Letters in applied microbiology
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Lett. Appl. Microbiol. · Apr 2015
New erythromycin derivatives enhance β-lactam antibiotics against methicillin-resistant Staphylococcus aureus.
Newly synthesized erythromycin derivatives were screened for synergy with oxacillin and other β-lactam antibiotics against methicillin-resistant Staphylococcus aureus (MRSA). MRSA ATCC43300 and some clinically isolated MRSA were used. Several erythromycin derivatives were found to possess high synergism with oxacillin against MRSA. The newly synthesized erythromycin derivatives were also tested for their inhibitory effects against MRSA, either separately or in combination with oxacillin, using serial broth dilution, disc diffusion, Etest strips, growth curves and time-kill curves. A representative derivative, SIPI-8294, could potentiate almost all β-lactam antibiotics tested against the model strain MRSA ATCC43300 from 4 to 128 times and had synergism with oxacillin against 12 of 16 clinical isolates of MRSA under one-fourth of the minimum inhibitory concentration (MIC) of the compounds. This is the first report on the synergistic activity of these new erythromycin derivatives. These findings provide a new choice for the treatment of infection caused by MRSA and lead us to further study the synergistic mechanism. ⋯ This study is the first report on the synergy of anti-MRSA between new erythromycin derivatives and β-lactam antibiotics in vitro. The results show that although the erythromycin derivatives have poor anti-MRSA effects alone, they possess high synergism with oxacillin against MRSA ATCC43300 and clinically isolated MRSA. These novel compounds can significantly reduce the dosage of β-lactam antibiotics against MRSA, while this synergistic effect is different from the combination of β-lactams and β-lactamase inhibitors. The research may provide a new choice for the treatment of infection caused by MRSA and be useful to the research and development of new combination of medicines.
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Studies describing the use of essential oil constituents as antimicrobial agents have steadily increased; however, some phyto-constituents are often overlooked due to unfavourable minimum inhibitory concentration (MIC) values. Virulence depends on transcriptional factors which are regulated by cell-to-cell communication called quorum sensing (QS). This study was undertaken to evaluate the antimicrobial and anti-QS properties of 29 compounds commonly found in essential oils using two bioreporter strains. QS-inhibitory activity was assessed qualitatively by agar diffusion and quantitatively by spectrophotometric assays. MICs of all the tested compounds ranged from 0·032 to >5 mg ml(-1). Twenty-two compounds displayed varying levels of QS inhibitory activity with zones of violacein inhibition ranging from 9 to 16 mm. Majority of tested molecules inhibited violacein and pyocyanin production in Chromobacterium violaceum and Pseudomonas aeruginosa, while seven compounds increased violacein and pyocyanin production. Interestingly, it was observed that the (+)-enantiomers of carvone, limonene and borneol increased violacein and pyocyanin production, while their levorotary analogues inhibited this production. α-Terpineol and cis-3-nonen-1-ol exhibited >90% violacein inhibition, suggesting their potential as QS inhibitors. This preliminary study indicates that plant volatiles have the potential to impede or promote bacterial communication and further studies need to be undertaken to explore the contribution of structural analogues and stereochemistry of molecules in this process. ⋯ Antimicrobial and antiquorum sensing (QS) properties of 29 common essential oil compounds were evaluated. Interruption of QS may lead to the development of therapeutic, antivirulence agents to control disease-causing pathogens which are preferable over antimicrobial agents as the latter drives selection pressure on microbial communities to acquire resistance. Twenty-two compounds inhibited QS, while seven promoted the QS to a variable extent in Chromobacterium violaceum and Pseudomonas aeruginosa. Preliminary results suggest that QS-inhibitory compounds of natural origin may inspire the formulation of new generation of antimicrobial agents to control infectious pathogens.
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Lett. Appl. Microbiol. · Mar 2014
'Prevalence and antimicrobial susceptibility of Listeria monocytogenes and methicillin-resistant Staphylococcus aureus strains from raw meat and meat products in Zaria, Nigeria.
