A prospective randomized clinical trial to assess antibiotic pocket irrigation on tissue expander breast reconstruction

Bacterial infection is the most common complication following staged post-mastectomy breast reconstruction initiated with a tissue expander (TE). To limit bacterial infection, antibiotic irrigation of the surgical site is commonly performed despite little high-quality data to support this practice. We performed a prospective randomized control trial to compare the impact of saline irrigation alone to a triple antibiotic irrigation regimen (1 g cefazolin, 80 mg gentamicin, and 50,000 units of bacitracin in 500 mL of saline) for breast implant surgery. The microbiome in breasts with cancer (n = 16) was compared to those without (n = 16), as all patients (n = 16) had unilateral cancers but bilateral mastectomies (n = 32). Biologic and prosthetic specimens procured both at the time of mastectomy and during TE removal months later were analyzed for longitudinal comparison. Outcomes included clinical infection, bacterial abundance, and relative microbiome composition. No patient in either group suffered a reconstructive failure or developed an infection. Triple antibiotic irrigation administered at the time of immediate TE reconstruction did not reduce bacterial abundance or impact microbial diversity relative to saline irrigation at the time of planned exchange. Implanted prosthetic material adopted the microbial composition of the surrounding host tissue. In cancer-naïve breasts, relative to saline, antibiotic irrigation increased bacterial abundance on periprosthetic capsules (P = 0.03) and acellular dermal matrices (P = 0.04) and altered the microbiota on both. These data show that, relative to saline only, the use of triple antibiotic irrigation in TE breast reconstruction does impact the bacterial abundance and diversity of certain biomaterials from cancer-naïve breasts. IMPORTANCE The lifetime risk of breast cancer is ~13% in women and is treated with a mastectomy in ~50% of cases. The majority are reconstructed, usually starting with a tissue expander to help restore the volume for a subsequent permanent breast implant or the women's own tissues. The biopsychosocial benefits of breast reconstruction, though, can be tempered by a high complication rate of at least 7% but over 30% in some women. Bacterial infection is the most common complication, and can lead to treatment delays, patient physical and emotional distress and escalating health care cost. To limit this risk, plastic surgeons have tried a variety of strategies to limit bacterial infection including irrigating the pocket created after removing the breast implant with antibiotic solutions, but good-quality data are scarce. Herein, we study the value of antibiotics in pocket irrigation using a robust randomized clinical trial design and molecular microbiology approaches.

In vitro killing of multidrug/extensively drug-resistant Pseudomonas aeruginosa by fosfomycin alone or in combination with antipseudomonal antibiotics

Pseudomonas aeruginosa is a leading cause of nosocomial infections. Given the constant rise in resistance, adequate therapy is increasingly demanding. Fosfomycin recently became an appealing treatment option of bacterial infections due to multidrug-resistant bacteria (MDR). So far, fosfomycin synergy with other antibiotics has been assessed in studies, but only a limited number focused on MDR P. aeruginosa and on the effect of these combinations on the duration of the postantibiotic effect (PAE). We investigated synergy of fosfomycin with an array of antipseudomonal antibiotics using gradient diffusion strip cross method and time-kill method, and their effect on the duration of PAE against 51 variously resistant P. aeruginosa isolates. The highest rate of synergy was observed for combination with ceftazidime (23.4%) and gentamicin (19.1%). The PAE of antibiotic combinations was superior to that of the drugs alone. Our findings indicate that fosfomycin combination therapy may be a valuable treatment alternative.

Klebsiella pneumoniae l-Fucose Metabolism Promotes Gastrointestinal Colonization and Modulates Its Virulence Determinants

