Polymyxin resistance in carbapenem-resistant Enterobacteriaceae isolates from patients without polymyxin exposure: a multicentre study in China

Polymyxins were recently approved for the clinical treatment of carbapenem-resistant Enterobacteriaceae (CRE) infections in China. The aim of this study was to determine the prevalence and molecular mechanisms of polymyxin-resistant CRE prior to the clinical application of polymyxin and to evaluate the potential for emerging polymyxin resistance in China. A total of 504 unique CRE isolates were collected from six tertiary-care hospitals in China between October 2016 and September 2017. All isolates underwent antimicrobial susceptibility testing. Clinical, demographic, antimicrobial exposure and infection data were collected from patients' medical charts. PCR detection, Sanger sequencing and reverse transcription real-time fluorescence quantitative PCR (RT-qPCR) were used to investigate the molecular mechanism of polymyxin resistance. A total 19 (3.8%) polymyxin-resistant isolates were identified, including Klebsiella pneumoniae, Escherichia coli, Klebsiella aerogenes and Enterobacter cloacae. Genetic analysis in K. pneumoniae strains identified insertion sequence (IS) elements (n = 3), a stop codon (n = 1) and gene deletion (n = 2) in mgrB and a pmrB missense mutation (T157P) (n = 1). Two E. coli isolates contained mcr-1 and an E. cloacae strain harboured a frameshift in mgrB. Further transcriptional analysis showed that pmrA, pmrB, pmrC and pmrK were significantly upregulated in polymyxin-resistant isolates. Despite the lack of polymyxin exposure, 3.8% of CRE were resistant to polymyxin in China. Both chromosomal and plasmid-encoded mechanisms were identified. Our study suggests that clinical practice should be alert to pre-existing polymyxin resistance among CRE isolates to avoid further dissemination of polymyxin resistance.

7X multiplexed, optofluidic detection of nucleic acids for antibiotic-resistance bacterial screening

Rapid and accurate diagnosis of bacterial infections resistant to multiple antibiotics requires development of new bio-sensors for differentiated detection of multiple targets. This work demonstrates 7x multiplexed detection for antibiotic-resistance bacterial screening on an optofluidic platform. We utilize spectrally multiplexed multi-spot excitation for simultaneous detection of nucleic acid strands corresponding to bacterial targets and resistance genes. This is enabled by multi-mode interference (MMI) waveguides integrated in an optofluidic device. We employ a combinatorial three-color labeling scheme for the nucleic acid assays to scale up their multiplexing capability to seven different nucleic acids, representing three species and four resistance genes.

The combined antibacterial and anticancer properties of nano Ce-containing Mg-phosphate ceramic

AIM

This paper was mainly aimed at synthesis of Ce-containing nano-Mg-phosphate ceramic as a multifunctional material.

MATERIALS AND METHODS

Two ceramics based on Mg₃(PO₄)₂ and Ce_0.2Mg_2.8(PO₄)₂ formulas (MP and MP-C, respectively) were synthesized. The synthesized powders were characterized by XRD, TEM, Zeta potential, and FTIR. Also, their dissolution behavior was tested in Tris-HCl buffer solution. Moreover, the antimicrobial efficacy was evaluated against gram-positive bacteria (Bacillus sphaericus MTCC 511 &Staphylococcus aureus MTCC 87) and gram-negative bacteria (Enterobacter aerogenes MTCC 111 &Pseudomonas aeruginosa MTCC 1034) using dick diffusion assay and microdilution method. Furthermore, the cell viability test was performed for the ceramics on Vero cells (African green monkey kidney cells), and their antitumor activity was determined by PC3 cell line (prostatic cancer). Also, the cellular uptake was determined by the flow cytometry.

KEY FINDINGS

The results showed that the substitution of Mg by Ce decreased the particle size from 40 to 90 nm for MP sample to 2-10 nm for MP-C sample and increased the degradation rate. Both samples showed excellent antimicrobial activities. Moreover, MP demonstrated more cell viability than MP-C on Vero cells at high concentrations, whereas, MP-C showed more antitumor activity on PC3 cells than MP sample. Moreover, MP-C showed a higher cell uptake than MP due to its smaller size and more negative charge.

SIGNIFICANCE

Mg-phosphate ceramic can be used in this study successfully as a delivery system for cerium ions and showed a high antitumor activity, which makes it highly recommended as safe and effective cancer treatment materials.

Structural investigation of some novel synthesized Schiff base Transition metal complexes derived from drug together with Antimicrobial study

A new series of copper (II), cobalt (II), zinc (II), nickel (II), manganese (II), iron (II) complexes with a novel Schiff base were synthesized by the condensation of sulphadizine and thiophene-2-carbaldehyde.The ligand and its complexes were characterized by using diverse instrumental procedures like microanalysis, thermo gravimetric examination and spectroscopy. The integrated ligand and its metal complexes were subjected to antibacterial studies. These studies demonstrated the enhanced activity of metal complexes against reported microbes with respect to the Schiff base.

Antimicrobial 1,3,4-trisubstituted-1,2,3-triazolium salts

A series of 1,3,4-trisubstituted-1,2,3-triazolium bromide salts were prepared by efficient two-step sequences of azide-alkyne cycloaddition and benzylic substitution. The antimicrobial activity of each triazolium salt and correlating triazole precursor was evaluated using a minimum inhibitory concentration (MIC) assay. MIC activities as low as 1 µM against Gram-positive bacteria, 8 µM against Gram-negative bacteria and 4 µM against fungi were observed for salt analogs, while neutral triazoles were inactive. Analogs representing selective and broad-spectrum antimicrobial activity were each identified. MIC structure-activity relationships observed within this motif indicate that the presence of cationic charge and balance of overall hydrophobicity are strongly impactful, while benzyl vs. aryl substituent identity and variation of substituent regiochemistry are not.

Isolation and characterization of antibiotic producing bacterial strains from red soil of Himalayan region of Pakistan

The emergence of multi drug resistant microbial pathogens has become a global health challenge and set a dire requirement of searching new effective antimicrobials. Soil is an ultimate reservoir of biologically active micro flora, which harbors trillions of microbial strains producing compounds of commercial interest. Hence aim of the present study was an attempt to isolate and identify the antibiotic producing microbial strains from the red soil of Himalayan an unexplored region of Pakistan. In this study from 10 different soil samples only one bacterial strain was isolated capable of antimicrobial activity. Strain was identified by biochemical characteristics and final identification was done by API 20 NE kit which showed 99% homology with P. aeruginosa. Hence the strain was identified as P. aeruginosa S2. Antibacterial and antifungal activity of the P. aeruginosa S2 showed that Staphylococcus aureus was extremely sensitive to it with a zone of inhibition of 42mm. Staphylococcus epidermidis, Enterobacter aerogenes, Aspergillus fumigatus and Candida albicans were also inhibited by the isolated strain. Effect of Glycerol, Copper sulphate (CuSo₄), Sodium sulphate (Na₂SO₄) and Glycerol on antibiotic production was also evaluated by supplementing growth media with these chemicals. Pseudomonas aeruginosa was grown in bulk quantity using solid state fermentation and crude extract was prepared using organic solvents and subjected to silica gel column chromatography for purification of active compound. Purified compound showed antibacterial against human pathogens. The unexplored Kashmir Himalayas are of great significance because of its richness in biodiversity and need to be explored for isolation and characterization of native microbes for biologically active secondary metabolites. This untouched region may be considered as hub of new antimicrobials and may have applications in natural product-based drug discovery.

