Comparative time-kill study of doxycycline, tigecycline, sulbactam, and imipenem against several clones of Acinetobacter baumannii

Eravacycline: The Tetracyclines Strike Back

Objective: To review the pharmacology, pharmacokinetics, efficacy, safety, and place in therapy of eravacycline, a novel fluorocycline antibiotic from the tetracycline family. Data Sources: A PubMed search was conducted for data between 1946 and March 2019 using MeSH terms eravacycline and TP-434. An internet search was conducted for unpublished clinical research. Study Selection and Data Extraction: The literature search was limited to English-language studies that described clinical efficacy, safety, and pharmacokinetics in humans and animals. Abstracts featuring prepublished data were also evaluated for inclusion. Data Synthesis: Eravacycline has in vitro activity against multidrug-resistant organisms, including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus, extended-spectrum β-lactamase-producing and carbapenem-resistant Enterobacteriaceae, and Acinetobacter. It was approved for the treatment of complicated intra-abdominal infections (cIAIs) in adults following favorable results of 2 phase III trials, IGNITE 1 and IGNITE 4, compared with ertapenem and meropenem, respectively. The most common adverse drug events associated with eravacycline were infusion site reactions (7.7%), nausea (6.5%), vomiting (3.7%), and diarrhea (2.3%). Relevance to Patient Care and Clinical Practice: Eravacycline will likely be most useful for resistant infections when lack of tolerability, resistant phenotypes, or allergies prevent the use of β-lactams. Conclusions: Eravacycline is a new tetracycline antibiotic with a broad spectrum of activity that has demonstrated efficacy in the treatment of cIAIs. Although it has activity against multidrug-resistant organisms, data are limited for other indications.

Bacteremia and meningitis caused by OXA-23-producing Acinetobacter baumannii - molecular characterization and susceptibility testing for alternative antibiotics

Background

Carbapenem-resistant Acinetobacter baumannii infection is a concern in developing countries due to high incidence, few therapeutic options, and increasing costs.

Objective

Characterize and analyze the antibiotic susceptibility patterns of carbapenem-resistant A. baumannii isolates and evaluate clinical data of meningitis and bacteremia caused by this microorganism.

Methods

Twenty-six A. baumannii isolates from 23 patients were identified by MALDI-TOF and automated methods and genotyped using pulsed field genotyping electrophoresis. Clinical data and outcomes were evaluated. Susceptibility of isolates to colistin, tigecycline, meropenem, imipenem, and doxycycline was determined.

Results

Mortality due to A. baumannii infections was 73.91%; all patients with meningitis and 7/8 patients with ventilator-associated pneumonia died. All isolates were susceptibility to polymyxin (100%; MIC₅₀, MIC₉₀: 1 μg/mL, 1 μg/mL) and colistin (100%; MIC₅₀, MIC₉₀: 2 μg/mL, 2 μg/mL), and 92% were susceptible to tigecycline (MIC₅₀, MIC₉₀: 1 μg/mL, 1 μg/mL) and doxycycline (MIC₅₀, MIC₉₀: 2 μg/mL, 2 μg/mL). bla_OXA-23 was identified in 24 isolates. Molecular typing showed 8 different patterns: 13 isolates belonged to pattern A (50%).

Conclusion

Carbapenem-resistant A. baumannii infections mortality is high. Alternative antimicrobial therapy (doxycycline) for selected patients with carbapenem-resistant A. baumannii infection should be considered.

Tetracycline Antibiotics and Resistance

Tetracyclines possess many properties considered ideal for antibiotic drugs, including activity against Gram-positive and -negative pathogens, proven clinical safety, acceptable tolerability, and the availability of intravenous (IV) and oral formulations for most members of the class. As with all antibiotic classes, the antimicrobial activities of tetracyclines are subject to both class-specific and intrinsic antibiotic-resistance mechanisms. Since the discovery of the first tetracyclines more than 60 years ago, ongoing optimization of the core scaffold has produced tetracyclines in clinical use and development that are capable of thwarting many of these resistance mechanisms. New chemistry approaches have enabled the creation of synthetic derivatives with improved in vitro potency and in vivo efficacy, ensuring that the full potential of the class can be explored for use against current and emerging multidrug-resistant (MDR) pathogens, including carbapenem-resistant Enterobacteriaceae, MDR Acinetobacter species, and Pseudomonas aeruginosa.

