Synergistic interactions of essential oil components with antibiotics against multidrug-resistant Corynebacterium striatum.

AIM: In this study, it was aimed to examine the antibacterial activity of the essential oil components (EOCs), carvacrol (CAR), cinnamaldehyde (CIN), thymol (TH), alpha pinene (α-PN), eucalyptol (EU), limonene (LIM), and the antibiotics, linezolid (LZD), vancomycin (VAN), gentamicin (GEN), ciprofloxacin (CIP), clindamycin (CLN), and penicillin (PEN) against 50 multidrug resistant Corynebacterium striatum strains, and the synergistic interactions of CAR and CIN with the antibiotics against 10 randomly selected Coryne. striatum strains to explore synergistic interactions to determine if their combined use could enhance antibiotic activity and potentially reduce resistance. METHODS AND RESULTS: The activity of the EOCs and the antibiotics against Coryne. striatum strains isolated from clinical specimens, was examined by broth microdilution method. The synergistic interactions of the EOCs with the antibiotics against 10 randomly selected Coryne. striatum strains were determined by checkerboard method. EOCs, CIN, and CAR and antibiotics, LZD, VAN, GEN, CIP, and CLN were detected to have antibacterial activity against Coryne. striatum strains alone and either synergistic interactions were observed in combinations of the antibiotics with EOCs. CONCLUSIONS: All Coryne. striatum strains were determined to be susceptible to VAN and LZD and resistant to GEN, PEN, CIP, and CLN. Synergistic interactions were observed in all combinations of antibiotics tested with CAR and CIN.

Recent advances in the exploration of oxazolidinone scaffolds from compound development to antibacterial agents and other bioactivities.

Bacterial infections cause a variety of life-threatening diseases, and the continuous evolution of drug-resistant bacteria poses an increasing threat to current antimicrobial regimens. Gram-positive bacteria (GPB) have a wide range of genetic capabilities that allow them to adapt to and develop resistance to practically all existing antibiotics. Oxazolidinones, a class of potent bacterial protein synthesis inhibitors with a unique mechanism of action involving inhibition of bacterial ribosomal translation, has emerged as the antibiotics of choice for the treatment of drug-resistant GPB infections. In this review, we discussed the oxazolidinone antibiotics that are currently on the market and in clinical development, as well as an updated synopsis of current advances on their analogues, with an emphasis on innovative strategies for structural optimization of linezolid, structure-activity relationship (SAR), and safety properties. We also discussed recent efforts aimed at extending the activity of oxazolidinones to gram-negative bacteria (GNB), antitumor, and coagulation factor Xa. Oxazolidinone antibiotics can accumulate in GNB by a conjugation to siderophore-mediated ß-lactamase-triggered release, making them effective against GNB.

Genomic characteristics of cfr and fexA carrying Staphylococcus aureus isolated from pig carcasses in Korea.

The emergence of transferable linezolid resistance genes poses significant challenges to public health, as it does not only confer linezolid resistance but also reduces susceptibility to florfenicol, which is widely used in the veterinary field. This study evaluated the genetic characteristics of linezolid-resistant Staphylococcus aureus strains isolated from pig carcasses and further clarified potential resistance and virulence mechanisms in a newly identified sequence type. Of more than 2500 strains isolated in a prior study, 15 isolated from pig carcasses exhibited linezolid resistance (minimum inhibitory concentration ≥ 8 mg/L). The strains were characterized in detail by genomic analysis. Linezolid-resistant S. aureus strains exhibited a high degree of genetic lineage diversity, with one strain (LNZ_R_SAU_64) belonging to ST8004, which has not been reported previously. The 15 strains carried a total of 21 antibiotic resistance genes, and five carried mecA associated with methicillin resistance. All strains harbored cfr and fexA, which mediate resistance to linezolid, phenicol, and other antibiotics. Moreover, the strains carried enterotoxin gene clusters, including the hemolysin, leukotoxin, and protease genes, which are associated with humans or livestock. Some genes were predicted to be carried in plasmids or flanked by ISSau9 and the transposon Tn554, thus being transmittable between staphylococci. Strains carrying the plasmid replicon repUS5 displayed high sequence similarity (99%) to the previously reported strain pSA737 in human clinical samples in the United States. The results illustrate the need for continuous monitoring of the prevalence and transmission of linezolid-resistant S. aureus isolated from animals and their products.