Enhanced dark hydrogen fermentation by addition of ferric oxide nanoparticles using Enterobacter aerogenes

Ferric oxide nanoparticles (FONPs) were used to facilitate dark hydrogen fermentation using Enterobacter aerogenes. The hydrogen yield of glucose increased from 164.5±2.29 to 192.4±1.14mL/g when FONPs concentration increased from 0 to 200mg/L. SEM images of E. aerogenes demonstrated the existence of bacterial nanowire among cells, suggesting FONPs served as electron conduits to enhance electron transfer. TEM showed cellular internalization of FONPs, indicating hydrogenase synthesis and activity was potentially promoted due to the released iron element. When further increasing FONPs concentration to 400mg/L, the hydrogen yield of glucose decreased to 147.2±2.54mL/g. Soluble metabolic products revealed FONPs enhanced acetate pathway of hydrogen production, but weakened ethanol pathway. This shift of metabolic pathways allowed more nicotinamide adenine dinucleotide for reducing proton to hydrogen.

Facile green fabrication of nanostructure ZnO plates, bullets, flower, prismatic tip, closed pine cone: Their antibacterial, antioxidant, photoluminescent and photocatalytic properties

Green synthesis of multifunctional Zinc oxide nanoparticles (NPs) with a variety of morphologies were achieved by low temperature solution combustion route employing neem (Azadirachta indica) extract as fuel. The nanoparticles were characterized by PXRD, FTIR, XPS, Raman and UV-Visible spectroscopic studies. The Morphologies were studied by SEM and TEM analysis. The NPs were subjected for photoluminescence, photocatalytic, antibacterial and antioxidant activity studies. PXRD pattern confirmed the hexagonal wurtzite structure of the product. SEM images indicated the transformation of mushroom like hexagonal disks to bullets, buds, cones, bundles and closed pine cone structured NPs with increase in the concentration of neem extract in reaction mixture. The NPs exhibited prominent green emission due to the presence of intrinsic defect centers. The as-formed bullet shaped ZnO with 4ml of neem extract was found to decolorize Methylene blue (MB) under Sunlight and UV light irradiation. The antibacterial studies indicated that ZnO NPs of concentration 500, 750 and 1000μg resulted in significant antibacterial activity on Klebsiella aerogenes and Staphylococcus aureus but not against Escherichia coli and Pseudomonas aeruginosa in agar well diffusion method. Further, ZnO NPs exhibited significant antioxidant activity against scavenging DPPH free radicals. The current investigation demonstrated green engineering method for the synthesis of multifunctional ZnO NPs with interesting morphologies using neem extract.

Role of the Outer Membrane and Porins in Susceptibility of β-Lactamase-Producing Enterobacteriaceae to Ceftazidime-Avibactam

This study examined the activity of the novel antimicrobial combination ceftazidime-avibactam against Enterobacteriaceae exhibiting different outer membrane permeability profiles, specifically with or without porins and with or without expression of the main efflux pump (AcrAB-TolC). The addition of the outer membrane permeabilizer polymyxin B nonapeptide increased the antibacterial activities of avibactam alone, ceftazidime alone, and ceftazidime-avibactam against the characterized clinical isolates of Escherichia coli, Enterobacter aerogenes, and Klebsiella pneumoniae. This enhancement of activities was mainly due to increased passive penetration of compounds since inhibition of efflux by the addition of phenylalanine-arginine β-naphthylamide affected the MICs minimally. OmpF (OmpK35) or OmpC (OmpK36) pores were not the major route by which avibactam crossed the outer membranes of E. coli and K. pneumoniae. In contrast, Omp35 and Omp36 allowed diffusion of avibactam across the outer membrane of E. aerogenes, although other diffusion channels for avibactam were also present in that species. It was clear that outer membrane permeability and outer membrane pore-forming proteins play a key role in the activity of ceftazidime-avibactam. Nevertheless, the MICs of ceftazidime-avibactam (with 4 mg/liter avibactam) against the ceftazidime-resistant clinical isolates of the three species of Enterobacteriaceae studied were ≤ 8 mg/liter, regardless of outer membrane permeability changes resulting from an absence of defined porin proteins or upregulation of efflux.

Synthesis, antimicrobial activity and toxicity of analogs of the scorpion venom BmKn peptides

Two analogs of the natural peptide BmKn1 and four of BmKn2 found in the venom of the scorpion Buthus martensii Karsh have been synthesized and tested to compare their antimicrobial and hemolytic activity with the natural ones. Modifications of the natural sequence were done on the hydrophobic side of the alpha helix by increasing the size and hydrophobicity of the residues with alanine (BmKn2A1), valine (BmKn2V1) and leucine (BmKn2L1) respectively, and on the hydrophilic side by increasing the charge from +2 to +3 with two lysines (BmKn2K7). In order to study observed peptide aggregation, two peptides with one (BmKn1-6Lys) and two (BmKn1L2K2) positive charges respectively in the hydrophobic side have been also designed. Results show that the valine substituted analog BmKn2V1 and lysine substituted analog BmKn2K7 have in general, the highest antibiotic and hemolytic activity of the group. Introduction of one positive charge on the hydrophobic side shows a significant increase in antibacterial activity compared with the original sequence except for Bacillus and Enterobacter where, unexpectedly, the activity flats-off. In contrast, the analog with two positive charges has minimal antibacterial or hemolytic activity.

Antimicrobial, antitumor and brine shrimp lethality assay of Ranunculus arvensis L. extracts

To investigate the antitumor activity, brine shrimp lethality assay, antibacterial and antifungal activity of Methanol Extract (ME), Water Extract (WE), Acetone Extract (AE), Chloroform Extract (CE), Methanol-Water Extract (MWE), Methanol-Acetone Extract (MAE), Methanol-Chloroform Extract (MCE) of Ranunculus arvensis (L.). Antitumor activity was evaluated with Agrobacterium tumefaciens (At10) induced potato disc assay. Cytotoxicity was evaluated with brine shrimp lethality assay. Antibacterial activity was evaluated with six bacterial strains including Escherichia coli, Enterobacter aerogenes, Bordetella bronchiseptica, Klebsiella pneumoniae, Micrococcus luteus and Streptococcus anginosus and antifungal screening was done against five fungal strains including Aspergillus niger, A. flavus, A. fumigates, Fusarium solani and Mucor species by using disc diffusion method. Best antitumor activity was obtained with ME and WE, having highest IC50 values 20.27 ± 1.62 and 93.01 ± 1.33μg/disc. Brine shrimp lethality assay showed LC50 values of AE, MAE and ME were obtained as 384.66 ± 9.42μg/ml, 724.11 ± 8.01μg/ml and 978.7 ±8.01 μg/ml respectively. WE of R. arvensis revealed weak antimicrobial result against the tested microorganisms. On the other hand, the antifungal activity of the plant extracts was found to be insignificant. These findings demonstrate that extracts of R. arvensis possesses significant antitumor activity. Further extensive study is necessary to assess the therapeutic potential of the plant.

