Methicillin-resistant Staphylococcus aureus infections in ICU patients

Prevalence and antibiotic resistance in bacterial isolates of dogs with ulcerative keratitis in São Paulo State, Brazil

OBJECTIVE

Identify microorganisms present in canine eyes affected by ulcerative keratitis and assess its resistance profile to available antimicrobial drugs.

METHODS

Samples were collected from 88 canine eyes that exhibited ulcerative keratitis. They were identified using MALDI-TOF and subjected to antimicrobial susceptibility testing by disk diffusion.

RESULTS

Among the assessed subjects, brachycephalic dogs accounted for 74.48% (50/83) of the evaluated canines. Among the 88 evaluated eyes, 90.9% (80/88) showed positive cultures, with 11.33% (10/88) of the samples isolating more than one species of bacteria. Of all bacterial isolates identified (90), Gram-positive bacteria accounted for 63.33% (57/90), while Gram-negative bacteria constituted 36.66% (33/90), with predominance of Staphylococcus spp. at 35.55% (32/90) being, Staphylococcus pseudintermedius at 68.75% (22/32), and Pseudomonas aeruginosa at 15.55% (14/90), respectively. Staphylococcus spp. exhibited resistance to penicillin (89.29%), sulfadiazine and trimethoprim (60.71%), and tetracycline (67.86%), while doxycycline (88.89%), cefotaxime (85.71%), chloramphenicol (82.14%), gentamicin, and moxifloxacin (78.57%) showed the highest sensitivity rates. Pseudomonas aeruginosa displayed sensitivity (100%) to gentamicin and imipenem, and resistance (8.33%) to norfloxacin, ciprofloxacin, and cefepime. Similarly, the Enterobacteriaceae family showed higher sensitivity to amikacin and gentamicin (88.89%), imipenem (88.24%), and levofloxacin (87.5%), with pronounced resistance to amoxicillin-clavulanate (50%) and cefazolin (47.06%). This highlights multiresistance in 23.33% (21/90) of the isolates.

CONCLUSIONS

The most isolated species in canine ulcerative keratitis are S. pseudintermedius and P. aeruginosa. However, other species were also isolated, demonstrating diversity in ocular microbiota infection. There is a high-rate multidrug resistance associated with canine ulcerative keratitis. Nevertheless, these strains exhibited sensitivity to antimicrobials commonly used in veterinary ophthalmology.

Methicillin Resistant Staphylococcus aureus and public fomites: a review

Staphylococcus genus is a Gram-positive coccus normally associated with skin and mucous membranes of warm-blooded animals. It is part of the commensal human microflora, or found in animals, or contaminating surfaces in the community and hospital settings. Staphylococcus aureus is the most pathogenic species belonging to this genus, as it possesses a collection of virulence factors that are expressed solely to evade the immune system. The increase in the misuse of antimicrobial agents predisposed S. aureus to develop antibiotic resistance, including the resistance to methicillin which led to the emergence of Methicillin-Resistant S. aureus (MRSA). MRSA is considered one of the most dangerous nosocomial pathogens causing many hard to treat infections in hospitals and was named as Hospital Associated MRSA (HA-MRSA). Over the past 20-25 years, MRSA was isolated from community settings and thus Community Associated MRSA (CA-MRSA) has emerged. Inside hospitals, MRSA has been isolated from fomites in contact with patients, as well as staff's protective and personal items. This review highlights the worldwide prevalence of MRSA on fomites within the contexts of hospital and community settings.

Fresh Garlic Extract Enhances the Antimicrobial Activities of Antibiotics on Resistant Strains in Vitro

Background:

Infections caused by strains with multi-drug resistance are difficult to treat with standard antibiotics. Garlic is a powerful remedy to protect against infections of many bacteria, fungi and viruses. However, little is known about the potentials of fresh garlic extract (FGE) to improve the sensitivity of multi-drug resistant strains to antibiotics.

Objectives:

In this study, we used the disk diffusion method to investigate the antimicrobial activities of FGE and the combination of antibiotics with FGE, on methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa and Candida albicans, to evaluate the interactions between antibiotics and FGE.