The bacterial genera Listeria and Staphylococcus have been frequently isolated from food products and are responsible for a number of animal and human diseases. The aim of the study was to simultaneously isolate and characterize L. monocytogenes and Staphylococcus species from 300 samples of raw meat and meat products, to determine the susceptibility of the organisms to commonly used antimicrobial agents and to determine the presence of haemolysin A (hyl) virulence gene in L. monocytogenes and staphylococcal cassette chromosome mecA (SCCmec) gene in the Staph. aureus isolates using PCR. Of the 85 Listeria isolates tested, 12 L. monocytogenes were identified and tested for their sensitivity to 14 antimicrobial agents. All the 12 isolates (100%) were resistant to nine antimicrobial agents, but however sensitive to gentamicin. Only one isolate was found to harbour the hylA gene. Twenty-nine isolates were confirmed as Staph. aureus by the Microbact 12S identification system and were all presumptively identified as methicillin-resistant Staph. aureus species using oxacillin-resistant Staph. aureus basal medium (ORSAB). The 29 Staph. aureus isolates were tested for their sensitivity to 16 antimicrobial agents, and 11 were resistant to methicillin. None of the 11 Staph. aureus isolates harboured the methicillin resistance, mecA gene. ⋯ Listeria monocytogenes and Staphylococcus aureus are important agents of foodborne diseases. Occurrence of these infectious agents was established in meat and meat products in Zaria, Nigeria. Majority of isolates obtained from this study, displayed multidrug resistance to commonly used antimicrobial agents, including methicillin resistance among the Staph. aureus isolates. The potential virulence of L. monocytogenes found in ready-to-eat food was documented by the carriage of hly A gene by one of the isolates. A different mechanism of methicillin resistance or different homologue of mec A gene may be circulating among Nigerian isolates.
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Lett. Appl. Microbiol. · Aug 2013
The antimicrobial effects of helium and helium-air plasma on Staphylococcus aureus and Clostridium difficile.
Healthcare-associated infections (HCAI) affect 5-10% of acute hospital admissions. Environmental decontamination is an important component of all strategies to prevent HCAI as many bacterial causes survive and persist in the environment, which serve as ongoing reservoirs of infection. Current approaches such as cleaning with detergents and the use of chemical disinfectant are suboptimal. We assessed the efficacy of helium and helium-air plasma in killing Staphylococcus aureus and Clostridium difficile on a glass surface and studied the impact on bacterial cells using atomic force microscopy (AFM). Both plasma types exhibited bactericidal effects on Staph. aureus (log3·6 - >log7), with increased activity against methicillin-resistant strains, but had a negligible effect on Cl. difficile spores (<1log). AFM demonstrated cell surface disruption. The addition of air increased the microbicidal activity of the plasma and decreased the exposure time required for an equivalent log reduction. Further evaluation of cold plasma systems is warranted with, for example, different bacteria and on surfaces more reminiscent of the health care environment as this approach has potential as an effective decontaminant. ⋯ Many bacterial causes of healthcare infection can survive in the inanimate environment for lengthy periods and be transmitted to patients. Furthermore, current methods of environmental decontamination such as detergents, chemical disinfectants or gaseous fumigation are suboptimal for a variety of reasons. We assessed the efficacy of helium and helium-air plasma as a decontaminant and demonstrated a significant reduction in bacterial counts of Staphylococcus aureus on a glass surface. Atomic force microscopy morphologically confirmed the impact on bacterial cells. This approach warrants further study as an alternative to current options for hospital hygiene.
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Lett. Appl. Microbiol. · Jul 2012
Bromelain, a cysteine protease from pineapple (Ananas comosus) stem, is an inhibitor of fungal plant pathogens.
This study aimed to evaluate the effect of bromelain, a cysteine protease isolated from pineapple (Ananas comosus), on growth of several agronomically important fungal pathogens. ⋯ The results support the use of a natural protease that accumulates at high levels in pineapple stems as alternative to the use of chemical fungicides for crop protection.