Acinetobacter is gaining importance as a pathogen in intensive care units (ICUs) due to the numerous outbreaks reported and the severity of the infections caused. Of particular interest in this project are neonates whose immune systems have not fully developed and affected by their prematurity, low birth weight, or various other conditions. The vulnerability of these neonates combined with the multidrug resistance of the clinical isolates of this organism poses a real threat to neonates. The understanding of its pathogenicity is still at an elementary stage despite the clinical evidence of nosocomial infections, and the concern of the FAOWHO (2006) regarding neonatal health due to the consumption of powdered infant formula (PIF). The ingestion of contaminated infant formula is a particularly unexplored mechanism of acquiring Acinetobacter infections. Therefore, this research work aimed to analyse the potential risk factors associated with the consumption of a contaminated infant formula administered enterally. The detection of the organism in PIF was examined. A selective chromogenic medium was designed, primarily for this purpose, and evaluated against other specific media. In addition, the desiccation persistence in infant formula was assessed. Biofilm formation inside nasogastric feeding tubes, survival in gastrointestinal fluids, and subsequent interactions with the host, as consequences of the ingestion of a feed containing Acinetobacter, were also investigated. Strains were finally screened for the presence of phospholipase genes. Based on the main findings, Acinetobacter showed the ability to persist over an extended storage period (2 years) in desiccated infant formula and recover after reconstitution. Bacterial cells in the contaminated formula formed biofilms and multiplied over time inside enteral feeding tubes causing all the subsequent fresh feeds to be also contaminated. When exposed to simulated gastrointestinal fluids, these cells did not show signs of complete viability loss except at an acidity level of pH 2.5 (lower than the normal neonatal stomach pH). Strains also successfully attached to colonic epithelial cells (Caco-2), and the majority were subsequently able invade the host cells. Twenty-four hour survival within the Caco-2 cells was also shown. Furthermore, Acinetobacter demonstrated the capacity to evade the bactericidal activity of macrophages, persist, and moreover multiply within these phagocytic cells. Genes encoding for the cytotoxic phospholipase enzymes were also detected in all the clinical isolates of this organism. In conclusion, Acinetobacter was established to possess multiple virulence factors that can potentially contribute to its pathogenicity once ingested.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:629234 |
| Date | January 2011 |
| Creators | Juma, N. A. H. |
| Publisher | Nottingham Trent University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://irep.ntu.ac.uk/id/eprint/126/ |
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