Investigation into the Environment Survival of Neisseria Meningitidis

Abstract

Meningococcal disease is a serious disease whose transmission is not fully understood. Neisseria meningitidis, the causative bacterium, is thought to be temperamental and unable to survive outside of the human host, thus transmission is accepted as being through aerosolized droplets in the form of coughing, sneezing or direct contact e.g. kissing. This thesis provides evidence that N. meningitidis can survive in the environment in a saliva analogue for up to eight days dried onto glass. Binary logistic modeling and statistical analysis of the survival of different strains under different environmental conditions found that survival varied depending on both strain type and humidity, and strain NZ98/254 (New Zealand’s epidemic strain type) showed a seasonality in survival that matches the seasonality in meningococcal disease rates. Proteomic studies were undertaken using two-dimensional polyacrylamide gel electrophoresis to create a proteome reference map of NZ98/254. This method visualized a total of 822 protein spots and identified 287 unique proteins covering most cellular functions and sub-cellular locations. iTRAQ™ labeling and two-dimensional liquid chromatography coupled to MALDI-TOF/TOF mass spectrometry was used to compare protein abundance levels between two meningococcal strains – one that survived well in the environment (NZ98/254) and one that survived poorly (H34). To help identify what caused their different survival abilities, a comparison was made between their growth under normal conditions, and their growth under the stressful conditions of 30°C & 30% relative humidity (RH) and 30°C & 22% RH. Over 200 proteins were detected using this technique and 18 were significantly differentially expressed in response to environmental stress in more than one experiment. Surprisingly, only one was directly involved in stress response, but analysis of all other significantly differentially expressed proteins, indicates that NZ98/254 grown under stressful conditions increased its metabolic activity, abundance of stress-related proteins, and proteins involved in desiccation tolerance. H34, in contrast, decreased most metabolic activities (except for translation at 22% RH), decreased cell division, decreased the abundance of most stress-related proteins, and only appeared to employ desiccation protection strategies at 22% RH. H34 appeared to be under general nutrient limitation stress. This work has shown that meningococci can survive outside of the host dried onto glass for lengths of time in excess of those during which people commonly share glassware. The number of bacteria that survive desiccation and the length of time they survive depended on both their strain type and the surrounding environmental conditions. This work indicates that fomite transmission of meningococci is plausible and supports the public health message to not “share spit”. This work is the first step towards identifying the mechanism by which meningococci are able to survive desiccation.