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PubMed2001

The evolution of methicillin resistance in Staphylococcus aureus: similarity of genetic backgrounds in historically early methicillin-susceptible and -resistant isolates and contemporary epidemic clones.

The key genetic component of methicillin resistance, the mecA determinant, is not native to Staphylococcus aureus. Thus, the evolution of methicillin-resistant S. aureus (MRSA) must have begun with the acquisition of the mecA determinant from an unknown heterologous source some time before the first reported appearance of MRSA isolates in clinical specimens in the U.K. and Denmark (in the early 1960s). We compared the genetic backgrounds and phenotypes of a group of methicillin-susceptible S. aureus (MSSA) isolates to the properties of MRSA strains isolated in Denmark and the U.K. during the same time period, and also to the genetic profiles of contemporary epidemic clones of MRSA. All early MRSA isolates resembled a large group of the early MSSA blood isolates in phenotypic and genetic properties, including phage group, antibiotype (resistance to penicillin, streptomycin, and tetracycline), pulsed-field gel electrophoresis pattern, and spaA type and multilocus sequence type, strongly suggesting that the early MSSA examined here represented the progeny of a strain that served as one of the first S. aureus recipients of the methicillin-resistance determinant in Europe. The genetic background of this group of early MSSA isolates was also very similar to that of the widely disseminated contemporary "Iberian clone" of MRSA, suggesting that genetic determinants present in early MSSA and essential for some aspects of the epidemicity and/or virulence of these strains may have been retained by this highly successful contemporary MRSA lineage.

Amino Acid Sequence↗

PubMed1997

Massive reduction in methicillin resistance by transposon inactivation of the normal PBP2 in a methicillin-resistant strain of Staphylococcus aureus.

Screening of a large transposon library constructed in the background of a highly and homogeneously methicillin-resistant Staphylococcus aureus (MRSA) strain (methicillin MIC 1,600 micrograms/ml) for Tn551 mutants with reduced resistance, identified mutant RUSA130 with a methicillin MIC of 12 micrograms/ml. Cloning in E. coli followed by sequencing located the Tn551 insert omega 703 near the C-terminal of the PBP2 gene. Penicillin-binding assays with mutant RUSA130 showed the presence of normal amounts of penicillin-binding protein 2A (PBP2A) but the absence of PBP2. These observations suggest that the mecA gene product PBP2A is not the sole catalyst of peptidoglycan synthesis in MRSA growing in the presence of beta-lactam antibiotics, since an intact PBP2 is also essential for the optimal expression of methicillin resistance in MRSA.

Bacterial Proteins↗

PubMed1983

Population analysis of susceptibility to methicillin, vancomycin, and three cephalosporines in two methicillin-resistant strains of Staphylococcus epidermidis.

Population analyses of susceptibility to methicillin, vancomycin, cephalothin, cefamandole, and cefoxitin were carried out with two strains of Staphylococcus epidermidis (S. epidermidis) resistant to penicillin, streptomycin, and methicillin. Two strains of Staphylococcus aureus (S. aureus), one sensitive to penicillin the other resistant, were used as controls. All strains were clinical isolates. From the strains of S. epidermidis it was possible to select sub-populations highly resistant to methicillin, cephalothin, cefamandole, and cefoxitin. The mutation-rate varied between c. 10(-3) and 10(-7). The two strains were homogeneous as regards vancomycin susceptibility. Methicillin was shown to be more penicillinase-stable than the cephalosporines. Treatment in vivo, with cephalothin and vancomycin did not increase the frequency of highly resistant bacteria against any of the antibiotics, but during treatment with cephalothin the majority-population became eight times more resistant to vancomycin and may explain why the treatment in vivo was not successful.

Cephalosporins↗

PubMed1983

Methicillin-resistant septal peptidoglycan synthesis in a methicillin-resistant Staphylococcus aureus strain.

In a methicillin-resistant Staphylococcus aureus strain, electron micrographs showed that cell wall septa continued to be formed in the presence of methicillin, although they became distorted and enlarged. The results indicated that peripheral cell wall synthesis was inhibited. It is concluded that a methicillin-resistant mode of septal peptidoglycan synthesis is an important determinant of methicillin resistance.

Bacterial Proteins↗

PubMed1988

Ciprofloxacin therapy of experimental endocarditis caused by methicillin-susceptible or methicillin-resistant Staphylococcus aureus.