Colonization of the gastrointestinal (GI) tract by Klebsiella pneumoniae is generally considered asymptomatic. However, gut colonization allows K. pneumoniae to either translocate to sterile site within the same host or transmit through the fecal-oral route to another host. K. pneumoniae gut colonization is poorly understood, but knowledge of this first step toward infection and spread is critical for combatting its disease manifestations. K. pneumoniae must overcome colonization resistance (CR) provided by the host microbiota to establish itself within the gut. One such mechanism of CR is through nutrient competition. Pathogens that metabolize a broad range of substrates have the ability to bypass nutrient competition and overcome CR. Herein, we demonstrate that in response to mucin-derived fucose, the conserved fucose metabolism operon (fuc) of K. pneumoniae is upregulated in the murine gut, and we subsequently show that fucose metabolism promotes robust gut colonization. Growth studies using cecal filtrate as a proxy for the gut lumen illustrate the growth advantage that the fuc operon provides K. pneumoniae. We further show that fucose metabolism allows K. pneumoniae to be competitive with a commensal Escherichia coli isolate (Nissle). However, Nissle is eventually able to outcompete K. pneumoniae, suggesting that it can be utilized to enhance CR. Finally, we observed that fucose metabolism positively modulates hypermucoviscosity, autoaggregation, and biofilm formation but not capsule biogenesis. Together, these insights enhance our understanding of the role of alternative carbon sources in K. pneumoniae gut colonization and the complex relationship between metabolism and virulence in this species.

Impact of Target Turnover on the Translation of Drug-Target Residence Time to Time-Dependent Antibacterial Activity

The translation of time-dependent drug-target occupancy to extended pharmacological activity at low drug concentration depends on factors such as target vulnerability and the rate of target turnover. Previously, we demonstrated that the postantibiotic effect (PAE) caused by inhibitors of bacterial drug targets could be used to assess target vulnerability, and that high levels of target vulnerability coupled with relatively low rates of target resynthesis resulted in a strong correlation between drug-target residence time and the PAE following compound washout. Although the residence time of inhibitors on UDP-3-O-acyl-N-acetylglucosamine deacetylase (LpxC) in Pseudomonas aeruginosa (paLpxC) results in significant PAE, inhibitors of the equivalent enzyme in Escherichia coli (ecLpxC) do not cause a PAE. Hyperactivity of the fatty acid biosynthesis enzyme FabZ or the inclusion of sub-MIC levels of azithromycin lead to the observation of a PAE for three inhibitors of ecLpxC. FabZ hyperactivity has been shown to stabilize ecLpxC, and using mass spectrometry, we demonstrate that the appearance of a PAE can be directly linked to a 3-fold increase in the stability of ecLpxC. These studies substantiate the importance of target turnover in time-dependent drug activity.

Ecology and Medicine Converge at the Microbiome-Host Interface

The human body is home to a dense and diverse population of bacteria, viruses, and eukaryotes, collectively termed the microbiome. Research on host-microbiome interactions continuously demonstrates the importance of this microbial community to human physiology and its involvement in a myriad of diseases. This, in turn, sparks great interest in developing means for beneficially modulating the microbiome, such as fecal microbiome transplantation and probiotics. However, these interventions show mixed efficacy in clinical trials and raise safety concerns. How these exogenous microorganisms interact with the microbiome might underlie the efficacy and safety of these therapeutics, yet the signaling mechanisms mediating microbe-microbe interactions between human-dwelling commensals are poorly understood. In this commentary, we discuss known and putative mechanisms of interactions between commensals in the gut and how they can be harnessed for improving microbiome-targeting therapeutics and facilitating translation of microbiome research to the clinic.

In Vitro Profiling of Antitubercular Compounds by Rapid, Efficient, and Nondestructive Assays Using Autoluminescent Mycobacterium tuberculosis