Activated mesenchymal stem cells increase drug susceptibility of methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa.

Methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa are major causes of hospital-acquired infections and sepsis. Due to increasing antibiotic resistance, new treatments are needed. Mesenchymal stem cells (MSCs) have antimicrobial effects, which can be enhanced by preconditioning with antibiotics. This study investigated using antibiotics to strengthen MSCs against MRSA and P. aeruginosa. MSCs were preconditioned with linezolid, vancomycin, meropenem, or cephalosporin. Optimal antibiotic concentrations were determined by assessing MSC survival. Antimicrobial effects were measured by minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and antimicrobial peptide (AMP) gene expression. Optimal antibiotic concentrations for preconditioning MSCs without reducing viability were 1 µg/mL for linezolid, meropenem, and cephalosporin and 2 µg/mL for vancomycin. In MIC assays, MSCs preconditioned with linezolid, vancomycin, meropenem, or cephalosporin inhibited MRSA or P. aeruginosa growth at lower concentrations than non-preconditioned MSCs (p ≤ 0.001). In MBC assays, preconditioned MSCs showed enhanced bacterial clearance compared to non-preconditioned MSCs, especially when linezolid and vancomycin were used against MRSA (p ≤ 0.05). Preconditioned MSCs showed increased expression of genes encoding the antimicrobial peptide genes hepcidin and LL-37 compared to non-preconditioned MSCs. The highest hepcidin expression was seen with linezolid and vancomycin preconditioning (p ≤ 0.001). The highest LL-37 expression was with linezolid preconditioning (p ≤ 0.001). MSCs' preconditioning with linezolid, vancomycin, meropenem, or cephalosporin at optimal concentrations enhances their antimicrobial effects against MRSA and P. aeruginosa without compromising viability. This suggests preconditioned MSCs could be an effective adjuvant treatment for antibiotic-resistant infections. The mechanism may involve upregulation of AMP genes.

Inhibition of S. aureus biofilm formation by linezolid alleviates sepsis-induced lung injury caused by S. aureus infection through direct inhibition of icaA activity.

Antibiotic-resistant S. aureus infections can be life-threatening. Linezolid is known to hinder S. aureus biofilm formation, but the underlying molecular mechanism remains unclear. Molecular docking revealed that linezolid can bind to icaA, and this was confirmed by thermal drift assays. Linezolid demonstrated a dose-dependent inhibition of icaA enzyme activity. Mutating Trp267, a key residue identified through molecular docking, significantly decreased linezolid binding and inhibitory effects on mutant icaA activity. However, the mutant icaA Trp267Ala showed only slight activity reduction compared to icaA. Linezolid had minimal impact on icaB's thermal stability and activity. The 50S ribosomal L3ΔSer145 mutant S. aureus exhibited similar growth and biofilm formation to the wild-type strain. Linezolid effectively suppressed the growth and biofilm formation of wildtype S. aureus. Although linezolid lost its ability to inhibit the growth of the mutant strain, it still effectively hindered its biofilm formation. Linezolid exhibited weaker attenuation of sepsis-induced lung injury caused by 50S ribosomal L3ΔSer145 mutant S. aureus compared to wild-type S. aureus. These findings indicate that linezolid hampers S. aureus biofilm formation by directly inhibiting icaA activity, independently of its impact on bacterial growth.

Characteristics of Gram-positive cocci infection and the therapeutic effect after liver transplantation. / è‚ç§»æ¤æœ¯åŽé©å °æ°é˜³æ€§çƒèŒçš„æ„ŸæŸ“ç‰¹ç‚¹åŠé˜²æ²»æ•ˆæžœ.

