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At least 19 recordsLinked to original sources

PubMed1989

Resistance to dicloxacillin, methicillin and oxacillin in methicillin-susceptible and methicillin-resistant Staphylococcus aureus detected by dilution and diffusion methods.

A total of 54 Staphylococcus aureus strains of varying methicillin resistance were investigated for their resistance to methicillin, oxacillin and dicloxacillin by different diffusion tests. Inhibition zones were measured around locally prepared paperdiscs with 10 micrograms methicillin, 5 and 10 micrograms oxacillin, 5 and 10 micrograms dicloxacillin, PDM paperdiscs with 10 micrograms methicillin or oxacillin and Neo-sensitabs tablets with methicillin or oxacillin. All diffusion tests were performed both with Mueller-Hinton agar and Danish Blood agar as well as at 37 degrees C and 30 degrees C and read after overnight incubation. Differences in zone diameter under different conditions were found to be independent of the susceptibility level of the strains. Seventeen of the strains were detected as methicillin-resistant (MRSA) by two methods including high inoculum and prolonged incubation at 30 degrees C. The minimum inhibitory concentration (MIC) of the 54 strains was determined by a plate dilution method at 30 degrees C and 37 degrees C. A 10 micrograms locally prepared methicillin disc detected all MRSA strains with no false reactions either at 37 degrees C or 30 degrees C on Mueller-Hinton agar. Investigations with oxacillin discs had to be performed at 30 degrees C or with a 5 microgram disc in order to detect correctly. PDM paperdiscs gave reactions identical to the corresponding locally prepared discs. Methicillin Neo-sensitabs detected all MRSA strains but also included a few susceptible strains among the resistant ones. Addition of blood increased the number of not-detected MRSA strains. All 17 MRSA strains were susceptible to dicloxacillin by the dilution method, and the disc diffusion test showed similar results. Dicloxacillin discs therefore did not detect the presence of MRSA strains. The implications of replacement of the methicillin/oxacillin disc by a dicloxacillin disc are discussed.

Denmark↗

PubMed1991

femA, which encodes a factor essential for expression of methicillin resistance, affects glycine content of peptidoglycan in methicillin-resistant and methicillin-susceptible Staphylococcus aureus strains.

femA is a chromosomally encoded factor, occurring naturally in Staphylococcus aureus, which is essential for the expression of high-level methicillin resistance in this organism. The production of a low-affinity penicillin-binding protein, PBP2a or PBP2', which is intimately involved with methicillin resistance in S. aureus, is not influenced by femA. To elucidate a possible physiological function of the 48-kDa protein encoded by femA, several related methicillin-resistant, methicillin-susceptible, and Tn551 insertionally inactivated femA mutants were analyzed for possible changes in cell wall structure and metabolism. Independent of the presence of mec, the methicillin resistance determinant, all femA mutants had a reduced peptidoglycan (PG) glycine content (up to 60% in the molar ratio of glycine/glutamic acid) compared to that of related femA+ parent strains. Additional effects of femA inactivation and the subsequent decrease in PG-associated glycine were (i) reduced digestion of PG by recombinant lysostaphin, (ii) unaltered digestion of PG by Chalaropsis B-muramidase, (iii) reduced cell wall turnover, (iv) reduced whole-cell autolysis, and (v) increased sensitivity towards beta-lactam antibiotics. Also, the PG-associated glycine content of a femA::Tn551 methicillin-susceptible strain was restored concomitantly with the methicillin resistance to a level almost equal to that of its femA+ methicillin-resistant parent strain by introduction of plasmid pBBB31, encoding femA.

Acetylglucosamine↗

PubMed1992

[The beta-lactamase activity in methicillin-resistant Staphylococcus aureus--a comparison of the beta-lactamase from a methicillin-resistant and from a methicillin-sensitive strain of Staphylococcus aureus].

Strains of Methicillin-resistant Staphylococcus aureus (MRSA) are more frequently beta-lactamase-negative than those of Methicillin-susceptible S. aureus (MSSA). In the strains of MRSA, the beta-lactamase activity tends to be inversely related to the MIC's of Methicillin. Such a marked tendency has been observed in recent years.

Methicillin↗

PubMed1990

The effect of methicillin on the fatty acid composition of total polar lipid in methicillin resistant Staphylococcus aureus.