Activity of levofloxacin in combination with colistin against Acinetobacter baumannii: In vitro and in a Galleria mellonella model

BACKGROUND/PURPOSE

Treatment of Acinetobacter baumannii infections is challenging owing to widespread multidrug-resistant A. baumannii (MDR-AB) and the lack of novel agents. Although recent data suggest that levofloxacin (LVX) may have unique activity against MDR-AB in combination with colistin (CST), further preclinical work is needed.

METHODS

We used a A. baumannii type strain ATCC19606, a CST-resistant strain AB19606R, and two clinical isolates (GN0624 and GN1115) of MDR-AB to investigate the in vitro and in vivo efficacy of LVX-CST combination. Synergy studies were performed using the microtiter plate chequerboard assay and time-kill methodology. Inhibitory activity of antibiotics against biofilms and the mutant prevention concentrations were also studied in vitro. A simple invertebrate model (Galleria mellonella) has been used to assess the in vivo activity of antimicrobial therapies.

RESULTS

The LVX-CST combination was bactericidal against the CST-susceptible clinical isolate (GN0624). In checkerboard assays, synergy (defined as a fractional inhibitory concentration index of < 0.5) was observed between CST and LVX in GN0624. The combination had antibiofilm properties on the preformed biofilms of four tested strains and could prevent the emergence of CST-resistant A. baumanni. Treatment of G. mellonella larvae infected with lethal doses of A. baumannii resulted in significantly enhanced survival rates when LVX was given with CST compared with CST treatment alone (p < 0.05).

CONCLUSION

In summary, a synergistic or additive effect between CST and LVX was observed in vitro and in vivo against CST-susceptible A. baumannii strains, although not against CST-resistant ones.

In vitro activity of minocycline alone or in combination in multidrug-resistant Acinetobacter baumannii isolates

Minocycline (MIN) usually shows good activity against Acinetobacter baumannii strains. The reintroduction to the market of intravenous MIN provides an additional agent to the limited options for the treatment of A. baumannii infections. The activity of MIN as a single agent and in combination with rifampicin (RIF), colistin (COL) or imipenem (IMI) was evaluated by means of killing curves and 24  h-time-kill curves in five A. baumannii isolates which were selected on the basis of different antimicrobial resistance profiles. MIN showed bacteriostatic activity in three isolates (2 ×  or 16 ×  MIC) and bactericidal activity in the other isolates (64 ×  MIC). In isolates harbouring the tetB gene, the associations studied were always indifferent. However, in isolates not harbouring tetB, the use of MIN in combination showed a rapid synergistic effect (at 4  h) in four out of nine combinations (two with RIF and one each with IMI and COL). At 24  h, this effect was observed in six out of nine combinations (two in each association). MIN in combination with RIF, IMI and COL showed bactericidal synergy in most of the isolates which did not harbour the tetB gene, but the combinations were not synergistic in tetB-positive isolates.