OBJECTIVES: Gram-positive cocci is the main pathogen responsible for early infection after liver transplantation (LT), posing a huge threat to the prognosis of liver transplant recipients. This study aims to analyze the distribution and drug resistance of Gram-positive cocci, the risk factors for infections and efficacy of antibiotics within 2 months after LT, and to guide the prevention and treatment of these infections. METHODS: In this study, data of pathogenic bacteria distribution, drug resistance and therapeutic efficacy were collected from 39 Gram-positive cocci infections among 256 patients who received liver transplantation from donation after citizens' death in the Third Xiangya Hospital of Central South University from January 2019 to July 2022, and risk factors for Gram-positive cocci infection were analyzed. RESULTS: Enterococcus faecium was the dominant pathogenic bacteria (33/51, 64.7%), followed by Enterococcus faecalis (11/51, 21.6%). The most common sites of infection were abdominal cavity/biliary tract (13/256, 5.1%) and urinary tract (10/256, 3.9%). Fifty (98%) of the 51 Gram-positive cocci infections occurred within 1 month after LT. The most sensitive drugs to Gram-positive cocci were teicoplanin, tigecycline, linezolid and vancomycin. Vancomycin was not used in all patients, considering its nephrotoxicity. Vancomycin was not administered to all patients in view of its nephrotoxicity.There was no significant difference between the efficacy of daptomycin and teicoplanin in the prevention of cocci infection (P>0.05). Univariate analysis indicated that preoperative Model for End-Stage Liver Disease (MELD) score >25 (P=0.005), intraoperative red blood cell infusion ≥12 U (P=0.013) and exposure to more than 2 intravenous antibiotics post-LT (P=0.003) were related to Gram-positive cocci infections. Multivariate logistic regression analysis revealed that preoperative MELD score >25 (OR=2.378, 95% CI 1.124 to 5.032, P=0.024) and intraoperative red blood cell transfusion ≥ 12 U (OR=2.757, 95% CI 1.227 to 6.195, P=0.014) were independent risk factors for Gram-positive cocci infections after LT. Postoperative Gram-positive cocci infections were reduced in LT recipients exposing to more than two intravenous antibiotics post-LT (OR=0.269, 95% CI 0.121 to 0.598, P=0.001). CONCLUSIONS: Gram-positive cocci infections occurring early after liver transplantation were dominated by Enterococcus faecalis infections at the abdominal/biliary tract and urinary tract. Teicoplanin, tigecycline and linezolid were anti-cocci sensitive drugs. Daptomycin and teicoplanin were equally effective in preventing cocci infections due to Gram-positive cocci. Patients with high preoperative MELD score and massive intraoperative red blood cell transfusion were more likely to suffer Gram-positive cocci infection after surgery. Postoperative Gram-positive cocci infections were reduced in recipients exposing to more than two intravenous antibiotics post-LT.

Complete genome sequence of cfr(B)-carrying Enterococcus raffinosus isolated from bile in a patient in Japan.

OBJECTIVES: Linezolid is an antibiotic used to treat infectious diseases caused by vancomycin-resistant enterococci and methicillin-resistant Staphylococcus aureus. Recently, Enterococcus Spp.-carrying mobile linezolid resistance genes were reported. Herein, we report the complete genome sequence of Enterococcus raffinosus JARB-HU0741, which was isolated from a bile sample of a patient in Japan on May 5, 2021, and carries a linezolid resistance gene, cfr(B). Nevertheless, this isolate was susceptible to linezolid. METHODS: Whole-genome sequencing was performed using HiSeq X FIVE (Illumina) and GridION (Oxford Nanopore Technologies). The sequence reads were assembled using Unicycler v0.4.8, and the complete genome was annotated using DFAST v1.2.18. Antimicrobial resistance genes were detected with Abricate v1.0.1, using the ResFinder database. The minimum inhibitory concentrations (MICs) were determined using broth microdilution and interpreted according to the guidelines of the Clinical and Laboratory Standards Institute. RESULTS: E. raffinosus JARB-HU0741 contained a 3 248 808-bp chromosome and a 1 156 277-bp megaplasmid. cfr(B) was present in the Tn6218-like transposon, which was inserted into a gene encoding a PRD domain-containing protein present in the megaplasmid, but the isolate was susceptible to linezolid (MIC, 0.5 µg/mL). The Tn6218-like transposon was similar to the Tn6218 of Clostridioides difficile Ox3196 and the Tn6218-like transposon of Enterococcus faecium UW11733; however, three genes encoding a topoisomerase, an S-adenosylmethionine-dependent methyltransferase, and a TetR family transcriptional regulator were present in the previous Tn6218- or Tn6218-like transposon. CONCLUSION: This is the first report of the complete genome sequence of E. raffinosus carrying cfr(B). E. raffinosus carrying cfr(B) without linezolid resistance poses a threat, as it could serve as a reservoir for mobile linezolid resistance genes.