EGCG assisted green synthesis of ZnO nanopowders: Photodegradative, antimicrobial and antioxidant activities

Zinc oxide nanopowders were synthesized by solution combustion method using Epigallocatechin gallate (EGCG) a tea catechin as fuel. The structure and morphology of the product was characterized by Powder X-ray Diffraction, Scanning Electron Microscopy, photoluminescence and UV-Visible spectroscopy. The nanopowders (Nps) were subjected to photocatalytic and biological activities such as antimicrobial and antioxidant studies. PXRD patterns demonstrate that the formed product belongs to hexagonal wurtzite system. SEM images show that the particles are agglomerated to form sponge like structure and the average crystallite sizes were found to be ∼10-20nm. PL spectra exhibit broad and strong peak at 590nm due to the Zn-vacancies, and O-vacancies. The prepared ZnO Nps exhibit excellent photocatalytic activity for the photodegradation of malachite green (MG) and methylene blue (MB) indicating that the ZnO NPs are potential photocatalytic semiconductor materials. ZnO NPs exhibit significant bactericidal activity against Klebsiella aerogenes, Pseudomonas aeruginosa, Escherichia coli and Staphylococcus aureus using the agar well diffusion method. Furthermore, the ZnO nano powders show good antioxidant activity by potentially scavenging DPPH radicals. The study successfully demonstrates synthesis of ZnO NPs by simple ecofriendly route employing EGCG as fuel that exhibit superior photodegradative, antibacterial and antioxidant activities.

Identification and structure elucidation of antimicrobial compounds from Lyngbya aestuarii and Aphanothece bullosa

Cyanobacteria are known to produce array of compounds. In an earlier report, we reported antibacterial and antifungal activities in methanolic crude extracts of laboratory grown Lyngbya aestuarii and Aphanothece bullosa isolated from Chilka Lake and local paddy field respectively. In this report the same methanolic crude extracts were subjected to TLC purification twice by altering the solvents and UV—illuminated bands bioassayed. Such UV illuminated potent bands obtained after 2nd TLC were subjected to spectroscopic analysis (UV, IR, 1H NMR and LCMS/MS). We have screened malyngolide and dragonamide C from L. aestuarii and a diterpenoid and majusculoic acid from A. bullosa. Dragonamide C and malyngolide were found to be antifungal while majusculoic acid and a diterpenoid as antibacterial. As far as our knowledge goes, this is the first ever report where fresh water A. bullosa was found to be a source of diterpenoid and majusculoic acid. Likewise, L. aestuarii was also established as a source of malyngolide and dragonamide C. This again indicated that cyanobacteria are inherently endowed with the capacity to produce metabolites according to niche and species specific manner emphasising fresh water cyanobacterial strain are as important as marine one.

Silver sucrose octasulfate (IASOS™) as a valid active ingredient into a novel vaginal gel against human vaginal pathogens: in vitro antimicrobial activity assessment

This in vitro study assessed the antimicrobial properties of a novel octasilver salt of Sucrose Octasulfate (IASOS) as well as of an innovative vaginal gel containing IASOS (SilSOS Femme), against bacterial and yeast pathogens isolated from human clinical cases of symptomatic vaginal infections. In BHI and LAPT culture media, different ionic silver concentrations and different pHs were tested. IASOS exerted a strong antimicrobial activity towards all the pathogens tested in both culture media. The results demonstrated that salts and organic compounds present in the culture media influenced IASOS efficacy only to a moderate extent. Whereas comparable MBCs (Minimal Bactericidal Concentrations) were observed for G. vaginalis (10 mg/L Ag+), E. coli and E. aerogenes (25 mg/L Ag+) in both media, higher MBCs were found for S. aureus and S. agalactiae in LAPT cultures (50 mg/L Ag+ versus 25 mg/L Ag+). No minimal concentration totally inhibiting the growth of C. albicans was found. Nevertheless, in both media at the highest ionic silver concentrations (50-200 mg/L Ag+), a significant 34-52% drop in Candida growth was observed. pH differently affected the antimicrobial properties of IASOS against bacteria or yeasts; however, a stronger antimicrobial activity at pH higher than the physiological pH was generally observed. It can be therefore concluded that IASOS exerts a bactericidal action against all the tested bacteria and a clear fungistatic action against C. albicans. The antimicrobial activity of the whole vaginal gel SilSOS Femme further confirmed the antimicrobial activity of IASOS. Overall, our findings support IASOS as a valid active ingredient into a vaginal gel.

Mitigation of the inhibitory effect of soap by magnesium salt treatment of crude glycerol--a novel approach for enhanced biohydrogen production from the biodiesel industry waste

Owing to its inhibitory effect on microbial growth, soap present in crude glycerol (CG) is a concern in biological valorization of the biodiesel manufacturing waste. By salting out strategy, up to 42% of the soap has been removed and the approach has beneficial effect on H2 production; however, removal of more than 7% of the soap was found to be inhibitory. Actually, soap is utilized as a co-substrate and due to removal; the carbon-nitrogen ratio of the medium might have decreased to reduce the production. Alternatively, without changing the carbon-nitrogen ratio of CG, MgSO4 treatment can convert the soap to its inactive form (scum). The approach was found to increase the H2 production rate (33.82%), cumulative H2 production (34.70%) as well as glycerol utilization (nearly 2.5-folds). Additionally, the treatment can increase the Mg (a nutrient) content of the medium from 0.57 ppm to 201.92 ppm.

Engineered Enterobacter aerogenes for efficient utilization of sugarcane molasses in 2,3-butanediol production

Sugarcane molasses is considered to be a good carbon source for biorefinery due to its high sugar content and low price. Sucrose occupies more than half of the sugar in the molasses. Enterobacter aerogenes is a good host strain for 2,3-butanediol production, but its utilization of sucrose is not very efficient. To improve sucrose utilization in E. aerogenes, a sucrose regulator (ScrR) was disrupted from the genomic DNA. The deletion mutation increased the sucrose consumption rate significantly when sucrose or sugarcane molasses was used as a carbon source. The 2,3-butanediol production from sugarcane molasses by the mutant was enhanced by 60% in batch fermentation compared to that by the wild type strain. In fed-batch fermentation, 98.69 g/L of 2,3-butanediol production was achieved at 36 h.

A possible role of partially pyrolysed essential oils in Australian Aboriginal traditional ceremonial and medicinal smoking applications of Eremophila longifolia (R. Br.) F. Muell (Scrophulariaceae)

ETHNOPHARMACOLOGICAL SIGNIFICANCE

Eremophila longifolia is one of the most respected of the traditional medicines used by Australian Aboriginal people. Customary use involves smoldering the leaves over hot embers of a fire to produce an acrid smoke, believed to have therapeutic effects broadly consistent with antimicrobial, antifungal and anti-inflammatory capacity.

