Engineering of Streptoalloteichus tenebrarius 2444 for Sustainable Production of Tobramycin

Tobramycin is a broad-spectrum aminoglycoside antibiotic agent. The compound is obtained from the base-catalyzed hydrolysis of carbamoyltobramycin (CTB), which is naturally produced by the actinomycete Streptoalloteichus tenebrarius. However, the strain uses the same precursors to synthesize several structurally related aminoglycosides. Consequently, the production yields of tobramycin are low, and the compound’s purification is very challenging, costly, and time-consuming. In this study, the production of the main undesired product, apramycin, in the industrial isolate Streptoalloteichus tenebrarius 2444 was decreased by applying the fermentation media M10 and M11, which contained high concentrations of starch and dextrin. Furthermore, the strain was genetically engineered by the inactivation of the aprK gene (∆aprK), resulting in the abolishment of apramycin biosynthesis. In the next step of strain development, an additional copy of the tobramycin biosynthetic gene cluster (BGC) was introduced into the ∆aprK mutant. Fermentation by the engineered strain (∆aprK_1-17L) in M11 medium resulted in a 3- to 4-fold higher production than fermentation by the precursor strain (∆aprK). The phenotypic stability of the mutant without selection pressure was validated. The use of the engineered S. tenebrarius 2444 facilitates a step-saving, efficient, and, thus, more sustainable production of the valuable compound tobramycin on an industrial scale.

241. Rural-urban differences in antibiotic prescribing for uncomplicated urinary tract infections

Background Identification of inappropriate antibiotic prescribing patterns is critical for designing antimicrobial stewardship programs. We sought to examine whether the risk of receipt of an inappropriate outpatient antibiotic prescription varied by rural-urban status among women with an uncomplicated urinary tract infection (UTI). Methods Using the IBM MarketScan Commercial Database, we identified U.S. women 18–44 years diagnosed with a new uncomplicated UTI and prescribed an oral antibiotic with activity against common uropathogens from April 2011 through June 2015. We classified first-line agents (nitrofurantoin, trimethoprim-sulfamethoxazole, and fosfomycin) as appropriate, non-first-line agents (fluoroquinolones and β-lactams) as inappropriate, and antibiotic duration as appropriate when the days’ supply was consistent with Infectious Diseases Society of America 2011 guidelines. Rural-urban status was defined by residence in a metropolitan statistical area. We used modified Poisson regression to determine the association between rural-urban status and inappropriate antibiotic receipt, accounting for patient- and provider-level characteristics. Results Of 670,450 women with uncomplicated UTI, 46.7% of antibiotic prescriptions were written for inappropriate agents and 76.1% for inappropriate durations (Figures 1 and 2). Use of inappropriate agents or durations did not change appreciably over the study period (2011–2013 vs. 2014–2015). Of 507,737 prescriptions with inappropriate duration, 501,496 (98.8%) were written for a days’ supply longer than recommended. Compared to urban women, rural women had similar risk of receipt of an inappropriate agent (adjusted risk ratio 0.99, 95% CI, 0.98–1.00) but were more likely to receive a prescription for an inappropriate duration (adjusted risk ratio 1.10, 95% CI, 1.09–1.11). Figure 1. Distribution of antibiotic agent by rural-urban status Figure 2. Distribution of the antibiotic prescription days’ supply by antibiotic agent and rural-urban status Conclusion Regardless of rural-urban status, the majority of antibiotic prescriptions for uncomplicated UTI were written for inappropriate agents and durations. Rural women were more likely to receive prescriptions with inappropriately long durations. Antimicrobial stewardship interventions are needed to improve outpatient UTI antibiotic prescribing and reduce unnecessary exposure to antibiotics, particularly in rural settings. Disclosures Margaret A. Olsen, PhD, MPH, Merck (Grant/Research Support)Pfizer (Consultant, Grant/Research Support)

Pharmacokinetics of Macrolide Antibiotics and Transport into the Interstitial Fluid: Comparison among Erythromycin, Clarithromycin, and Azithromycin

Recent research has found higher levels and longer total exposure of azithromycin, a macrolide antibiotic agent, in the interstitial fluid of the skin than in the plasma. This unique distribution is expected to contribute to its antimicrobial activity at the primary infection site. However, it remains unclear whether this characteristic distribution in the extracellular tissue space is common to macrolide antibiotics or if it is azithromycin-specific, with most macrolides largely localized intracellularly. In this study, we investigated pharmacokinetic characteristics of erythromycin and clarithromycin in the interstitial fluid of the skin of rats after intravenous drug administration, and compared the results with our previously reported results on azithromycin. Interstitial fluid samples were directly collected from a pore on the skin using a dissolving microneedle array. We found that the total macrolide concentrations in the interstitial fluid were significantly different among three macrolides. The rank order of the interstitial fluid-plasma concentration ratio was azithromycin (3.8 to 4.9) > clarithromycin (1.2 to 1.5) > erythromycin (0.27 to 0.39), and this ratio was stable after dosing, whereas higher drug levels in the skin tissue than in the plasma were observed for all three macrolides. Our results suggest that lower erythromycin concentrations in the interstitial fluid than in the plasma contributes to the emergence of bacterial resistance in the extracellular tissue space. Monitoring of total macrolide concentrations in interstitial fluid may provide valuable information regarding antimicrobial effects and the emergence of bacterial resistance for the development of an appropriate pharmacokinetics–pharmacodynamics-based dosing strategy.

Novel Antibiotics for Multidrug-Resistant Gram-Positive Microorganisms

Increasing multidrug-resistance to Gram-positive pathogens, particularly to staphylococci, enterococci and streptococci, is a major problem, resulting in significant morbidity, mortality and healthcare costs. In recent years, only a small number of novel antibiotics effective against Gram-positive bacteria has been approved. This review will discuss the current evidence for novel branded antibiotics that are highly effective in the treatment of multidrug-resistant infections by Gram-positive pathogens, namely ceftobiprole, ceftaroline, telavancin, oritavancin, dalbavancin, tedizolid, besifloxacin, delafloxacin, ozenoxacin, and omadacycline. The mechanism of action, pharmacokinetics, microbiological spectrum, efficacy and safety profile will be concisely presented. As for any emerging antibiotic agent, resistance is likely to develop against these highly effective antibiotics. Only through appropriate dosing, utilization and careful resistance development monitoring will these novel antibiotics continue to treat Gram-positive pathogens in the future.