Clinical characteristics and antibiotic resistance profile of invasive MRSA infections in newborn inpatients: a retrospective multicenter study from China.

BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) can cause invasive infections with significant mortality in neonates. This study aimed to analyze the clinical characteristics and antibiotic resistance profiles of invasive MRSA infections and determine risk factors associated with invasive MRSA infections in newborn inpatients. METHODS: This multicenter retrospective study of inpatients from eleven hospitals in the Infectious Diseases Surveillance of Pediatrics (ISPED) group of China was performed over a two-year period (2018-2019). Statistical significance was calculated by applying the χ2 test or by Fisher's exact test in the case of small sample sizes. RESULTS: A total 220 patients were included. Among included cases, 67 (30.45%) were invasive MRSA infections, including two deaths (2.99%), while 153 (69.55%) were noninvasive infections. The invasive infections of MRSA occurred at a median age of 8 days on admission, which was significantly younger compared to 19 days in noninvasive cases. Sepsis (86.6%) was the most common invasive infection, followed by pneumonia (7.4%), bone and joint infections (3.0%), central nervous system infection (1.5%), and peritonitis (1.5%). Congenital heart disease, low birth weight infant (<2500 g), but not preterm neonates, and bronchopulmonary dysplasia, were more commonly found in invasive MRSA infections. All these isolates were susceptible to vancomycin and linezolid and were resistant to penicillin. Additionally, 69.37% were resistant to erythromycin, 57.66% to clindamycin, 7.04% to levofloxacin, 4.62% to sulfamethoxazole-trimethoprim, 4.29% to minocycline, 1.33% to gentamicin, and 3.13% were intermediate to rifampin. CONCLUSION: Low age at admission (≤8 days), congenital heart disease, and low birth weight were associated with invasive MRSA infections in neonates, and no isolates resistant to vancomycin and linezolid were found. Determining these risks in suspected neonates may help identify patients with imminent invasive infections who may require intensive monitoring and therapy.

Can platelet-rich fibrin act as a natural carrier for antibiotics delivery? A proof-of-concept study for oral surgical procedures.

OBJECTIVES: Evaluate the role of platelet-rich fibrin (PRF) as a natural carrier for antibiotics delivery through the analysis of drug release and antimicrobial activity. MATERIALS AND METHODS: PRF was prepared according to the L-PRF (leukocyte- and platelet-rich fibrin) protocol. One tube was used as control (without drug), while an increasing amount of gentamicin (0.25 mg, G1; 0.5 mg, G2; 0.75 mg, G3; 1 mg, G4), linezolid (0.5 mg, L1; 1 mg, L2; 1.5 mg, L3; 2 mg, L4), vancomycin (1.25 mg, V1; 2.5 mg, V2; 3.75 mg, V3; 5 mg, V4) was added to the other tubes. At different times the supernatant was collected and analyzed. Strains of E. coli, P. aeruginosa, S. mitis, H. influenzae, S. pneumoniae, S. aureus were used to assess the antimicrobial effect of PRF membranes prepared with the same antibiotics and compared to control PRF. RESULTS: Vancomycin interfered with PRF formation. Gentamicin and linezolid did not change the physical properties of PRF and were released from membranes in the time intervals examined. The inhibition area analysis showed that control PRF had slight antibacterial activity against all tested microorganisms. Gentamicin-PRF had a massive antibacterial activity against all tested microorganisms. Results were similar for linezolid-PRF, except for its antibacterial activity against E. coli and P. aeruginosa that was comparable to control PRF. CONCLUSIONS: PRF loaded with antibiotics allowed the release of antimicrobial drugs in an effective concentration. Using PRF loaded with antibiotics after oral surgery may reduce the risk of post-operative infection, replace or enhance systemic antibiotic therapy while preserving the healing properties of PRF. Further studies are needed to prove that PRF loaded with antibiotics represents a topical antibiotic delivery tool for oral surgical procedures.

Effects of Antibacterial Agents on Cancerous Cell Proliferation.

