Synthesis and potent antimicrobial activity of some novel methyl or ethyl 1H-benzimidazole-5-carboxylates derivatives carrying amide or amidine groups

A series of benzimidazole-5-carboxylic acid alkyl ester derivatives carrying amide or amidine substituted methyl or phenyl groups at the position C-2 were synthesised and evaluated for antibacterial and antifungal activities against S. aureus, methicillin resistant S. aureus (MRSA), S. faecalis, methicillin resistant S. epidermidis (MRSE), E. coli and C. albicans. The results showed that while all simple acetamides are essentially inactive, aromatic amides and amidines have potent antibacterial activities. Aromatic amidine derivatives 13 f-h exhibited the best inhibitory activity with 1.56-0.39 microg/mL MIC values against MRSA and MRSE.     

Antibacterial and bactericidal activities of tea extracts and catechins against methicillin resistant Staphylococcus aureus]

We examined tea extract, (-) epigallocatechin gallate (EGCg) and theaflavin digallate (TF3) for their antibacterial and bactericidal activities against methicillin resistant Staphylococcus aureus (MRSA) and food poisoning strains of S. aureus. Twenty percent tea extract (50 microliters), EGCg (63 micrograms) and TF3 (125 micrograms) added to one ml of culture medium each inhibited the growth of all strains of MRSA and food poisoning S. aureus tested. Tea extract showed also a bactericidal activity against MRSA even at the same concentration of as in ordinarily brewed tea. EGCg at a concentration of 250 micrograms/ml showed a bactericidal activity against MRSA but not against food poisoning S. aureus, but at 500 micrograms/ml reduced markedly the viable number within 48h. These results suggest that tea and catechin can be used as prophylactic agents against MRSA infection.     

Anti-MRSA activity of alkyl gallates.

A series of alkyl gallates (3,4,5-trihydroxybenzoates) was found to show antibacterial activity against Gram-positive bacteria including methicillin resistant Staphylococcus aureus (MRSA) strains. For example, dodecyl (C(12)) gallate (1) exhibited bactericidal activity against MRSA ATCC 33591 strain with the minimum bactericidal concentration (MBC) of 25 microg/mL (74 microM). The time-kill curve study showed that dodecyl gallate is bactericidal against this MRSA strain. This bactericidal activity comes in part from its ability to inhibit respiratory electron transport systems. The length of the alkyl chain is not a major contributor but plays an important role in eliciting the activity.     

Comparison of methods for the detection of methicillin resistance in Staphylococcus aureus isolates from food products

AIMS: To compare several methods for detection of methicillin resistance in Staphylococcus aureus isolates from food. METHODS AND RESULTS: Two hundred S. aureus isolates from food of animal origin were screened for methicillin resistance by a PCR assay specific for the mecA gene, an oxacillin agar screen test and a cefoxitin disk diffusion test. Six out of 200 strains (3%) were found to be methicillin-resistant Staphylococcus aureus (MRSA) by PCR. The oxacillin agar screen test detected only one of the MRSA isolates (sensitivity of 16.7%) and mischaracterized three additional strains as MRSA (specificity of 98.45%). None of the MRSA strains was detected by the cefoxitin test (sensitivity of 0%), while 15 methicillin-susceptible S. aureus (MSSA) strains were misclassified as resistant (specificity of 92.3%). Fifteen MSSA strains displayed a beta-lactamase hyperproducer-like phenotype. The six MRSA (mecA-positive) strains resembled the characteristics of heteroresistant strains. CONCLUSIONS: As MRSA of animal origin may display atypical phenotypes, PCR appears to be more reliable for detection of methicillin resistance in animal strains. SIGNIFICANCE AND IMPACT OF THE STUDY: The study stresses the need for implementing the methods of screening S. aureus from food of animal origin for methicillin resistance.     

Antimicrobial protein from Streptomyces fulvissimus inhibitory to methicillin resistant Staphylococcus aureus

Fermented culture of Streptomyces fulvissimus was found to secrete an antibacterial protein inhibitory to Micrococcus luteus, Bacillus subtilis, Bacillus cereus and methicillin resistant Staphylococcus aureus (MRSA) strains. The extracellular protein from the fermented culture on concentration revealed a high molecular weight peptide of 63kDa on SDS-PAGE gel and the region on gel displayed inhibitory activity against methicillin resistant Staphylococcus aureus. Bioactivity of the extra cellular protein was non-sensitive to proteinase K, alpha chymotrypsin, protease, EDTA (ethylene diamine tetra acetic acid), PMSF (phenyl methyl sulfonyl fluoride) and DMSO (dimethyl sulfoxide) but partially susceptible to amylase and heat. Glycoprotein nature of the proteinaceous compound was confirmed by periodic acid schiffs (PAS) staining. The secretary protein of S. fulvissimus demonstrated a significant activity against MRSA strain. It could be an important source for developing new drugs to control multidrug resistant gram positive bacteria.     