Materials and Methods:

Clinical isolates were isolated from clinical specimens obtained from the inpatients at the First Affiliated Hospital of Xi’an Jiaotong University Health Science Center. The isolates consisted of MRSA, (n = 30), C. albicans (n = 30) and P. aeruginosa (n = 30). Quality control for CLSI (Clinical and Laboratory Standards Institute) disk diffusion was performed using S. aureus ATCC®25923, C. albicans ATCC®90028 and P. aeruginosa ATCC®27853. The 93 microorganisms were divided into four groups in a factorial design: control (deionized water), FGE, antibiotics without FGE, and antibiotics with FGE. Next, antibacterial activity was evaluated by measuring the diameter of inhibition zones according to performance standards for antimicrobial susceptibility testing of the Clinical and Laboratory Standards Institute (CLSI, formerly NCCLS).

Results:

Fresh garlic extract displayed evident inhibition properties against C. albicans and MRSA, yet weak inhibition properties against P. aeruginosa. Additionally, FGE showed the potential to improve the effect of antibiotics on antibiotic resistant pathogens. The synergism of fluconazole and itraconazole with FGE on C. albicans yielded larger sized inhibition zones compared with fluconazole and itraconazole without FGE (P < 0.01). The factorial analysis represents intense positive interaction effects (P < 0.01). The synergism of cefotaxime and ceftriaxone with FGE on P. aeruginosa yielded larger sized inhibition zones than cefotaxime and ceftriaxone without FGE (P < 0.01). The factorial analysis represents intense positive interaction effects (P < 0.01).

Conclusions:

The results suggest that FGE can improve the antibiotic sensitivity of these pathogens to some antibiotics.

Monte Carlo simulation analysis of ceftobiprole, dalbavancin, daptomycin, tigecycline, linezolid and vancomycin pharmacodynamics against intensive care unit-isolated methicillin-resistant Staphylococcus aureus

The aim of the present study was to compare the potential of ceftobiprole, dalbavancin, daptomycin, tigecycline, linezolid and vancomycin to achieve their requisite pharmacokinetic/pharmacodynamic (PK/PD) targets against methicillin-resistant Staphylococcus aureus isolates collected from intensive care unit (ICU) settings. Monte Carlo simulations were carried out to simulate the PK/PD indices of the investigated antimicrobials. The probability of target attainment (PTA) was estimated at minimum inhibitory concentration values ranging from 0.03 to 32 μg/mL to define the PK/PD susceptibility breakpoints. The cumulative fraction of response (CFR) was computed using minimum inhibitory concentration data from the Canadian National Intensive Care Unit study. Analysis of the simulation results suggested the breakpoints of 4 μg/mL for ceftobiprole (500 mg/2 h t.i.d.), 0.25 μg/mL for dalbavancin (1000 mg), 0.12 μg/mL for daptomycin (4 mg/kg q.d. and 6 mg/kg q.d.) and tigecycline (50 mg b.i.d.), and 2 μg/mL for linezolid (600 mg b.i.d.) and vancomycin (1 g b.i.d. and 1.5 g b.i.d.). The estimated CFR were 100, 100, 70.6, 88.8, 96.5, 82.4, 89.4, and 98.3% for ceftobiprole, dalbavancin, daptomycin (4 mg/kg/day), daptomycin (6 mg/kg/day), linezolid, tigecycline, vancomycin (1 g b.i.d.) and vancomycin (1.5 g b.i.d.), respectively. In conclusion, ceftobiprole and dalbavancin have the highest probability of achieving their requisite PK/PD targets against methicillin-resistant Staphylococcus aureus isolated from ICU settings. The susceptibility predictions suggested a reduction of the vancomycin breakpoint to 1 μg/mL.

Methicillin-resistant Staphylococcus aureus (MRSA) in an Austrian urological department: 10 years experience covering 95.161 patients

PURPOSE

So far, few data is available on Methicillin-resistant Staphylococcus aureus (MRSA) infections in urology. To obtain a better insight into MRSA infections, we studied prevalence, colonization and infection site and clinical implications of MRSA in a urological department over a 10-year period.

METHODS

A retrospective study of all patients diagnosed with MRSA for the first time over a 10-year period was set-up.

