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Analysis and Characterization of Proteins Associated with Outer Membrane Vesicles Secreted by Cronobacter spp.

ABSTRACT: Little is known about secretion of outer membrane vesicles (OMVs) by Cronobacter. In this study, OMVs isolated from Cronobacter sakazakii, Cronobacter turicensis, and Cronobacter malonaticus were examined by electron microscopy (EM) and their associated outer membrane proteins (OMP) and genes were analyzed by SDS-PAGE, protein sequencing, BLAST, PCR, and DNA microarray. EM of stained cells revealed that the OMVs are secreted as pleomorphic micro-vesicles which cascade from the cell's surface. SDS-PAGE analysis identified protein bands with molecular weights of 18 kDa to >100 kDa which had homologies to OMPs such as GroEL; OmpA, C, E, F, and X; MipA proteins; conjugative plasmid transfer protein; and an outer membrane auto-transporter protein (OMATP). PCR analyses showed that most of the OMP genes were present in all seven Cronobacter species while a few genes (OMATP gene, groEL, ompC, mipA, ctp, and ompX) were absent in some phylogenetically-related species. Microarray analysis demonstrated sequence divergence among the OMP genes that was not captured by PCR. These results support previous findings that OmpA and OmpX may be involved in virulence of Cronobacter, and are packaged within secreted OMVs. These results also suggest that other OMV-packaged OMPs may be involved in roles such as stress response, cell wall and plasmid maintenance, and extracellular transport.

SUBMITTER: Kothary MH

PROVIDER: S-EPMC5299011 | biostudies-literature | 2017

REPOSITORIES: biostudies-literature

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Analysis and Characterization of Proteins Associated with Outer Membrane Vesicles Secreted by Cronobacter spp.

Kothary Mahendra H MH Gopinath Gopal R GR Gangiredla Jayanthi J Rallabhandi Prasad V PV Harrison Lisa M LM Yan Qiong Q QQ Chase Hannah R HR Lee Boram B Park Eunbi E Yoo YeonJoo Y Chung Taejung T Finkelstein Samantha B SB Negrete Flavia J FJ Patel Isha R IR Carter Laurenda L Sathyamoorthy Venugopal V Fanning Séamus S Tall Ben D BD

Frontiers in microbiology 20170209

Little is known about secretion of outer membrane vesicles (OMVs) by Cronobacter. In this study, OMVs isolated from Cronobacter sakazakii, Cronobacter turicensis, and Cronobacter malonaticus were examined by electron microscopy (EM) and their associated outer membrane proteins (OMP) and genes were analyzed by SDS-PAGE, protein sequencing, BLAST, PCR, and DNA microarray. EM of stained cells revealed that the OMVs are secreted as pleomorphic micro-vesicles which cascade from t ...[more]

PMID: 28232819

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Project description:β-lactamases from Gram-negative bacteria are generally regarded as soluble, periplasmic enzymes. NDMs have been exceptionally characterized as lipoproteins anchored to the outer membrane. A bioinformatics study on all sequenced β-lactamases was performed that revealed a predominance of putative lipidated enzymes in the Class D OXAs. Namely, 60% of the OXA Class D enzymes contain a lipobox sequence in their signal peptide, that is expected to trigger lipidation and membrane anchoring. This contrasts with β-lactamases from other classes, which are predicted to be mostly soluble proteins. Almost all (>99%) putative lipidated OXAs are present in Acinetobacter spp. Importantly, we further demonstrate that OXA-23 and OXA-24/40 are lipidated, membrane-bound proteins in Acinetobacter baumannii. In contrast, OXA-48 (commonly produced by Enterobacterales) lacks a lipobox and is a soluble protein. Outer membrane vesicles (OMVs) from A. baumannii cells expressing OXA-23 and OXA-24/40 contain these enzymes in their active form. Moreover, OXA-loaded OMVs were able to protect A. baumannii, Escherichia coli, and Pseudomonas aeruginosa cells susceptible to piperacillin and imipenem. These results permit us to conclude that membrane binding is a bacterial host-specific phenomenon in OXA enzymes. These findings reveal that membrane-bound β-lactamases are more common than expected and support the hypothesis that OMVs loaded with lipidated β-lactamases are vehicles for antimicrobial resistance and its dissemination. This advantage could be crucial in polymicrobial infections, in which Acinetobacter spp. are usually involved, and underscore the relevance of identifying the cellular localization of lactamases to better understand their physiology and target them.IMPORTANCEβ-lactamases represent the main mechanism of antimicrobial resistance in Gram-negative pathogens. Their catalytic function (cleaving β-lactam antibiotics) occurs in the bacterial periplasm, where they are commonly reported as soluble proteins. A bioinformatic analysis reveals a significant number of putative lipidated β-lactamases, expected to be attached to the outer bacterial membrane. Notably, 60% of Class D OXA β-lactamases (all from Acinetobacter spp.) are predicted as membrane-anchored proteins. We demonstrate that two clinically relevant carbapenemases, OXA-23 and OXA-24/40, are membrane-bound proteins in A. baumannii. This cellular localization favors the secretion of these enzymes into outer membrane vesicles that transport them outside the boundaries of the cell. β-lactamase-loaded vesicles can protect populations of antibiotic-susceptible bacteria, enabling them to thrive in the presence of β-lactam antibiotics. The ubiquity of this phenomenon suggests that it may have influenced the dissemination of resistance mediated by Acinetobacter spp., particularly in polymicrobial infections, being a potent evolutionary advantage.

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Analysis and Characterization of Proteins Associated with Outer Membrane Vesicles Secreted by Cronobacter spp.

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Analysis and Characterization of Proteins Associated with Outer Membrane Vesicles Secreted by <i>Cronobacter</i> spp.

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