The effect of two concentrations of methicillin on the fatty acid (FA) distribution in intracellular total polar lipid (TPL) of the log-phase cultures of a methicillin resistant Staphylococcus aureus strain No. 5814R was studied during a period of 2 h. Half the MIC of methicillin (= 1000 micrograms/ml) caused 18.6% increase in branched-FAs and a same decrease in straight-FAs, while one MIC (= 2000 micrograms/ml) of the drug induced a moderate change in those of TPL. The ratio of branched-FAs to straight-FAs increased from 1.24 to 1.56 in the presence of 1/2 x MIC of methicillin and reduced from 1.24 to 0.87 in the presence of 1 X MIC of the antibiotic. In TPL of the control cultures it gradually decreased from 1.24 to 0.77. It is concluded that under the effect of methicillin, FA composition of TPL in methicillin resistant cocci does not change as dramatically as in methicillin sensitive ones indicating lipid synthesis in methicillin resistant S. aureus to be less sensitive to the action of methicillin than in methicillin susceptible strains. This may contribute to the resistance against the lytic effect of the drug. Membrane lipid properties seem to be involved in the mechanisms of methicillin resistance.

Fatty Acids↗

PubMed1990

Induction of beta-lactamase and methicillin resistance in unusual strains of methicillin-resistant Staphylococcus aureus.

Two unusual, heterogeneously-resistant, strains of Staphylococcus aureus appeared resistant to oxacillin, but susceptible to methicillin by disc diffusion methods. In agar dilution tests, both strains were oxacillin-resistant. One was susceptible to methicillin, and the other gave a paradoxical reaction, with growth only on plates containing low (0.5, 1 and 2 mg/l) and high (32 and 64 mg/l) concentrations of antibiotic. Induction of methicillin resistance was tested by inoculating each strain on to agar plates containing an inhibitory concentration of methicillin (8 mg/l), and then placing discs containing inducers (oxacillin, nafcillin, methicillin and CBAP [2-(2'-carboxyphenyl) benzoyl-6-aminopenicillanic acid]) on the agar surface. Colonies grew only around discs containing effective inducers. Oxacillin and CBAP were much more potent inducers of methicillin resistance and beta-lactamase than was nafcillin or methicillin. These data suggest that the mechanism that regulates induction of the low-affinity penicillin binding protein (PBP-2') may be altered in these strains. Similar mechanisms appear to induce both beta-lactamase and methicillin resistance.

Bacterial Proteins↗

PubMed1988

The in vitro activity of ramoplanin (A-16686/MDL 62,198), vancomycin and teicoplanin against methicillin-susceptible and methicillin-resistant Staphylococcus spp.

Ramoplanin (A-16686/MDL 62,198) is a novel lipoglycopeptide antimicrobial, comprised of three closely related polypeptides containing chlorinated phenyl moieties and D-mannose, isolated from the fermentation products of Actinoplanes sp. ATCC 33076. The antimicrobial activity of ramoplanin is limited to Gram-positive bacteria and its reportedly unacceptable administration side-effects suggest that any potential clinical role will be limited to the topical therapy of superficial skin infections and the eradication of bacteria, representing a possible nosocomial cross-infection source, from carriage sites. In this study the MICs of ramoplanin have been determined for methicillin-susceptible and methicillin-resistant isolates of Staphylococcus aureus, S. epidermidis and S. haemolyticus and compared with those of two glycopeptide antimicrobials, vancomycin and teicoplanin. MICs were determined using an agar incorporation technique in Mueller-Hinton medium with an inoculum of 10(5) cfu. Ramoplanin was 2-8 times more active than either vancomycin or teicoplanin against methicillin-susceptible and methicillin-resistant isolates of S. aureus and methicillin-susceptible isolates of S. epidermidis. Isolates of methicillin-resistant S. epidermidis and both methicillin-susceptible and -resistant isolates of S. haemolyticus were generally less susceptible to teicoplanin than to vancomycin. Ramoplanin was significantly more active than either vancomycin or teicoplanin against these isolates. These results suggest that the clinical evaluation of ramoplanin as a topical antibacterial agent for the control of superficial infections caused by Staphylococcus spp. and for the eradication of methicillin-resistant S. aureus from carriage sites, is justified.

Anti-Bacterial Agents↗

PubMed1991

Genetic characterisation of resistance to metal ions in methicillin-resistant Staphylococcus aureus: elimination of resistance to cadmium, mercury and tetracycline with loss of methicillin resistance.

