Suppression of intrinsic resistance to penicillins in Staphylococcus aureus by polidocanol, a dodecyl polyethyleneoxid ether

Mechanisms of Action of Corilagin and Tellimagrandin I That Remarkably Potentiate the Activity of β-Lactams against Methicillin-ResistantStaphylococcus aureus

Corilagin and tellimagrandin I are polyphenols isolated from the extract of Arctostaphylos uvaursi and Rosa canina L. (rose red), respectively. We have reported that corilagin and tellimagrandin I remarkably reduced the minimum inhibitory concentration (MIC) of beta-lactams in methicillin-resistant Staphylococcus aureus(MRSA). In this study, we investigated the effect of corilagin and tellimagrandin I on the penicillin binding protein 2 '(2a) (PBP2 '(PBP2a)) which mainly confers the resistance to beta-lactam antibiotics in MRSA. These compounds when added to the culture medium were found to decrease production of the PBP2 '(PBP2a) slightly. Using BOCILLIN FL, a fluorescent-labeled benzyl penicillin, we found that PBP2 '(PBP2a) in MRSA cells that were grown in medium containing corilagin or tellimagrandin I almost completely lost the ability to bind BOCILLIN FL. The binding activity of PBP2 and PBP3 were also reduced to some extent by these compounds. These results indicate that inactivation of PBPs, especially of PBP2 '(PBP2a), by corilagin or tellimagrandin I is the major reason for the remarkable reduction in the resistance level of beta-lactams in MRSA. Corilagin or tellimagrandin I suppressed the activity of beta-lactamase to some extent.

In vitro antimicrobial effect of the tissue conditioner containing silver nanoparticles

PURPOSE

The aim of this study was to identify in vitro antimicrobial activity of the tissue conditioner containing silver nanoparticles on microbial strains, Staphylococcus aureus, Streptococcus mutans and Candida albicans.

MATERIALS AND METHODS

Experimental disc samples (20.0×3.0 mm) of tissue conditioner (GC Soft-Liner, GC cooperation, Tokyo, Japan) containing 0.1 - 3.0% silver nanoparticles (0%: control) were fabricated. Samples were placed on separate culture plate dish and microbial suspensions (100 µL) of tested strains were inoculated then incubated at 37℃. Microbial growth was verified at 24 hrs and 72 hrs and the antimicrobial effects of samples were evaluated as a percentage of viable cells in withdrawn suspension (100 µL). Data were recorded as the mean of three colony forming unit (CFU) numerations and the borderline of the antimicrobial effect was determined at 0.1% viable cells.

RESULTS

A 0.1% silver nanoparticles combined to tissue conditioner displayed minimal bactericidal effect against Staphylococcus aureus and Streptococcus mutans strains, a 0.5% for fungal strain. Control group did not show any microbial inhibitory effect and there were no statistical difference between 24 hrs and extended 72 hrs incubation time (P > .05).

CONCLUSION

Within the limitation of this in vitro study, the results suggest that the tissue conditioner containing silver nanoparticles could be an antimicrobial dental material in denture plaque control. Further mechanical stability and toxicity studies are still required.

ILSMRs (intensifier of beta-lactam-susceptibility in methicillin-resistant Staphylococcus aureus) from Tara [Caesalpinia spinosa (Molina) Kuntze]

Four quinic acid gallates were isolated from the dried pods of Tara [Caesalpinia spinosa (Molina) Kuntze]. These compounds intensified the susceptibility of methicillin-resistant Staphylococcus aureus (MRSA) to oxacillin. 3,4,5-Tri-O-galloylquinic acid methyl ester (2) was the most effective compound of them.

Variation in synergistic activity by flavone and its related compounds on the increased susceptibility of various strains of methicillin-resistant Staphylococcus aureus to beta-lactam antibiotics

We found that some flavonoids had a weak antibacterial effect on methicillin-resistant Staphylococcus aureus (MRSA), but that at sub-MIC concentrations they greatly increased the susceptibility of these strains to beta-lactam antibiotics. Flavone showed diverse synergistic effects on the susceptibility of MRSA to beta-lactam antibiotics. The variation of the synergistic effects of the flavones to increase the susceptibility of strains of MRSA to beta-lactam antibiotics coincided with their varying effects on growth-inhibition of these strains. Based on these findings, we have proposed a model for the mechanisms of high resistance of MRSA to beta-lactams and the massive reduction in the beta-lactams MIC caused by flavones.

