Treatment of infection and colonization caused by methicillin-resistant Staphylococcus aureus

Alkynyl-containing phenylthiazoles: Systemically active antibacterial agents effective against methicillin-resistant Staphylococcus aureus (MRSA)

The promising activity of phenylthiazoles against multidrug-resistant bacterial pathogens, in particular MRSA, has been hampered by their limited systemic applicability, due to their rapid metabolism by hepatic microsomal enzymes, resulting in short half-lives. Here, we investigated a series of phenylthiazoles with alkynyl side-chains that were synthesized with the objective of improving stability to hepatic metabolism, extending the utility of phenylthiazoles from topical applications to treatment of a more invasive, systemic MRSA infections. The most promising compounds inhibited the growth of clinically-relevant isolates of MRSA in vitro at concentrations as low as 0.5 μg/mL, and exerted their antibacterial effect by interfering with bacterial cell wall synthesis via inhibition of undecaprenyl diphosphate synthase and undecaprenyl diphosphate phosphatase. We also identified two phenylthiazoles that successfully eradicated MRSA inside infected macrophages. In vivo PK analysis of compound 9 revealed promising stability to hepatic metabolism with a biological half-life of ∼4.5 h. In mice, compound 9 demonstrated comparable potency to vancomycin, and at a lower dose (20 mg/kg versus 50 mg/kg), in reducing the burden of MRSA in a systemic, deep-tissue infection, using the neutropenic mouse thigh-infection model. Compound 9 thus represents a new phenylthiazole lead for the treatment of MRSA infections that warrants further development.

Methicillin-resistant S. aureus infections among patients in the emergency department

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) is increasingly recognized in infections among persons in the community without established risk factors for MRSA.

METHODS

We enrolled adult patients with acute, purulent skin and soft-tissue infections presenting to 11 university-affiliated emergency departments during the month of August 2004. Cultures were obtained, and clinical information was collected. Available S. aureus isolates were characterized by antimicrobial-susceptibility testing, pulsed-field gel electrophoresis, and detection of toxin genes. On MRSA isolates, we performed typing of the staphylococcal cassette chromosome mec (SCCmec), the genetic element that carries the mecA gene encoding methicillin resistance.

RESULTS

S. aureus was isolated from 320 of 422 patients with skin and soft-tissue infections (76 percent). The prevalence of MRSA was 59 percent overall and ranged from 15 to 74 percent. Pulsed-field type USA300 isolates accounted for 97 percent of MRSA isolates; 74 percent of these were a single strain (USA300-0114). SCCmec type IV and the Panton-Valentine leukocidin toxin gene were detected in 98 percent of MRSA isolates. Other toxin genes were detected rarely. Among the MRSA isolates, 95 percent were susceptible to clindamycin, 6 percent to erythromycin, 60 percent to fluoroquinolones, 100 percent to rifampin and trimethoprim-sulfamethoxazole, and 92 percent to tetracycline. Antibiotic therapy was not concordant with the results of susceptibility testing in 100 of 175 patients with MRSA infection who received antibiotics (57 percent). Among methicillin-susceptible S. aureus isolates, 31 percent were USA300 and 42 percent contained pvl genes.

CONCLUSIONS

MRSA is the most common identifiable cause of skin and soft-tissue infections among patients presenting to emergency departments in 11 U.S. cities. When antimicrobial therapy is indicated for the treatment of skin and soft-tissue infections, clinicians should consider obtaining cultures and modifying empirical therapy to provide MRSA coverage.

Methicillin-resistant Staphylococcus aureus in community-acquired skin infections

Community-associated methicillin-resistant Staphylococcus aureus (MRSA) is the most common pathogen among patients with skin and soft tissue infections seeking treatment at a Los Angeles (USA) area emergency department. The proportion caused by MRSA increased from 29% in 2001 to 2002 to 64% in 2003 to 2004. No clinical or historical features reliably predict MRSA etiology.

Daptomycin susceptibility tests: interpretive criteria, quality control, and effect of calcium on in vitro tests

Daptomycin MICs were determined for 844 Gram-positive bacteria in three concentrations of Ca(++) and compared with the MICs of vancomycin and teicoplanin. Daptomycin was twofold to fourfold more active against most species when tested in 50 microg/ml of Ca(++) than in 25 microg/ml. In 50 microg/ml of Ca(++) daptomycin was more active against methicillin-resistant staphylococci and vancomycin-resistant enterococci than teicoplanin or vancomycin; 100% of these isolates were susceptible to < or =2.0 microg/ml of daptomycin. Different lots of Mueller-Hinton agar were variable in Ca(++) content, and daptomycin disk diffusion zone diameters were affected, i.e., zones were 1 to 15 mm smaller on one lot of agar with only 6 microg/ml of Ca(++) compared to another lot with 28 microg/ml. The previously proposed daptomycin interpretive breakpoints performed satisfactorily when MICs were determined in Mueller-Hinton broth with 50 microg/ml of Ca(++) and when the agar gave appropriate zones with quality control strains. To define those control limits, replicate tests with four quality control strains were performed in ten laboratories using broth microdilution tests (with Ca(++) supplemented broth) and disk diffusion tests on Mueller-Hinton agar without cation adjustments.