Susceptibility to six metal ions--cadmium (Cd), mercury (Hg), arsenate (Asa), arsenite (Asi), antimony (Sb) and zinc (Zn)--was tested in 23 independent isolates of methicillin-resistant Staphylococcus aureus (MRSA) obtained from Guy's Hospital (GH) during 1984-1986, which included 10 isolates of the UK epidemic EMRSA-1 strain. Strains were also tested for resistance to antibiotics and the nucleic-acid-binding compounds propamidine isethionate and ethidium bromide. A further 19 methicillin-resistant isolates, including 10 EMRSA-1 were obtained from other sources. Ten methicillin-sensitive, antibiotic sensitive isolates were from Guy's Hospital. Resistance to Hg was associated with methicillin resistance in 19 of the 20 EMRSA-1 isolates, all of which were resistant to Cd. Resistance to Cd and Hg was found in 13 out of 22 other MRSA isolates. Hg resistance was not present in the methicillin-sensitive isolates which were often (13 out of 19) moderately resistant to Cd. Multiple resistance to metal ions, including resistance to Hg, Asa, Asi and Sb, was uncommon. Resistance to Cd (MIC greater than 32 mg/L or 8-16 mg/L) was associated with increased resistance to Zn. In 11 of the consecutive MRSA isolates from Guy's Hospital seven distinct strains were recognised by phage type. Methicillin resistance in these strains varied from 16 to 1024 mg/L at 30 degrees C with a 2-8-fold lower minimum inhibitory concentration at 37 degrees C indicating some degree of heterogeneity. Representatives of the EMRSA-1 strain had the higher levels of resistance. Loss of methicillin resistance occurred in 0.2-5.0% of colonies tested after storage at room temperature in 10 of these isolates.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteriophages↗

PubMed1992

Survey of the methicillin resistance-associated genes mecA, mecR1-mecI, and femA-femB in clinical isolates of methicillin-resistant Staphylococcus aureus.

The restriction site polymorphism of the chromosomal femAB region and the first appearance of the regulatory element mecR1-mecI associated with the methicillin resistance determinant (mec) were analyzed in 192 initially methicillin resistant (Mcr) Staphylococcus aureus clinical isolates collected between 1965 and 1990 in the Zurich area. Forty-three of the strains lost the resistance spontaneously. All isolates that were still Mcr hybridized with mecA, the gene for the low-affinity penicillin-binding protein PBP 2'. Mcr strains isolated before 1977 lacked sequences that hybridized with mecR1-mecI, a regulatory element controlling the expression of mecA; exceptions to this were one strain isolated in 1966 and one strain isolated in 1972. The size of the EcoRV fragment carrying femA, a chromosomally encoded factor involved in pentaglycine side chain formation of the peptidoglycan and essential for the expression of methicillin resistance, was conserved in all strains but one, which was susceptible to methicillin even though it carried a functional mecA gene. The methicillin susceptibility of this particular strain was presumably due to a spontaneous femA-like mutation. The 192 strains belonged to seven different EcoRV restriction fragment patterns recognizable with a 10.5-kb probe covering the femAB region. Some 93% of the 149 Mcr strains belonged to pattern A, and the remaining Mcr strains shared patterns A' and B. The 42 isolates which spontaneously lost their resistance upon storage and revival represented all seven different patterns. This strong conservation of femA suggests an important role for femA in cell wall metabolism and methicillin resistance.

Genes, Bacterial↗

PubMed1990

Presence of an additional penicillin-binding protein in methicillin-resistant Staphylococcus epidermidis, Staphylococcus haemolyticus, Staphylococcus hominis, and Staphylococcus simulans with a low affinity for methicillin, cephalothin, and cefamandole.

The presence of an additional penicillin-binding protein (PBP) was demonstrated in methicillin-resistant strains of Staphylococcus epidermidis, S. haemolyticus, S. hominis, and S. simulans. In these four species, the apparent molecular mass of this protein was analogous to that of PBP 2' of methicillin-resistant S. aureus SR 1550-9. It exhibited a low affinity for methicillin, cephalothin, and cefamandole; and its synthesis was methicillin inducible. Peptide mapping of this PBP from the four species yielded identical results that were analogous to those obtained with S. aureus SR 1550-9. These results suggest that this protein is similar to, if not the same as, PBP 2' of S. aureus and that it is involved in methicillin resistance in the four species studied.

Bacterial Proteins↗

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↗

PubMed1992

Development of new antibiotic resistance in methicillin-resistant but not methicillin-susceptible Staphylococcus aureus.

