In Vitro Activity of Sodium New Houttuyfonate Alone and in Combination with Oxacillin or Netilmicin against Methicillin-Resistant Staphylococcus aureus

Background

Staphylococcus aureus can cause severe infections, including bacteremia and sepsis. The spread of methicillin-resistant Staphylococcus aureus (MRSA) highlights the need for novel treatment options. Sodium new houttuyfonate (SNH) is an analogue of houttuynin, the main antibacterial ingredient of Houttuynia cordata Thunb. The aim of this study was to evaluate in vitro activity of SNH and its potential for synergy with antibiotics against hospital-associated MRSA.

Methodology

A total of 103 MRSA clinical isolates recovered in two hospitals in Beijing were evaluated for susceptibility to SNH, oxacillin, cephalothin, meropenem, vancomycin, levofloxacin, minocycline, netilmicin, and trimethoprim/sulfamethoxazole by broth microdilution. Ten isolates were evaluated for potential for synergy between SNH and the antibiotics above by checkerboard assay. Time-kill analysis was performed in three isolates to characterize the kill kinetics of SNH alone and in combination with the antibiotics that engendered synergy in checkerboard assays. Besides, two reference strains were included in all assays.

Principal Findings

SNH inhibited all test strains with minimum inhibitory concentrations (MICs) ranging from 16 to 64 µg/mL in susceptibility tests, and displayed inhibition to bacterial growth in concentration-dependent manner in time-kill analysis. In synergy studies, the combinations of SNH-oxacillin, SNH-cephalothin, SNH-meropenem and SNH-netilmicin showed synergistic effects against 12 MRSA strains with median fractional inhibitory concentration (FIC) indices of 0.38, 0.38, 0.25 and 0.38 in checkerboard assays. In time-kill analysis, SNH at 1/2 MIC in combination with oxacillin at 1/128 to 1/64 MIC or netilmicin at 1/8 to 1/2 MIC decreased the viable colonies by ≥2log₁₀ CFU/mL.

Conclusions/Significance

SNH demonstrated in vitro antibacterial activity against 103 hospital-associated MRSA isolates. Combinations of sub-MIC levels of SNH and oxacillin or netilmicin significantly improved the in vitro antibacterial activity against MRSA compared with either drug alone. The SNH-based combinations showed promise in combating MRSA.     

Synergistic effects between silibinin and antibiotics on methicillin-resistant Staphylococcus aureus isolated from clinical specimens

Methicillin-resistant Staphylococcus aureus (MRSA) is a dangerous microorganism, and creates serious medical problems. It causes many types of infections in humans and often acquires multi-drug resistance. In this study, silibinin was evaluated against 20 clinical isolates of MRSA, either alone or in combination with ampicillin or oxacillin, using a checkerboard assay. The silibinin exhibited good activity against isolates of MRSA, and MRSA ATCC33952 and MSSA ATCC25923, with minimum inhibitory concentrations/minimum bactericidal concentrations (MICs/MBCs) ranging between 2-8/4-16 μg/mL, for ampicillin 2-1024/2-2048 μg/mL, and for oxacillin 0.25-32/0.5-64 μg/mL. The range of MIC(50) and MIC(90) were 0.5-4 μg/mL and 2-8 μg/mL, respectively. The MICs/MBCs for the combination of silibinin plus oxacillin or ampicillin were reduced by ≥4-fold against the MRSA isolates tested, demonstrating a synergistic effect, as defined by a fractional inhibitory concentration index (FICI) of ≤0.5. Furthermore, a time-kill study evaluating the growth of the tested bacteria showed that growth was completely attenuated after 2-5 h of treatment with the 1/2 MIC of silibinin, regardless of whether it was administered alone or with oxacillin (1/2 MIC) or ampicillin (1/2 MIC). In conclusion, silibinin exerted synergistic effects when administered with oxacillin or ampicillin and the antibacterial activity and resistant regulation of silibinin against clinical isolates of MRSA might be useful in controlling MRSA infections.     

