Activity of Telavancin against Staphylococcus aureus Isolates, Including Those with Decreased Susceptibility to Ceftaroline, from Cystic Fibrosis Patients

Resistance Profiles and Biological Characteristics of Rifampicin-Resistant Staphylococcus aureus Small-Colony Variants

Background

Staphylococcus aureus (S. aureus) is a major contributor to nosocomial and community-acquired infections. S. aureus small colony variants (SCVs) which changed in relevant phenotype have made more limited and difficult for therapeutic options against S. aureus infections increasingly. Rifampicin is considered as the "last-resort" antibiotic against S. aureus. Our study investigated resistance profiles and biological characteristics of rifampicin-resistant S. aureus SCVs.

Methods

We collected S. aureus SCVs that were selected from 41 rifampicin-resistant clinical isolates. Then, biological characteristics, resistance spectrum, and rifampicin resistance mechanisms of tested S. aureus SCVs and corresponding parental strains were investigated by classic microbiological methods, agar dilution method, polymerase chain reaction (PCR). Moreover, the fitness cost of S. aureus SCVs, including growth, biofilm formation ability, and virulence profile, was also determined by bacterial growth curve assay, biofilm formation assay, and Galleria mellonella infection model.

Results

There were three S. aureus SCVs (JP310 SCVs, JP1450 SCVs, JP1486 SCVs) that were selected from 41 rifampicin-resistant S. aureus. S. aureus SCVs colonies were tiny, with decreased pigmentation, and the hemolysis circle was not obvious compared with corresponding parental strains. And SCVs could not be restored to normal-colony phenotype after hemin, menaquinone, or thymidine supplementation. Different rpoB mutations occurred in JP1486 SCVs. Antimicrobial susceptibility testing revealed MICs of SCVs were higher than corresponding parental strains. Besides, the growth ability and virulence of SCVs were lower, and biofilm formation ability of which increased compared with parental strains.

Conclusion

S. aureus SCVs share the rifampicin resistance mechanisms with parental strains, although there were some differences in the position of rpoB mutations. Moreover, we found that the biological characteristics of SCVs were significantly different from corresponding parental strains. In contrast, decreased susceptibility to other antibiotics of SCVs was observed during phenotype switch. Furthermore, SCVs incur the fitness cost.

Methicillin-Resistant Staphylococcus aureus Infection and Treatment Options

Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of infection worldwide, including a wide array of both hospital- and community-acquired infections-most commonly bacteremia, upper and lower respiratory tract infection, skin and soft-tissue infection, osteomyelitis, and septic arthritis. This chapter describes the epidemiology of MRSA infection, its ability to confer antibiotic resistance and produce a wide array of virulence factors, and its pivotal role in human infection, especially cystic fibrosis. It also provides an introduction to the strategies for treatment of both chronic and acute MRSA infections.

Pharmacokinetics of Telavancin in Adult Patients with Cystic Fibrosis during Acute Pulmonary Exacerbation

Adults with cystic fibrosis (CF) frequently harbor Staphylococcus aureus, which is increasingly antibiotic resistant. Telavancin is a once-daily rapidly bactericidal antibiotic active against methicillin-, linezolid-, and ceftaroline-resistant S. aureus Because CF patients experience alterations in pharmacokinetics, the optimal dose of telavancin in this population is unknown. Adult CF patients (n = 18) admitted for exacerbations received 3 doses of telavancin 7.5 mg/kg of body weight (first 6 patients) or 10 mg/kg (final 12 patients) every 24 h (q24h). Population pharmacokinetic models with and without covariates were fitted using the nonparametric adaptive grid algorithm in Pmetrics. The final model was used to perform 5,000-patient Monte Carlo simulations for multiple telavancin doses. The best fit was a 2-compartment model describing the volume of distribution of the central compartment (V_c ) as a multiple of total body weight (TBW) and the volume of distribution of the central compartment scaled to total body weight (V _θ) normalized by the median observed value (V_c  = V _θ × TBW/52.1) and total body clearance (CL) as a linear function of creatinine clearance (CRCL) (CL = CL_NR + CL_θ × CRCL), where CL_NR represents nonrenal clearance and CL_θ represents the slope term on CRCL to estimate renal clearance. The mean population parameters were as follows: V _θ, 4.92  ± 0.76 liters · kg^-1; CL_NR, 0.59  ± 0.30 liters · h^-1; CL_θ, 5.97 × 10^-3 ± 1.24 × 10^-3; V_p (volume of the peripheral compartment), 3.77  ± 1.41 liters; Q (intercompartmental clearance), 4.08  ± 2.17 liters · h^-1 The free area under the concentration-time curve (fAUC) values for 7.5 and 10 mg/kg were 30  ± 4.6 and 52  ± 12 mg · h/liter, respectively. Doses of 7.5 mg/kg and 10 mg/kg achieved 76.5% and 100% probability of target attainment (PTA) at a fAUC/MIC threshold of >215, respectively, for MIC of ≤0.12 mg/liter. The probabilities of reaching the acute kidney injury (AKI) threshold AUC (763 mg · h · liter^-1) for these doses were 0% and 0.96%, respectively. No serious adverse events occurred. Telavancin 10 mg/kg yielded optimal PTA and minimal risk of AKI, suggesting that this FDA-approved dose is appropriate to treat acute pulmonary exacerbations in CF adults. (The clinical trial discussed in this study has been registered at ClinicalTrials.gov under identifier NCT03172793.).