Antibiotic resistant Staphylococcus aureus: a paradigm of adaptive power

Nothing documents better the spectacular adaptive capacity of Staphylococcus aureus than the response of this important human and animal pathogen to the introduction of antimicrobial agents into the clinical environment. The effectiveness of penicillin introduced in the early 1940s was virtually annulled within a decade because of the plasmid epidemics that spread the ss-lactamase gene through the entire species of S. aureus. In 1960 within one to two years of the introduction of penicillinase resistant ss-lactams (methicillin), methicillin resistant S. aureus (MRSA) strains were identified in clinical specimens. By the 1980s, epidemic clones of MRSA acquired multidrug resistant traits and spread worldwide to become one of the most important causative agents of hospital acquired infections. In the early 2000s, MRSA strains carrying the Tn1546 transposon-based enterococcal vancomycin resistant mechanism were identified in clinical specimens, bringing the specter of a totally resistant bacterial pathogen closer to reality. Then, in the late 1990s, just as effective hygienic and antibiotic use policies managed to bring down the frequency of MRSA in hospitals of several countries, MRSA strains began to show up in the community.     

Characterization of cell membrane parameters of clinical isolates of Staphylococcus aureus with varied susceptibility to alpha-melanocyte stimulating hormone

Staphylococcus aureus (S. aureus), a major human pathogen of hospital and community acquired infections, is becoming resistant to almost all commercially available antibiotics. This has prompted development of antimicrobial peptides as therapeutic options. Alpha melanocyte stimulating hormone (α-MSH) is one such peptide known to possess antimicrobial properties. In the present study, we analyzed the antimicrobial activity of α-MSH against 75 clinical strains of S. aureus including both methicillin susceptible S. aureus (MSSA) and methicillin resistant S. aureus (MRSA) strains. Results of our previous study showed that membrane damage is the major mechanism of staphylocidal activity of α-MSH. In this context, we compared the various bacterial membrane parameters, viz., membrane fluidity, lipid composition, and surface charge of a few selected MSSA and MRSA strains that showed variable susceptibility to the melanocortin peptide. Our results showed that α-MSH killed both type of strains efficiently (≥70% killing in 84% clinical strains after exposure with 6μM of α-MSH for 1h). It was observed that compared to the α-MSH-susceptible strains, the α-MSH-non-susceptible strains had a different membrane order and phospholipid pattern. There was no consistent pattern of cell surface charge to distinguish α-MSH-susceptible strain from a non-susceptible strain. In conclusion, α-MSH possessed potential staphylocidal activity for both against MSSA and MRSA strains. S. aureus strains not susceptible to the peptide exhibited a rigid membrane and a higher amount of the cationic phospholipid as compared to the α-MSH-susceptible strains.     

Synthesis and structure-activity relationships of 2-vinylchroman-4-ones as potent antibiotic agents

A series of novel 2-vinylchroman-4-ones, analogues of the natural products Aposphaerin A and B, were identified as potent antibiotics. Derivatives exhibit a significant activity against multiresistant strains of S. aureus, such as MRSA (methicillin resistant S. aureus). The 2-vinylchroman-4-ones were efficiently prepared by Lewis acid mediated conjugate addition of vinylmagnesium bromide to chromones.     

Nasal carriage of methicillin resistant Staphylococcus aureus and their antibiotic susceptibility patterns in children attending day-care centers

Nasal colonization with community acquired methicillin resistant Staphylococcus aureus (CA-MRSA) is being increasingly reported, especially in places where people are in close contact and in reduced hygiene, such as day-care centers. In this study we investigated the frequency of MRSA colonization and their antibiotic susceptibility patterns in 1-6 years old children of day-care centers in Hamadan, West of Iran.Five hundred nasal swabs were collected from children of 27 day-care centers that had no risk factors for colonization by S. aureus. The specimens were cultured for isolation of S. aureus by standard methods. Antimicrobial susceptibility testing was performed according to the Clinical and Laboratory Standards Institute (CLSI) guidelines. For evaluation of the frequency of erythromycin induced clindamycin resistance, disk approximation test (D-test) was applied.Totally, 148 (29.6%) children were colonized by S. aureus. Out of 260 male, 94 (36.2%) and of 240 female, 54 (22.5%) cases were nasal carriers of S. aureus (P value = 0.001). Six (4.1%) of the 148 S. aureus isolated from children were MRSA strains. None of MRSA and methicillin susceptible S. aureus (MSSA) was resistant to vancomycin and clindamycin. Three of the 6 strains of MRSA and 7 (4.9%) of the 142 MSSA strains were resistant to erythromycin, and D-test was positive in all of them.We conclude that the rate of colonization by S. aureus is high in children attending day-care centers but colonization with MRSA is not common in our areas. Clindamycin or trimethoprim-sulfamethoxazol could be used in mild to moderataly severe diseases caused by CA-MRSA. However, if the CA-MRSA isolates are erythromycin resistant, D-test should be carried out for detection of inducible clindamycin resistance.     

