In vivo impact of the MexAB-OprM efflux system on β-lactam efficacy in an experimental model of Pseudomonas aeruginosa infection

A systematic review of optimal pharmacokinetic/pharmacodynamic parameters for beta-lactam therapy in infective endocarditis

BACKGROUND

Beta-lactam antibiotics are the mainstay of therapy for most bacterial causes of infective endocarditis (IE). Traditionally considered as agents with a broad therapeutic index, there is increasing recognition that standard doses may be subtherapeutic or toxic in critically ill patients. Optimizing therapy for efficacy requires a defined pharmacokinetic (PK)/pharmacodynamic (PD) target associated with clinical and microbiological cure.

OBJECTIVES

To elucidate the factors that influence beta-lactam PK and PD variability in IE and to examine optimal PK/PD target parameters for therapy.

METHODS

The review was conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Clinical and laboratory in vivo animal or human studies examining PK and/or PD of beta-lactam antibiotics in IE were eligible. Ovid MEDLINE, Embase and Cochrane Central Registry were searched using defined terms. The Office of Health Assessment and Translation (OHAT) tool was used for assessing risk of bias.

RESULTS

From 2677 abstracts, 62 articles were selected for review and synthesis, comprising: 45 animal studies investigating the broad categories of beta-lactam diffusion into vegetations, PK/PD determinants of outcome, mode of antibiotic delivery and synergistic impact of agents; and 17 human studies totalling 347 participants. Findings supported the importance of time-dependent killing for beta-lactams but heterogeneous data limited the determination of an optimal PK/PD target for IE treatment.

CONCLUSION

Beta-lactam PK and PD in endocarditis are variable and specific to the particular antibiotic-organism combination. Time-dependent killing is important, consistent with non-endocarditis studies, but there is little agreement on optimal drug exposure. Clinical studies examining PK/PD targets in endocarditis are required to further inform drug selection and dosing.

Ceftolozane-Tazobactam in the Treatment of Experimental Pseudomonas aeruginosa Pneumonia in Persistently Neutropenic Rabbits: Impact on Strains with Genetically Defined Mechanisms of Resistance

Ceftolozane-tazobactam (C/T) is a novel cephalosporin with in vitro activity against Pseudomonas aeruginosa that is resistant to extended-spectrum penicillins and antipseudomonal cephalosporins. In order to assess the antimicrobial effect of C/T in treatment of Pseudomonas pneumonia, we investigated the pharmacokinetics and efficacy of C/T in persistently neutropenic rabbits. Pseudomonas pneumonia was established by direct endotracheal inoculation. Treatment groups consisted of C/T, ceftazidime (CAZ), piperacillin-tazobactam (TZP), and untreated controls (UC). Rabbits received a dosage of C/T of 80 mg/kg every 4 h (q4h) intravenously (i.v.) (53 mg/kg ceftolozane/26 mg/kg tazobactam) to match the free drug time above the MIC as well as a comparable plasma area under the concentration-time curve (AUC) (humanized doses of ceftolozane-tazobactam of 3 g [2 g/1 g]) q8h, due to the more rapid elimination of ceftolozane in rabbits (0.75 h) than in humans (2.5 h). Four molecularly characterized clinical P. aeruginosa isolates from patients with pneumonia were studied, including one isolate from each classification group: pan-susceptible (PS), outer membrane porin D (OPRD) porin loss (OPRDPL), efflux pump expression (EPE), and AmpC hyperexpression (ACHE). Treatment was continued for 12 days. Treatment with ceftolozane-tazobactam resulted in a ≥10⁵ reduction in residual pulmonary and bronchoalveolar lavage (BAL) fluid bacterial burdens caused by all 4 strains (P ≤ 0.01). This antibacterial activity coincided with reduction of lung weight (an organism-mediated pulmonary injury marker) (P < 0.05). CAZ was less active in ACHE-infected rabbits, and TZP had less activity against EPE, ACHE, and OPRDPL strains. Survival was prolonged in the C/T and CAZ treatment groups in comparison to the TZP and UC groups (P < 0.001). Ceftolozane-tazobactam is highly active in treatment of experimental P. aeruginosa pneumonia in persistently neutropenic rabbits, including infections caused by strains with the most common resistance mechanisms.