Anti-infective drug discovery is greatly facilitated by the availability of in vitro assays that are more proficient at predicting the preclinical success of screening hits. Tuberculosis (TB) drug discovery is hindered by the relatively slow growth rate of Mycobacterium tuberculosis and the use of whole-cell-based in vitro assays that are inherently time-consuming, and for these reasons, rapid, noninvasive bioluminescence-based assays have been widely used in anti-TB drug discovery and development. In this study, in vitro assays that employ autoluminescent M. tuberculosis were optimized to determine MIC, minimum bactericidal concentration (MBC), time-kill curves, activity against macrophage internalized M. tuberculosis (90% effective concentration [EC₉₀]), and postantibiotic effect (PAE) to provide rapid and dynamic biological information. Standardization of the luminescence-based MIC, MBC, time-kill, EC_90, and PAE assays was accomplished by comparing results of established TB drugs and two ClpC1-targeting TB leads, ecumicin and rufomycin, to those obtained from conventional assays and/or to previous studies. Cumulatively, the use of the various streamlined luminescence-based in vitro assays has reduced the time for comprehensive in vitro profiling (MIC, MBC, time-kill, EC_90, and PAE) by 2 months. The luminescence-based in vitro MBC and EC₉₀ assays yield time and concentration-dependent kill information that can be used for pharmacokinetic-pharmacodynamic (PK-PD) modeling. The MBC and EC₉₀ time-kill graphs revealed a significantly more rapid bactericidal activity for ecumicin than rufomycin. The PAEs of both ecumicin and rufomycin were comparable to that of the first-line TB drug rifampin. The optimization of several nondestructive, luminescence-based TB assays facilitates the in vitro profiling of TB drug leads in an efficient manner.

Efficacy of Topical Vancomycin- and Gentamicin-Loaded Calcium Sulfate Beads or Systemic Antibiotics in Eradicating Polymicrobial Biofilms Isolated from Diabetic Foot Infections within an In Vitro Wound Model

Diabetic foot ulcers are notoriously difficult to heal, with ulcers often becoming chronic, in many cases leading to amputation despite weeks or months of antibiotic therapy in addition to debridement and offloading. Alternative wound biofilm management options, such as topical rather than systemic delivery of antimicrobials, have been investigated by clinicians in order to improve treatment outcomes. Here, we collected blood and tissue from six subjects with diabetic foot infections, measured the concentrations of antibiotics in the samples after treatment, and compared the microbiota within the tissue before treatment and after 7 days of antibiotic therapy. We used an in vitro model of polymicrobial biofilm infection inoculated with isolates from the tissue we collected to simulate different methods of antibiotic administration by simulated systemic therapy or topical release from calcium sulfate beads. We saw no difference in biofilm bioburden in the models after simulated systemic therapy (representative of antibiotics used in the clinic), but we did see reductions in bioburden of between 5 and 8 logs in five of the six biofilms that we tested with topical release of antibiotics via calcium sulfate beads. Yeast is insensitive to antibiotics and was a component of the sixth biofilm. These data support further studies of the topical release of antibiotics from calcium sulfate beads in diabetic foot infections to combat the aggregate issues of infectious organisms taking the biofilm mode of growth, compromised immune involvement, and poor systemic delivery of antibiotics via the bloodstream to the site of infection in patients with diabetes.

Clostridioides difficile-Associated Antibiotics Alter Human Mucosal Barrier Functions by Microbiome-Independent Mechanisms

A clinically relevant risk factor for Clostridioides difficile-associated disease (CDAD) is recent antibiotic treatment. Although broad-spectrum antibiotics have been shown to disrupt the structure of the gut microbiota, some antibiotics appear to increase CDAD risk without being highly active against intestinal anaerobes, suggesting direct nonantimicrobial effects. We examined cell biological effects of antibiotic exposure that may be involved in bacterial pathogenesis using an in vitro germfree human colon epithelial culture model. We found a marked loss of mucosal barrier and immune function with exposure to the CDAD-associated antibiotics clindamycin and ciprofloxacin, distinct from the results of pretreatment with an antibiotic unassociated with CDAD, tigecycline, which did not reduce innate immune or mucosal barrier functions. Importantly, pretreatment with CDAD-associated antibiotics sensitized mucosal barriers to C. difficile toxin activity in primary cell-derived enteroid monolayers. These data implicate commensal-independent gut mucosal barrier changes in the increased risk of CDAD with specific antibiotics and warrant further studies in in vivo systems. We anticipate this work to suggest potential avenues of research for host-directed treatment and preventive therapies for CDAD.