Efficacy of Combined Vancomycin and Fosfomycin against Methicillin-Resistant Staphylococcus aureus in Biofilms In Vivo

Infection by methicillin-resistant Staphylococcus aureus (MRSA) is a life-threatening condition, and formation of biofilms can lead to treatment failure in a clinical setting. The aim of this study was to demonstrate the in vivo bactericidal effects of a combination of vancomycin (VAN) and fosfomycin (FOS) against MRSA in a rat carboxymethyl cellulose-pouch biofilm model. The results of the time-kill assay showed that the combination therapy was capable of killing at low minimal inhibitory concentrations (MIC) (½× MIC VAN +1× MIC FOS and 1× MIC VAN + 1× MIC FOS). In the in vivo study, a synergistically bactericidal effect was observed when using the combination therapy on MRSA embedded in the mature biofilm model. In comparison with the untreated control group and the groups receiving either VAN or FOS alone, the rats treated with combination therapy had lower MRSA colony counts in exudates from the pouch, lower white blood cell and neutrophil counts, and C-reactive protein (CRP) in peripheral blood. Furthermore, histological analysis of the pouch wall indicated combination therapy resulted in disappearance of biofilm-like structures, marked decrease in necrosis, and formation of granular tissue. In conclusion, the combination of VAN with FOS had a synergistic bactericidal effect on chronic MRSA infection embedded in biofilm, providing an alternative approach to treating this condition.     

Synthesis and anti Methicillin resistant Staphylococcus aureus activity of substituted chalcones alone and in combination with non-beta-lactam antibiotics

A total of 30 chalcone analogues was synthesized via a base catalyzed Claisen Schmidt condensation and screened for their in vitro antibacterial activity against Methicillin-sensitive Staphylococcus aureus (MSSA) and Methicillin-resistant Staphylococcus aureus (MRSA) alone or in combination with non beta-lactam antibiotics namely ciprofloxacin, chloramphenicol, erythromycin, vancomycin, doxycycline and gentamicin. In the checkerboard technique, fractional inhibitory concentration indices (FICI) show that the following combinations like ciprofloxacin with 25 (4'-bromo-2-hydroxychalcone); doxycycline with 21 (4-hydroxychalcone); doxycycline with 25; and doxycycline with 4 (2',2-dihydroxychalcone) were synergistic against MRSA. In term SAR study, the relationship between chalcone structure and their antibacterial activity against S. aureus and synergy with tested antibiotics were discussed. Possible mechanisms for antibacterial activity of chalcones alone as well as the synergistic effect in combinations were proposed by molecular modeling studies, respectively. Combinations of chalcones with conventional antibiotics could be an effective alternative in the treatment of infection caused by MRSA.     

Bacteriocins as alternative agents for control of multiresistant staphylococcal strains

AIMS: To investigate the activity of seven staphylococcins, bacteriocins produced by staphylococci, against multiresistant Staphylococcus aureus and coagulase-negative staphylococci (CNS) involved in human infections. METHODS AND RESULTS: Four bacteriocins produced by Staph. epidermidis (Pep5, epidermin, epilancin K7 and epicidin 280) and three produced by Staph. aureus (aureocins A70, A53 and 215FN) were tested. Sixteen Staph. aureus strains, including a representative strain of the endemic Brazilian methicillin-resistant clone (MRSA), and 57 CNS strains were used as indicators. Among the staphylococcins used, Pep5 was able to inhibit 77.2% of the CNS strains and 87.5% of the Staph. aureus strains tested, including the Brazilian MRSA endemic clone, responsible for a large number of hospital-acquired infections in Brazil. On the other hand, aureocin A53 and epidermin presented a high antagonistic activity only against the Staph. aureus strains, being able to inhibit, respectively, 87.5% and 81.3% of them, including also the Brazilian MRSA endemic clone. The remaining bacteriocins inhibited only a low percentage of the nosocomial staphylococcal strains tested. CONCLUSIONS: Aureocin A53 and epidermin have potential applications against MRSA, whereas Pep5 seems to be an attractive agent against both MRSA and CNS, including mupirocin-resistant strains and the Brazilian endemic clone of MRSA, which is also found disseminated in other countries. SIGNIFICANCE AND IMPACT OF THE STUDY: Bacteriocins may represent alternative agents to control important nosocomial pathogens.     