The emergence and evolution of methicillin-resistant Staphylococcus aureus

Significant advances have been made in recent years in our understanding of how methicillin resistance is acquired by Staphylococcus aureus. Integration of a staphylococcal cassette chromosome mec (SCCmec) element into the chromosome converts drug-sensitive S. aureus into the notorious hospital pathogen methicilin-resistant S. aureus (MRSA), which is resistant to practically all beta-lactam antibiotics. SCCmec is a novel class of mobile genetic element that is composed of the mec gene complex encoding methicillin resistance and the ccr gene complex that encodes recombinases responsible for its mobility. These elements also carry various resistance genes for non-beta-lactam antibiotics. After acquiring an SCCmec element, MRSA undergoes several mutational events and evolves into the most difficult-to-treat pathogen in hospitals, against which all extant antibiotics including vancomycin are ineffective. Recent epidemiological data imply that MRSA has embarked on another evolutionary path as a community pathogen, as at least one novel SCCmec element seems to have been successful in converting S. aureus strains from the normal human flora into MRSA.     

耐甲氧西林金黄色葡萄球菌及其肠毒素的检测和耐药性分析

目的评价乳胶结合试验检测耐甲氧西林金黄色葡萄球菌(MRSA)及其肠毒素(SE),并进行耐药性分析.方法收集130株金黄色葡萄球菌临床分离株,通过药敏试验将其分为耐甲氧西林金黄色葡萄球菌和甲氧西林敏感金黄色葡萄球菌(MSSA),用反向间接血凝试验(RPHA)检测金黄色葡萄球菌肠毒素.结果67株MR-SA产肠毒素,19株MSSA产肠毒素,MRSA产肠毒素率为100%,MSSA产肠毒素率为30%.结论实验室应重视金黄色葡萄球菌肠毒素的检测.     

Antibacterial activity of α-mangostin against vancomycin resistant Enterococci (VRE) and synergism with antibiotics

alpha-Mangostin, isolated from the stem bark of Garcinia mangostana L., was found to be active against vancomycin resistant Enterococci (VRE) and methicillin resistant Staphylococcus aureus (MRSA), with MIC values of 6.25 and 6.25 to 12.5 microg/ml, respectively. Our studies showed synergism between alpha-mangostin and gentamicin (GM) against VRE, and alpha-mangostin and vancomycin hydrochloride (VCM) against MRSA. Further studies showed partial synergism between alpha-mangostin and commercially available antibiotics such as ampicillin and minocycline. These findings suggested that alpha-mangostin alone or in combination with GM against VRE and in combination with VCM against MRSA might be useful in controlling VRE and MRSA infections.     

Combinatorial modification of natural products: synthesis and in vitro analysis of derivatives of thiazole peptide antibiotic GE2270 A: A-ring modifications

Thiazole peptide GE2270 A (1) possesses potent antimicrobial activity against many gram-positive pathogens, including methicillin resistant Staphylococcus aureus (S. aureus, MRSA; MIC(90)=0.06 microg/mL) and vancomycin resistant Enterococcus spp. (VRE; MIC(90)=0.03 microg/mL); however its poor aqueous solubility has prohibited its development for the clinical treatment of infections. An integrated combinatorial and medicinal chemistry program was employed to identify derivatives of 1 that retain activity but possess greatly enhanced aqueous solubility.     

Sensitivity of methicillin-resistant Staphylococcus aureus strains to some antibiotics, antiseptics and disinfectants

The effects of antibiotics, antiseptics and disinfectants against some methicillin resistant (MRSA) and methicillin-sensitive (MSSA) Staphylococcus aureus strains have been studied. The MRSA and MSSA strains were equally sensitive to phenols, esters of para(4)-hydroxybenzoit acid and chlorhexidine but MRSA strains were slightly more resistant to quaternary ammonium compounds and considerably more so to dibromopropamidine isothionate. Some MRSA strains were also resistant to phenylmercuric nitrate (but not another organomercurial, thiomersal), mercuric chloride and cadmium chloride. All MRSA strains produced β-lactamase. Strains from the Royal Free Hospital, London were highly resistant to β-lactam antibiotics, erythromycin, trimethoprim and tetracyctines but were sensitive to other antibiotics. One strain from the University Hospital of Wales, Cardiff was resistant to gentamicin but sensitive to tetracycline and trimethoprim.     