RESULTS

Between 2000 and 2009, a total of 95.161 in- and outpatients were seen at our department. The prevalence of patients with newly diagnosed MRSA was low, that is, <0.1 % per year (mean 0.07%, 0.02-0.1 %). In total, 62 MRSA cases were identified over a 10-year period. MRSA incidence was 10 times higher in inpatients (0.2 %) than in outpatients (0.02 %). Asymptomatic MRSA colonization was present in 25/62 patients (40.3 %), the remaining 59.7 % (37/62) showed clinical symptoms: MRSA positive swabs from open wounds were seen in 10/62 patients (16.1 %). Urinary tract infections were seen in 26/10 patients (41.9 %), while life-threatening MRSA sepsis occurred in one patient only over a decade.

CONCLUSIONS

In summary, we observed very low rates of MRSA colonization and infection. Still, complications like delayed wound healing, development of abscess and even sepsis may occur.

Molecular epidemiologic analysis of methicillin-resistant Staphylococcus aureus isolates from bacteremia and nasal colonization at 10 intensive care units: multicenter prospective study in Korea

We investigated molecular epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) isolated at 10 intensive care units (ICUs) in Korea. MRSA isolates from bacteremia and nasal colonization were collected prospectively from October 2008 through May 2009 at 10 University-affiliated hospital ICUs. A total of 83 and 175 MRSA strains were isolated from bacteremia and nasal colonization, respectively. Acquired group accounted for 69.9% (n = 58) of bacteremia and 73.1% (n = 128) of nasal colonization. Pulsed-field gel electrophoresis (PFGE) type B (SCCmec type II/ST5) was dominant in the acquired group followed by PFGE type D (SCCmec type IVA/ST72; a community genotype). Seven of 58 (12.1%) acquired bacteremia and 15 of 128 (11.8%) acquired nasal colonizations had SCCmec type IVA/ST72 genotype, which indicated that the community genotype had already emerged as a cause of ICU acquired MRSA infection or colonization. Antibiotic resistance rates to ciprofloxacin, tetracycline, clindamycin and trimethoprim/ sulfamethoxazole were 84.4%, 67.1%, 78.1%, and 12.0%, respectively. Susceptibility to ciprofloxacin best predicted a community genotype (sensitivity 96.5%; specificity 96.9%; odds ratio 861; 95% confidence interval 169-4,390, P < 0.001) and the positive predictive value was 90.2%. Among 23 nasal re-colonized strains, 7 MRSA strains (30.4%) were different from the originally colonized strains on the basis of PFGE types.

Antimicrobial resistance of bacterial isolates from respiratory care wards in Taiwan: a horizontal surveillance study comparison of the characteristics of nosocomial infection and antimicrobial-resistant bacteria in adult Intensive Care Units and two respiratory care facilities for mechanically ventilated patients at a tertiary care centre in Taiwan

The objectives of this study were to compare the incidence of nosocomial infections (NIs) and the distribution of resistant nosocomial pathogens in adult Intensive Care Units (ICUs) and two respiratory care facilities for prolonged mechanically ventilated patients [i.e. the respiratory care centre (RCC) and the respiratory care ward (RCW)] in a 1100-bed tertiary care hospital in Taiwan from 2003 to 2006. The overall incidences of NI for adult ICUs, the RCC and the RCW were 14.0, 10.3 and 5.0 per 1000 patient-days, respectively. Urinary tract infections, bloodstream infections and pneumonias occurred most frequently. The most common reported microorganisms in adult ICUs were non-fermentative Gram-negative bacilli (NFGNB) (33.0%), Enterobacteriaceae (26.5%), Candida spp. (18.2%), Staphylococcus aureus (8.9%), coagulase-negative staphylococci (CoNS) (4.9%) and enterococci (4.5%). In comparison, RCW patients had a higher proportion of NIs caused by S. aureus [odds ratio (OR)=1.9], enterococci (OR=2.2) and Enterobacteriaceae (OR=2.2), but a lower proportion of CoNS (OR=0.3), NFGNB (OR=0.5) and Candida spp. (OR=0.2). RCW patients had higher incidence rates of methicillin-resistant S. aureus (OR=4.91) and extended-spectrum β-lactamase-producing Enterobacteriaceae (OR=4.06) than ICU patients. Further study is needed to delineate the mechanisms responsible for the differences in resistance profile amongst pathogens associated with nosocomial infection in ICUs, RCCs and RCWs.