Antibacterial Effects of Green Tea Polyphenols on Clinical Isolates of Methicillin-Resistant <Emphasis Type="Italic">Staphylococcus aureus</Emphasis>

The antibacterial effects of tea polyphenols (TPP) extracted from Korean green tea (Camellia sinensis) against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) were evaluated. Characterization of the minimal inhibitory concentration (MIC) of oxacillin for 30 S. aureus strains isolated from patients treated with oxacillin identified 13 strains with an oxacillin MIC ≥ 4 μg/mL as methicillin-resistant Staphylococcus aureus (MRSA) (range: 8 to 512 μg/mL), while 17 strains were methicillin-susceptible Staphylococcus aureus (MSSA) (range: 0.25–0.5 μg/mL). The MICs of TPP ranged from 50 to 180 μg/mL for both the MSSA and the MRSA strains. The MICs of oxacillin for each of the 13 MRSA strains were reduced between 8- and 128-fold when these strains were coincubated with sub-MIC (≤0.5× MIC) levels of TPP, demonstrating that the combination of TPP plus oxacillin was synergistic for all of the clinical MRSA isolates. Two-dimensional polyacrylamide gel electrophoresis identified 14 extracellular proteins of MRSA-13 down-regulated and 3 proteins up-regulated by exposure to TPP. These studies demonstrate that TPP can differentially stimulate the expression of various proteins in these bacteria and synergize the bactericidal activity of oxacillin for MRSA.     

Synergistic effect between dieckol from <Emphasis Type="Italic">Ecklonia stolonifera</Emphasis> and β-lactams against methicillin-resistant <Emphasis Type="Italic">Staphylococcus aureus</Emphasis>

We have been attempting for some time to discover a compound evidencing antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). The dieckol isolated from Ecklonia stolonifera has been shown to exhibit antibacterial activity against methicillin-susceptible S. aureus (MSSA) and MRSA. The minimum inhibitory concentrations (MICs) of dieckol were determined in a range of 32 to 64 μg/mL against standard MSSA and MRSA strains. Furthermore, dieckol clearly reversed the high-level ampicillin and penicillin resistance of MRSA. The MICs of ampicillin against two standard strains of MRSA were dramatically reduced from 512 to 0.5 μg/mL in combination with 1/4 MIC of dieckol (16 μg/mL). The fractional inhibitory concentration (FIC) indices of ampicillin and penicillin were measured from 0.066 to 0.266 in combination with 8 or 16 μg/mL of dieckol against all tested MRSA strains, thereby suggesting that dieckol-ampicillin or dieckol-penicillin combinations exert a synergistic effect against MRSA. The results of this study indicate that dieckol, administered in combination with β-lactams, may prove effective in the treatment of MRSA infections. Our finding may also contribute to the development of an alternative phytotherapeutic anti-MRSA agent.     

Synergy of aminoglycoside antibiotics by 3-Benzylchroman derivatives from the Chinese drug Caesalpinia sappan against clinical methicillin-resistant Staphylococcus aureus (MRSA)

The in vitro antimicrobial activities of three 3-Benzylchroman derivatives, i.e. Brazilin (1), Brazilein (2) and Sappanone B (3) from Caesalpinia sappan L. (Leguminosae) were assayed, which mainly dealt with synergistic evaluation of aminoglycoside and other type of antibiotics against methicillin-resistant Staphylococcus aureus (MRSA) by the three compounds through the Chequerboard and Time-kill curve methods. The results showed that Compounds 1–3 alone exhibited moderate to weak activity against methicillin-susceptible S. aureus (MSSA) and other standard strains by MICs/MBCs ranged from 32/64 to >1024/>1024 μg/ml, with the order of activity as 1 > 2 > 3. Chequerboard method showed significant anti-MRSA synergy of 1/Aminoglycosides (Gentamicin, Amikacin, Etimicin and Streptomycin) combinations with (FICIs)₅₀ at 0.375–0.5. The combined (MICs)₅₀ values (μg/ml) reduced from 32–128/16–64 to 4–8/4–16, respectively. The percent of reduction by MICs ranged from 50% to 87.5%, with a maximum of 93.8% (1/16 of the alone MIC). Combinations of 2 and 3 with Aminoglycosides and the other antibiotics showed less potency of synergy. The dynamic Time-killing experiment further demonstrated that the combinations of 1/aminoglycoside were synergistically bactericidal against MRSA. The anti-MRSA synergy results of the bacteriostatic (Chequerboard method) and bactericidal (time-kill method) efficiencies of 1/Aminoglycoside combinations was in good consistency, which made the resistance reversed by CLSI guidelines. We concluded that the 3-Benzylchroman derivative Brazilin (1) showed in vitro synergy of bactericidal activities against MRSA when combined with Aminoglycosides, which might be beneficial for combinatory therapy of MRSA infection.     