Ciprofloxacin was more effective (P less than 0.01) than either imipenem or nafcillin therapy of experimental methicillin-susceptible Staphylococcus aureus endocarditis in rabbits after 2 or 3 days of treatment. There was no significant difference between results of treatment of methicillin-susceptible S. aureus experimental endocarditis with ciprofloxacin and results with the combination of nafcillin and gentamicin. Ciprofloxacin was more effective (P less than 0.01) than vancomycin therapy of experimental methicillin-resistant S. aureus endocarditis after 3 days of treatment. After 5 days of treatment, there was no significant difference between the results of treatment of experimental methicillin-resistant S. aureus endocarditis with ciprofloxacin and results with vancomycin.

Animals↗

PubMed1984

Activity of eleven antimicrobial agents against methicillin-, methicillin- and rifampin-resistant Staphylococcus aureus.

Activity of eleven antimicrobial agents against methicillin-, methicillin- and rifampin-resistant Staphylococcus aureus was studied using a microtiter broth dilution technique. Coumermycin was the most active agent. Vancomycin, rifampin, fusidic acid and N-formimidoyl-thienamycin showed excellent activity against methicillin-resistant St. aureus (MRSA). Antimicrobial susceptibility pattern was similar for MRSA and methicillin- and rifampin-resistant St. aureus. 8% of MRSA were resistant to trimethoprim and sulfamethoxazole.

Anti-Bacterial Agents↗

PubMed2003

Comparative in vitro activity of linezolid and five other antimicrobials against nosocomial isolates of methicillin-resistant Staphylococcus aureus, methicillin-resistant Staphylococcus epidermidis and vancomycin-resistant Enterococcus faecium.

The activity of linezolid in comparison to vancomycin, teicoplanin, oxacillin, clindamycin and gentamicin was tested against 60 strains of methicillin-resistant Staphylococcus aureus, 60 strains of methicillin-resistant Staphylococcus epidermidis isolated from patients with nosocomial infections and 24 strains of vancomycin-resistant Enterococcus faecium isolated from feces of hospitalized patients. Minimum Inhibitory Concentrations (MICs) were determined by the Epsilometer test method. All tested strains were sensitive to linezolid and specifically all methicillin-resistant S. aureus had MIC range 0.25-3.00, MIC50 = 0.75, MIC90 = 1.5, all methicillin-resistant S. epidermidis had MIC range 0.125-1.5, MIC50 = 0.5, MIC90 = 1 and all vancomycin-resistant E. faecium had MIC range 0.5-1.5, MIC50 = 1, MIC90 = 1. Linezolid is the first of a novel antimicrobial class, the oxazolidinones, which is a promising treatment for serious Gram-positive infections, including multiresistant strains.

Acetamides↗

PubMed1989

In vitro activity of dicloxacillin against methicillin-susceptible and methicillin-resistant Staphylococcus-aureus.

A total of 54 strains of Staphylococcus aureus, 37 methicillin-susceptible (MSSA) and 17 methicillin-resistant (MRSA), were investigated for their susceptibility to dicloxacillin as compared to methicillin and oxacillin by agar plate dilution at two different temperatures of incubation (30 degrees C and 37 degrees C). Against MSSA strains we found a slight but significant increase (0-2 dilution steps) in minimal inhibitor concentrations (MICs) for all three antibiotics with decrease in incubation temperature. Against MRSA strains methicillin and oxacillin showed a 3-6 fold increase in median MIC with decrease incubation temperature. For dicloxacillin, in contrast, there were no significant differences in median MICs (i.e. 0.4 mg/l) against MSSA strains at 30 degrees C or MRSA strains at either incubation temperature. Population-analysis of the MRSA strains revealed, however, that a highly dicloxacillin-resistant subpopulation appeared with a frequency of 10(-6) to 10(-7). Such heterogenous resistance of MRSA strains to dicloxacillin probably prohibits the use of dicloxacillin against serious infections caused by these pathogens.

Dicloxacillin↗

PubMed1982

[Characteristics of the protein spectra of methicillin-resistant and methicillin-sensitive staphylococcal strains].

Differences in the protein-composition of methicillin resistant (MR) and methicillin sensitive (MS) staphylococci were shown by means of disk electrophoresis. Extracellular proteins of MR and MS staphylococci were studied electrophoretically. The study revealed no relation between the culture grouping by the protein spectra and resistance to methicillin. Comparison of the spectra of soluble intracellular proteins showed a certain correlation with methicillin resistance.