In vitro evaluation of antibiotics' combinations for empirical therapy of suspected methicillin resistant Staphylococcus aureus severe respiratory infections

Background

Methicillin resistant Staphylococcus aureus (MRSA) is an increasingly common cause of nosocomial infections, causing severe morbidity and mortality worldwide, and accounting in some hospitals for more than 50% of all S. aureus diseases. Treatment of infections caused by resistant bacterial pathogens mainly relies on two therapeutic modalities: development of new antimicrobials and use of combinations of available antibiotics.

Combinations of antibiotics used in the empiric treatment of infections with suspected methicillin resistant Staphylococcus aureus etiology were investigated.

Methods

Double (vancomycin or teicoplanin with either levofloxacin or cefotaxime) and triple (vancomycin or teicoplanin + levofloxacin + one among amikacin, ceftazidime, cefepime, imipenem, piperacillin/tazobactam) combinations were evaluated by means of checkerboard assay and time kill curves. Mutational rates of single and combined drugs at antimicrobial concentrations equal to the resistance breakpoints were also calculated.

Results

Vancomycin or teicoplanin + levofloxacin showed synergy in 16/50 and in 9/50 strains respectively, while vancomycin or teicoplanin + cefotaxime resulted synergic for 43/50 and 23/50 strains, respectively. Triple combinations, involving teicoplanin, levofloxacin and ceftazidime or piperacillin/tazobactam gave synergy in 20/25 strains. Teicoplanin + levofloxacin gave synergy in triple combinations more frequently than vancomycin + levofloxacin.

For single antibiotics, mutational frequencies ranged between 10^-5 and <10^-9 for levofloxacin, cefotaxime, amikacin and imipenem, and <10^-9 for vancomycin and teicoplanin. When tested in combinations, mutational frequencies fell below 10^-9 for all the combinations.

Conclusion

In vitro evidence of synergy between glycopeptides, fluoroquinolones (levofloxacin) and β-lactams and of reduction of mutational frequencies by combinations are suggestive for a potential role in empirical therapy of severe pneumonia with suspected MRSA etiology.

Biosensor incorporating cell barrier architectures for detecting Staphylococcus aureus alpha toxin

Alpha toxin is a common virulent factor of Staphylococcus aureus and is believed to play crucial roles in pathogenicity induced by S. aureus. Alpha toxin is also known to induce permeability to endothelial cell monolayers in vitro due to the formation of interendothelial gaps. The present study is directed towards measuring alpha toxin using a whole-cell-based biosensor. The biosensor, consisting of a confluent monolayer of human umbilical vein endothelial cells (HUVECs) on a potassium ion-selective electrode, takes advantage of cell permeability dysfunction to detect the presence of small quantities of alpha toxin. When a confluent monolayer of cells was formed on the membrane surface, the response of the electrode toward the marker ion, potassium, was inhibited. Upon exposing this sensor to varying concentrations of alpha toxin for 20 min, an increase in sensor response to potassium was observed. The response thus obtained was indirectly related to the concentration of alpha toxin. The detection limit of this sensor for alpha toxin was found to be 0.1 ng/ml. Cell monolayers were stained with silver nitrate to quantify the formation of intercellular gaps as well as to study the effect of this toxin on HUVECs morphology. A strong positive correlation was observed between the response obtained from the biosensor and the area of the intercellular gaps. Silver staining also revealed the tendency of cells to round up upon being exposed to alpha toxin.

Drotrecogin Alfa (Activated) for Nonmenstrual Toxic Shock Syndrome Associated with Methicillin Resistant Staphylococcus aureus Infection

Nonmenstrual toxic shock syndrome (TSS) due to Staphylococcus aureus can lead to significant morbidity and mortality. While drotrecogin alfa (DA) has been employed in patients with Methicillin-resistant Staphylococcus aureus (MRSA) severe sepsis and septic shock, its utility in TSS remains unclear. The authors report a case of severe sepsis in the setting of MRSA-associated TSS that responded to treatment with DA. This case illustrates a potential role for DA in the treatment of toxic shock syndromes and emphasizes the importance of aggressive diagnostic and therapeutic modalities in approaching these conditions.