Development of novel antibacterial agents against methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) poses a serious threat to public health because of its resistance to multiple antibiotics most commonly used to treat infection. In this study, we report the unique ability of the cyclooxygenase-2 (COX-2) inhibitor celecoxib to kill Staphylococcus aureus and MRSA with modest potency. We hypothesize that the anti-Staphylococcus activity of celecoxib could be pharmacologically exploited to develop novel anti-MRSA agents with a distinct mechanism. Examination of an in-house, celecoxib-based focused compound library in conjunction with structural modifications led to the identification of compound 46 as the lead agent with high antibacterial potency against a panel of Staphylococcus pathogens and different strains of MRSA. Moreover, this killing effect is bacteria-specific, as human cancer cells are resistant to 46. In addition, a single intraperitoneal administration of compound 46 at 30 mg/kg improved the survival of MRSA-infected C57BL/6 mice. In light of its high potency in eradicating MRSA in vitro and its in vivo activity, compound 46 and its analogues warrant continued preclinical development as a potential therapeutic intervention against MRSA.     

Synergistic effects between aminoethyl-chitosans and β-lactams against methicillin-resistant Staphylococcus aureus (MRSA)

Two kinds of aminoethyl-chitosans (AEC), AEC90 and AEC50, which had degrees of deacetylation of 90% and 50%, respectively, were prepared and their synergistic effects in combination with β-lactams including ampicillin, penicillin, and oxacillin against two standard methicillin-resistant Staphylococcus aureus (MRSA) strains and twelve clinical isolated MRSA strains were investigated. When AECs and β-lactams were combined, synergistic effects were observed with fractional inhibitory concentration (FIC) indices of 0.252–0.508, and the MICs of β-lactams in the presence of AECs were dramatically reduced.     

Evaluation of susceptibility to antibiotics of Staphylococcus aureus strains resistant to methicillin]

Methicillin-resistant strains of Staphylococcus aureus (MRSA) constitute a serious diagnostic and therapeutic problem. Over 500 strains of Staphylococcus aureus were tested for susceptibility to methicillin. By application of a screening method, 13.7% of these strains were classified as methicillin-resistant. Over 95% of these strains were isolated from hospital infections. Applying criteria of belonging of these strains to methicillin-resistance classes it was found that 49.3% belonged to class II, 31.2% to class III and 19.5% to class IV. Analysis of susceptibility to antibiotics of MRSA strains demonstrated significant differences between class II and between class III and IV in resistance to imipenem, gentamycin, erythromycin and tetracycline. All tested strains were susceptible to ciprofloxacin, ofloxacin, vancomycin and teicoplanin. The screening method (25 mg methicillin/l of TSA medium) results in obtaining of univocal results of determination of methicillin-resistance in S. aureus.     

Remarkable synergies between baicalein and tetracycline, and baicalein and beta-lactams against methicillin-resistant Staphylococcus aureus

During the screening of compounds that potentiate the effect of antimicrobial agents against methicillin-resistant Staphylococcus aureus(MRSA), we found that an extract of thyme (Thymus vulgaris L) leaves greatly reduced the minimum inhibitory concentration (MIC) of tetracycline against MRSA. We isolated the effective compound and identified it as baicalein (5, 6, 7-trihydroxyflavone). One of the clinically isolated MRSA strains possessed tetK, a gene encoding active efflux pump for tetracycline. We examined the effect of baicalein on the efflux of tetracycline, using Escherichia coli KAM32/pTZ1252 carrying the tetK. The E. coli KAM32/pTZ1252 showed 8 to 16 times higher MIC than E. coli KAM32. We observed strong inhibition of transport of tetracycline by baicalein with membrane vesicles prepared from E. coli KAM32/pTZ1252. Baicalein also showed synergy with tetracycline in a MRSA strain that doesn't possess tetK, or with beta-lactams. Thus, mechanisms of the synergies seem to be versatile.     

