Understanding bacteria and challenges in microbiology
In 2020 we celebrate 75 years of the anniversary of our founding with a year of activities dedicated to demonstrating the impact of microbiologists’ past, present and future – bringing together and empowering communities that help shape the future of microbiology. We are launching new collections of digital content throughout the anniversary year. The second digital hub is 'Understanding bacteria and the challenges in microbiology', which will explore novel antimicrobial strategies, the world of biofilms and bacteria in industry.
Collection Contents
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Expression of adhesin genes and biofilm formation among Klebsiella oxytoca clinical isolates from patients with antibiotic-associated haemorrhagic colitis
Purpose. Biofilm formation and resistance to last-line antibiotics have restricted chemotherapy options toward infection eradication.
Methodology. Fifty K. oxytoca isolates were collected from patients with antibiotic-associated haemorrhagic colitis (AAHC). Antibiotic susceptibility tests were conducted and phenotypic biofilm formation was assessed using microtitre tissue plate (MTP) assay. PCR was employed to amplify the adhesins, extended-spectrum β-lactamases (ESBLs), carbapenemase and colistin resistance genes. The expression of adhesin genes was evaluated using quantitative real-time PCR (RT-qPCR).
Results/Key findings. The previous antibiotic consumption and hospitalization (P<0.05) and older ages (P=0.0033) were significantly associated with AAHC. None of the isolates produced biofilm strongly, but 70% of them produced moderate-level biofilm. The bla CTX-M (12/14), the bla IMP (8/14 MICIMI =4 µg ml−1 ) and bla OXA-48-like (5/14) and mcr-1 (4/14) genes were predominant, three of which harbouring all the genes. The expression of matB (0.023) and mrkA (0.011) was significantly different between multidrug-resistant and susceptible isolates. Furthermore, moderately biofilm producer isolates significantly exhibited higher expression of fimA (P=.0117), pilQ (P=0.002) and mrkA (P=0.020) genes compared to biofilm non-producers. No significant difference regarding gene expression was observed among ESBL alleles.
Conclusion. Bacterial attachment by adhesins and biofilm formation among extensive drug-resistant K. oxytoca isolates hinder the efficient infection eradication. Hence, control and surveillance studies should be performed and other therapeutic auspicious approaches must be taken into account against AAHC, biofilm formation and drug resistance spread. Furthermore, previous antibiotic consumption and long-term hospitalization should be controlled.
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Efficient bio-production of citramalate using an engineered Escherichia coli strain
More LessCitramalic acid is a central intermediate in a combined biocatalytic and chemocatalytic route to produce bio-based methylmethacrylate, the monomer used to manufacture Perspex and other high performance materials. We developed an engineered E. coli strain and a fed-batch bioprocess to produce citramalate at concentrations in excess of 80 g l−1 in only 65 h. This exceptional efficiency was achieved by designing the production strain and the fermentation system to operate synergistically. Thus, a single gene encoding a mesophilic variant of citramalate synthase from Methanococcus jannaschii, CimA3.7, was expressed in E. coli to convert acetyl-CoA and pyruvate to citramalate, and the ldhA and pflB genes were deleted. By using a bioprocess with a continuous, growth-limiting feed of glucose, these simple interventions diverted substrate flux directly from central metabolism towards formation of citramalate, without problematic accumulation of acetate. Furthermore, the nutritional requirements of the production strain could be satisfied through the use of a mineral salts medium supplemented only with glucose (172 g l−1 in total) and 1.4 g l−1 yeast extract. Using this system, citramalate accumulated to 82±1.5 g l−1, with a productivity of 1.85 g l−1 h−1 and a conversion efficiency of 0.48 gcitramalate g−1 glucose. The new bioprocess forms a practical first step for integrated bio- and chemocatalytic production of methylmethacrylate.
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An endophytic Fusarium sp. isolated from Monarda citriodora produces the industrially important plant-like volatile organic compound hexanal
More LessAn endophytic fungus, MC_25L, has been isolated from the leaves of MonardacitriodoraCerv. ex Lag., a medicinal and aromatic herb from the northwestern Himalayas. It produces a fruity fragrance while growing on potato dextrose agar, suggesting that it is producing volatile organic compounds (VOCs). The endophyte inhibited the growth of plant pathogens such asSclerotiniasp. and Aspergillusflavus by virtue of VOCs. Identification of MC_25L based on morphological and microscopic features, as well as ITS-based rDNA sequence analysis, revealed that it is a Fusariumsp. GC–MS analysis revealed that this endophyte produces a unique array of VOCs, in particular hexanal, p-fluoroanisole, pentafluoropropionic acid 2-ethylhexyl, (5E)-5-ethyl-2-methyl-5-hepten-3-one, 2-butyl-2-hexanol, (7E)-2-methyl-7-hexadecene and acoradiene. Three major compounds were hexanal, (5E)-5-ethyl-2-methyl-5-hepten-3-one and acoradiene, and they account for around 84.57 % of the total VOCs. Moreover, of interest was the presence of hexanal, which has applications in the food and cosmetic industries, as well as in mycofumigation. This is the first report of a fungal endophyte producing the industrially important plant-like VOC hexanal. Hexanal is also active biologically. Thus this study indicates that Fusariumsp. (MC_25L) is a potential candidate for the up-scaling of hexanal.
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