Alkyl gallates, intensifiers of beta-lactam susceptibility in methicillin-resistant Staphylococcus aureus

We found that ethyl gallate purified from a dried pod of tara (Caesalpinia spinosa) intensified beta-lactam susceptibility in methicillin-resistant and methicillin-sensitive strains of Staphylococcus aureus (MRSA and MSSA strains, respectively). This compound and several known alkyl gallates were tested with MRSA and MSSA strains to gain new insights into their structural functions in relation to antimicrobial and beta-lactam susceptibility-intensifying activities. The maximum activity of alkyl gallates against MRSA and MSSA strains occurred at 1-nonyl and 1-decyl gallate, with an MIC at which 90% of the isolates tested were inhibited of 15.6 microg/ml. At concentrations lower than the MIC, alkyl gallates synergistically elevated the susceptibility of MRSA and MSSA strains to beta-lactam antibiotics. Such a synergistic activity of the alkyl gallates appears to be specific for beta-lactam antibiotics, because no significant changes were observed in the MICs of other classes of antibiotics examined in this study. The length of the alkyl chain was also associated with the modifying activity of the alkyl gallates, and the optimum length was C5 to C6. The present work clearly demonstrates that the length of the alkyl chain has a key role in the elevation of susceptibility to beta-lactam antibiotics.

Flavone Markedly Affects Phenotypic Expression of β-Lactam Resistance in Methicillin-Resistant Staphylococcus aureus Strains Isolated Clinically

Flavone and its derivatives had very weak antibacterial effects on methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive S. aureus, but dramatically intensified MRSA's susceptibility to beta-lactams. We named these compounds "ILSMR (intensifier of beta-lactam-susceptibility in MRSA)." We also found discrepancies among MRSA strains in their responses to flavone; some strains showed phenotypic susceptibility to methicillin while others showed phenotypic resistance to it. To understand the mechanism underlying this discrepancy, we characterized 20 MRSA strains in detail, analyzed their conventional and molecular typings, and examined each strain's resistance to beta-lactams, with COL serving as a reference. Neither SCCmec typing nor coagulase typing explained the diverse effects of flavone on the beta-lactam MICs of these strains. Likewise, changes in pulsed-field gel electrophoresis (PFGE) type were not associated with the profiles of ILSMR effects. However, the present observations suggest that the ILSMR effects on MRSA is strain-specific, and that this effect depends on an as-yet unknown mechanism that is essential for the expression of the phenotype conferring beta-lactam resistance to MRSA strains, independently of an interaction with the mecA-encoded penicillin-binding protein 2a or with the beta-lactamase.

Marked potentiation of activity of beta-lactams against methicillin-resistant Staphylococcus aureus by corilagin

We found that an extract of Arctostaphylos uva-ursi markedly reduced the MICs of beta-lactam antibiotics, such as oxacillin and cefmetazole, against methicillin-resistant Staphylococcus aureus. We isolated the effective compound and identified it as corilagin. Corilagin reduced the MICs of various beta-lactams by 100- to 2,000-fold but not the MICs of other antimicrobial agents tested. The effect of corilagin and oxacillin was synergistic. Corilagin showed a bactericidal action when added to the growth medium in combination with oxacillin.

Restoration of effectiveness of beta-lactams on methicillin-resistant Staphylococcus aureus by tellimagrandin I from rose red

We found that extract from petals of Rosa canina L. (rose red) strikingly reduced the minimum inhibitory concentration of beta-lactams in methicillin-resistant Staphylococcus aureus. We isolated two compounds that reduced the minimum inhibitory concentrations of beta-lactams from the extract, tellimagrandin I and rugosin B. Tellimagrandin I was very effective regarding the reduction of the minimum inhibitory concentration, and rugosin B showed some effect. Tellimagrandin I showed a weak bactericidal action when added together with oxacillin. Judging from the fractional inhibitory concentration index, the effect of tellimagrandin I and oxacillin was synergistic. Tellimagrandin I also significantly reduced the minimum inhibitory concentration of tetracycline in some strains of methicillin-resistant Staphylococcus aureus.