Evaluation of chromogenic medium (ORSAB) for routine identification of methicillin resistant Staphylococcus aureus (MRSA)

Performance of chromogenic medium (ORSAB) for routine detection of methicillin resistant S. aureus (MRSA) was evaluated on 510 specimens collected from patients suspected of MRSA infection or colonization. Addition of ORSAB plates to the routine protocol allowed MRSA identification in 24 hours from samples plating. In 18 samples MRSA colonies were identified only on ORSAB plates, those cases would have been missed by routine protocol alone.     

Antibacterial activity of anacardic acid and totarol, alone and in combination with methicillin, against methicillinresistant 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 6·25 μg ml^-1 of anacardic acid and 0·78 μg 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 6·25 μg 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 1·56 μg ml^-1 for MRSA ATCC 33591, and from 800 to 6·25 μg 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.     

Molecular design of multifunctional antibacterial agents against methicillin resistant Staphylococcus aureus (MRSA)

Antibacterial activity of a series of alkyl gallates (3,4,5-trihydroxybenzoates) against Gram-positive bacteria, especially methicillin resistant Staphylococcus aureus (MRSA) strains was evaluated. Gram-positive bacteria are all susceptible to alkyl gallates. Dodecyl gallate was the most effective against MRSA ATCC 33591 strain with the minimum bactericidal concentration (MBC) of 25 microg/mL (74 microM). The time-kill curve study showed that dodecyl gallate was bactericidal against this MRSA strain at any growth stage. This activity was observed even in the chloramphenicol-treated cells, but the rate of decrease of cell number was slower than that in the exponentially growing cells. The bactericidal activity of medium-chain alkyl gallates was noted in combination with their ability to disrupt the native membrane-associated function nonspecifically as surface-active agents (surfactants) and to inhibit the respiratory electron transport. Subsequently, the same series of alkyl protocatechuates (3,4-dihydroxybenzoates) were studied and the results obtained are similar to those found for alkyl gallates. The length of the alkyl chain is not a major contributor but is related to the activity.     

Identification and discrimination of Staphylococcus aureus strains using matrix-assisted laser desorption/ionization-time of flight mass spectrometry

Staphylococcus aureus is an important human pathogen frequently resistant to a wide range of antibiotics. Methicillin-resistant S. aureus (MRSA) strains are common nosocomial pathogens that pose a world-wide problem. Rapid and accurate discrimination between methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus is essential for appropriate therapeutic management and timely intervention for infection control. We report here the application of matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) for monitoring the bacterial fingerprints expressed by two well characterized S. aureus strains ATCC 29213 (MSSA) and ATCC 43330 (MRSA). Consistent strain-specific data were obtained from subcultures analyzed over a period of three months as well as after changing the growth media from Mueller-Hinton to blood agar indicating the reliability of the method. The bacterial fingerprints of these two strains were compared to independent clinical isolates of S. aureus. A uniform signature profile for MRSA could not be identified. However, the bacterial fingerprints obtained proved to be specific for any given strain. This study demonstrates that MALDI-TOF MS is a powerful method for rapid identification of clonal strains of S. aureus, which might be useful for tracking nosocomial outbreaks of MRSA and for epidemiologic studies of infections diseases in general.     

Human antibody response during sepsis against targets expressed by methicillin resistant Staphylococcus aureus

The identification of target structures is a prerequisite for the development of new treatment options, like antibody based therapy, against methicillin resistant Staphylococcus aureus (MRSA). In this study we identified immunodominant structures which were expressed in vivo during sepsis caused by MRSA. Using human sera we compared the immune response of humans with MRSA sepsis with the immune response of normal individuals and asymptomatically colonized individuals. We identified and characterized four staphylococcal specific antigenic structures. One target is a staphylococcal protein of 29 kDa that exhibited 29% identity to secreted protein SceA precursor of Staphylococcus carnosus. The putative function of this protein, which was designated IsaA (immunodominant staphylococcal antigen), is unknown. The second target is an immunodominant protein of 17 kDa that showed no homology to any currently known protein. This immunodominant protein was designated IsaB. The third and fourth antigens are both immunodominant proteins of 10 kDa. One of these proteins showed 100% identity to major cold shock protein CspA of S. aureus and the other protein was identified as the phosphocarrier protein Hpr of S. aureus. The identified immunodominant proteins may serve as potential targets for the development of antibody based therapy against MRSA.