The challenge of efflux-mediated antibiotic resistance in Gram-negative bacteria

The global emergence of multidrug-resistant Gram-negative bacteria is a growing threat to antibiotic therapy. The chromosomally encoded drug efflux mechanisms that are ubiquitous in these bacteria greatly contribute to antibiotic resistance and present a major challenge for antibiotic development. Multidrug pumps, particularly those represented by the clinically relevant AcrAB-TolC and Mex pumps of the resistance-nodulation-division (RND) superfamily, not only mediate intrinsic and acquired multidrug resistance (MDR) but also are involved in other functions, including the bacterial stress response and pathogenicity. Additionally, efflux pumps interact synergistically with other resistance mechanisms (e.g., with the outer membrane permeability barrier) to increase resistance levels. Since the discovery of RND pumps in the early 1990s, remarkable scientific and technological advances have allowed for an in-depth understanding of the structural and biochemical basis, substrate profiles, molecular regulation, and inhibition of MDR pumps. However, the development of clinically useful efflux pump inhibitors and/or new antibiotics that can bypass pump effects continues to be a challenge. Plasmid-borne efflux pump genes (including those for RND pumps) have increasingly been identified. This article highlights the recent progress obtained for organisms of clinical significance, together with methodological considerations for the characterization of MDR pumps.

oprM as a new target for reversion of multidrug resistance in Pseudomonas aeruginosa by antisense phosphorothioate oligodeoxynucleotides

Multidrug-resistant Pseudomonas aeruginosa (MDR-PA) is one of the leading Gram-negative organisms associated with nosocomial infections. The increasing frequency of MDR-PA has represented a huge challenge in conventional antibacterial therapy. The loss of effectiveness of commonly used antibiotics calls for the immediate need to develop an alternative strategy for combating MDR-PA infections. The multiantibiotic resistance of MDR-PA is largely attributable to the production of multidrug efflux pumps, MexAB-OprM. OprM forms the antibiotic-ejecting duct and plays a crucial role in exporting incoming chemotherapeutic agents across the membranes. Disruption of the OprM expression may inhibit the function of multidrug efflux pumps and lead to restoration of MDR-PA susceptibility to antibiotics. In this study, we developed a novel anion liposome for encapsulating and delivering specific anti-oprM phosphorothioate oligodeoxynucleotide (PS-ODN617) and polycation polyethylenimine (PEI) complexes. The additions of the encapsulated anti-oprM PS-ODN617/PEI to MDR-PA isolates caused a significant reduction of oprM expression and inhibition of MDR-PA growth in the presence of piperacillin in a concentration-dependent manner. The encapsulated PS-ODN617 treatment also reduced minimal inhibitory concentrations of five most commonly used antibiotics to the sensitive margin values on MDR-PA clinical isolates, respectively. The results of present study firstly indicate that PS-ODN targeted to oprM can significantly restore the susceptibility of MDR-PA to existing antibiotics, which appears to be a novel strategy for treating MDR-PA infections.

Efficacy of doripenem in the treatment of Pseudomonas aeruginosa experimental pneumonia versus imipenem and meropenem

OBJECTIVES

The aim of this study was to compare doripenem with imipenem and meropenem in an experimental rabbit model of Pseudomonas aeruginosa pneumonia and then to compare different doripenem doses and methods of intravenous administration.

METHODS

Using a rabbit experimental model of pneumonia, efficacy was assessed following 2 days of treatment by colony counts of different tissues (lung, spleen and blood culture).

RESULTS

Mean pulmonary bacterial loads were 3.17 ± 0.53, 3.42 ± 0.61 and 2.75 ± 0.59 log(10) cfu/g for imipenem, doripenem (0.5 g three times daily) and meropenem, respectively, compared with 7.57 ± 0.99 cfu/g for control animals. At a higher dose (1 g three times daily), doripenem showed significantly better efficacy (2.70 ± 0.65 log(10) cfu/g) than the standard regimen of doripenem. Sterilization of spleen cultures was achieved with standard regimens of imipenem (1 g three times daily) and a higher dose of doripenem.

CONCLUSIONS

In this model of P. aeruginosa pneumonia, doripenem had an efficacy equivalent to that of meropenem and imipenem at a high dose of 1 g three times a day and lower efficacy at a standard dose (0.5 g three times daily) than the other two agents in terms of bacteria cultivated from spleens. Doripenem is a new drug that offers new therapeutic options, especially for difficult-to-treat infections such as pneumonia due to non-fermenting Gram-negative bacteria.

Efflux-mediated drug resistance in bacteria: an update

Drug efflux pumps play a key role in drug resistance and also serve other functions in bacteria. There has been a growing list of multidrug and drug-specific efflux pumps characterized from bacteria of human, animal, plant and environmental origins. These pumps are mostly encoded on the chromosome, although they can also be plasmid-encoded. A previous article in this journal provided a comprehensive review regarding efflux-mediated drug resistance in bacteria. In the past 5 years, significant progress has been achieved in further understanding of drug resistance-related efflux transporters and this review focuses on the latest studies in this field since 2003. This has been demonstrated in multiple aspects that include but are not limited to: further molecular and biochemical characterization of the known drug efflux pumps and identification of novel drug efflux pumps; structural elucidation of the transport mechanisms of drug transporters; regulatory mechanisms of drug efflux pumps; determining the role of the drug efflux pumps in other functions such as stress responses, virulence and cell communication; and development of efflux pump inhibitors. Overall, the multifaceted implications of drug efflux transporters warrant novel strategies to combat multidrug resistance in bacteria.