AIM OF THE STUDY

The current study aims to examine the contribution of partially pyrolysed and non-pyrolysed essential oils in traditional usage of Eremophila longifolia.

MATERIALS AND METHODS

Non-pyrolysed and partially pyrolysed essential oils were produced by hydrodistillation and part-wet/part-dry distillation, respectively. All samples were tested for antimicrobial activity by broth dilution. Some of these samples were further treated to an incrementally stepped temperature profile in a novel procedure employing a commercial thermocycler in an attempt to mimic the effect of temperature gradients produced during smoking ceremonies. Components from the pyrodistilled oils were compared with the non-pyrodistilled oils, using GC-MS, GC-FID and HPLC-PAD. The 2,2-diphenyl-1-picrylhydrazyl method, was used to compare free radical scavenging ability.

RESULTS

Partially pyrolysed oils had approximately three or more times greater antimicrobial activity, enhanced in cultures warmed incrementally to 60°C and held for 30s and further enhanced if held for 2 min. Partially pyrolysed oils showed a radical scavenging capacity 30-700 times greater than the corresponding non-pyrolysed oils. HPLC-PAD revealed the presence of additional constituents not present in the fresh essential oil.

CONCLUSION

These results, by showing enhanced antimicrobial and antioxidant activities, provide the first known Western scientific justification for the smoking ceremonies involving leaves of Eremophila longifolia. During customary use, both partially pyrolysed as well as non-pyrolysed essential oils may contribute significantly to the overall intended medicinal effect.

Antibacterial activity of some actinomycetes from Tamil Nadu, India

OBJECTIVE

To isolate novel actinomycetes and to evaluate their antibacterial activity.

METHODS

Three soil samples were collected from Vengodu (village) in Kanchipuram district, Tamil Nadu, India. Actinomycetes were isolated using serial dilution and plating method on actinomycetes isolation agar.

RESULTS

Totally 35 isolates were obtained on the basis of colony characteristics on actinomycetes isolation agar. All the isolates were screened for antibacterial activity by cross streak method. Medium and optimization of day were done for the potent strains using Nathan's agar well diffusion method. Isolation of bioactive compounds from significant active isolates was done by using different media. The most active isolate VAS 10 was identified as Actinobacterium Loyola PBT VAS 10 (accession No. JF501398) using 16s rRNA sequence method. The hexane, ethyl acetate, dichloromethane and butanol extracts of VAS 10 were tested against bacteria. The maximum antibacterial activity was observed in dichloromethane and ethyl acetate; maximum zones of inhibition were observed against Enterococcus durans. The rRNA secondary structure and the restriction sites of Actinobacterium Loyola VAS 10 were predicted using Genebee and NEBCutter online tools respectively.

CONCLUSIONS

The present study showed that among the isolated actinomycetes, Actinobacterium Loyola PBT VAS 10 (accession No. JF501398) showed good antibacterial activity against the tested bacteria.

Antimicrobial activity of Ulopterol isolated from Toddalia asiatica (L.) Lam.: a traditional medicinal plant

ETHNOPHARMACOLOGICAL RELEVANCE

The leaves of Toddalia asiatica (L.) Lam. (Rutaceae) are widely used in folk medicine in India to treat various ailments like cough, malaria, indigestion, influenza lung diseases and rheumatism, fever, stomach ailments, cholera and diarrhea. In our earlier communication we have reported the antimicrobial study on the various extracts of the leaves and the isolation and identification of Flindersine, a quinolone alkaloid as the major active principle. In the present study, we report the antibacterial and antifungal activities of Ulopterol, a coumarin isolated as another major active antimicrobial principle.

MATERIALS AND METHODS

The leaves were successively extracted with hexane, chloroform, ethyl acetate, methanol and water. The extracts were studied for their antimicrobial activity against selected bacteria and fungi by using disc-diffusion method. The ethyl acetate extract which was found to possess highest antimicrobial activity was subjected to activity guided fractionation by column chromatography over silica gel. This resulted in the isolation of the coumarin, Ulopetrol, an active principle besides Flindersine which was reported by us earlier. The structure of the compound was elucidated using physical and spectroscopic data. Flindersine and Ulopterol were quantified by HPLC.

RESULTS

Ulopterol showed activity against the bacteria viz. Staphylococcus epidermidis, Enterobacter aerogenes, Shigella flexneri, Klebsiella pneumoniae (ESBL-3967), Escherichia coli (ESBL-3984) and fungi viz. Aspergillus flavus, Candida krusei and Botrytis cinerea. Quantification by HPLC showed the content of Flindersine and Ulopterol to be 0.361% and 0.266% respectively on dry weight basis of the leaves.

CONCLUSIONS

Ethyl acetate extract (successive extraction) contained Ulopterol, a coumarin, besides Flindersine, a quinolone alkaloid, as a major active principle in the antimicrobial studies. This is the first report of the antimicrobial activity of Ulopterol and also its first report from the plant.

Isolation and identification of chromium-resistant bacteria: Test application for prevention of chromium toxicity in plant

The purpose of this study was to isolate chromium resistant bacteria and characterize in depth before being applied for bioremediation or construction of chromium biosesnors. One of the major objectives was to identify the most useful strains with respect to chromium removal efficiency. Chromium resistant bacteria were isolated from tannery waste samples. These were characterized through biochemical tests and antibiotic assays. Cross metal reactivity, plasmid curing and cysteine quantifications were also performed. Gene sequencing was done for all the isolates and accession numbers received after submission to National Center for Biotechnology Information (NCBI). The removal capacity was also studied in broth cultures. The results were very encouraging since six new bacteria were recognised to withstand high concentrations of chromium. Out of these six bacteria, three i.e. Enterobacter aerogenes, Aeromonas sp., Acinetobacter sp. PD 12 performed very well by removing about 99% (average) from initial 19.8 ppm of Cr(VI) from a synthetic culture media. Enterobacter aerogenes, being the most efficient strain, was used to remediate hexavalent chromium from soil of potted plants- very encouraging results were obtained. These bacteria may be exploited for bioremediation of Cr (VI) and construction of microbial sensor in future.

Anti-inflammatory amino acid derivatives from the ascidian Herdmania momus

Four new amino acid derivatives, herdmanines A-D (1-4), were isolated from the marine ascidian Herdmania momus. Herdmanines A-C contain the unusual D-form of arginine. Compounds 3 and 4 had a moderate suppressive effect on the production of NO, with IC₅₀ values of 96 and 9 μM, respectively. These compounds were found to inhibit the mRNA expression of iNOS. The inhibitory activities on the production and mRNA expression of pro-inflammatory cytokines such as TNF-α, IL-1β, and IL-6 were evaluated.