Prolonged antimicrobial effect of tissue conditioners containing silver-zeolite

OBJECTIVES

The purpose of this study was to elucidate the in vitro antimicrobial effect of tissue conditioners containing silver-zeolite on Candida albicans and nosocomial respiratory infection-causing bacteria, Staphylococcus aureus and Pseudomonas aeruginosa.

METHODS

Five commercially available tissue conditioners were selected: Visco-gel (VG), GC Soft-Liner (SL), Fitt (FT), SR-Ivoseal (IV) and Shofu Tissue Conditioner (TC). Samples, 10 x 10 x 2.5 mm in size, contained silver-zeolite (SZ sample) and no SZ (N sample). The antimicrobial effects of these two samples were evaluated as a percentage of viable cells (CFU) in a microbial suspension (100 microliter) in phosphate-buffered saline with or without immersion in artificial saliva for four weeks. The borderline of the antimicrobial effect was determined at 0.1% viable cells.

RESULTS

With the SZ samples, all tested microbes were killed under both conditions of no immersion and immersion in saliva. In non-immersed N samples, however, no cells of C. albicans (except with VG) and S. aureus survived, whereas the percentage of viable cells of P. aeruginosa was similar to that found in the control. However, with immersion in saliva, viable cells of C. albicans in some N samples (VG, SL and TC) increased compared with non-immersion samples by more than 0.1%.

CONCLUSION

Tissue conditioners containing SZ have been shown to have antimicrobial effects for four weeks on C. albicans and nosocomial respiratory infection-causing bacteria in saliva in vitro.

Regulation of beta-lactamase synthesis as a novel site of action for suppression of methicillin resistance in Staphylococcus aureus

Nearly all clinical isolates of methicillin resistant Staphylococcus aureus (MRSA) produce beta-lactamase as well as an additional low-affinity penicillin-binding protein called PBP2a or PBP2', the main factor for mediating methicillin resistance. Polidocanol (PDO), a dodecyl polyethyleneoxide ether, resensitizes clinical isolates of MRSA to methicillin; in addition, their resistance to benzylpenicillin (BP) is reduced. The action of PDO is based on the inhibition of the induced syntheses of PBP2a and beta-lactamase. Induction in our study was performed with 2-(2'-carboxyphenyl)benzoyl-6-aminopenicillanic acid (CBAP). Inducible PBP2a production in MRSA strains is under the control of the same regulatory system which is responsible for the induction of beta-lactamase synthesis. BlaR1, a membrane-spanning protein with a penicillin sensor and a signal transducer domain represents the starting point of this induction cascade. Based on its amphiphilic properties, it is likely that the action of PDO is located in the bacterial membrane. Therefore we investigated the possibility that BlaR1 might be the main target for PDO action. We were able to detect the BlaR1 sensor domain in resistant staphylococcal cells even in the noninduced state by fluorography. In a competition assay, CBAP was bound specifically, with a high affinity to the penicillin sensor. Moreover, the binding of CBAP was very stable. As concerns PDO, no significant interaction with the penicillin binding site of BlaR1 was detectable. This is why the BlaR1 transducer domain is thought to be the actual target area of PDO. In this case, PDO would interfere with the transmission of the signal, generated by the receptor binding of CBAP, through the membrane via BlaR1 into the staphylococcal cell. This assumption could be confirmed by the analysis of the concentration-effect relationship, whereafter PDO does not work as a competitive, but as a noncompetitive antagonist of CBAP. Our results demonstrate that BlaR1 could be an attractive new target for the development of new drugs to overcome methicillin resistance.

The intrinsic antimicrobial activity of selected sclerosing agents in sclerotherapy

BACKGROUND

Detergent sclerosing agents may have intrinsic antimicrobial properties. In addition, they may have synergistic effects with other antibiotics such as penicillin. They may induce suppression of intrinsic resistance to penicillin in Staphylococcus aureus.

OBJECTIVE

It is in this setting that the present study was carried out in order to determine the degree of suppression of resistance to methicillin and oxacillin in S. aureus by two detergent sclerosing solutions.