Antimicrobial resistance in staphylococci. Epidemiology, molecular mechanisms, and clinical relevance

Staphylococcal infections continue to pose important clinical problems in children and adults. Antibiotic resistance among the staphylococci has rendered therapy of these infections a therapeutic challenge. Despite early, uniform susceptibility to penicillin, staphylococci acquired a gene elaborating beta-lactamase that rendered penicillin inactive and that is borne by nearly all clinical isolates. "Penicillinase-resistant beta-lactams," such as methicillin, were introduced in the early 1960s, but resistance to them has become an increasing concern. The mechanism of the so-called "methicillin resistance" is complex. Moreover, once confined to the ecology of hospitals and other institutions, a recent increase in community-acquired methicillin-resistant S. aureus infections has been observed. Glycopeptides, until now the only uniformly reliable therapeutic modality, have been increasingly used for therapy of staphylococcal infections. The recent recognition of clinical isolates with reduced susceptibility to glycopeptides is of concern.

Eradication of methicillin-resistant Staphylococcus aureus from the lower respiratory tract of patients with cystic fibrosis

Two of 95 patients followed in an adult cystic fibrosis clinic consistently grew methicillin-resistant Staphylococcus aureus (mrsa) on sputum culture. Sputum Gram stain consistently showed +4 polymorphonuclear leukocytes and +4 Gram-positive cocci in clusters. Both patients were co-infected with Pseudomonas aeruginosa and required multiple hospitalizations for treatment of pulmonary exacerbation, resulting in significant infection control concerns. Multiple courses of antibiotics, including ciprofloxacin and clindamycin regimens, failed to eliminate the mrsa. A combination of oral rifampin and clindamycin was successful in eradicating the organism from both patients. Over a 12-month period following therapy, in both patients none of 13 sputums showed Gram-positive cocci in clusters on Gram stain and none of 13 sputum cultures grew mrsa. Successful eradication of mrsa has greatly simplified infection control measures on subsequent hospitalizations, reducing costs and enhancing patient comfort.

Methicillin resistant Staphylococcus aureus: the scale of the problem in a Shri Lankan hospital

A three month surveillance study of methicillin resistant Staphylococcus aureus (MRSA) was carried out in the male surgical unit of the General Hospital, Peradeniya, Shri Lanka. Nose, throat, axillary, perineal and wound swabs were taken from 251 patients and 35 staff members. Eighty-four (27.5%) of 305 isolates of S. aureus from patients were MRSA. Seventy-three of these isolates were also resistant to penicillin, tetracycline, erythromycin, gentamicin, chloramphenicol and co-trimoxazole. All isolates were sensitive to fusidic acid, clindamycin, vancomycin and rifampicin. The acquisition of MRSA was higher than of methicillin sensitive S. aureus (MRSA). No deaths occurred due to MRSA. Staff carriage was only 6%. The treatment and management of MRSA in hospitals with very poor resources requires further study of interventions which are practicable in this situation.

Potent in vitro bactericidal activity of polymyxin B against methicillin-resistant Staphylococcus aureus (MRSA)

Eradication of methicillin-resistant Staphylococcus aureus (MRSA) carried by inpatients or healthy hospital personnel by topical use of antibiotics is an important step for preventing outbreak of MRSA nosocomial infection. In the screening of the antibiotic best suited for this purpose, we have found that polymyxin B, a commonly used antibiotic for gram-negative infection, had an unexpected strong cytokilling activity towards MRSA clinical strains, which was more potent than that of vancomycin or gentamicin. The data suggested that polymyxin B could be an antibiotic of choice in the treatment of topical carriage of or infection caused by MRSA.

An overview of nosocomial infections, including the role of the microbiology laboratory

An estimated 2 million patients develop nosocomial infections in the United States annually. The increasing number of antimicrobial agent-resistant pathogens and high-risk patients in hospitals are challenges to progress in preventing and controlling these infections. While Escherichia coli and Staphylococcus aureus remain the most common pathogens isolated overall from nosocomial infections, coagulase-negative staphylococci (CoNS), organisms previously considered contaminants in most cultures, are now the predominant pathogens in bloodstream infections. The growing number of antimicrobial agent-resistant organisms is troublesome, particularly vancomycin-resistant CoNS and Enterococcus spp. and Pseudomonas aeruginosa resistant to imipenem. The active involvement and cooperation of the microbiology laboratory are important to the infection control program, particularly in surveillance and the use of laboratory services for epidemiologic purposes. Surveillance is used to identify possible infection problems, monitor infection trends, and assess the quality of care in the hospital. It requires high-quality laboratory data that are timely and easily accessible.