Susceptibility of the multi-drug resistant strain of Enterobacter aerogenes EA289 to the terpene alcohols from Cistus ladaniferus essential oil

The essential oil (EO) of Cistus ladaniferus was separated into non polar, moderately polar and polar fractions by column chromatography. The EO and its fractions were analysed by gas chromatography in combination with retention indices [GC-(RI)] and 13C nuclear magnetic resonance (13C NMR) spectroscopy. A minimum inhibitory concentration (MIC) assay was used to evaluate their antibacterial activity against Gram-positive and Gram-negative pathogens of clinical relevance, including a multi-drug resistant (MDR) strain. The most polar fraction, constituted by mono- and sesquiterpene alcohols, strongly inhibited the growth of all tested bacteria with MIC values ranging from 0.05 to 0.8 mg/mL. More importantly, this fraction displayed high activity against the MDR strain of Enterobacter aerogenes EA289. Transmission electron microscopy (TEM) observations of the MDR bacteria treated with the terpene alcohol-rich fraction revealed cell wall distortion with an outer cytoplasmic membrane detachment. The susceptibility of the MDR strain of E. aerogenes EA289 to the polar fraction of C. ladaniferus oil suggests the possible use of these natural products to treat infections caused by highly resistant bacteria.

Cerebrosides and 2-pyridone alkaloids from the halotolerant fungus Penicillium chrysogenum grown in a hypersaline medium

Five new cerebrosides, chrysogesides A-E (1-5), and two new 2-pyridone alkaloids, chrysogedones A and B (6 and 7), were isolated from the fermentation broth of Penicillium chrysogenum PXP-55, a halotolerant fungus grown in a hypersaline medium. Among them, chrysogesides B-D (2-4) are the first cerebrosides that contain an unsaturated C(19)-fatty acid. Their structures were identified by spectroscopic and chemical methods, including CD spectroscopy as well as the modified Mosher's method. Compound 2 showed antimicrobial activity against Enterobacter aerogenes with an MIC value of 1.72 μM.

Antioxidative and antibacterial effects of seeds and fruit rind of nutraceutical plants belonging to the Fabaceae family

In the present study, the seeds and fruit rind of six plants of the Fabaceae family were selected to evaluate their potential as antioxidant and antibacterial agents. The dried powders were individually extracted with various organic solvents by the cold percolation method, were evaluated for antibacterial activity and methanol extracts used for antioxidant activities. Total phenol, protein and sugar contents were also measured. Antioxidant activities were measured by DPPH free radical scavenging activity, superoxide anion radical scavenging activity and reducing capacity assessment. Antibacterial activity was measured by the agar well diffusion method against four Gram positive and four Gram negative bacteria. The methanol extract of the fruit rind of C. indica showed the maximum DPPH free radical scavenging activity, superoxide anion radical scavenging activity, a high reducing capacity assessment and also had the highest total phenol content. There was a direct correlation between the phenol content and the antioxidant activity. The antibacterial activity of all the extracts was more pronounced on Gram positive bacteria than on Gram negative bacteria. Thus, the fruit rind of C. indica showed the best antioxidant and antibacterial activities.

Antiviral and anti-inflammatory diterpenoids from the soft coral Sinularia gyrosa

Chemical investigation of the soft coral Sinularia gyrosa led to the purification of three new diterpenoids, designated as gyrosanols A-C (1-3). The structures of 1-3 were elucidated through extensive spectroscopic analyses. Compounds 1 and 2 exhibited antiviral activity against HCMV with IC(50)'s of 2.6 and 3.7 microM, respectively. In addition, compounds 1 and 2 showed significant anti-inflammatory activity by reducing the levels of the COX-2 protein (19.6 + or - 3.9% and 29.1 + or - 9.6%, respectively) in RAW 264.7 macrophages.

Clinical characteristics and predictors of mortality in patients with Enterobacter aerogenes bacteremia

BACKGROUND AND PURPOSE

Enterobacter aerogenes is increasingly encountered in nosocomial infections. This study aimed to clarify the clinical characteristics and to identify the predictors of mortality in patients with E. aerogenes bacteremia.

METHODS

From March 2001 to April 2007, all patients with positive blood cultures for E. aerogenes at Taipei Veterans General Hospital, Taipei, Taiwan, were enrolled in this retrospective study. The medical records were reviewed for clinical and laboratory data.

RESULTS

Eighty eight patients were included, 9 (10.2%) of whom died of E. aerogenes bacteremia. Most of the patients had comorbidities. Seventy nine patients (89.8%) had nosocomial infections, and 43 patients (48.9%) had polymicrobial infections. Eighty four patients (95.5%) presented with fever. Empirical antimicrobial therapy was administered for 80 patients (90.9%), but was appropriate for only 55 patients (62.5%). Of the 9 patients who died, 8 had polymicrobial infection, 5 of whom had nosocomial pneumonia, and 6 did not receive appropriate antimicrobial therapy. Multivariate analysis indicated that high Acute Physiology and Chronic Health Evaluation (APACHE) II score (>16) [odds ratio (OR), 16.569; 95% confidence interval (CI), 1.24-221.24; p = 0.034] and strains not susceptible to extended-spectrum cephalosporins (OR, 9.21; 95% CI, 1.02-83.04; p = 0.048) were independent risk factors for mortality.

CONCLUSIONS

The severity of E. aerogenes bacteremia, reflected by high APACHE II score and isolation of strains with no susceptibility to extended-spectrum cephalosporins, were independent risk factors for mortality. Patients with severe illness and isolates resistant to extended-spectrum cephalosporins should be treated with more potent antimicrobial agents.

Antibacterial activity in vitro of Thymus capitatus from Jordan

This study was carried out to evaluate the antibacterial activity of aqueous and organic extracts of Thymus capitatus L. (Lamiaceae) leaves and stems. Dried ground powder leaves and stems were extracted with water (aqueous extracts), ethanol, dichloromethane and hexane (Soxhlet extracts). The antibacterial activity of these extracts was evaluated against bacteria using disc diffusion method. The result obtained showed that the leaves had stronger antibacterial activity than the stems extracts. The ethanolic extract had the highest yield products and the high antibacterial activity than all other solvents. The results suggest that essential oil as non-polar organic compounds could be the main active compounds in this plant. Therefore the antibacterial activity of leaves ethanol extracts (LEE) was compared with essential oils leaves extracts (LEO) of T. capitatus. The LEO showed greater antibacterial activity than LEE. The LEO showed a broad spectrum of antibacterial activity and the Pseudomonas aeruginosa was the most sensitive bacteria.

Ceramide and cerebrosides from the octocoral Sarcophyton ehrenbergi

Chemical investigation of the octocoral Sarcophyton ehrenbergi, collected at the Dongsha Islands, Taiwan, has led to the isolation of a known ceramide (1) and two new cerebrosides, sarcoehrenosides A (2) and B (4), along with three known cerebrosides (3, 5, and 6). The structures of the new compounds were established by spectroscopic and chemical methods. Sarcoehrenoside A (2) differs from previously known marine cerebrosides in that it possesses a rare alpha-glucose moiety. Compounds 1-6 were evaluated for antimicrobial activity against a small panel of bacteria and for anti-inflammatory activity using RAW 264.7 macrophages.