The frequency of infections caused by multidrug-resistant Staphylococcus aureus continues to increase while the numbers of alternative therapeutic agents remain limited. To investigate the changing patterns of in-vitro susceptibility of S. aureus to 16 antibiotics, 190 clinical isolates from two different years were studied. The MICs of methicillin-susceptible (MSSA) and methicillin-resistant (MRSA) strains isolated in 1987 were compared with those of similar numbers of strains isolated in 1989. For MRSA > or = 90% of isolates from both years were resistant to clindamycin, gentamicin and erythromycin. These strains remained highly susceptible to vancomycin (100%), minocycline (90%) and rifampicin (100%). The greatest increase in resistance was observed for ofloxacin (2% in 1987 vs 62% in 1989); cross-resistance to all of the quinolones tested was demonstrated. MSSA strains remained susceptible to vancomycin (100%), minocycline (98%), rifampicin (100%), clindamycin (90%), gentamicin (90%) and ciprofloxacin (98%). It is concluded that methicillin susceptibility is a useful marker for selecting potential agents for the treatment of infections caused by S. aureus. A combination of minocycline and rifampicin may be a useful alternative to vancomycin for treating MRSA infections.

Drug Resistance, Microbial↗

PubMed1991

Tn554 inserts in methicillin-resistant Staphylococcus aureus from Australia and England: comparison with an American methicillin-resistant group.

We have compared methicillin-resistant (Mcr) Staphylococcus aureus isolates from Australia, the UK and the USA with regard to chromosomal inserts of the macrolides-lincosamides-streptogramin B (MLS)-resistance transposon Tn554. The American isolates were known to have a distinctive Tn554 insert, designated insert 6, which was closely associated epidemiologically with the methicillin-resistance phenotype. Southern blots of DNA from Australian and London, UK Mcr isolates were hybridized with a range of probes related to Tn554. The isolates had similar or identical Tn554 inserts, and we consider them to be a single group, designated 'Australondon'. Australondon isolates were compared in detail with a deletion mutant, ANS62, that had lost the methicillin-resistance determinant mec, plus other resistance determinants resident in the mec region of the chromosome, and with an American Mcr isolate containing Tn554 insert 6. The Australondon isolates had three Tn554 inserts. Sequence analysis with the polymerase chain reaction showed that all of these inserts differed from classical Tn554 in that the 3'-terminal residues of the transposons were reverse complements of the usual GATGTA. One of the Australondon inserts, designated 6B, closely resembled Tn554 insert 6 in the sequence of its left flanking chromosomal DNA. This insert was found to abut the deletion from the mec region which results in strain ANS62. We infer that Tn554 insert 6B is part of the mec region of the chromosome in Australondon isolates, supporting the idea that insert 6 of the American isolates is also part of this chromosomal region.

Australia↗

PubMed1992

DNA polymorphisms in methicillin-susceptible and methicillin-resistant strains of Staphylococcus aureus.

Restriction fragment length polymorphisms in methicillin-susceptible and methicillin-resistant (MRSA) strains of Staphylococcus aureus isolated in the same hospital over a 4-month period were studied by using SmaI and ApaI digestion of genomic DNA and pulsed-field gel electrophoresis. Each of the 20 methicillin-susceptible strains had a unique SmaI pattern, but the 27 MRSA strains showed only seven SmaI patterns. More than half of the SmaI fragments in all of these seven patterns were identical, as were those in the patterns from two unrelated MRSA strains. Digestion with ApaI, which cuts staphylococcus DNA into at least twice as many fragments, confirmed the results obtained with SmaI. Lastly, the plasmid contents of MRSA strains showing identical SmaI and ApaI electrophoretic patterns were not identical. These results are interpreted as supporting the hypothesis that all MRSA strains arose from a single clone and emphasize the need to use several methods in epidemiological investigations of MRSA outbreaks.

Bacterial Typing Techniques↗

PubMed1992

A comparison of clinical virulence of nosocomially acquired methicillin-resistant and methicillin-sensitive Staphylococcus aureus infections in a university hospital.

OBJECTIVES: To compare the clinical virulence of nosocomially acquired methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive S aureus (MSSA) infections in 1989. DESIGN: A retrospective comparison of host factors, in-hospital exposures, sites of infections, and outcomes of patients with nosocomial MRSA and MSSA infections. SETTING: University of Illinois Hospital, Chicago, Illinois. PARTICIPANTS: Forty-four adult patients with nosocomial S aureus infections. RESULTS: The 22 MRSA-infected and 22 MSSA-infected persons were similar regarding mean age, gender, underlying diseases, and exposure to surgery. Before developing infection, MRSA-infected persons were more likely to have received antibiotics (73% compared with 27%, odds ratio = 7.1, 95% confidence interval [CI95] = 2.0-25.8 p = .003) and to have stayed in the hospital > 2 weeks (64% compared with 18%, odds ratio = 7.9, CI95 = 2.0-31.6, p = .002). Bacteremia was the most common presentation in the MRSA and MSSA groups (55% and 59%, respectively). Infectious complications and death were infrequent in both groups. CONCLUSIONS: MRSA and MSSA strains infect patients with similar demographic features and underlying diseases, but MRSA infections are significantly more common among patients with previous antibiotic therapy and a prolonged preinfection hospital stay. Clinical presentations and outcomes did not differ significantly between the 2 groups. Thus, similar to studies in the early 1980s, our findings do not suggest greater intrinsic virulence of MRSA.