Bacterial Proteins↗

PubMedDate not supplied

Methicillin-resistant Staphylococcus aureus and methicillin-resistant coagulase-negative staphylococci from conjunctivas of preoperative patients.

To evaluate the incidence and characteristics of carriers of conjunctival methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant coagulase-negative Staphylococci (MRCNS) among preoperative patients at an eye clinic, bacterial growth was studied in 978 conjunctival specimens of 628 preoperative patients without signs of ocular infection. Specimens were evaluated for growth of bacteria on nutrient agar plate, blood agar plate, or chocolate agar plate for 2 days at 37 degrees C. Methicillin resistance was confirmed by disk diffusion and agar screening methods. Susceptibilities of the bacterial strain to ampicillin (ABPC), cefazolin (CEZ), minocycline (MINO), gentamicin (GM), erythromycin (EM), vancomycin (VCM), and ofloxacin (OFLX) were determined by the disk diffusion method. Of the 628 patients (978 eyes), 352 patients (580 eyes) had positive bacterial growth. Among them, 8 (13 eyes) had MRSA growth and 2 (4 eyes) had MRCNS growth. The rate of nasolacrimal duct obstruction was significantly higher in eyes with positive bacterial growth than in eyes with negative growth. Of the 10 patients (17 eyes) with MRSA or MRCNS growth, 8 were older than 80 years, 5 had the same bacterial strains in the anterior nares and throat, 6 had nasolacrimal duct obstruction, 3 had dry eye, and 9 had been recently hospitalized. All 10 bacterial strains were resistant to ABPC, CEZ, and EM, but were sensitive to MINO and OFLX. Five strains were resistant and 5 were sensitive to GM. Two strains examined were sensitive to VCM. After topical antibiotic use for 0.5 to 6 months, the bacterial strains were eliminated. Two of the 17 eyes with MRSA or MRCNS growth did not undergo surgery. No postoperative endophthalmitis developed in 976 of the 978 eyes. Ophthalmologists should be aware that about 50% of preoperative patients without signs of ocular infection may have bacterial growth on the conjunctiva, and that elderly patients with nasolacrimal duct obstruction, dry eye, and recent hospital stays may be carriers of MRSA or MRCNS.

Adolescent↗

PubMed2003

Emergence of phenotypic resistance to ciprofloxacin and levofloxacin in methicillin-resistant and methicillin-sensitive Staphylococcus aureus strains.

The emergence of phenotypic resistance to ciprofloxacin and levofloxacin in methicillin-sensitive and methicillin-resistant Staphylococcus aureus (MRSA) strains was studied. Twenty MRSA and 77 methicillin-sensitive S.aureus (MSSA) strains susceptible to both quinolones were investigated for resistance after single step or serial passages. No growth of 20 MRSA strains was observed at 4xMIC of levofloxacin after 48 h incubation, but 4 of 77 (5%) MSSA strains grew at the same concentration. At 4xMIC concentration of ciprofloxacin, 10 MSSA (13%) and five MRSA (25%) strains were grown. In the serial passages of MRSA strains, resistance to ciprofloxacin was 75 and 5% for levofloxacin by the third passage. In the seventh passage this resistance was 100 and 15%, respectively. In MSSA strains, resistance to ciprofloxacin was 75 and 19% to levofloxacin at the third passage and at the seventh passage, 100 and 61%, respectively. Emergence of ciprofloxacin resistance was more common and developed more rapidly than resistance to levofloxacin in both MRSA and MSSA strains.

Ciprofloxacin↗

PubMed2003

Epidemiological comparison of true methicillin-resistant and methicillin-susceptible coagulase-negative staphylococcal bacteremia at hospital admission.

We performed 2 case-control studies among 108 patients with true coagulase-negative staphylococcal (CoNS) bacteremia diagnosed within 48 h of hospital admission. Seventy-nine patients (73%) with methicillin-resistant (MR) CoNS bacteremia and 29 patients (27%) with methicillin-susceptible (MS) CoNS bacteremia were compared with 79 randomly selected control patients without CoNS bacteremia. The presence of a central venous catheter was an independent risk factor for both MR- and MS-CoNS bacteremia (P<.001). Patients with MR-CoNS bacteremia were more frequently admitted from health care facilities (P=.02), more likely to have had previous MR Staphylococcus aureus infection or colonization (P=.02), and more likely to have received antibiotics in the previous 30 days (P=.02). The probability that bacteremia was caused by an MR strain, rather than an MS strain, was 62% among patients admitted from the community and 84% among patients admitted from health care facilities. This study identified epidemiological characteristics that can be used to distinguish between MR- and MS-CoNS bacteremia and found high rates of methicillin resistance among CoNS isolates recovered from patients admitted from the community, as well as from health care facilities.