Accumulation of plasmid-mediated fluoroquinolone resistance genes, qepA and qnrS1, in Enterobacter aerogenes co-producing RmtB and class A beta-lactamase LAP-1

A new plasmid-mediated fluoroquinolone efflux pump gene, qepA, is known to be associated with the rmtB gene, which confers high-level resistance to aminoglycosides. We investigated the qepA gene in 573 AmpC-producing Enterobacteriaceae including one Citrobacter freundii known to harbor rmtB. Of them, two clonally unrelated E. aerogenes harbored qepA. Both isolates co-harbored rmtB, qnrS1, qepA, and bla(LAP-1) on an IncFI type plasmid. The qepA was flanked by two copies of IS26 containing ISCR3C, tnpA, tnpR, bla(TEM), and rmtB. The qnrS1 and bla(LAP-1) were located upstream of qepA. All the resistance determinants (qepA, qnrS1, rmtB, and bla(LAP-1)) were co-transferred to E. coli J53 by filter mating from both isolates. Although the prevalence of qepA is currently low, considering the presence of ISCR3C and the possibility of co-selection and co-transferability of plasmids, more active surveillance for these multi-drug resistant bacteria and prudent use of antimicrobials are needed.

Incidence of multiple antibiotic resistant Gram-negative bacteria isolated from surface and underground water sources in south western region of Nigeria

In most rural and urban settlements, particularly in Nigeria, wells, spring, streams or rivers and lakes serves as major sources of water supply for drinking and other domestic purposes. Unfortunately, many of the available water sources are not potable without some form of treatment which is seldom available in most settings. The use of untreated surface water sources for drinking and for domestic purposes remains a major threat to public health as these could serve as reservoirs the for transfer of antibiotic resistant pathogens. The incidence of resistant bacteria isolated from surface and underground water in six rural settlements in Ekiti State Nigeria was thus investigated. Gram-negative bacteria were isolated from wells, streams and boreholes in six rural settlements in Ekiti State Nigeria between January and April, 2006 and the prevalence of organisms exhibiting multiple antibiotic resistance to tetracycline, amoxicillin, cotrimoxazole, nitofurantoin, gentamicin, nalidixic acid and ofloxacin was observed. Gram-negative bacterial isolates comprised Escherichia coli (22.7%), Enterobacter aerogenes (2.5%), Salmonella spp. (13.3%), Shigella spp. (19.3%), Proteus spp. (18.5%), Klebsiella spp. (19.3%) and Pseudomonas aeruginosa (4.2%). Over 10% of the bacteria were resistant to four or more antibiotic. Antibiotic resistance was highest in members of the genera Enterobacter, Pseudomonas, and Proteus. Given the prevalence of appalling sanitary facilities and inappropriate public antibiotic use, the possibility of antibiotic resistance selection, faecal dissemination and subsequent contamination of local water sources available for rural residents of the developing world is highlighted. The implication for clinical practice of infections caused by antibiotic resistant strains especially among immunodeficient individuals is also discussed.

Design, synthesis and biological evaluation of novel lipoamino acid-based glycolipids for oral drug delivery

A series of lipoamino acid-based glycolipids were synthesised. Suitably derivatised lipoamino acid derivatives were prepared and conjugated to monosaccharides (including glycosyl azides, isothiocyanates, thiols and sulphones) to yield novel O-, N-, S- and C-linked glycolipids in good yields. Their potential to improve the oral absorption of piperacillin is reported.

Antibacterial activity of snake, scorpion and bee venoms: a comparison with purified venom phospholipase A2 enzymes

AIMS

Venoms of snakes, scorpions, bees and purified venom phospholipase A(2) (PLA(2)) enzymes were examined to evaluate the antibacterial activity of purified venom enzymes as compared with that of the crude venoms.

METHODS AND RESULTS

Thirty-four crude venoms, nine purified PLA(2)s and two L-amino acid oxidases (LAAO) were studied for antibacterial activity by disc-diffusion assay (100 microg ml(-1)). Several snake venoms (Daboia russelli russelli, Crotalus adamanteus, Naja sumatrana, Pseudechis guttata, Agkistrodon halys, Acanthophis praelongus and Daboia russelli siamensis) showed activity against two to four different pathogenic bacteria. Daboia russelli russelli and Pseudechis australis venoms exhibited the most potent activity against Staphylococcus aureus, while the rest showed only a moderate activity against one or more bacteria. The order of susceptibility of the bacteria against viperidae venoms was -S. aureus > Proteus mirabilis > Proteus vulgaris > Enterobacter aerogenes > Pseudomonas aeruginosa and Escherichia coli. The minimum inhibitory concentrations (MIC) against S. aureus was studied by dilution method (160-1.25 microg ml(-1)). A stronger effect was noted with the viperidae venoms (20 microg ml(-11)) as compared with elapidae venoms (40 microg ml(-1)). The MIC were comparable with those of the standard drugs (chloramphenicol, streptomycin and penicillin).

CONCLUSION

The present findings indicate that viperidae (D. russelli russelli) and elapidae (P. australis) venoms have significant antibacterial effects against gram (+) and gram (-) bacteria, which may be the result of the primary antibacterial components of laao, and in particular, the PLA(2) enzymes. The results would be useful for further purification and characterization of antibacterial agents from snake venoms.

SIGNIFICANCE AND IMPACT OF THE STUDY

The activity of LAAO and PLA(2) enzymes may be associated with the antibacterial activity of snake venoms.

Effect of Some nitrosative agents on the growth of vgb-bearing Enterobacter aerogenes strains

The effect of transnitrosation intermediate between S-nitroso-N-acetylcysteine (NACysNO) and cysteine on the growth of vgb-bearing Enterobacter aerogenes was investigated using three parameters: the ratio of the specific growth rates, the inhibition zone, and alpha-amylase synthesis for the culture exposed to stressors to that of the same stressor-free cultures. The effect of NACysNO/cysteine on the growth of Enterobacter strains was distinctive as compared with the CysNO, NACysNO, and their combination. At a higher concentration (2 mM), the extents of inhibition based on the mu(NACysNO/cysteine)/mu(no stress) ratio for these cultures were 57%, 62%, and 68% for VHb-expressing, parental, and pUC9-harboring cells, respectively. The inhibition caused by 2 mM: NACysNO in the presence of 1 mM cysteine in all bacterial strains was almost twofold that achieved by NACysNO alone. Based on the diameter of the inhibition zone and alpha-amylase productivity, the four compounds (NACysNO/Cysteine, CysNO, NACysNO, and their combinations) affected the E. aerogenes strains in a concentration-dependent and negative manner. This negative effect was lower in vgb-bearing than vgb-lacking strains. Thus, sulfur-to-sulfur transnitrosation was an efficient NO release and significantly (P < 0.05) affects the growth of Enterobacter strains, to a lesser extent in vgb-bearing strains.

