Apramycin overcomes the inherent lack of antimicrobial bactericidal activity in Mycobacterium abscessus

Antibiotic therapy of infections caused by the emerging pathogen Mycobacterium abscessus is challenging due to the organism’s inherent resistance towards clinically available antimicrobials. The low bactericidal potency of currently available treatment regimens is of concern and testifies to the poor therapeutic outcome in pulmonary M. abscessus infections. Mechanistically, we here demonstrate that the acetyltransferase Eis2 is responsible for the lack of bactericidal activity of amikacin, the standard aminoglycoside used in combination treatment. In contrast, the distinct structure aminoglycoside apramycin is not modified by any of the pathogen’s innate aminoglycoside resistance mechanisms nor is it affected by the multi-drug resistance regulator WhiB7. As a consequence, apramycin uniquely shows potent bactericidal activity against M. abscessus . This favourable feature of apramycin is reflected in a mouse model of M. abscessus lung infection, which demonstrates superior activity over amikacin. These findings encourage the development of apramycin for the treatment of M. abscessus infections and suggest that M. abscessus eradication in lung pulmonary disease may be within therapeutic reach.

UHRF1 drives the poor prognosis associated with RB loss in osteosarcoma

ABSTRACTLoss of function mutations at the retinoblastoma (RB1) gene are associated with increased mortality, metastasis and poor therapeutic outcome in several cancers, including osteosarcoma. However, the mechanism(s) through which RB1 loss worsens clinical outcome remain to be elucidated. Ubiquitin-like with PHD and Ring Finger domains 1 (UHRF1) has been identified as a critical downstream effector of the RB/E2F signaling pathway that is overexpressed in various cancers. Here, we show that UHRF1 upregulation is critical in rendering osteosarcoma cells more aggressive. We confirmed that UHRF1 is transcriptionally regulated by the RB/E2F pathway and overexpressed in osteosarcoma. Using novel genetically engineered mouse models, we determined that Uhrf1 loss dramatically reverses the effects of Rb1 loss. Based on gain- and loss-of-function assays, we report that UHRF1 promotes cell proliferation, migration, invasion, and metastasis. Furthermore, transcriptome analyses revealed the involvement of urokinase-type plasminogen activator (uPA) in UHRF1-mediated cell mobility. Our work presents a new mechanistic insight into RB1 loss-associated poor prognosis, revealing UHRF1 as a critical driver of tumor promotion, progression, and metastasis in osteosarcoma. This study provides substantial support for targeting UHRF1 or its downstream effectors as novel therapeutic options to improve current treatment for osteosarcoma and other cancers with RB/E2F pathway inactivation.

Microbial biofilm correlates with an increased antibiotic tolerance and poor therapeutic outcome in infective endocarditis

Background Infective endocarditis (IE) is associated with high rates of mortality. Prolonged treatments with high-dose intravenous antibiotics often fail to eradicate the infection, frequently leading to high-risk surgical intervention. By providing a mechanism of antibiotic tolerance, which escapes conventional antibiotic susceptibility profiling, microbial biofilm represents a key diagnostic and therapeutic challenge for clinicians. This study aims at assessing a rapid biofilm identification assay and a targeted antimicrobial susceptibility profile of biofilm-growing bacteria in patients with IE, which were unresponsive to antibiotic therapy. Results Staphylococcus aureus was the most common isolate (50%), followed by Enterococcus faecalis (25%) and Streptococcus gallolyticus (25%). All microbial isolates were found to be capable of producing large, structured biofilms in vitro. As expected, antibiotic treatment either administered on the basis of antibiogram or chosen empirically among those considered first-line antibiotics for IE, including ceftriaxone, daptomycin, tigecycline and vancomycin, was not effective at eradicating biofilm-growing bacteria. Conversely, antimicrobial susceptibility profile of biofilm-growing bacteria indicated that teicoplanin, oxacillin and fusidic acid were most effective against S. aureus biofilm, while ampicillin was the most active against S. gallolyticus and E. faecalis biofilm, respectively. Conclusions This study indicates that biofilm-producing bacteria, from surgically treated IE, display a high tolerance to antibiotics, which is undetected by conventional antibiograms. The rapid identification and antimicrobial tolerance profiling of biofilm-growing bacteria in IE can provide key information for both antimicrobial therapy and prevention strategies.

A prospective study of antimicrobial drug utilization in infective diseases in pediatrics at Navodaya Medical College Hospital of Raichur, Karnataka, India

Background: There is increased concern regarding the inappropriate use of antimicrobials resulting in emergence of resistant strains, unnecessary adverse effects and poor therapeutic outcome. This present study has been taken up with a view to analyze the use of various antimicrobial agents alone and/or in combination to combat diseases of infective origin in a proposed manner.Methods: This was a prospective study carried out for a period of 1 year from January 2011 to December 2011. The prescriptions of all eligible patients were reviewed on daily basis and all the relevant data were retrieved to assess the utilization pattern of antimicrobials and also their safety and potential interactions.Results: A total of 500 patients were selected randomly who satisfied the inclusion criteria. Of the total selected patients with infectious diseases, 493 patients (98.6%) received one or more antimicrobials. Use of antimicrobials was high in the age group of ‘6 months to 3 years’, ‘rural patients’ constituted 62% and were mostly from ‘Lower Socio-economic status’ (46%). Respiratory diseases constituted 38% of the patients. Fever was the notable symptom in 68.4%. Cephalosporins (48.6%) were the most frequently prescribed class of antimicrobials. Combination of ‘Parenteral therapy followed by oral therapy’ was the preferred route in 92%, and a combination of two antimicrobials was seen in 34.4%. Majority of the patients (81%) were discharged on advice and most of the patients (37.6%) had duration of stay of 7-9 days. 25.8% reported ‘Adverse Drug Reactions’ including predictable and unpredictable reactions.Conclusions: Antimicrobial prescribing is common in pediatric infectious diseases. As inappropriate usage of systemic antimicrobials was observed, it is essential that appropriate guidelines on the use of systemic antimicrobials are implanted to ensure rational prescribing of antimicrobials.

Lack of Antimicrobial Bactericidal Activity in Mycobacterium abscessus

ABSTRACTAntibiotic therapy of infections caused by the emerging pathogenMycobacterium abscessusis challenging due to the organism's natural resistance toward most clinically available antimicrobials. We investigated the bactericidal activity of antibiotics commonly administered inM. abscessusinfections in order to better understand the poor therapeutic outcome. Time-kill curves were generated for clinicalM. abscessusisolates,Mycobacterium smegmatis, andEscherichia coliby using antibiotics commonly categorized as bactericidal (amikacin and moxifloxacin) or bacteriostatic (tigecycline and linezolid). In addition, the impact of aminoglycoside-modifying enzymes on the mode of action of substrate and nonsubstrate aminoglycosides was studied by usingM. smegmatisas a model organism. While amikacin and moxifloxacin were bactericidal againstE. coli, none of the tested compounds showed bactericidal activity againstM. abscessus. Further mechanistic investigations of the mode of action of aminoglycosides inM. smegmatisrevealed that the bactericidal activity of tobramycin and gentamicin was restored by disruption of the chromosomalaac(2′) gene in the mycobacterial genome. The lack of bactericidal antibiotics in currently recommended treatment regimens provides a reasonable explanation for the poor therapeutic outcome inM. abscessusinfection. Our findings suggest that chromosomally encoded drug-modifying enzymes play an important role in the lack of aminoglycoside bactericidal activity against rapidly growing mycobacteria.