Bacteremia↗

PubMed2006

Impact of antibiotics on expression of virulence-associated exotoxin genes in methicillin-sensitive and methicillin-resistant Staphylococcus aureus.

Extracellular protein toxins contribute to the pathogenesis of a wide variety of Staphylococcus aureus infections. The present study investigated the effects that cell-wall active antibiotics and protein-synthesis inhibitors have on transcription and translation of genes for Panton-Valentine leukocidin, alpha-hemolysin, and toxic-shock syndrome toxin 1, in both methicillin-sensitive and methicillin-resistant S. aureus. Subinhibitory concentrations of nafcillin induced and prolonged mRNA for Panton-Valentine leukocidin, alpha-toxin, and toxic-shock syndrome toxin 1 and increased toxin production. In contrast, clindamycin and linezolid markedly suppressed translation, but not transcription, of toxin genes. These results suggest (1) that protein-synthesis inhibition is an important consideration in the selection of antimicrobial agents to treat serious infections caused by toxin-producing gram-positive pathogens and (2) that, by inducing and enhancing toxin production, inadvertent use of beta-lactam antibiotics to treat methicillin-resistant S. aureus infections may contribute to worse outcomes.

Acetamides↗

PubMed2006

Detection of methicillin/oxacillin resistance and typing in aminoglycoside-susceptible methicillin-resistant and kanamycin-tobramycin-resistant methicillin-susceptible Staphylococcus aureus.

Eighty-five atypical isolates of Staphylococcus aureus divided into 73 aminoglycoside-susceptible methicillinresistant (AS-MRSA) and 12 kanamycin-tobramycin-resistant methicillin-susceptible (KTR-MSSA) were phenotypically and genotypically examined for methicillin resistance. Among these tests, the diffusion method using the oxacillin and cefoxitin disks on Mueller-Hinton agar with and without NaCl, the incubation at 35 degrees C or 30 degrees C for 24 or 48 hr, respectively, and the determination of oxacillin MICs by E-test were performed. We also examined the presence of the mecA gene by PCR and its product PBP 2a by the Slidex MRSA Detection test after induction by cefoxitin disk. All of the AS-MRSA strains (100%) were detected by the cefoxitin disk in all conditions and by the oxacillin disk on Mueller-Hinton agar with 2% of NaCl at 35 degrees C. Without NaCl, the sensitivity fell to 97.2% by oxacillin disk. The oxacillin MICs for these isolates ranged from 2 to 128 mg/L. The mecA gene determinant and its product PBP 2a were detected in all AS-MRSA strains. All KTR-MSSA strains were phenotypically methicillin-susceptible and oxacillin MICs were below or borderline of breakpoint (< or =2 mg/L). The mecA gene determinant and its product were detected in one strain. Pulsed-field gel electrophoresis (PFGE) was applied and revealed the presence of two major patterns A (36.9%) and B (46.2%) in AS-MRSA isolates and seven patterns in the KTR-MSSA strains.

Aminoglycosides↗

PubMed2002

Methicillin-resistant Staphylococcus aureus and methicillin-resistant coagulase-negative Staphylococcus ocular surface infection efficacy of chloramphenicol eye drops.

PURPOSE: Methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant coagulase-negative Staphylococcus (MR-CNS) are two major multidrug-resistant pathogens. In this paper we report the prevalence of MRSA and MR-CNS in ocular surface infections. METHODS: We investigated the proportion of MRSA and MR-CNS in bacterial isolates from conjunctiva of elderly patients with and without bacterial conjunctivitis. The relationship between conjunctival MRSA carriers and general background conditions was studied. We evaluated the efficacy of chloramphenicol eye drops in the treatment of MRSA conjunctivitis. We also investigated the presence of MRSA and MR-CNS in lid skin and conjunctiva of patients with atopic dermatitis. RESULTS: In conjunctival bacterial flora of elderly patients the proportion of MRSA in S. aureus was 57%, and the proportion of MR-CNS in coagulase-negative Staphylococcus was 25%. Conjunctival MRSA carriers were more likely to have anemia, malignant tumor, liver dysfunction, and dementia, and to be postoperation and chronically bedridden. The efficacy rate of chloramphenicol eye drops in the treatment of MRSA conjunctivitis was 81%. In conjunctival sacs of patients with atopic dermatitis, S. aureus was the most frequent species (48%), and the proportion of MRSA was 18%. CONCLUSION: Methicillin-resistant S. aureus and MR-CNS are widespread in elderly hospitalized patients and in patients with atopic dermatitis. Chloramphenicol eye drops were useful for the treatment of MRSA ocular surface infections.