Synthesis, partition coefficients and antibacterial activity of 3'-phenyl (substituted)-6'-aryl-2' (1H)-cis-3',3'a-dihydrospiro [3-H-indole-3,5'-pyrazolo (3',4'-d)-thiazolo-2-(1H)-ones]

Condensation of isatin with primary aryl amines gave a series of Schiff bases (1) which on reaction with thioglycolic acid in 1,4-dioxane afforded the formation of the corresponding 4- thiazolidinones (2). Compound 2 on condensation with substituted benzaldehydes in anhydrous sodium acetate furnished 3-aryl -5'-phenyl (substituted) spiro [3H-indole-3,2'-thiazolidines]-2-(1H), 4'(5'H)-diones (3). The latter (3) on reaction with hydrazine hydrochloride in anhydrous sodium acetate gave 3'-phenyl (substituted) -6'-aryl-2'(1H)-cis-3',3'a-dihydrospiro [3H-indole-3,5'-pyrazolo (3',4'-d)-thiazolo-2-(1H)-ones] (4). The structure has been established on the basis of spectral data. The partition coefficient for n-octanol/water solvent system and in vitro antibacterial activity of the 2'(1H)-cis-3',3'a-dihydrospiro [3H-indole-3,5'-pyrazolo (3',4'-d)-thiazolo-2-(1H)-one] derivatives have been evaluated.

Management of risk of microbial cross-contamination from uncooked frozen hamburgers by alcohol-based hand sanitizer

This research was undertaken to determine the effectiveness of an alcohol-based hand sanitizer on hands contaminated with a nonpathogen surrogate for Escherichia coli O157:H7, where the source of the contamination was frozen hamburger patties. A nonpathogenic nalidixic acid-resistant food-grade strain of Enterobacter aerogenes was used to inoculate frozen hamburger patties composed of 76% lean beef and 24% fat. Thirty-two individuals participated to produce the data used in this study. Each participant handled nine patties at least three times, a sample for microbiological analysis was collected from the surface of one hand, the participant sanitized both hands, and a sample was collected from the other hand. Burger handling created perceptible and visible food debris on the hands of most participants. Computer simulations also were used to perform a variety of risk calculations. The average reduction in bacteria from the use of sanitizer on hands contaminated by frozen burgers containing E. aerogenes was 2.6 +/- 0.7 log CFU per hand. An experiment designed to simultaneously test the effect of sanitizer on E. aerogenes and E. coli O157:H7 also revealed no significant difference in sanitizer effectiveness against the two organisms. The results of the real-world risk estimation calculations (using the actual prevalence and concentration of E. coli O157:H7 in ground beef) predict that once in 1 million trials, a single pathogen cell will be transferred to a single lettuce piece. The effectiveness of this sanitizer intervention was similar to that for hand washing and glove use previously reported. The person-to-person microbial reduction variability from sanitizer use is similar to published data for glove use and was less variable than published data on hand washing effectiveness.

Quinoline derivatives as promising inhibitors of antibiotic efflux pump in multidrug resistant Enterobacter aerogenes isolates

Efflux pumps protect the bacterial cell by expelling toxic compounds before they reach intracellular targets. Because this mechanism actively contributes to the resistance of a given bacterium to more than one class of antibiotics, molecules that are able to block the relevant efflux pump are of potential significance to combat drug resistance caused by efflux pumps. Different quinoline derivatives including alkoxy, alkylamino, thioalkoxy and chloroquinolines have been previously reported to make Enterobacter aerogenes resistant isolates that over express the mechanism of efflux, noticeably more susceptible to structurally unrelated antibiotics. In addition, various quinoline derivatives significantly increase the intracellular concentration of chloramphenicol as reported with other inhibitors, thereby suggesting the inhibition of the drug transport by AcrAB-TolC pump, which is fully active in the clinicaly resistant isolates investigated. Here, we discuss the respective properties of this molecular family, taking into account the recent insights into the structural data of AcrB pump.

Chloroquinolines block antibiotic efflux pumps in antibiotic-resistant Enterobacter aerogenes isolates

Efflux mechanisms protect bacterial cells by pumping out toxic compounds and actively contribute to bacterial multidrug resistance. Agents inhibiting efflux pumps are of interest for the control of multidrug-resistant bacterial infections. Herein we report the effects of new chloroquinoline derivatives that render resistant Enterobacter aerogenes isolates noticeably more susceptible to structurally unrelated antibiotics. In addition, some of these chloroquinolines increase the intracellular concentration of chloramphenicol. Some of the molecules tested in this work are able to inhibit the main efflux pump (AcrAB-TolC), which is involved in E. aerogenes antibiotic resistance.

In vivo selection of Enterobacter aerogenes with reduced susceptibility to cefepime and carbapenems associated with decreased expression of a 40 kDa outer membrane protein and hyperproduction of AmpC beta-lactamase

The mechanism(s) of resistance or decreased susceptibility to cefepime (FEP) and/or imipenem (IMP) in three consecutive isolates of Enterobacter aerogenes (Ea1, Ea2 and Ea3) cultured from bronchial aspirates of the same patient after treatment with ceftriaxone and FEP were studied. Identification was performed with the VITEK 2 system. All three isolates showed identical pulsed-field gel electrophoresis patterns and were resistant (minimum inhibitory concentrations (MICs)) to cefoxitin (MIC, >1024 mg/L), cefotaxime (CTX; MIC, 32-128 mg/L) and ceftazidime (CAZ; MIC, 32-128 mg/L) but susceptible to meropenem (MIC, <or=0.5 mg/L) according to the National Committee for Clinical Laboratory Standards (NCCLS). MICs of FEP were 0.5 mg/L (Ea1), 2 mg/L (Ea2) and 16 mg/L (Ea3), whereas MICs of IMP were <or=0.5 mg/L (Ea1 and Ea3) and 8 mg/L (Ea2). Clavulanic acid (CLV) did not affect the MICs of CTX and FEP. In contrast, the MICs of CTX were reduced 32-128 times by BRL 42715 (BRL) or cloxacillin (CLX), whereas the MICs of FEP were reduced 2-128 times by BRL and 16-64 times by CLX. Production of extended-spectrum beta-lactamases (ESBLs) was not detected using the disk diffusion method (NCCLS) or Etest (CTX/CTX-CLV and CAZ/CAZ-CLV). TEM- or SHV-type ESBL genes were not detected by polymerase chain reaction amplification. The three isolates showed the same pattern of five beta-lactamases (isoelectric points 7.9-8.3, inhibited by CLX but not by CLV) by isoelectric focusing of crude extracts. Hydrolysis (nmol/mg) of cefaloridine (CF) was 3741.0 (Ea1), 4000.6 (Ea2) and 3797.4 (Ea3), suggesting that AmpC is hyperproduced. Hydrolysis of FEP was much lower than that of CF: 1.3 (Ea1), 2.1 (Ea2) and 17.3 (Ea3). The nucleotide sequences of the ampR-ampC genes of Ea1 and Ea2 were identical to that of E. aerogenes strain deposited in GenBank (accession no.). For Ea3, however, a point mutation in position 311 of ampC caused a change of Val-->Glu. Three outer membrane proteins (OMPs) of 51 kDa, 40 kDa and 38 kDa were observed in the three isolates by sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE) (10% polyacrylamide gels with 4 M urea), although expression of the 40 kDa OMP was reduced in Ea2. In conclusion, decreased susceptibility to FEP and IMP in Ea2 is related to reduced expression of a 40 kDa OMP and hyperproduction of AmpC, whereas resistance to FEP in Ea3 is associated with hyperproduction of an altered AmpC.