Efficacy of newly generated short antimicrobial cationic lipopeptides against methicillin-resistant Staphylococcus aureus (MRSA)

INTRODUCTION

Infection caused by methicillin-resistant Staphylococcus aureus (S. aureus) (MRSA) is a serious clinical challenge and research to develop new antimicrobials is imperative.

METHODS

This study investigated the in vitro and in vivo efficacy of the short cationic dialkyl lipopeptides (C₁₀)₂-KKKK-NH₂ and (C₁₂)₂-KKKK-NH₂. The antibacterial efficacy of (C₁₀)₂-KKKK-NH₂ and (C₁₂)₂-KKKK-NH₂ was evaluated in representative clinical methicillin-susceptible S. aureus and MRSA strains by both in vitro (MIC, time-kill curve) and in vivo (wax worms model) approaches.

RESULTS

These studies revealed that both (C₁₀)₂-KKKK-NH₂ and (C₁₂)₂-KKKK-NH₂ have rapid bactericidal activity, with a decrease of > 3 log₁₀ colony forming units (CFU)/mL achieved in the first 6 hours of treatment. Furthermore, (C₁₀)₂-KKKK-NH₂ performed similarly to daptomycin, with a sustained bacterial killing after 24 hours. Wax worms infected and treated with these lipopeptides showed a decreased survival rate of 90% to 50% within the first day of treatment. Scanning electron microscopy determined that the effect of the short lipopeptides in S. aureus was associated with important morphological structural changes that may suggest cell membrane perturbation.

CONCLUSION

These findings suggest that the short lipopeptides (C₁₀)₂-KKKK-NH₂ and (C₁₂)₂-KKKK-NH₂ may be potential new options for treating MRSA infections.

Evolution of resistance mechanisms and biological characteristics of rifampicin-resistant Staphylococcus aureus strains selected in vitro

Background

We aimed to determine the evolutionary pathways of rifampicin resistance in Staphylococcus aureus, and the impact of resistance mutations in the rpoB gene on fitness.

Methods

Three clinical strains and one reference strain were used to select for rifampicin-resistant S. aureus variants. The mutations responsible for rifampicin resistance in all of the selected isolates in vitro were investigated by polymerase chain reaction (PCR) and DNA sequencing. To compare the fitness cost of rpoB mutations against their corresponding original isolates, we performed bacterial growth curve assays, static biofilm assays, in vitro competition experiments and an infection model of Galleria mellonella larvae.

Results

We obtained four rifampicin-resistant S. aureus isolates that showed high levels of resistance to rifampicin with a minimal inhibitory concentration (MIC) of 128 mg/L, and all isolates had a mutation at position 481 (H481F/Y) in RpoB. A broth microdilution assay indicated that mutation of H481F/Y did not affect susceptibility to common antibacterial drugs but slightly increased the vancomycin MIC. To identify the pathways involved in the development of rifampicin resistance, 32 variants (eight mutants for each strain) and four original isolates were selected for gene sequencing. Different generations of isolates were found to harbor various mutations sites. Compared with the corresponding original isolates, an in vitro fitness assay of the variant isolates showed that growth and virulence were reduced, with a statistically significantly decreased fitness, whereas the capacity for biofilm formation was elevated.

Conclusions

Our findings suggested that the acquisition of rifampicin resistance in S. aureus was dynamic and was associated with a significant fitness cost.

Electronic supplementary material

The online version of this article (10.1186/s12866-019-1573-9) contains supplementary material, which is available to authorized users.

Methicillin-resistant Staphylococcus aureus in solid organ transplantation-Guidelines from the American Society of Transplantation Infectious Diseases Community of Practice

These updated guidelines from the American Society of Transplantation Infectious Diseases Community of Practice review the epidemiology, diagnosis, prevention, and management of methicillin-resistant Staphylococcus aureus (MRSA) infections in solid organ transplantation. Despite an increasing armamentarium of antimicrobials active against MRSA, improved diagnostic tools, and overall declining rates of infection, MRSA infections remain a substantial cause of morbidity and mortality in solid organ transplant recipients. Pre- and post-transplant MRSA colonization is a significant risk factor for post-transplant MRSA infection. The preferred initial treatment of MRSA bacteremia remains vancomycin. Hand hygiene, chlorhexidine bathing in the ICU, central-line bundles that focus on reducing unnecessary catheter use, disinfection of patient equipment, and the environment along with antimicrobial stewardship are all aspects of an infection prevention approach to prevent MRSA transmission and decrease healthcare-associated infections.