Reactive Oxygen Species Production Is a Major Factor Directing the Postantibiotic Effect of Fluoroquinolones in Streptococcus pneumoniae

We studied the molecular mechanisms involved in the postantibiotic effect of the fluoroquinolones levofloxacin and moxifloxacin in Streptococcus pneumoniae Wild-type strain R6 had postantibiotic effects of 2.05 ± 0.10 h (mean ± standard deviation [SD]) and 3.23 ± 0.45 h at 2.5× and 10× MIC of levofloxacin, respectively. Moxifloxacin exhibited lower effects of 0.87 ± 0.1 and 2.41 ± 0.29 h at 2.5× and 10× MIC, respectively. Fluoroquinolone-induced chromosome fragmentation was measured at equivalent postantibiotic effects for levofloxacin (2.5× MIC) and moxifloxacin (10× MIC). After 2 h of drug removal, reductions were approximately 7-fold for levofloxacin and 3-fold for moxifloxacin, without further decreases at later times. Variations in reactive oxygen species production were detected after 4 to 6 h of drug withdrawals, with decreases ≥400-fold for levofloxacin and ≥800-fold for moxifloxacin at 6 h. In accordance, after 4 to 6 h of drug withdrawal, the levofloxacin-induced upregulation of the fatCDEB operon, introducing iron in the bacteria, decreased up to 2- to 3-fold, and the moxifloxacin-induced upregulation of several genes involved in the production of pyruvate was reduced 3- to 7-fold. In accordance, lower postantibiotic effects (up to 1 h) were observed in strain R6 ΔspxB, lacking the main enzyme involved in oxygen peroxide production, than in R6. Although no change in the recovery of chromosome fragmentation was observed between R6 and R6 ΔspxB, 3.5 × 10³-fold lower reactive oxygen species production was observed in R6 ΔspxB, without changes after drug removal. These results show that reactive oxygen species are the main factors directing the postantibiotic effect of levofloxacin and moxifloxacin in S. pneumoniae.

Postantibiotic and Sub-MIC Effects of Exebacase (Lysin CF-301) Enhance Antimicrobial Activity against Staphylococcus aureus

CF-301 (exebacase) is a recombinantly produced bacteriophage-derived lysin (cell wall hydrolase) and is the first agent of this class to enter clinical development in the United States for treating bacteremia including endocarditis due to Staphylococcus aureus Whereas rapid bactericidal activity is the hallmark in vitro and in vivo response to CF-301 at exposures higher than the MIC, prolonged antimicrobial activity, mediated by cell wall damage, is predicted at concentrations less than the MIC. In the current study, a series of in vitro pharmacodynamic parameters, including the postantibiotic effect (PAE), postantibiotic sub-MIC effect (PA-SME), and sub-MIC effect (SME), were studied to determine how short-duration and sub-MIC CF-301 exposures affect the growth of surviving staphylococci and extend its antimicrobial activity. Mean PAE, PA-SME, and SME values up to 4.8, 9.3, and 9.8 h, respectively, were observed against 14 staphylococcal strains tested in human serum; growth delays were extended by 6 h in the presence of daptomycin. Exposures to CF-301 at sub-MIC levels as low as 0.001× to 0.01× MIC (∼1 to 10 ng/ml) resulted in aberrant cell wall ultrastructure, increased membrane permeability, dissipation of membrane potential, and inhibition of virulence phenotypes, including agglutination and biofilm formation. A mouse thigh infection model designed to study the PAE was used to confirm our findings and demonstrate in vivo growth delays of ≥19.3 h. Our findings suggest that at CF-301 concentrations less than the MIC during therapeutic use, sustained reductions in bacterial fitness and virulence may substantially enhance efficacy.