Myelosuppression, a side effect of anticancer drugs, makes people more susceptible to infectious diseases by compromising the immune system. When a cancer patient develops a contagious disease, treatment with an anticancer drug is suspended or postponed to treat the infectious disease. If there was a drug that suppresses the growth of cancer cells among antibacterial agents, it would be possible to treat both infectious diseases and cancer. Therefore, this study investigated the effect of antibacterial agents on cancer cell development. Vancomycin (VAN) had little effect on cell proliferation against the breast cancer cell, MCF-7, prostate cancer cell, PC-3, and gallbladder cancer cell, NOZ C-1. Alternatively, Teicoplanin (TEIC) and Daptomycin (DAP) promoted the growth of some cancer cells. In contrast, Linezolid (LZD) suppressed the proliferation of MCF-7, PC-3, and NOZ C-1 cells. Therefore, we found a drug that affects the growth of cancer cells among antibacterial agents. Next, when we examined the effects of the combined use of existing anticancer and antibacterial agents, we found VAN did not affect the growth suppression by anticancer agents. However, TEIC and DAP attenuated the growth suppression of anticancer agents. In contrast, LZD additively enhanced the growth suppression by Docetaxel in PC-3 cells. Furthermore, we showed that LZD inhibits cancer cell growth by mechanisms that involve phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway suppression. Therefore, LZD might simultaneously treat cancer and infectious diseases.

Linezolid resistance: detection of the cfr(B) gene in French clinical MRSA strains.

OBJECTIVES: To describe two linezolid-resistant MRSA strains carrying the cfr(B) gene detected in the French National Reference Centre for staphylococci. METHODS: Two linezolid-resistant MRSA strains isolated from cystic fibrosis patients in two different French hospitals in 2017 and 2019 were examined to explore the mechanisms of linezolid resistance. Antimicrobial susceptibility was tested using broth microdilution and gradient strips. The genetic determinants of linezolid resistance were assessed by a multiplex PCR targeting cfr/cfr(B), optrA and poxtA genes, by amplification and sequencing of individual 23S rRNA genes and by WGS using both Illumina and Nanopore technologies. RESULTS: The two MRSA strains were resistant to linezolid but susceptible to tedizolid, and PCR-positive for cfr/cfr(B). The WGS analysis indicated that they belonged to two different STs (ST8-MRSA-IV and ST5382-MRSA-IV) and that they both harboured the cfr(B) gene on the same 9.7 kb Tn6218-like chromosomal transposon, a finding only previously reported in Enterococcus sp. and Clostridioides difficile. CONCLUSIONS: To the best of our knowledge, this is the first description of the presence of cfr(B) in staphylococci, more specifically in linezolid-resistant MRSA strains. This finding illustrates the risk of horizontal intergenus transfer of oxazolidinone resistance genes in Staphylococcus aureus and highlights the need to monitor such emergence in this species.

Development and validation of a resazurin assay for in vitro susceptibility testing of Actinomadura madurae: a common causative agent of actinomycetoma.

OBJECTIVES: Actinomycetoma is a chronic granulomatous disease affecting skin, subcutaneous tissue, fascia, muscle and bones. With increasing resistance against commonly used treatment regimens, susceptibility testing is urgently needed. METHODS: We developed an in vitro susceptibility assay for Actinomadura madurae, one of the common causative agents of actinomycetoma, employing resazurin for endpoint reading. Using this assay, reproducible MICs were determined for the most commonly used antibacterial agents for actinomycetoma treatment. The tested antibacterial agents included trimethoprim/sulfamethoxazole, amikacin, streptomycin, amoxicillin, ceftriaxone, gentamicin, ciprofloxacin, doxycycline, imipenem, linezolid, penicillin G and rifampicin. RESULTS: Following the clinical breakpoints as stated by CLSI, 100% of the tested strains were susceptible to trimethoprim/sulfamethoxazole (MIC 0.03/0.59-1/19 mg/L), amikacin (MIC 0.0078-0.25 mg/L), doxycycline (MIC <0.25-1 mg/L) and linezolid (MIC <0.25-2 mg/L), 90% to ciprofloxacin (MIC <0.25-2 mg/L), 80% to ceftriaxone (MIC <0.5 to >64 mg/L) and imipenem (MIC <0.25-32 mg/L) and only 20% to amoxicillin (MIC <0.5 to >64 mg/L) and rifampicin (MIC 0.5 to >32 mg/L). CONCLUSIONS: Determinations of MICs by visual readings of colour changes versus spectrophotometric readings were comparable. This convenient visual reading has the advantage of feasible implementation in endemic settings.