Synergism between Medihoney and Rifampicin against Methicillin-Resistant Staphylococcus aureus (MRSA)

Skin and chronic wound infections caused by highly antibiotic resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) are an increasing and urgent health problem worldwide, particularly with sharp increases in obesity and diabetes. New Zealand manuka honey has potent broad-spectrum antimicrobial activity, has been shown to inhibit the growth of MRSA strains, and bacteria resistant to this honey have not been obtainable in the laboratory. Combinational treatment of chronic wounds with manuka honey and common antibiotics may offer a wide range of advantages including synergistic enhancement of the antibacterial activity, reduction of the effective dose of the antibiotic, and reduction of the risk of antibiotic resistance. The aim of this study was to investigate the effect of Medihoney in combination with the widely used antibiotic rifampicin on S. aureus. Using checkerboard microdilution assays, time-kill curve experiments and agar diffusion assays, we show a synergism between Medihoney and rifampicin against MRSA and clinical isolates of S. aureus. Furthermore, the Medihoney/rifampicin combination stopped the appearance of rifampicin-resistant S. aureus in vitro. Methylglyoxal (MGO), believed to be the major antibacterial compound in manuka honey, did not act synergistically with rifampicin and is therefore not the sole factor responsible for the synergistic effect of manuka honey with rifampicin. Our findings support the idea that a combination of honey and antibiotics may be an effective new antimicrobial therapy for chronic wound infections.     

Detection and partial characterisation of two antibacterial factors from the excretions/secretions of the medicinal maggot Lucilia sericata and their activity against methicillin-resistant Staphylococcus aureus (MRSA)

Maggot therapy is a simple and highly successful method for cleansing infected and necrotic wounds. The use of maggots has become increasingly important in the treatment of non-healing wounds, particularly those infected with the multidrug-resistant pathogen, methicillin-resistant Staphylococcus aureus (MRSA). The increasing challenge concerning the treatment of MRSA infections and the recent finding of vancomycin-resistant strains of MRSA have elicited the search for novel antibacterial compounds and, in particular, investigations into the potent antibacterial mechanism(s) behind maggot therapy. In this study, we report that excretions/secretions (ES) from the blowfly, Lucilia sericata, exhibit potent, thermally stable, protease resistant antibacterial activity against MRSA in vitro. We describe the initial characterisation of two antibacterial factors from native ES of L. sericata. A small, <500 Da factor with significant antibacterial activity against MRSA was partially isolated using ultrafiltration techniques. The potent activity of this factor was comparable to that of native excretions/secretions. A larger, 0.5-3-kDa factor with significant activity against S. aureus was also partially characterised.     

Evaluation of Trimethoprim/Sulfamethoxazole (SXT), Minocycline,Tigecycline, Moxifloxacin,and Ceftazidime Alone and in Combinations for SXT-Susceptible and SXT-Resistant Stenotrophomonas maltophilia by In Vitro Time-Kill Experiments

Background

The optimal therapy for infections caused by Stenotrophomonas maltophilia (S. maltophilia) has not yet been established. The objective of our study was to evaluate the efficacy of trimethoprim/sulfamethoxazole (SXT), minocycline, tigecycline, moxifloxacin, levofloxacin, ticarcillin-clavulanate, polymyxin E, chloramphenicol, and ceftazidime against clinical isolated S. maltophilia strains by susceptibility testing and carried out time-kill experiments in potential antimicrobials.

Methods

The agar dilution method was used to test susceptibility of nine candidate antimicrobials, and time-killing experiments were carried out to evaluate the efficacy of SXT, minocycline, tigecycline, moxifloxacin, levofloxacin, and ceftazidime both alone and in combinations at clinically relevant antimicrobial concentrations.

Results

The susceptibility to SXT, minocycline, tigecycline, moxifloxacin, levofloxacin, ticarcillin-clavulanate, chloramphenicol, polymyxin E, and ceftazidime were 93.8%, 95.0%, 83.8%, 80.0%, 76.3%, 76.3%, 37.5%, 22.5%, and 20.0% against 80 clinical consecutively isolated strains, respectively. Minocycline and tigecycline showed consistent active against 22 SXT-resistant strains. However, resistance rates were high in the remaining antimicrobial agents against SXT-resistant strains. In time-kill experiments, there were no synergisms in most drug combinations in time-kill experiments. SXT plus moxifloxacin displayed synergism when strains with low moxifloxacin MICs. Moxifloxacin plus Minocycline and moxifloxacin plus tigecycline displayed synergism in few strains. No antagonisms were found in these combinations. Overall, compared with single drug, the drug combinations demonstrated lower bacterial concentrations. Some combinations showed bactericidal activity.

