AbstractThe last decade witnessed the emergence of Staphylococcus aureus- a versatile human pathogen, as a deadly superbug. The enormous genetic plasticity of the organism assists it to endlessly evolve resistance mechanisms against existing anti-infectives thus necessitating the need to control the spread of resistant staphylococcal isolates in hospitals and health care settings. This in turn demands the incessant exploration of newer biological matrices in search of diverse chemical entities with novel drug targets. Since time immemorial higher plants continue to be the best source of newer compounds with high therapeutic potential. Lead fractions from same or different plants can be developed into effective antibacterial polyherbal formulations. A lead fraction from methanolic extract of leaves of Callistemon rigidus exhibited a dose dependent antistaphylococcal activity during in vitro agar well assay against a panel of twenty seven clinical multidrug resistant S. aureus isolates. Further, minimal inhibitory concentration (MIC) evaluation by in vitro 96-well microplate based assay established a MIC range of 1.25–80 μg/ml as compared to 5–320 μg/ml of positive control, Cefuroxime sodium. The MIC50 and MIC90 of the methanolic lead fraction were 5 μg/ml and 40 μg/ml respectively. The present study thus signifies the vast potential of the lead fraction from Callistemon rigidus for future development into a herbal drug/ formulation and to impede global health crisis due to multidrug resistant Staphylococcus aureus.

In vitro investigation of the antimicrobial activity of a crude methanol extract of leaves of Callistemon rigidus R.Br. (Myrtaceae) revealed potential antibacterial activity against a broad spectrum of multidrug-resistant human pathogens. Agar well diffusion assays of the test extract established significant concentration-dependent antibacterial activity against methicillin-resistant Staphylococcus aureus, vancomycin-intermediate Staphylococcus aureus, vancomycin-resistant Escherichia coli, extended spectrum b-lactamase-producing E. coli, and multidrug-resistant Pseudomonas spp.

AbstractStaphylococcus aureus is the third most dreaded pathogen posing a severe threat due to its refractory behavior against the current armamentarium of antimicrobial drugs. This is attributed to the evolution of an array of resistance mechanisms responsible for morbidity and mortality globally. Local and international travel has resulted in the movement of drug resistant S. aureus clones from hospitals into communities and further into different geographical areas where they have been responsible for epidemic outbreaks. Thus, there is a dire necessity to refrain further cross movement of these multidrug resistant clones across the globe. The plausible alternative to prevent this situation is by thorough implementation of regulatory aspects of sanitation, formulary usage and development of new therapeutic interventions. Various strategies like exploring novel antibacterial targets, high throughput screening of microbes, combinatorial and synthetic chemistry, combinatorial biosynthesis and vaccine development are being extensively sought to overcome multidrug resistant chronic Staphylococcal infections. The majority of the antibacterial drugs are of microbial origin and are prone to being resisted. Anti-staphylococcal plant natural products that may provide a new alternative to overcome the refractory S.aureus under clinical settings have grossly been unnoticed. The present communication highlights the new chemical entities and therapeutic modalities that are entering the pharmaceutical market or are in the late stages of clinical evaluation to overcome multidrug resistant Staphylococcal infections. The review also explores the possibility of immunity and enzyme-based interventions as new therapeutic modalities and highlights the regulatory concerns on the prescription, usage and formulary development in the developed and developing world to keep the new chemical entities and therapeutic modalities viable to overcome antimicrobial resistance in S. aureus.

The rising incidents of invasive infections due to multidrug resistant Staphylococcus aureus necessitate the exploration of newer targets for development of antibiotics. Pathogenicity of S. aureus is attributed to a wide range of virulence factors. The aim of this study was to screen the production of three virulence factors viz. extracellular protease, extracellular lipase and superoxide dismutase in human pathogenic strains of S. aureus for development of a test panel which could aid in screening of natural products of plant and microbial origin. 27 clinical isolates were compared for their enzyme expression profiles of which eight were finally selected. Sau G5 was the only protease producing organism selected in the test panel, while Sau G3 and Sau G9 were best SOD producers and Sau G16, Sau G18, Sau G22, Sau A5 and Sau A2 exhibited highest expression among different groups of clinical staphylococci.

The present study assesses the reliability of the in vitro susceptibility tests E-test, disc diffusion and Alamar blue-based microbroth dilution assays for evaluating the efficacy of chloramphenicol, ciprofloxacin and cefaclor against clinical and reference isolates of Staphylococcus aureus, Escherichia coli and Pseudomonas spp. for use in empirical therapy. Ciprofloxacin showed 82% agreement between E-test and microbroth dilution by the visible dye reduction method against all organisms. This figure was 67% for cefaclor and 60% for chloramphenicol. E-test and microbroth dilution showed excellent correlation against S. aureus with all three antibiotics; however, correlation was not observed in Pseudomonas spp. between E-test and microbroth dilution by the percentage dye reduction method. E. coli did not show significant correlation, indicating the presence of heteroresistance. Chloramphenicol, being bacteristatic in nature, did not show clear agreement between the susceptibility test methods used. This study indicates that E-test provides an indication of minimum inhibitory concentration (MIC) of a panel of antibiotics against clinical isolates; however, microbroth dilution (dye reduction) is the most sensitive method for the determination of MIC due to intracellular enzymatic reduction of the dye to formazan, which only occurs in viable organisms. The study highlights the need for harmonisation between E-test and microbroth dilution methods in clinical trials of new antibiotics and in monitoring the drug resistance patterns in community and healthcare settings.