Use of bedaquiline in spinal osteomyelitis and soft tissue abscess caused by multidrug-resistant Mycobacterium tuberculosis: A case report.

INTRODUCTION: Spinal Tuberculosis (STB) represents between 1% and 2% of total tuberculosis cases. STB management remains challenging; the first-line approach consists of medical treatment, while surgery is reserved for patients with complications. No data regarding STB treatment with bedaquiline-containing regimens are available in the literature. CASE DESCRIPTION: Herein, we report the case of a 21-year-old man from Côte d'Ivoire with a multidrug resistance STB with subcutaneous abscess. After approval of the hospital off-label drug committee, we started bedaquiline 400 mg daily for two weeks, followed by 200 mg three times per week, for 22 weeks, associated with linezolid 600 mg daily, rifabutin 450 mg daily, and amikacin 750 mg daily (interrupted after eight weeks). During treatment, we performed a weekly EKG. No QT prolongation was shown, but inverted T waves appeared, requiring several cardiological consultations and cardiac MRI, but no cardiac dysfunction was found. After 24 weeks, bedaquiline was replaced with moxifloxacin 400 mg daily. The patient continued treatment for another year. We performed another computer tomography at the end of treatment, confirming the cure. DISCUSSION: A salvage regimen containing bedaquiline proved effective in treating multidrug-resistance tuberculosis spinal infection without causing severe adverse effects. However, further studies are needed to evaluate better bedaquiline bone penetration and the correct duration of treatment with bedaquiline in MDR spinal tuberculosis.

Contezolid in complicated skin and soft tissue infection.

Contezolid (MRX-I, Youxitai) is an oral oxazolidinone drug being developed by MicuRx Pharmaceutical Co., Ltd., Shanghai, China. It was approved by China's National Medical Products Administration (NMPA) in June 2021, attaining its first approval for the treatment of complicated skin and soft tissue infections (cSSTIs). It is also under clinical development for acute bacterial skin and skin structure infections (ABSSSIs) in the U.S. after receiving qualified infectious disease product (QIDP) classification and fast track status by U.S. Food and Drug Administration (FDA) in September 2018. Contezolid is effective against a broad range of Gram-positive bacteria including activity against methicillin-resistant Staphylococcus aureus (MRSA), penicillin-resistant Streptococcus pneumoniae and vancomycin-resistant Enterococci (VRE). It provides a major benefit over the most popular drug of its class, linezolid (Zyvox), by offering an improved safety profile and minimal effects concerning myelosuppression and monoamine oxidase (MAO) inhibition, two independent adverse events limiting linezolid use in the clinic. The recommended dosage regimen of contezolid is 800 mg every 12 hours for 7-14 days with regular food intake and it can be extended if required. At the mentioned dose under fed conditions, satisfactory efficacy against MRSA with a 90%; or higher cumulative fraction of response and probability of target attainment was achieved. Additionally, contezolid also exhibits activity against Mycobacterium tuberculosis and Mycobacterium abscessus.

Regulatory relationship between macrophage autophagy and PVL-positive methicillin-resistant Staphylococcus aureus.