METHODS

Four strains of S. aureus including a quality control strain were isolated. The minimal inhibitory concentration (MIC) of Sotradecol 1.0% and Polidocanol 0.5% were determined in Mueller Hinton Broth. These dilutions were subsequently seeded with 10(5) organisms of the strain of S. aureus being tested. Serial dilutions of penicillin were made and then the sclerosing agents were added in the appropriate dilutions.

RESULTS

Sotradecol 1.0% produced a MIC of 1/64 in two strains of S. aureus and 1/128 in two other variant strains. Polidocanol 0.5% produced a MIC of 1/64 against two strains of S. aureus and an MIC of 1/8 and 1/4 with two other variant strains. In addition, in three of the four S. aureus strains both sclerosing agents had synergistic activity with penicillin and augmented its activity approximately 16-fold.

CONCLUSION

This study presents the first successful modification in which detergent sclerosing solutions influence methicillin resistance in a Staphylococcal species. This points out a new potential therapeutic indication for this class of agents.

Growth inhibition of Malassezia species by pharmacological concentrations of polidocanol

In vitro antifungal properties of polidocanol (Thesi), a hydroxypolyethoxydecan, were investigated against various yeasts at concentrations of 0.05-10% (w/w) by means of the agar diffusion test; in the case of lipophilic Malassezia furfur, polidocanol-containing olive oil was used additionally for sensitivity study. Six strains of M. furfur of different clinical origin were tested as well as strains of C. albicans (3), C. krusei (3), C. parapsilosis (2), C. robusta (2), Tr. cutaneum (2) and one strain each of C. guilliermondii, C. glabrata, C. tropicalis and M. pachydermatis. Both test systems revealed predominantly fungistatic activity against M. furfur, with a minimal inhibitory concentration (MIC) of 1% polidocanol (w/w), while yeasts of other genera (Candida species, Trichosporum species) showed no or only transitory (C. krusei) inhibition of growth. M. pachydermatis was also found to be sensitive with a MIC of 0.1%; this suggests a specific inhibitory effect against the genus Malassezia. Polidocanol, which has been used for decades as an antipruritic and analgesic in various topical preparations at concentrations between 3% and 5%, might therefore be suitable for prophylaxis of recurrent pityriasis versicolor or in veterinary medicine.

Low-level methicillin resistance in strains of Staphylococcus aureus

Two strains of Staphylococcus aureus expressing borderline or low-level methicillin resistance by one or more in vitro test methods were examined for resistance in vivo and for biochemical and genetic markers of methicillin resistance. In vivo, nafcillin was equally effective against experimental aortic valve endocarditis in rabbits, regardless of whether they were infected by a fully susceptible or a low-level-resistant strain. Resistance did not emerge during therapy. For the more resistant of the two low-level-resistant strains, methicillin was as effective as nafcillin. Nafcillin was ineffective against endocarditis caused by a truly methicillin-resistant strain, and resistance emerged on therapy. The low-level-resistant strains did not produce the low-affinity penicillin-binding protein 2a that is associated with methicillin resistance and did not contain DNA that hybridized with probes that recognized the methicillin resistance determinant. Low-level resistance in S. aureus is a phenomenon that is biochemically and genetically distinct from true methicillin resistance. These strains actually are susceptible to beta-lactam antibiotics. The clinical problem posed by these strains is not a therapeutic one but, instead, one of how to differentiate them from those that are truly methicillin resistant.

Methicillin-resistant staphylococci

Strains of staphylococci resistant to methicillin were identified immediately after introduction of this drug. Methicillin-resistant strains have unusual properties, the most notable of which is extreme variability in expression of the resistance trait. The conditions associated with this heterogeneous expression of resistance are described. Methicillin resistance is associated with production of a unique penicillin-binding protein (PBP), 2a, which is bound and inactivated only at high concentrations of beta-lactam antibiotics. PBP2a appears to be encoded by the mec determinant, which also is unique to methicillin-resistant strains. The relationships between PBP2a and expression of resistance and implications for the mechanism of resistance are discussed. The heterogeneous expression of methicillin resistance by staphylococci poses problems in the detection of resistant strains. Experience with several susceptibility test methods is reviewed and guidelines for performance of these tests are given. Treatment of infections caused by methicillin-resistant staphylococci is discussed. Vancomycin is the treatment of choice. Alternatives have been few because methicillin-resistant strains often are resistant to multiple antibiotics in addition to beta-lactam antibiotics. New agents which are active against methicillin-resistant staphylococci are becoming available, and their potential role in treatment is discussed.