Antimicrobial resistance in Acinetobacter baumannii: From bench to bedside

Acinetobacter baumannii (A. baumannii) is undoubtedly one of the most successful pathogens in the modern healthcare system. With invasive procedures, antibiotic use and immunocompromised hosts increasing in recent years, A. baumannii has become endemic in hospitals due to its versatile genetic machinery, which allows it to quickly evolve resistance factors, and to its remarkable ability to tolerate harsh environments. Infections and outbreaks caused by multidrug-resistant A. baumannii (MDRAB) are prevalent and have been reported worldwide over the past twenty or more years. To address this problem effectively, knowledge of species identification, typing methods, clinical manifestations, risk factors, and virulence factors is essential. The global epidemiology of MDRAB is monitored by persistent surveillance programs. Because few effective antibiotics are available, clinicians often face serious challenges when treating patients with MDRAB. Therefore, a deep understanding of the resistance mechanisms used by MDRAB can shed light on two possible strategies to combat the dissemination of antimicrobial resistance: stringent infection control and antibiotic treatments, of which colistin-based combination therapy is the mainstream strategy. However, due to the current unsatisfying therapeutic outcomes, there is a great need to develop and evaluate the efficacy of new antibiotics and to understand the role of other potential alternatives, such as antimicrobial peptides, in the treatment of MDRAB infections.

Antibacterial and antiviral evaluation of sulfonoquinovosyldiacylglyceride: a glycolipid isolated from Azadirachta indica leaves

Assessment of antibacterial as well as antiherpes virus activity of sulfonoquinovosyldiacylglyceride (SQDG), a glycolipid, isolated from the leaves of Azadirachta indica has been described. Antimicrobial activity was evaluated against Gram-positive, Gram-negative bacteria and herpes simplex virus. SQDG showed significant inhibitory activity against Salmonella typhi and two isolates of Shigella dysenteriae with MIC values 32 μg ml(-1) , while three isolates of Salm. typhi, Escherichia coli and Vibrio cholerae were inhibited at 64 μg ml(-1) and have shown zone diameter ranging from 6.2 to 12.3 mm. The growth kinetics study of SQDG on Salm. typhi and Sh. dysenteriae revealed that the growths were completely inhibited at their MIC values within 24 h of exposure. Interestingly, SQDG inhibits herpes simplex virus (HSV) type 1 and 2 with the EC50 of 9.1 and 8.5 μg ml(-1) , compared with acyclovir (2.2 and 2.8 μg ml(-1) against HSV-1 and HSV-2). The selectivity index (SI) was found to be 12.4 against HSV-1 and 13.41 with HSV-2. Furthermore, the expression of proinflammatory cytokines of HSV-infected and SQDG-treated macrophages using ELISA kit revealed that SQDG significantly downregulated the production of TNF-α, IL-1β, IL-12 and IL-6.

SIGNIFICANCE AND IMPACT OF THE STUDY

The water-soluble metabolite sulfonoquinovosyldiacylglyceride (SQDG) isolated from Azadirachta indica (Neem) possess significant antibacterial as well as anti-HSV activity. The efficacies as well as the solubility factor of SQDG substantiate a greater attention for its use as phytotherapeutic drug for controlling microbial infections as most consumers have better acceptance of phytomedicines than synthetic drugs.

Visible light responsive photocatalyst induces progressive and apical-terminus preferential damages on Escherichia coli surfaces

Background

Recent research shows that visible-light responsive photocatalysts have potential usage in antimicrobial applications. However, the dynamic changes in the damage to photocatalyzed bacteria remain unclear.

Methodology/Principal Findings

Facilitated by atomic force microscopy, this study analyzes the visible-light driven photocatalyst-mediated damage of Escherichia coli. Results show that antibacterial properties are associated with the appearance of hole-like structures on the bacteria surfaces. Unexpectedly, these hole-like structures were preferentially induced at the apical terminus of rod shaped E. coli cells. Differentiating the damages into various levels and analyzing the percentage of damage to the cells showed that photocatalysis was likely to elicit sequential damages in E. coli cells. The process began with changing the surface properties on bacterial cells, as indicated in surface roughness measurements using atomic force microscopy, and holes then formed at the apical terminus of the cells. The holes were then subsequently enlarged until the cells were totally transformed into a flattened shape. Parallel experiments indicated that photocatalysis-induced bacterial protein leakage is associated with the progression of hole-like damages, further suggesting pore formation. Control experiments using ultraviolet light responsive titanium-dioxide substrates also obtained similar observations, suggesting that this is a general phenomenon of E. coli in response to photocatalysis.