Chicago↗

PubMed1992

Comparison of in vitro adherence of methicillin-sensitive and methicillin-resistant Staphylococcus aureus to human nasal epithelial cells.

Reported nasal carriage rates of personnel caring for patients with methicillin-resistant Staphylococcus aureus (MRSA) range from 1% to 6% in contrast to nasal carriage rates of 45%-65% for methicillin-sensitive S. aureus (MSSA) in health care personnel under nonepidemic conditions. One proposed explanation for these conflicting observations was examined, namely that MSSA and MRSA differ in their ability to adhere to nasal epithelial cells. The adherence of 6 genotypically distinct strains of MSSA and MRSA to nasal epithelial cells from 5 healthy donors was compared using a radioisotope assay system (coefficient of variation, 26%). The effect of pretreating epithelial cells with S. aureus-derived ribitol teichoic acid, a known adhesin of S. aureus for epithelial cells, was also examined. The mean (+/- SE) adherence of MRSA compared with MSSA in 108 assays was 125 +/- 11.9 versus 129 +/- 8.3 viable bacteria per cell (P = .67). Dose-dependent competitive inhibition by ribitol teichoic acid was linear and equivalent for MRSA and MSSA (r, .949, P less than .001). As these in vitro results correlate to adherence in vivo, it would be anticipated that MRSA and MSSA would have an equal likelihood of nasal carriage. A critical review of published epidemiologic studies comparing MRSA and MSSA carriage rates also supports this hypothesis.

Bacterial Adhesion↗

PubMed1990

Hong Kong strains of methicillin-resistant and methicillin-sensitive Staphylococcus aureus have similar virulence.

While most authorities agree that methicillin-resistant Staphylococcus aureus (MRSA) are as pathogenic as methicillin-sensitive strains (MSSA), some believe that MRSA are relatively avirulent opportunists, and that their importance has been exaggerated. We present evidence that Hong Kong strains of MRSA and MSSA are equally pathogenic: they have similar virulence in animal models; they are isolated in similar proportions from both deep and superficial clinical sites including blood; in patients with hospital-acquired bacteraemias mortality rates are similar when adjusted for clinical factors; and in both animals and patients with systemic MRSA infection, mortality rates are significantly reduced by vancomycin therapy. Efforts to control the spread of MRSA are justified, and in invasive sepsis early treatment with vancomycin may be life-saving.

Animals↗

PubMed1992

Fosfomycin enhances the expression of penicillin-binding protein 2 in methicillin-sensitive and methicillin-resistant Staphylococcus aureus strains.

The effects of fosfomycin on penicillin-binding proteins (PBPs) were studied on the methicillin-resistant Staphylococcus aureus strain CIP (Collection de l'Institut Pasteur, Paris, France) 65-25 and on a methicillin-susceptible S. aureus strain CIP 65-6. The combinations of fosfomycin and oxacillin were synergistic, additive or antagonistic, depending on antibiotic concentrations. Fosfomycin induced modifications of the PBP profile of the two strains studied. In particular, it increased the expression of PBP2. This suggested that this protein is inducible; the only PBP not affected by fosfomycin was PBP3.

Bacterial Proteins↗

PubMed1992

Characterization of methicillin-susceptible and methicillin-resistant Staphylococcus aureus isolates by molecular typing methods.

Two groups of clinical Staphylococcus aureus isolates were examined by molecular typing methods. Detailed protocols for the technical procedures are described. By means of plasmid DNA profiles, plasmid DNA restriction enzyme digestion, as well as whole-cell DNA endonuclease digestions subjected to conventional agarose gel electrophoresis and pulsed-field gel electrophoresis, eight methicillin-susceptible S. aureus strains from three patients segregated into three different groups. Consecutive isolates from the same patient revealed identical fingerprints. Generally, good agreement between different molecular typing methods also was achieved in the investigation of 28 methicillin-resistant isolates. However, compared to whole-cell DNA restriction endonuclease analysis, plasmid DNA profiling (all but one strain had detectable plasmid DNA) showed a somewhat greater discriminatory ability. The techniques evaluated were reproducible and relatively easy to perform and provided valuable tools for studying the epidemiology of S. aureus in hospitals.

Bacterial Typing Techniques↗