Aged↗

PubMed1996

Antibacterial activity of anacardic acid and totarol, alone and in combination with methicillin, against methicillin-resistant Staphylococcus aureus.

The inhibitory and bactericidal activities of anacardic acid and totarol, alone and in combination with methicillin, were investigated against methicillin-resistant Staphylococcus aureus (MRSA). The growth of two MRSA strains was inhibited by 6 x 25 microg ml-1 of anacardic acid and 0 x 78 microg ml-1 of totarol. The time-kill curve study showed that these two compounds were bactericidal against MRSA. Anacardic acid killed MRSA cells more rapidly than totarol, and no viable cells were detected after being exposed to 6 x 25 microg ml-1 of anacardic acid for 6 h. Anacardic acid showed bactericidal activity against MRSA at any stage of growth, and also even when cell division was inhibited by chloramphenicol. In the combination studies, the minimal inhibitory concentration (MIC) of methicillin was lowered from 800 to 1 x 56 microg ml-1 for MRSA ATCC 33591, and from 800 to 6 x 25 microg ml-1 for MRSA ATCC 33592, by combining with 1/2 x MIC of anacardic acid. The time-kill curves demonstrated synergistic bactericidal activities for these combinations.

Abietanes↗

PubMed2004

Comparative analysis of antibiotic and antimicrobial biocide susceptibility data in clinical isolates of methicillin-sensitive Staphylococcus aureus, methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa between 1989 and 2000.

AIMS: To analyse population minimum inhibitory concentrations (MICs) data from clinical strains of Staphylococcus aureus and Pseudomonas aeruginosa for changes over a 10-year period and to look for correlations between the antimicrobials tested. METHODS AND RESULTS: Data from the MIC study of 256 clinical isolates of Staph. aureus [169 methicillin-sensitive Staph. aureus (MSSA), 87 methicillin-resistant Staph. aureus (MRSA)] and 111 clinical isolates of Ps. aeruginosa against eight antimicrobial biocides and several clinically relevant antibiotics was analysed using anova, Spearman-Rho correlation and principal component analysis. Comparisons suggest that alterations in the mean susceptibility of Staph. aureus to antimicrobial biocides have occurred between 1989 and 2000, but that these changes were mirrored in MSSA and MRSA suggests that methicillin resistance has little to do with these changes. Between 1989 and 2000 a sub-population of MRSA has acquired a higher resistance to biocides, but this has not altered the antibiotic susceptibility of that group. In both Staph. aureus and Ps. aeruginosa several correlations (both positive and negative) between antibiotics and antimicrobial biocides were found. CONCLUSIONS: From the analyses of these clinical isolates it is very difficult to support a hypothesis that increased biocide resistance is a cause of increased antibiotic resistance either in Staph. aureus or in Ps. aeruginosa. SIGNIFICANCE AND IMPACT OF THE STUDY: The observation of negative correlations between antibiotics and biocides may be a useful reason for the continued use of biocides promoting hygiene in the hospital environment.

Anti-Bacterial Agents↗

PubMed1999

Potentiation of methicillin activity against methicillin-resistant Staphylococcus aureus by diterpenes.

Totarol is a diterpene compound extracted from the totara tree. Totarol and eight other diterpenes were found to potentiate methicillin, one reducing the minimum inhibitory concentration of methicillin against resistant Staphylococcus aureus 256-fold. Totarol did not inhibit the synthesis of DNA or peptidoglycan in S. aureus, but reduced the respiration rate by 70%. Under potentiation conditions, diterpenes had only a slight effect on the respiration rate, but had a significant effect on expression of PBP 2a. We conclude that the primary staphylococcal target for totarol is the respiratory chain, but that potentiation of methicillin by diterpenes is by interference with PBP 2a expression.

Bacterial Proteins↗