of choice, but its penetration into the cerebrospinal fluid is poor, especially in cases without severe meningeal inflammation. We successfully used linezolid to treat a case of posttraumatic MRSE meningitis with a low-level inflammatory response. Therapeutic effectiveness was documented microbiologically and by the simultaneous measurement of linezolid levels in serum and cerebrospinal fluid.     

Elimination of linezolid by an in vitro extracorporeal circuit model

Linezolid is an oxazolidinone antibiotic with activity against important grampositive aerobic bacteria, including nosocomial pathogens. It is not known whether dosage adjustments are necessary in patients treated with continuous renal replacement therapies. This in vitro study was conducted to investigate the elimination of linezolid in an in vitro continuous hemo(dia)filtration model using different filter materials (polysulfone, polyacrylonitrile, polyamide), surface areas, and different modes of renal replacement therapies. Linezolid was measured using HPLC with UV-detection. No adsorption of linezolid to any of the tested membranes was detected. Recovery of linezolid in the ultrafiltrate was 98.2 +/- 10.5% in the filtration mode. During dialysis, recovery was significantly less (87.6 +/- 16.1%; p = 0.02). Linezolid elimination was not altered by filter size, when polysulfone filters with surface areas of 0.7 m2 and 1.3 m2 were tested. In conclusion, the dosage recommendations for linezolid are independent of the filter materials. However, the elimination is significantly higher during hemofiltration compared to dialysis.     

Evaluation of antimicrobial susceptibilities of non-tuberculous mycobacteria against linezolid and tigecycline

Mycobacterial susceptibility testing is important for the management of nontuberculous mycobacteria (NTM) infections. The aim of the study is to determine the susceptibilities of tigecycline (TGC) and linezolid (LZD) against NTM. The study was carried out using stocks of NTM strains in the tuberculosis department of the microbiology laboratory. It was designed a retrospective study. LZD and TGC sensitivities of study isolates were analyzed by microdilution. Forty NTM isolates have been studied. LZD and TGC sensitivities varied according to the NTM type. It is concluded that each isolate should be individually evaluated due to variable susceptibilities to LZD and TGC.     

Comparative activity of linezolid against staphylococci and enterococci isolated in Italy

The activity of linezolid, a new oxazolidinone, was tested against 862 Gram-positive cocci isolated in Italy and compared with the activities of 12 antibiotics. Overall, MIC₉₀s for linezolid (2–4 mg/L) indicated an in vitro activity comparable to that of vancomycin in methicillin-resistant Staphylococcus aureus (4 mg/L), S. epidermidis (2 mg/L) and methicillin-susceptible strains. Enterococcus faecalis strains were susceptible to linezolid (MIC₉₀ 2–4 mg/L), glycopeptides and β -lactams. In E. faecium , only glycopeptides (MIC₉₀ 2 mg/L) and linezolid (MIC₉₀ 2 mg/L) were active. Linezolid was the only drug active against two strains of Enterococcus showing a VanA phenotype. Owing to its antibacterial profile, linezolid represents a promising drug for the treatment of Gram-positive infections.     

Minimal inhibitory concentrations of linezolid against clinical isolates of coryneform bacteria

In order to evaluate the efficacy of linezolid for treating severe infections with coryneform bacteria, the activity of linezolid was tested in vitro against 425 clinically relevant isolates of coryneform bacteria and compared with the activity of penicillin and erythromycin. The minimal inhibitory concentration of linezolid did not exceed 2 μg/ml for any of the isolates tested, indicating that this agent has very good activity against coryneform bacteria. These results suggest linezolid is a possible alternative antimicrobial agent for the treatment of severe infections caused by coryneform bacteria.