Effects of Ceftiofur and Chlortetracycline on the Resistomes of Feedlot Cattle

Treatment of food-producing animals with antimicrobial drugs (AMD) is controversial because of concerns regarding promotion of antimicrobial resistance (AMR). To investigate this concern, resistance genes in metagenomic bovine fecal samples during a clinical trial were analyzed to assess the impacts of treatment on beef feedlot cattle resistomes. Four groups of cattle were exposed, using a 2-by-2 factorial design, to different regimens of antimicrobial treatment. Injections of ceftiofur crystalline-free acid (a third-generation cephalosporin) were used to treat all cattle in treatment pens or only a single animal, and either chlortetracycline was included in the feed of all cattle in a pen or the feed was untreated. On days 0 and 26, respectively, pre- and posttrial fecal samples were collected, and resistance genes were characterized using shotgun metagenomics. Treatment with ceftiofur was not associated with changes to β-lactam resistance genes. However, cattle fed chlortetracycline had a significant increase in relative abundance of tetracycline resistance genes. There was also an increase of an AMR class not administered during the study, which is a possible indicator of coselection of resistance genes. Samples analyzed in this study had previously been evaluated by culture characterization (Escherichia coli and Salmonella) and quantitative PCR (qPCR) of metagenomic fecal DNA, which allowed comparison of results with this study. In the majority of samples, genes that were selectively enriched through culture and qPCR were not identified through shotgun metagenomic sequencing in this study, suggesting that changes previously documented did not reflect changes affecting the majority of bacterial genetic elements found in the predominant fecal resistome.IMPORTANCE Despite significant concerns about public health implications of AMR in relation to use of AMD in food animals, there are many unknowns about the long- and short-term impact of common uses of AMD for treatment, control, and prevention of disease. Additionally, questions commonly arise regarding how to best measure and quantify AMR genes in relation to public health risks and how to determine which genes are most important. These data provide an introductory view of the utility of using shotgun metagenomic sequencing data as an outcome for clinical trials evaluating the impact of using AMD in food animals.

Long-Term Exposure of Agricultural Soil to Veterinary Antibiotics Changes the Population Structure of Symbiotic Nitrogen-Fixing Rhizobacteria Occupying Nodules of Soybeans (Glycine max)

Antibiotics are entrained in agricultural soil through the application of manures from medicated animals. In the present study, a series of small field plots was established in 1999 that receive annual spring applications of a mixture of tylosin, sulfamethazine, and chlortetracycline at concentrations ranging from 0.1 to 10 mg · kg-1 soil. These antibiotics are commonly used in commercial swine production. The field plots were cropped continuously for soybeans, and in 2012, after 14 annual antibiotic applications, the nodules from soybean roots were sampled and the occupying bradyrhizobia were characterized. Nodules and isolates were serotyped, and isolates were distinguished using 16S rRNA gene and 16S to 23S rRNA gene intergenic spacer region sequencing, multilocus sequence typing, and RSα fingerprinting. Treatment with the antibiotic mixture skewed the population of bradyrhizobia dominating the nodule occupancy, with a significantly larger proportion of Bradyrhizobium liaoningense organisms even at the lowest dose of 0.1 mg · kg-1 soil. Likewise, all doses of antibiotics altered the distribution of RSα fingerprint types. Bradyrhizobia were phenotypically evaluated for their sensitivity to the antibiotics, and there was no association between in situ treatment and a decreased sensitivity to the drugs. Overall, long-term exposure to the antibiotic mixture altered the composition of bradyrhizobial populations occupying nitrogen-fixing nodules, apparently through an indirect effect not associated with the sensitivity to the drugs. Further work evaluating agronomic impacts is warranted.IMPORTANCE Antibiotics are entrained in agricultural soil through the application of animal or human waste or by irrigation with reused wastewater. Soybeans obtain nitrogen through symbiotic nitrogen fixation. Here, we evaluated the impact of 14 annual exposures to antibiotics commonly used in swine production on the distribution of bradyrhizobia occupying nitrogen-fixing nodules on soybean roots in a long-term field experiment. By means of various sequencing and genomic fingerprinting techniques, the repeated exposure to a mixture of tylosin, sulfamethazine, and chlortetracycline each at a nominal soil concentration of 0.1 mg · kg-1 soil was found to modify the diversity and identity of bradyrhizobia occupying the nodules. Nodule occupancy was not associated with the level of sensitivity to the antibiotics, indicating that the observed effects were not due to the direct toxicity of the antibiotics on bradyrhizobia. Altogether, these results indicate the potential for long-term impacts of antibiotics on this agronomically important symbiosis.