[Staphylococcus aureus infections: new challenges from an old pathogen]

Staphylococcus aureus is a versatile organism with several virulent characteristics and resistance mechanisms at its disposal. It is also a significant cause of a wide range of infectious diseases in humans. S. aureus often causes life-threatening deep seated infections like bacteremia, endocarditis and pneumonia. While traditionally confined mostly to the hospital setting, methicillin-resistant S. aureus (MRSA) is now rapidly becoming rampant in the community. Community-acquired MRSA is particularly significant because of its potential for unchecked spread within households and its propensity for causing serious skin and pulmonary infections. Because of the unfavorable outcome of many MRSA infections with the standard glycopeptide therapy, new antimicrobial agents belonging to various classes have been introduced and have been evaluated in clinical trials for their efficacy in treating resistant staphylococcal infections. A number of preventive strategies have also been suggested to contain the spread of such infections. In this review, we address the recent changes in the epidemiology of S. aureus and their impact on the clinical manifestations and management of serious infections. We also discuss new treatment modalities for MRSA infections and emphasize the importance of preventive approaches.

Managing methicillin-resistant staphylococci: a paradigm for preventing nosocomial transmission of resistant organisms

Multidrug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), are endemic in healthcare settings in the United States and many other countries of the world. Nosocomial transmission of MRSA serves as a source of hospital outbreaks, and recent reports of vancomycin-resistant S aureus strains in the United States emphasize the need for better control of MRSA and other resistant bacteria within healthcare settings. Colonization with S aureus or MRSA is relatively common in both healthy and hospitalized individuals, most often involves the anterior nares, and is frequently asymptomatic. Colonization increases risk of infection. Patient-to-patient transmission of MRSA within healthcare settings primarily occurs via carriage on the hands of healthcare workers. The Society for Healthcare Epidemiology of America (SHEA) has developed guidelines for the prevention of transmission of MRSA and vancomycin-resistant enterococci within healthcare settings, and chief among the recommendations is an emphasis on adherence to hand hygiene guidelines. Other measures that may prevent the nosocomial transmission of MRSA include improved antibiotic stewardship, staff cohorting, maintenance of appropriate staffing ratios, reductions in length of hospital stays, contact isolation, active microbiologic surveillance, and better staff education. Currently, the efficacy of many of these individual infection control interventions remain in doubt. Many studies reporting improvement in infection control outcomes (eg, reduced transmission, decreasing prevalence) involve simultaneous institution of several of these measures, making it impossible to tease out the effects of any of the individual components. Nonetheless, the best approach in the current environment probably involves hand hygiene plus a careful assessment of an institution's particular circumstances, applying more aggressive procedures such as patient isolation, staff cohorting, and active surveillance cultures, as indicated.

Managing methicillin-resistant staphylococci: a paradigm for preventing nosocomial transmission of resistant organisms

Multidrug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), are endemic in healthcare settings in the United States and many other countries of the world. Nosocomial transmission of MRSA serves as a source of hospital outbreaks, and recent reports of vancomycin-resistant S aureus strains in the United States emphasize the need for better control of MRSA and other resistant bacteria within healthcare settings. Colonization with S aureus or MRSA is relatively common in both healthy and hospitalized individuals, most often involves the anterior nares, and is frequently asymptomatic. Colonization increases risk of infection. Patient-to-patient transmission of MRSA within healthcare settings primarily occurs via carriage on the hands of healthcare workers. The Society for Healthcare Epidemiology of America (SHEA) has developed guidelines for the prevention of transmission of MRSA and vancomycin-resistant enterococci within healthcare settings, and chief among the recommendations is an emphasis on adherence to hand hygiene guidelines. Other measures that may prevent the nosocomial transmission of MRSA include improved antibiotic stewardship, staff cohorting, maintenance of appropriate staffing ratios, reductions in length of hospital stays, contact isolation, active microbiologic surveillance, and better staff education. Currently, the efficacy of many of these individual infection control interventions remain in doubt. Many studies reporting improvement in infection control outcomes (e.g., reduced transmission, decreasing prevalence) involve simultaneous institution of several of these measures, making it impossible to tease out the effects of any of the individual components. Nonetheless, the best approach in the current environment probably involves hand hygiene plus a careful assessment of an institution's particular circumstances, applying more aggressive procedures such as patient isolation, staff cohorting, and active surveillance cultures, as indicated.

MRSA in Urology: A UK Hospital Experience

OBJECTIVE

Methicillin-resistant Staphylococcus aureus (MRSA) infection appears to be increasing, the UK has one of the worst MRSA rates in Europe. As urological patients are at high risk, the aim of this study was to determine the number of newly diagnosed cases of MRSA detected in a urology ward.