Conclusions

In S. maltophilia infections, susceptibility testing suggests that minocycline and SXT may be considered first-line therapeutic choices while tigecycline, moxifloxacin, levofloxacin, and ticarcillin-clavulanate may serve as second-line choices. Ceftazidime, colistin, and chloramphenicol show poor active against S. maltophilia. However, monotherapy is inadequate in infection management, especially in case of immunocompromised patients. Combination therapy, especially SXT plus moxifloxacin, may benefit than monotherapy in inhibiting or killing S. maltophilia.     

深圳市人民医院近五年临床分离金黄色葡萄球菌的分布及耐药性分析

目的 分析医院感染患者金黄色葡萄球菌的临床分布特征及耐药性变化,为临床治疗金黄色葡萄球菌感染提供依据。方法 回顾性分析2012年1月至2016年12月我院从临床各类标本中分离获得的1 141株金黄色葡萄球菌,统计其在各类标本和病区中的分布特点,并用Ｋ-Ｂ法测定该菌对常用抗菌药物的敏感性。结果 5年中共分离出1 141株金黄色葡萄球菌,标本来源构成比最多的是伤口分泌物（43.3%）、呼吸道标本（24.0%）和血液标本（10.2%）。耐甲氧西林金黄色葡萄球菌（MRSA）共有339株,占29.7%。各年MRSA的检出数依次为53株（31.9%）、51株（26.0%）、82株（35.2%）、81株（30.3%）和72株（26.0%）。MRSA主要分离自神经外科（13.8%）、呼吸监护室（10.6%）、重症监护室（8.8%）和骨科（7.7%）。MRSA对抗菌药物的耐药性普遍高于MSSA,二者比较差异有统计学意义（P＜0.05）。未发现对万古霉素、利奈唑胺、替考拉宁耐药的金黄色葡萄球菌。结论 MRSA感染多发生于长期使用抗菌药物,有皮肤软组织伤口及侵入性操作的科室及患者。MRSA具有多重耐药性,应严格掌握抗菌药物的使用适应证;同时临床治疗应根据药物敏感性报告针对性地合理用药,以便及时有效地控制感染并防止耐药菌株的扩散。     

Monoclonal Antibody Targeting Staphylococcus aureus Surface Protein A (SasA) Protect Against Staphylococcus aureus Sepsis and Peritonitis in Mice

Epidemic methicillin-resistant Staphylococcus aureus (MRSA) imposes an increasing impact on public health. Due to multi-antibiotics resistance in MRSA strains, there is an urgent need to develop novel therapeutics such as effective monoclonal antibodies (mAbs) against MRSA infections. Staphylococcus aureus surface protein A (SasA), a large surface-located protein (~240 kDa), is one of MSCRAMMs (microbial surface components recognizing adhesive matrix molecules) and a potential target for immunotherapeutic approaches against S. aureus infections. In the present study, we analyzed the sequence of SasA with bioinformatics tools and generated a protective monoclonal antibody (2H7) targeting the conserved domain of SasA. 2H7 was shown to recognize wild-type S. aureus and promote opsonophagocytic killing of S. aureus. In both sepsis and peritoneal infection models, prophylactic administration of 2H7 improved the survival of BALB/c mice challenged by S. aureus strain USA300 and ST239 (prevalent MRSA clones in North America and Asian countries, respectively) and enhanced bacterial clearance in kidneys. Additionally, 2H7 prophylaxis prevented the formation of intraperitoneal abscess in a murine model of peritoneal infection and therapeutic administration of 2H7 showed protective efficacy in a murine sepsis model. Our results presented here provide supporting evidences that an anti-SasA mAb might be a potential component in an antibody-based immunotherapeutic treatment of MRSA infections.     