Drug detoxification dynamics explain the postantibiotic effect

The postantibiotic effect (PAE) refers to the temporary suppression of bacterial growth following transient antibiotic treatment. This effect has been observed for decades for a wide variety of antibiotics and microbial species. However, despite empirical observations, a mechanistic understanding of this phenomenon is lacking. Using a combination of modeling and quantitative experiments, we show that the PAE can be explained by the temporal dynamics of drug detoxification in individual cells after an antibiotic is removed from the extracellular environment. These dynamics are dictated by both the export of the antibiotic and the intracellular titration of the antibiotic by its target. This mechanism is generally applicable for antibiotics with different modes of action. We further show that efflux inhibition is effective against certain antibiotic motifs, which may help explain mixed cotreatment success.

Gepotidacin (GSK2140944) In Vitro Activity against Gram-Positive and Gram-Negative Bacteria

Gepotidacin is a first-in-class, novel triazaacenaphthylene antibiotic that inhibits bacterial DNA replication and has in vitro activity against susceptible and drug-resistant pathogens. Reference in vitro methods were used to investigate the MICs and minimum bactericidal concentrations (MBCs) of gepotidacin and comparator agents for Staphylococcus aureus, Streptococcus pneumoniae, and Escherichia coli Gepotidacin in vitro activity was also evaluated by using time-kill kinetics and broth microdilution checkerboard methods for synergy testing and for postantibiotic and subinhibitory effects. The MIC₉₀ of gepotidacin for 50 S. aureus (including methicillin-resistant S. aureus [MRSA]) and 50 S. pneumoniae (including penicillin-nonsusceptible) isolates was 0.5 μg/ml, and for E. coli (n = 25 isolates), it was 4 μg/ml. Gepotidacin was bactericidal against S. aureus, S. pneumoniae, and E. coli, with MBC/MIC ratios of ≤4 against 98, 98, and 88% of the isolates tested, respectively. Time-kill curves indicated that the bactericidal activity of gepotidacin was observed at 4× or 10× MIC at 24 h for all of the isolates. S. aureus regrowth was observed in the presence of gepotidacin, and the resulting gepotidacin MICs were 2- to 128-fold higher than the baseline gepotidacin MICs. Checkerboard analysis of gepotidacin combined with other antimicrobials demonstrated no occurrences of antagonism with agents from multiple antimicrobial classes. The most common interaction when testing gepotidacin was indifference (fractional inhibitory concentration index of >0.5 to ≤4; 82.7% for Gram-positive isolates and 82.6% for Gram-negative isolates). The postantibiotic effect (PAE) of gepotidacin was short when it was tested against S. aureus (≤0.6 h against MRSA and MSSA), and the PAE-sub-MIC effect (SME) was extended (>8 h; three isolates at 0.5× MIC). The PAE of levofloxacin was modest (0.0 to 2.4 h), and the PAE-SME observed varied from 1.2 to >9 h at 0.5× MIC. These in vitro data indicate that gepotidacin is a bactericidal agent that exhibits a modest PAE and an extended PAE-SME against Gram-positive and -negative bacteria and merits further study for potential use in treating infections caused by these pathogens.

In Vitro Activity of Gepotidacin (GSK2140944) against Neisseria gonorrhoeae

Gepotidacin (formerly GSK2140944) is a novel, first-in-class, triazaacenaphthylene antibacterial that inhibits bacterial DNA gyrase and topoisomerase IV via a unique mechanism and has demonstrated in vitro activity against Neisseria gonorrhoeae, including drug-resistant strains, and also targets pathogens associated with other conventional and biothreat infections. Broth microdilution was used to evaluate the MIC and minimum bactericidal concentration (MBC) activity of gepotidacin and comparators against 25 N. gonorrhoeae strains (including five ciprofloxacin-nonsusceptible strains). Gepotidacin activity was also evaluated against three N. gonorrhoeae strains (including a ciprofloxacin-nonsusceptible strain) for resistance development, against three N. gonorrhoeae strains (including two tetracycline- and azithromycin-nonsusceptible strains) using time-kill kinetics and checkerboard methods, and against two N. gonorrhoeae strains for the investigation of postantibiotic (PAE) and subinhibitory (PAE-SME) effects. The MIC₅₀ and MIC₉₀ for gepotidacin against the 25 N. gonorrhoeae isolates tested were 0.12 and 0.25 μg/ml, respectively. The MBC₅₀ and MBC₉₀ for gepotidacin were 0.25 and 0.5 μg/ml, respectively. Gepotidacin was bactericidal, and single-step resistance selection studies did not recover any mutants, indicating a low rate of spontaneous single-step resistance. For combinations of gepotidacin and comparators tested using checkerboard methods, there were no instances where antagonism occurred and only one instance of synergy (with moxifloxacin; fractional inhibitory concentration, 0.375). This was not confirmed by in vitro time-kill studies. The PAE for gepotidacin against the wild-type strain ranged from 0.5 to >2.5 h, and the PAE-SME was >2.5 h. These in vitro data indicate that further study of gepotidacin is warranted for potential use in treating infections caused by N. gonorrhoeae.

