Molecular epidemiology of Escherichia coli causing neonatal meningitis

Escherichia coli is the second cause of neonatal meningitis which is a major cause of neonatal mortality and is associated with a high incidence of neurological sequelae. E. coli neonatal meningitis (ECNM) strains, as other extraintestinal pathogenic E. coli, mainly belong to the phylogenetic group B2 and to a lesser extent to group D, but are distributed in fewer clonal groups. One of these, the O18:K1:H7 clone is worldwide distributed meanwhile others such as O83:K1 and O45:K1 are restricted to some countries. Over the past few years, major progress has been made in the understanding of the pathophysiology of E. coli O18:K1:H7 neonatal meningitis. In particular, specific virulence factors have been identified and are known to be carried by ectochromosomal DNA in most cases. Molecular epidemiological studies, including characterization of virulence genotypes and phylogenetic analysis are important to lead to a comprehensive picture of the origins and spread of virulence factors within the population of ECNM strains. To date, all the known genetic determinants obtained in ECNM strains are not sufficient to explain their virulence in their globality and further studies on clonal groups different from the archetypal O18:K1:H7 clone are needed. These studies would serve to find common pathogenic mechanisms among different ECNM clonal groups that may be used as potential target for a worldwide efficacious prevention strategy.

Clinical characteristics of adult Escherichia coli meningitis

The clinical characteristics and therapeutic outcomes of adult meningitis due to Escherichia coli alone have not been examined adequately. In this study, we analyzed the clinical and laboratory data of 15 adult patients with monomicrobial E. coli meningitis. The 15 patients, collected over a period of 18 years (January 1986-December 2003), included 7 men and 8 women, aged 45-77 years. They accounted for 5% (15/306) of our adult bacterial meningitis with single pathogen infection. This study also revealed that a post-neurosurgical state is the most important factor predisposing adult patients to develop E. coli meningitis. In this study, all of the tested E. coli strains showed their susceptibility to imipenem and/or meropenem, however, E. coli strains that are not susceptible to third-generation cephalosporin have emerged since 2001. As to the therapeutic results of these 15 cases, all 4 patients without appropriate antibiotic treatment died and the other 11 patients with appropriate antibiotic treatment showed a mortality rate of 27%. The emergence of third-generation cephalosporin non-susceptible E. coli strains in adult bacterial meningitis, as shown in this study, has caused a therapeutic challenge in choosing initial empirical antibiotics for treating adult patients with post-neurosurgical meningitis. Our results emphasize that the timely use of appropriate antibiotics is essential for the management of this potentially fatal central nervous system infection. However, it should be noted that the number of cases examined in this study is too small to reach a therapeutic conclusion regarding adult E. coli meningitis, and further large-scale studies will be needed for this purpose.

[Virulence factors associated with E. coli neonatal meningitis]

Escherichia coli K1 is the leading cause of gram-negative bacterial meningitis in neonates. It is associated with a mortality rate as high as 40%, and more than half of the survivors have neurologic sequelae. Bacterial meningitis is the result of bacterial translocation from gastrointestinal tract to the blood and from blood to the central nervous system. Successful crossing of the BBB by E. coli K1 requires (a) a high degree of bacteremia and (b) several E. coli determinants contributing to invasion of BMEC such as the K1 capsule, Sfa, Ibe proteins, and CNF1. A better understanding for the molecular basis of E. coli K1 penetration of the BBB could potentially lead to the development of novel therapeutic and preventative strategies for E. coli K1 meningitis.

Effect of hypothermia on brain cell membrane function and energy metabolism in experimental Escherichia coli meningitis in the newborn piglet

We evaluated the anti-inflammatory and neuroprotective effects of hypothermia during the early phase of experimental Escherichia coli meningitis in the newborn piglet. Hypothermia significantly attenuated the meningitis-induced acute inflammatory responses such as increased intracranial pressure, decreased glucose level, increased lactate concentration, increased tumor necrosis factor-alpha level and leukocytosis in the cerebrospinal fluid. Decreased cerebral cortical cell membrane Na+,K+-ATPase activity and increased lipid peroxidation products, indicative of meningitis-induced brain damage, were significantly improved with hypothermia. Hypothermia also significantly improved the meningitis-induced reduction in brain ATP and phosphocreatine levels. In summary, hypothermia significantly attenuated the acute inflammatory responses and the ensuing brain injury in experimental neonatal bacterial meningitis.