Synergistic effects of the combination of galangin with gentamicin against methicillin-resistant <Emphasis Type="Italic">Staphylococcus aureus</Emphasis>

The antimicrobial killing activity toward methicillin-resistant Staphylococcus aureus (MRSA) has been a serious emerging global issue. New effective antimicrobials and/or new approaches to settle this issue are urgently needed. The oriental herb, Alpinia officinarum, has been used in Korea for several hundreds of years to treat various infectious diseases. As it is well known, one of the active constituents of Alpinia officinarum is galangin. Against the 17 strains, the minimum inhibitory concentrations (MICs) of galangin (GAL) were in the range of 62.5 ~ 125 microg/ml, and the MICs of gentamicin (GEN) ranged from 1.9 microg/ml to 2,000 microg/ml. The fractional inhibitory concentrations (FICs) of GAL, in combination with GEN, against 3 test strains were 0.4, 3.9, and 250 microg/ml, and were all 15.62 microg/ml in GEN. The FIC index showed marked synergism in the value range of 0.19 to 0.25. By determining time-kill curves, also confirmed the low synergism of the GAL and GEN combination against 4 h, 8 h, 12 h, and 24 h cultured MRSA. The time-kill study results indicated a low synergistic effect against 3 test strains. Thus, the mixture of GAL and GEN could lead to the development of new combination antibiotics against MRSA infection.     

Surface disinfection properties of the combination of an antimicrobial peptide,ranalexin, with an endopeptidase,lysostaphin, against methicillin‐resistant Staphylococcus aureus (MRSA)

Aims: To characterize the antibacterial synergy of the antimicrobial peptide, ranalexin, used in combination with the anti‐staphylococcal endopeptidase, lysostaphin, against methicillin‐resistant Staphylococcus aureus (MRSA), and to assess the combination’s potential as a topical disinfectant or decolonizing agent for MRSA. MRSA causes potentially lethal infections, and pre‐operative patients colonized with MRSA are often treated with chlorhexidine digluconate and mupirocin cream to eradicate carriage. However, chlorhexidine is unsuitable for some patients, and mupirocin resistance is increasingly encountered, indicating new agents are required. Methods and Results: Using an ex vivo assay, ranalexin and lysostaphin tested in combination reduced viable MRSA on human skin to a greater extent than either compound individually. The combination killed bacteria within 5 min and remained effective and synergistic even in high salt and low pH conditions. Conclusions: The combination is active against MRSA on human skin and under conditions that may be encountered in sweat. Significance and Impact of the Study: Although the exact mechanism of activity remains unresolved, considering its specific spectrum of activity, fast killing kinetics and low likelihood of resistance arising, the combination of ranalexin with lysostaphin warrants consideration as a new agent to eradicate nasal and skin carriage of Staph. aureus, including MRSA.     

Molecular analysis of repeated methicillin-resistant Staphylococcus aureus infections in children

Background

Methicillin-resistant Staphylococcus aureus (MRSA) is a major pathogen that causes severe morbidity and mortality in hospitalized patients. It is unclear whether repeated MRSA infections in pediatric patients are caused by relapse of previous infecting strains or by acquiring new strains from extrinsic sources. The study aimed to define the genetic relatedness of MRSA isolates from children with repeated infections.

Methodology/Principal Findings

Children with multiple MRSA infections during 2004–2006 were identified in a teaching hospital. Repeated infections were confirmed by chart review and the responsible isolates were genotyped and screened for Panton-Valentine leukocidin (PVL) genes. Two consecutive episodes comprised an infection pair, and strain relatedness was defined for each pair as indistinguishable, highly related, or distinct if the isolates were of the same subtype, the same genotype, or different genotype, respectively. A total of 114 episodes comprising 66 infection pairs were identified in 48 children. The interval of infection pairs ranged from 15 days to 346 days, with a median duration of 57.5 days. Genotypings classified all isolates into 7 genotypes and 31 subtypes. Of 66 pairs, 46 (69.7%), 13 (19.7%) and 7 (10.6%) pairs were caused by indistinguishable, highly related and distinct strains, respectively. Subsequent infections caused by indistinguishable strains were more common for PVL-positive strains (17/18, 94.4%) than for PVL-negative strains (29/48, 60.4%, P = 0.007). The strain relatedness was not affected by the durations of interval between infections.

Conclusions/Significance

Most repeated MRSA infections in children are caused by indistinguishable strains even after a long period of interval, suggesting that persistent carriage and relapse of initial infecting strains were responsible for the majority of recurrent MRSA infections.