Bacterial Lysis through Interference with Peptidoglycan Synthesis Increases Biofilm Formation by Nontypeable Haemophilus influenzae

Most, if not all, bacteria form a biofilm, a multicellular structure that protects them from antimicrobial actions of the host immune system and affords resistance to antibiotics. The latter is especially disturbing with the increase in multiresistant bacterial clones worldwide. Bacterial biofilm formation is a multistep process that starts with surface adhesion, after which attached bacteria divide and give rise to biomass. The actual steps required for Haemophilus influenzae biofilm formation are largely not known. We show that interference with peptidoglycan biosynthesis increases biofilm formation because of the release of bacterial genomic DNA. Subinhibitory concentrations of β-lactam antibiotics, which are often prescribed to treat H. influenzae infections, increase biofilm formation through a similar mechanism. Therefore, when β-lactam antibiotics do not reach their MIC in vivo, they might not only drive selection for β-lactam-resistant clones but also increase biofilm formation and resistance to other antimicrobial compounds.

Nontypeable Haemophilus influenzae (NTHi) is an opportunistic pathogen that mainly causes otitis media in children and community-acquired pneumonia or exacerbations of chronic obstructive pulmonary disease in adults. A large variety of studies suggest that biofilm formation by NTHi may be an important step in the pathogenesis of this bacterium. However, the underlying mechanisms involved in this process are poorly elucidated. In this study, we used a transposon mutant library to identify bacterial genes involved in biofilm formation. The growth and biofilm formation of 4,172 transposon mutants were determined, and the involvement of the identified genes in biofilm formation was validated in in vitro experiments. Here, we present experimental data showing that increased bacterial lysis, through interference with peptidoglycan synthesis, results in elevated levels of extracellular DNA, which increased biofilm formation. Interestingly, similar results were obtained with subinhibitory concentrations of β-lactam antibiotics, known to interfere with peptidoglycan synthesis, but such an effect does not appear with other classes of antibiotics. These results indicate that treatment with β-lactam antibiotics, especially for β-lactam-resistant NTHi isolates, might increase resistance to antibiotics by increasing biofilm formation.

IMPORTANCE Most, if not all, bacteria form a biofilm, a multicellular structure that protects them from antimicrobial actions of the host immune system and affords resistance to antibiotics. The latter is especially disturbing with the increase in multiresistant bacterial clones worldwide. Bacterial biofilm formation is a multistep process that starts with surface adhesion, after which attached bacteria divide and give rise to biomass. The actual steps required for Haemophilus influenzae biofilm formation are largely not known. We show that interference with peptidoglycan biosynthesis increases biofilm formation because of the release of bacterial genomic DNA. Subinhibitory concentrations of β-lactam antibiotics, which are often prescribed to treat H. influenzae infections, increase biofilm formation through a similar mechanism. Therefore, when β-lactam antibiotics do not reach their MIC in vivo, they might not only drive selection for β-lactam-resistant clones but also increase biofilm formation and resistance to other antimicrobial compounds.

The postantibiotic effect and post-β-lactamase-inhibitor effect of ceftazidime, ceftaroline and aztreonam in combination with avibactam against target Gram-negative bacteria

The magnitudes of the postantibiotic effect (PAE) and post-β-lactamase-inhibitory effect (PLIE) of ceftazidime-avibactam, ceftaroline-avibactam, and aztreonam-avibactam were determined against isolates of Enterobacteriaceae and Pseudomonas aeruginosa that either harboured genes encoding serine and/or metallo-β-lactamases, or did not harbour bla genes. The bla genes included ones that encoded extended spectrum β-lactamases, AmpC and KPC β-lactamases, and one metallo-β-lactamase, NDM-1. No substantial PAE was observed for any combination against any isolate. One substantial PLIE was found: a value of 1·9 h for ceftazidime-avibactam against Klebsiella pneumoniae (blaKPC-2 ). From comparison with results in the literature, we propose that the existence of a substantial PLIE depends on the bacterial isolate and on the specific β-lactamase inhibitor and β-lactam combination.