The present study intends to clarify the hypothesis that PVL-positive Methicillin-resistant S. aureus strain (PVL+-MRSA)-infected macrophages regulate autophagy and thus in turn inhibit phagocytosis through the in vitro and in vivo experiments. The autophagy of mouse macrophage cell line RAW264.7 was observed by fluorescence microscopy, and counted based on the number of each cell dot-like structure GFP-LC3. The protein levels of the phagocytic factors associated with autophagy were determined by western blotting. The phagocytosis of RAW264.7 on MRSA was determined by counting the colony. The clinically isolated and identified PVL+-MRSA strain was used to infect BALB/c mice (left nasal drip) to establish a mouse pneumonia model. PVL+-MRSA mice were then treated with 3-MA or linezolid. Bronchoalveolar lavage fluid (BALF) from mice was collected for macrophage counting by Flow cytometry assay. The right lung was aseptically isolated for counting the amount of bacteria. The results showed that PVL+-MRSA could induced the autophagy of macrophages, which in turn reduced the damage from macrophages, which were respectively alleviated by 3-MA and aggravated by rapamycin. Exogenous rPVL administrated into PVL--MRSA-infected macrophages caused the autophagy of macrophage. Exogenous rPVL, particularly A-Luk S-PV, administrated into macrophages also caused the autophagy of macrophage, which was reversed by PMX53, a C5aR antagonist. In a mouse pneumonia model, PVL+-MRSA could induced the autophagy of macrophages, which in turn reduced the damage from macrophages, which were respectively alleviated by 3-MA or linezolid. In conclusion, this study indicated PVL+-MRSA regulated macrophage autophagy, which in turns inhibit the phagocytosis of S. aureus by macrophage. This study may provide a potential target against S. aureus infection.

Long-term use of tedizolid for pulmonary nocardiosis.

Nocardiosis usually occurs in immunocompromised patients and causes infections in various organs, including the lungs, skin, and organs of the central nervous system. Herein, we report the case of a patient with minimal change nephrotic syndrome who had been on immunosuppressive drugs and developed pulmonary nocardiosis due to Nocardia nova complex and Pneumocystis pneumonia. For pulmonary nocardiosis, trimethoprim-sulfamethoxazole, linezolid, and clarithromycin were initiated sequentially, but were subsequently discontinued due to side effects; the treatment was completed with tedizolid. Tedizolid was used safely for 200 out of 286 days of antibiotic treatment, and clinical improvement was observed. Tedizolid is a bacteriostatic oxazolidine antibiotic that inhibits bacterial protein synthesis, the same mechanism as its predecessor, linezolid. Tedizolid is thought to cause less frequent myelosuppression than linezolid, at least for short-term use. In the future, tedizolid may be a promising alternative to linezolid in cases of nocardiosis that usually require long-term treatment.

Persistence of a multidrug-resistant worldwide-disseminated methicillin-resistant Staphylococcus epidermidis clone harbouring the cfr linezolid resistance gene in a French hospital with evidence of interspecies transfer to several Staphylococcus aureus lineages.

BACKGROUND: Resistance to linezolid has become a worldwide concern since it is one of the last-resort antibiotics to treat multidrug-resistant staphylococcal and enterococcal infections. OBJECTIVES: We investigated staphylococcal infections caused by 16 cfr-positive linezolid-resistant Staphylococcus epidermidis and Staphylococcus aureus isolates in a French university hospital from 2015 to 2018. METHODS: Antimicrobial susceptibility of isolates was tested by broth microdilution and gradient strips. Genetic determinants of linezolid resistance (including cfr gene and 23S rRNA mutations) were assessed by PCR and WGS; the latter was also used to characterize the cfr-carrying plasmids in S. epidermidis and S. aureus, and to explore the clonal relationship of isolates. RESULTS: All linezolid-resistant staphylococcal isolates harboured the same cfr-carrying plasmid, sharing 99% identity with the previously described pSA737. The three S. aureus isolates belonged to different STs (ST8, ST72, ST2416); the 13 methicillin-resistant S. epidermidis (MRSE) belonged to ST2 and harboured both cfr and mutations in genes encoding 23S rRNA and ribosomal proteins. Phylogenetic analysis grouped the MRSE isolates into two clusters, one of which (n = 12 isolates) belonged to the recently reported multidrug-resistant worldwide-disseminated S. epidermidis lineages. CONCLUSIONS: The results presented herein highlight the persistence and efficient spread of a cfr-carrying plasmid in a hospital related both to the dissemination of a multidrug-resistant S. epidermidis clone and the in vivo interspecies transfer of cfr between S. epidermidis and S. aureus. The emergence of linezolid-resistant strains should be closely monitored, and the mechanisms involved systematically explored in order to limit the spread of plasmid-mediated resistance.

Structural basis for PoxtA-mediated resistance to phenicol and oxazolidinone antibiotics.