PATIENTS AND METHODS

The urology department serves an annual local population of greater than 500,000 with 30 inpatient beds and a tertiary population of 1 million. Over a five year period, we retrospectively recorded all patients with a new diagnosis of MRSA. We also determined colonization site and if the diagnosis of MRSA was made in an elective surgical patient or a patient admitted as an emergency.

RESULTS

The mean number of newly diagnosed cases of MRSA was 20.6 per year. The percentage of patients with a new diagnosis of MRSA was less than or equal to 1% per year with no significant difference of new cases of MRSA over five years. Emergency patients had a trend towards a mean higher rate of MRSA. The commonest site of MRSA colonization was from catheters (32%) and open wounds (18%).

DISCUSSION

MRSA is of concern, as compared to methicillin-sensitive staphylococcus aureus, because it is associated with high rates of clinically relevant infection, increased hospital stay and cost, greater mortality and high vancomycin usage. Mandatory reporting has shown a steady increase in the number of cases of MRSA infection over the past four years. We found that the number of newly diagnosed cases of MRSA was low, at less than or equal to 1% of patients per year. Furthermore, the number of new cases of MRSA remained constant over five years suggesting low acquisition rates in a busy UK urology ward.

Perturbation of endothelial junction proteins by Staphylococcus aureus alpha-toxin: inhibition of endothelial gap formation by adrenomedullin

Endothelial hyperpermeability is a hallmark of an inflammatory reaction and contributes to tissue damage in severe infections. Loss of endothelial cell-cell adhesion leads to intercellular gap formation allowing paracellular fluid flux. Although Staphylococcus aureus alpha-toxin significantly contributed to staphylococci disease, little is known about its mechanism of endothelial hyperpermeability induction. Here, we demonstrate that in a model of isolated perfused rat ileum discontinuation of capillary vascular-endothelial-cadherin (VE-cadherin) was observed after bolus application of S. aureus alpha-toxin being inhibited by the endogenous peptide adrenomedullin (ADM). In vitro, alpha-toxin exposure induced loss of immunoreactivity of VE-cadherin and occludin in human cultured umbilical vein endothelial cells. Likewise, ADM blocked alpha-toxin-related junctional protein disappearance from intercellular sites. Additionally, cyclic AMP elevation was shown to stabilize endothelial barrier function after alpha-toxin application. Although no RhoA activation was noted after endothelial alpha-toxin exposure, inhibition of Rho kinase and myosin light chain kinase blocked loss of immunoreactivity of VE-cadherin and occludin as well as intercellular gap formation. In summary, stabilization of endothelial junctional integrity as indicated by interendothelial immunostaining might be an interesting approach to stabilize endothelial barrier function in severe S. aureus infections.

Systemic antibacterial activity of novel synthetic cyclic peptides

Cyclic peptides with an even number of alternating d,l-alpha-amino acid residues are known to self-assemble into organic nanotubes. Such peptides previously have been shown to be stable upon protease treatment, membrane active, and bactericidal and to exert antimicrobial activity against Staphylococcus aureus and other gram-positive bacteria. The present report describes the in vitro and in vivo pharmacology of selected members of this cyclic peptide family. The intravenous (i.v.) efficacy of six compounds with MICs of less than 12 microg/ml was tested in peritonitis and neutropenic-mouse thigh infection models. Four of the six peptides were efficacious in vivo, with 50% effective doses in the peritonitis model ranging between 4.0 and 6.7 mg/kg against methicillin-sensitive S. aureus (MSSA). In the thigh infection model, the four peptides reduced the bacterial load 2.1 to 3.0 log units following administration of an 8-mg/kg i.v. dose. Activity against methicillin-resistant S. aureus was similar to MSSA. The murine pharmacokinetic profile of each compound was determined following i.v. bolus injection. Interestingly, those compounds with poor efficacy in vivo displayed a significantly lower maximum concentration of the drug in serum and a higher volume of distribution at steady state than compounds with good therapeutic properties. S. aureus was unable to easily develop spontaneous resistance upon prolonged exposure to the peptides at sublethal concentrations, in agreement with the proposed interaction with multiple components of the bacterial membrane canopy. Although additional structure-activity relationship studies are required to improve the therapeutic window of this class of antimicrobial peptides, our results suggest that these amphipathic cyclic d,l-alpha-peptides have potential for systemic administration and treatment of otherwise antibiotic-resistant infections.