SIGNIFICANCE AND IMPACT OF THE STUDY

A wave of new β-lactamase inhibitors is entering either therapeutic use or clinical trials. The present work characterizes the postantibiotic effect (PAE) and post-β-lactamase-inhibitory effect (PLIE) of the clinically most advanced of these compounds, avibactam. We show that the existence of a measurable PLIE is strain- (and possibly compound-) dependent, and cannot be relied upon as a standard component of the primary pharmacology of a new β-lactamase inhibitor. This variability was not reported in earlier studies of clavulanic acid or sulbactam.

Extended-Interval Aminoglycoside Use in Cystic Fibrosis Exacerbation in Children and Young Adults: A Prospective Quality Improvement Project

This is a prospective quality improvement project for patients with cystic fibrosis who are 5 years of age and older who were admitted for intravenous antibiotic administration as part of treatment of cystic fibrosis exacerbation. The goal of this project was to compare the pharmacokinetics of once-daily versus thrice-daily aminoglycoside use when treating cystic fibrosis exacerbation in different age groups. Of the total of 119 patient encounters, 82.4% were started on once-daily dosing, and the remainder were started on thrice-daily dosing. Patients with pharmacokinetics allowing the continuation of once-daily dosing differed from patients who required a switch to thrice-daily dosing in terms of baseline forced expiratory volume in 1 second, forced expiratory flow from 25% to 75% of vital capacity, age, and body mass index (BMI) but were similar in BMI percentiles. The once-daily dosing group had higher mean 18-hour level, higher mean half-life, higher mean area under the curve, and lower mean elimination constant. This study showed that aminoglycoside clearance is higher in younger children.

Postantibiotic effect and postantibiotic sub-minimum inhibitory concentration effect of valnemulin against Staphylococcus aureus isolates from swine and chickens

The postantibiotic effect (PAE) and postantibiotic sub-minimum inhibitory concentration (MIC) effect (PA-SME) of valnemulin against Staphylococcus aureus were investigated in vitro using a spectrophotometric technique and classic viable count method. A standard curve was constructed by regression analysis of the number of colonies and the corresponding optical density (OD) at 630 nm of the inoculum. After exposure to valnemulin at different concentrations for an hour, the antibiotic was removed by centrifuging and washing. The PA-SMEs were measured after initial exposure to valnemulin at 4 × the MIC, and then, valnemulin was added to reach corresponding desired concentrations in the resuspended culture. Samples were collected hourly until the culture became turbid. The results were calculated by converting the OD values into the counts of bacteria in accordance with the curve. The MIC of valnemulin against eight strains was identically 0.125 μg ml(-1) . The mean PAEs were 2.12 h (1 × MIC) and 5.06 h (4 × MIC), and the mean PA-SMEs were 6.85 h (0.1 × MIC), 9.12 h (0.2 × MIC) and 10.8 h (0.3 × MIC). The results showed that the strains with identical MICs exhibited different PAEs and PA-SMEs. Valnemulin produced prolonged PAE and PA-SME periods for Staph. aureus, supporting a longer dosing interval while formulating a daily administration dosage.

SIGNIFICANCE AND IMPACT OF THE STUDY

In this study, valnemulin demonstrated prolonged postantibiotic effects and postantibiotic sub-MIC effects on strains of Staphylococcus aureus. The strains with identical MICs of valnemulin exhibited different PAEs and PA-SMEs. Staphylococcus aureus isolated from different species has little impact on the postantibiotic effect of valnemulin. The result suggests a longer dosing interval while formulating a daily administration dosage, and it may play a valuable role of valnemulin in treating Staph. aureus infections in animals.