Effect of NaCl and nafcillin on penicillin-binding protein 2a and heterogeneous expression of methicillin resistance in Staphylococcus aureus

Expression of methicillin resistance in heterogeneous strains of Staphylococcus aureus is enhanced by 2 to 5% NaCl in the medium and by selection with beta-lactam antibiotics. Resistance is associated with production of a penicillin-binding protein (PBP), PBP 2a, with low affinity for binding beta-lactam antibiotics. Therefore, the effects of NaCl and nafcillin on amounts of PBP 2a produced and its binding affinity were examined and correlated with expression of resistance. Nafcillin-triggered autolysis also was examined. No relationships between the level of resistance expressed and (i) relative amounts of PBP 2a, (ii) inducibility of PBP 2a by nafcillin, or (iii) binding affinity of nafcillin for PBP 2a were found. A protective effect of NaCl for the susceptible subpopulation, corresponding to inhibition of autolysis, was observed for heterogeneous strains. Even in the absence of NaCl, highly resistant cells were relatively tolerant to nafcillin-triggered autolysis. These results support the hypothesis that high levels of resistance require an additional factor besides PBP 2a. This factor may act within the autolytic pathway.

Antimicrobial resistance of Staphylococcus aureus: genetic basis

Images

Effects of growth of methicillin-resistant and -susceptible Staphylococcus aureus in the presence of beta-lactams on peptidoglycan structure and susceptibility to lytic enzymes

Growth of methicillin-resistant Staphylococcus aureus DU4916 in the presence of methicillin yielded crude cell walls that showed an increased rate of autolysis and purified cell walls (PCW) and peptidoglycan (PG) that had increased susceptibilities to autolysin extracted with LiCl and to lysozyme. The PG of cells grown in the presence of methicillin had markedly decreased cross-linking and O acetylation. Growth of the methicillin-susceptible strain H in the presence of subinhibitory concentrations of cefoxitin, a specific inhibitor of penicillin-binding protein (PBP) 4, caused a substantial decrease in PG cross-linking and O acetylation and increased susceptibilities of PCW and PG to LiCl-extracted autolysin and to lysozyme. Strain DU4916 cells grown in the presence of methicillin did not show an increased rate of autolysis or an increased susceptibility to vancomycin- or D-cycloserine-induced lysis, even though their PG was hypo-cross-linked. This implies that the potential for increased autolysis is controlled in intact cells and that this regulation may be involved in the methicillin resistance phenomenon. Growth of the methicillin-susceptible strain DU4916S in the presence of methicillin yielded PCW and PG that showed small increases in susceptibilities to LiCl-extracted autolysin and to lysozyme and a small decrease in PG cross-linking. Comparison of the PBPs of a penicillinase-nonproducing derivative of strain DU4916 (DU4916-K7) with those of strain DU4916S in intact cells and isolated membranes revealed that PBPs 1 to 4 had similar high beta-lactam antibiotic affinities in both strains and identified an additional PBP, PBP2(1), with low beta-lactam affinity in the methicillin-resistant strain DU4916-K7. The low degree of cross-linking of PG in strain DU4916 cells grown with methicillin was probably due mainly to inhibition of the secondary cross-linking function of PBP 4.

Methicillin-resistant S. aureus and S. epidermidis strains: modern hospital pathogens

The international recognition of the emergence of methicillin-resistantStaphylococcus aureusas major nosocomial pathogens dates to the late 1970s. The weight of evidence from many institutions suggests that transmission involves spread from patient to patient of the same or very similar strain and that effective control, if not elimination, involves isolation of infected and colonized patients.

More recently, a number of reports have suggested the emergence of methicillin-resistantS. epidermidisand other coagulase-negative staphylococci as significant nosocomial pathogens. Although the organisms undoubtedly share many similarities with methicillin-resistant strains ofS. aureus, it is certain that biologic differences exist which are important for infection control.