Production of the cryptic EefABC efflux pump in Enterobacter aerogenes chloramphenicol-resistant mutants

OBJECTIVES

AcrAB-TolC is the major tripartite multidrug efflux pump in Enterobacter aerogenes while EefABC is a cryptic efflux system. This study was conducted to identify and characterize E. aerogenes mutants producing the EefABC efflux pump.

METHODS

Four spontaneous chloramphenicol-resistant (CMR) mutants were isolated. The expression level of the eefABC promoter and the production of the EefA and B proteins were analysed in the mutants. Antibiotic susceptibilities were compared for wild-type and mutant strains. Efflux activity was investigated using an efflux pump inhibitor.

RESULTS

The activation of the eefABC promoter was detected in four CMR mutants. These mutants showed increased resistance to erythromycin and ticarcillin, but not to fluoroquinolones, ketolides and detergents. Two additional efflux proteins were detected in the mutants. The CMR mutants bear no mutation in hns, which encodes a repressor of eefABC. No alteration of porin expression, a phenotype observed in marA or ramA multidrug-resistant mutants, was detected in the mutants.

CONCLUSIONS

These observations suggest that eefABC activation can occur in vitro independently of the H-NS, MarA or RamA global regulators.

High-dose cefepime as an alternative treatment for infections caused by TEM-24 ESBL-producing Enterobacter aerogenes in severely-ill patients

This study evaluated retrospectively the efficacy of treatment with cefepime vs. a carbapenem, in combination with amikacin or ciprofloxacin, for seriously-ill patients infected with ESBL-producing Enterobacter aerogenes who were admitted to an intensive care unit. Forty-four episodes of infection were investigated in 43 patients: 21 treated with cefepime; 23 with a carbapenem. The two treatment groups did not differ statistically in terms of age, APACHE II scores, and infection sites, but the average duration of antibiotic exposure was significantly shorter in the cefepime group (8.5 days vs. 11.4 days; p 0.04). Clinical improvement was seen in 62% of patients receiving cefepime vs. 70% of patients receiving a carbapenem (p 0.59). Bacteriological eradication was achieved in 14% of patients receiving cefepime vs. 22% of patients receiving a carbapenem (p 0.76). The 30-day mortality rates related to infection were 33% in the cefepime group and 26% in the carbapenem group (p 0.44). Thus, outcome parameters did not differ significantly between the two groups. Nevertheless, a statistically significant increase in failure to eradicate ESBL-producing E. aerogenes was observed as the MICs of cefepime rose (p 0.017). Pulsed-field gel electrophoresis revealed three distinct clones, but one predominant clone harbouring the bla(TEM-24) gene was associated with most (42/44) of the episodes of infection. It was concluded that cefepime may be an alternative agent for therapy of severe infections caused by TEM-24 ESBL-producing E. aerogenes, although further studies are required to confirm these observations.

[Evaluation of the bacteriological safety of wares made from different metals]

The determination of the integral toxicity of a liquid after its contact with different metallic wares could provide a comparative assessment of the hazards of this ware to living organisms. The distilled water and physiological solution exposed to silverware even for a short period of time (15 min) proved to be deleterious to the specially selected bacterial strains differing in their resistance to different chemical substances while aluminum ware was quite harmless to them after their long (4-day) standing of liquids.

A solvent tolerant isolate of Enterobacter aerogenes

A solvent tolerant strain of Enterobacter aerogenes was isolated from soil by cyclohexane enrichment. Presence of cyclohexane (20%) in culture media prolonged the lag phase and caused reduction in biomass. Transmission electron micrographs showed convoluted cell membrane and accumulation of solvent in case of the cells grown in cyclohexane. The Enterobacter isolate was able to grow in the range of organic solvents having log P above 3.2 and also in presence of mercury, thus showing potential for treatment of solvent rich wastes.

[Phenotypic and genotypic characterization of resistance to third-generation cephalosporins in Enterobacter spp]

Enterobacter spp. are becoming increasingly frequent nosocomial pathogens with multiple resistance mechanism to beta-lactam antibiotics. We carried out the phenotypic and genotypic characterization of beta-lactamases in 27 Enterobacter spp. (25 Enterobacter cloacae y 2 Enterobacter aerogenes), as well as the ability of different extended spectrum-lactamase (ESBL) screening methods. Resistance to third generation cephalosporins was observed in 15/27 (63%) isolates. Twelve resistant isolates produced high level chromosomal encoded AmpC beta-lactamase; 6 of them were also producers of PER-2. Resistance to third generation cephalosporins in the remaining 3 isolates was due to the presence of ESBLs, PER-2 in 2 cases, and CTX-M-2 in the other. Only CTX-M-2 production was detected with all tested cephalosporins using difusion synergy tests, while cefepime improved ESBLs detection in 7/8 PER-2 producers, 4/8 in the inhibitor approximation test and 7/8 with double disk test using cefepime containing disk with and without clavulanic acid. Dilution method, including cephalosporins with and without the inhibitor detected 1/9 ESBLs producers.

Spread of novel expanded-spectrum β-lactamases in Enterobacteriaceae in a university hospital in the Paris area, France

In 2002, 28 non-duplicate enterobacterial isolates producing extended-spectrum beta-lactamases (ESBLs) were collected from infected patients at the Bicêtre Hospital in Paris, France. Escherichia coli was the predominant ESBL-positive enterobacterial species, comprising ten (36%) of the isolates. CTX-M enzymes (CTX-M-3, CTX-M-10, CTX-M-14 and CTX-M-15) were produced by 11 (39%) of the isolates (six E. coli, two Enterobacter cloacae, one Enterobacter aerogenes, one Proteus mirabilis and one Citrobacter freundii). Other ESBLs, such as VEB-1 and PER-1, were also detected, but less frequently.

Successive emergence of Enterobacter aerogenes strains resistant to imipenem and colistin in a patient

Enterobacter aerogenes is an agent of hospital-acquired infection that exhibits a remarkable resistance to beta-lactam antibiotics during therapy. Five successive isolates of E. aerogenes infecting a patient and exhibiting a multiresistance phenotype to beta-lactam antibiotics and fluoroquinolones were investigated. Among these clinical strains, four presented resistant phenotypes during successive imipenem and colistin treatments. The involved resistance mechanisms exhibited by the successive isolates were associated with alterations of the outer membrane that caused a porin decrease and lipopolysaccharide modifications.

Beta-lactam screening by specific residues of the OmpF eyelet

Beta-lactams use aqueous channels of porins to penetrate Gram-negative bacteria. The L3 loop of Escherichia coli OmpF porin is a key feature that actively contributes to both channel size and electrostatic properties. Acid residues D113, E117, and D121 are responsible for the negative part of the local electrostatic field on this loop. Two substitutions, D113A and D121A, located in the negatively charged cluster of the OmpF eyelet, increase the likelihood of producing bacteria susceptible to several beta-lactams. D113A substitution results in an increase in the ampicillin, cefoxitin, and ceftazidime susceptibility. Molecular modeling suggests that the charges harbored by the beta-lactam molecules interact with the charged residues located inside the porin eyelet.