Identification of physiological and virulence traits of clinical strains of Cronobacter malonaticus

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Alsonosi, A.M., 2017. Identification of physiological and virulence traits of clinical strains of Cronobacter malonaticus. PhD, Nottingham Trent University.

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Abstract

The Cronobacter malonaticus is a member of the genus Cronobacter which is considered an opportunistic pathogen. The significance of C. malonaticus has recently increased since it was documented to be involved in several serious neonatal infections. In addition, more than 40% of C. malonaticus in Cronobacter MLST-database was clinical or infant formula isolates. Unlike previous Cronobacter projects, this study is mainly focused on C. malonaticus and is aimed to investigate its physiological and virulence characteristics that enable this species to survive different stresses and cause adult and neonatal infections.

This project first used a collection of 51 clinical Cronobacter isolates which were not speciated. The 51 strains were predominated by C. sakazakii ST4 (63 %, 32/51) and C. malonaticus ST7 (33 %, 17/51). Interestingly, despite the high clonality of Cronobacter, pulsed-field gel electrophoresis (PFGE) profiles differentiated strains within each sequence type into 15 pulsotypes. Furthermore, this study shows the value of applying multilocus sequence typing (MLST) to bacterial population studies with strains from two patient cohorts, combined with PFGE for further discrimination of strains.

Six sequence type 7 (ST7) strains were selected to represent the 5 C. malonaticus pulse types of the first part study and an additional 14 C. malonaticus strains were chosen from the Cronobacter MLST-database to represent different STs. C. malonaticus has shown ability to form biofilms, produce capsules, produce cellulose, express curli fimbriae, resist acid condition, survive human serum, produce siderophores, haemolysins, protease, and tolerate the used metals. The antibiotic sensitivity test revealed the sensitivity of C. malonaticus to the majority of antibiotics; however, C. malonaticus was resistant to tetracycline and some were resistant to chloramphenicol and intermediate resistant to cefotaxime. The presence of associated genes has been confirmed using the genomes of tested strains.

C. malonaticus showed an ability to adhere and invade Caco-2, HBMEC, A549 and T24 cell lines. Moreover, the result shows that certain strains of C. malonaticus (including 1827 and 2018) were able to persist in macrophages. However, ST7 strains 1827 and 2018 proved to be the most invasive strains among all used strains. The CDC strain 1569 (ST307) which was isolated from the blood of a fatal neonatal case showed also significant results in this study. The analysis of the genomes of tested strains revealed the presence of several virulence associated genes such as curli fimbrial genes, apaH, ompA, ompX, ygdP, papC, ppk1, ibeB, Hfh, OatA, Clp proteins and others.

Finally, the results of this project demonstrate the ability of C. malonaticus to overcome several stresses that could be faced either in the general environments or in the host body. Moreover, the findings of this study confirm the potential ability of C. malonaticus to cause serious infections in neonates or adults such as necrotising enterocolitis, meningitis, bacteremia, pneumonia and urinary tract infection.

Item Type:	Thesis
Creators:	Alsonosi, A.M.
Date:	February 2017
Rights:	You may copy up to 5% of this work for the private study or personal, non-commercial research. Any information used from this thesis should be fully cited.
Divisions:	Schools > School of Science and Technology
Record created by:	Linda Sullivan
Date Added:	03 Nov 2017 09:07
Last Modified:	20 Aug 2021 10:46
URI:	https://irep.ntu.ac.uk/id/eprint/31949