Conclusion/Significance

The photocatalysis-mediated localization-preferential damage to E. coli cells reveals the weak points of the bacteria. This might facilitate the investigation of antibacterial mechanism of the photocatalysis.

Isolation and identification of the antibacterial active compound from petroleum ether extract of neem oil

From a petroleum ether extract of neem oil (Azadirachta indica A. Juss) the new tetrahydrofuranyl diester 1 was isolated as an anti-bacterial constituent. 1 showed significant activities against three standard bacterial strains, including Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922 and Salmonella enteritidis CMCC (B) 50041.

Pharmacokinetic-pharmacodynamic modeling of the in vitro activities of oxazolidinone antimicrobial agents against methicillin-resistant Staphylococcus aureus

Linezolid is the first FDA-approved oxazolidinone with activity against clinically important gram-positive pathogens, including methicillin (meticillin)-resistant Staphylococcus aureus (MRSA). RWJ-416457 is a new oxazolidinone with an antimicrobial spectrum similar to that of linezolid. The goal of the present study was to develop a general pharmacokinetic (PK)-pharmacodynamic (PD) model that allows the characterization and comparison of the in vitro activities of oxazolidinones, determined in time-kill curve experiments, against MRSA. The in vitro activities of RWJ-416457 and the first-in-class representative, linezolid, against MRSA OC2878 were determined in static and dynamic time-kill curve experiments over a wide range of concentrations: 0.125 to 8 microg/ml (MIC, 0.5 microg/ml) and 0.25 to 16 microg/ml (MIC, 1 microg/ml), respectively. After correction for drug degradation during the time-kill curve experiments, a two-subpopulation model was simultaneously fitted to all data in the NONMEM VI program. The robustness of the model and the precision of the parameter estimates were evaluated by internal model validation by nonparametric bootstrap analysis. A two-subpopulation model, consisting of a self-replicating, oxazolidinone-susceptible and a persistent, oxazolidinone-insusceptible pool of bacteria was appropriate for the characterization of the time-kill curve data. The PK-PD model identified was capable of accounting for saturation in growth, delays in the onsets of growth and drug-induced killing, as well as naturally occurring bacterial death. The simultaneous fit of the proposed indirect-response, maximum-effect model to the data resulted in concentrations that produced a half-maximum killing effect that were significantly (P < 0.05) lower for RWJ-416457 (0.41 microg/ml) than for linezolid (1.39 microg/ml). In combination with the appropriate PK data, the susceptibility-based two-subpopulation model identified may provide valuable guidance for the selection of oxazolidinone doses or dose regimens for use in clinical studies.

In vitro antibacterial activity of tigecycline against resistant Gram-negative bacilli and enterococci by time-kill assay

This time-kill study was performed with 65 genetically unique clinical isolates of Gram-negative bacilli and enterococci to further define the antibacterial activity of tigecycline. To our knowledge, this is the largest published time-kill study evaluating tigecycline activity to date. Isolates evaluated were 10 meropenem-resistant Acinetobacter baumannii; 15 Escherichia coli, including 10 extended-spectrum beta-lactamase (ESBL) producers; 15 Klebsiella pneumoniae, including 10 ESBL producers; 20 vancomycin-resistant Enterococcus faecium (VRE), including 10 that were linezolid resistant; and 5 vancomycin-susceptible Enterococcus faecalis. Time-kill testing was performed using tigecycline concentrations of 1x, 2x, and 4x MIC with colony-forming units (CFU) per milliliter determined at 0, 4, 8, 12, 24, 36, and 48 h. Tigecycline MICs (microg/mL) were < or =1 for E. coli and K. pneumoniae, regardless of the isolates' ESBL production; A. baumannii, 0.06 to 4; 9/10 (90%) were < or =2; E. faecalis < or =0.12; and VRE < or =0.25, regardless of linezolid susceptibility. In the time-kill assay, tigecycline significantly inhibited bacterial growth when compared with the growth control. The reduction in growth was <3 log(10) CFU/mL for all isolates, indicative of a bacteriostatic effect.