PoxtA and OptrA are ATP binding cassette (ABC) proteins of the F subtype (ABCF). They confer resistance to oxazolidinone and phenicol antibiotics, such as linezolid and chloramphenicol, which stall translating ribosomes when certain amino acids are present at a defined position in the nascent polypeptide chain. These proteins are often encoded on mobile genetic elements, facilitating their rapid spread amongst Gram-positive bacteria, and are thought to confer resistance by binding to the ribosome and dislodging the bound antibiotic. However, the mechanistic basis of this resistance remains unclear. Here we refine the PoxtA spectrum of action, demonstrate alleviation of linezolid-induced context-dependent translational stalling, and present cryo-electron microscopy structures of PoxtA in complex with the Enterococcus faecalis 70S ribosome. PoxtA perturbs the CCA-end of the P-site tRNA, causing it to shift by ∼4 Šout of the ribosome, corresponding to a register shift of approximately one amino acid for an attached nascent polypeptide chain. We postulate that the perturbation of the P-site tRNA by PoxtA thereby alters the conformation of the attached nascent chain to disrupt the drug binding site.

Co-occurrence of cfr-mediated linezolid-resistance in ST398 LA-MRSA and non-aureus staphylococci isolated from a pig farm.

Linezolid resistance, mediated by the cfr gene, which confers resistant phenotypes to phenicols, lincosamides, oxazolidinones, pleuromutilins, and streptogramin A antimicrobials, has emerged in S. aureus and non-aureus staphylococci (NAS). Moreover, due to the transferable potential via plasmids, the spread of cfr among staphylococci is of great concern. In the present study, we investigated the prevalence of cfr-mediated linezolid resistance in ST398 methicillin-resistant S. aureus (MRSA) and NAS strains isolated from a pig farm. Among the 26 staphylococci isolates collected from a pig farm, 14 cfr-harboring ST398 MRSA and NAS (S. epidermidis, S. pasteuri, S. cohnii, and S. rostri) strains were resistant to linezolid and also carried the fexA gene. Comparative genome analysis of cfr-carrying linezolid-resistant ST398 MRSA and NAS (S. pasteuri, S. cohnii, and S. epidermidis) strains revealed that the segments harboring cfr in different staphylococcal strains showed ≥ 99 % sequence identity and the corresponding region containing the cfr, fexA, and Tn558 elements were located in a 38-kb plasmid, designated pSA12 of ST398 MRSA. These observations indicate that the cfr-carrying plasmids and/or fragments may be disseminated among staphylococci in a pig farm and possibly transmitted to staphylococci of human origin, subsequently posing a threat to public health. This is the first report of the co-existence of cfr in linezolid-resistant ST398 MRSA and NAS isolated from a pig farm in South Korea.

In-Host Emergence of Linezolid Resistance in a Complex Pattern of Toxic Shock Syndrome Toxin-1-Positive Methicillin-Resistant Staphylococcus aureus Colonization in Siblings with Cystic Fibrosis.

Methicillin-resistant Staphylococcus aureus (MRSA) can cause chronic lung infections in patients with Cystic Fibrosis (CF). One option for managing them is the use of linezolid. We hereby report the in-host emergence of linezolid resistance (LR) in MRSA in CF siblings via a population analysis. A collection of 171 MRSA strains from 68 samples were characterized by determining their linezolid Minimal Inhibitory Concentrations (MICs), analyzing the locus of staphylococcal protein A (spa) and whole genome sequencing. Courses of linezolid were retraced. Strains belonged to three spa types (t002, t045, t127) and two sequence types (ST1, ST5). Emergence of LR occurred under treatment, one year apart in both siblings, in the CC5-MRSA-I Geraldine clone harboring the toxic shock syndrome toxin-1-encoding gene. Resistance was related to a G2576T substitution present in a variable number of 23S rRNA gene copies. Susceptible and resistant strains were co-isolated within samples. Single Nucleotide Polymorphism-based analysis revealed complex colonizations by highly diversified, clonally related populations. LR remains rare in MRSA and there are very few longitudinal analyses documenting its emergence. Analyzing a large MRSA collection revealed new aspects of LR emergence: it emerges in specific subclonal lineages resulting from adaptive diversification of MRSA in the CF lung and this heterogeneity of intra-sample resistance may contribute to compromising antibiotic management.