ENVIRONMENTAL EFFECTS ON BACTERIAL COMMUNICATION AND COMMUNAL BEHAVIOR

Despite their autonomous nature, bacteria can often reside within complex, multicellular communities. One benefit of communal organization is the protection it offers from hazardous environments around the cells, which can come in the form of physical shielding or collective adaptive behaviors that arise from cell aggregation. This dissertation explores how environmental conditions itself might modulate or trigger these collective cell behaviors. We first explored how the environment can affect the active coordination of collective cell behavior, which involves cell-to-cell communication mechanisms such as quorum sensing (QS). Using a microfluidic platform to modulate the environment, we showed that existing explanations of environmental dependence pertaining to modulation of signal retention alone were inadequate in explaining the response. Instead, a dynamics-based analysis coupled with a mathematical model revealed a regulatory mechanism that is defined by the growth-mediated balance between synthesis and dilution of the signaling machinery proteins. This mechanism is able to account for the temporal and spatial properties observed during the onset and propagation of the collective response. These properties culminated in a cell education strategy that effectively combines response diversification with cell signaling to accelerate the onset of the collective cell behavior, which can have tremendous implications for the fitness of the cells that can exhibit this behavior. In addition, we also examined the effects of direct environmental cues, such as mechanical cues, on the emergence of collective cell behaviors. We found that physical confinement of bacterial colonies can lead to a buildup of self-imposed mechanical stress, which can elicit a biological stress response and the secretion of biofilm-related extracellular materials. We demonstrate that this renders the colony biofilm-like, with the associated functional consequence of increased antibiotic tolerance. Across these studies, we combined engineering approaches with experimentation and computational modeling to explore the relationship between bacterial colonies and its surrounding environment and found a high degree of dependence, most often reflected in spatial dependences of responses. As the appreciation for the importance of the microenvironment and its influence on bacterial colonies grow, we anticipate that the interdisciplinary approaches presented here will prove to be valuable tools in helping us understand the workings of bacterial collective cell behavior

The lift industry in Hong Kong : regulatory action and capacity building

published_or_final_versionPolitics and Public AdministrationMasterMaster of Public Administratio

Direct microscopy versus sputum cytology analysis and bleach sedimentation for diagnosis of tuberculosis: a prospective diagnostic study.

ABSTRACT: BACKGROUND: Diagnostic options for pulmonary tuberculosis in resource-poor settings are commonly limited to smear microscopy. We investigated whether bleach concentration by sedimentation and sputum cytology analysis (SCA) increased the positivity rate of smear microscopy for smear-positive tuberculosis. METHODS: We did a prospective diagnostic study in a Medecins Sans Frontieres-supported hospital in Mindouli, Republic of Congo. Three sputum samples were obtained from 280 consecutive pulmonary tuberculosis suspects, and were processed according to WHO guidelines for direct smear microscopy. The remainder of each sputum sample was homogenised with 2.6% bleach, sedimented overnight, smeared, and examined blinded to the direct smear result for acid-fast bacilli (AFB). All direct smears were assessed for quality by SCA. If a patient produced fewer than three good-quality sputum samples, further samples were requested. Sediment smear examination was performed independently of SCA result on the corresponding direct smear. Positivity rates were compared using McNemar's test. RESULTS: Excluding SCA, 43.2% of all patients were diagnosed as positive on direct microscopy of up to three samples. 47.9% were diagnosed on sediment microscopy, with 48.2% being diagnosed on direct microscopy, sediment microscopy, or both. The positivity rate increased from 43.2% to 47.9% with a case definition of one positive smear ([greater than or equal to]1 AFB/100 high power fields) of three, and from 42.1% to 43.9% with two positive smears. SCA resulted in 87.9% of patients producing at least two good-quality sputum samples, with 75.7% producing three or more. Using a case definition of one positive smear, the incremental yield of bleach sedimentation was 14/121, or 11.6% (95% CI 6.5-18.6, p=0.001) and in combination with SCA was 15/121, or 12.4% (95% CI 7.1-19.6, p=0.002). Incremental yields with two positive smears were 5/118, or 4.2% (95% CI 1.4-9.6, p=0.062) and 7/118, or 5.9% (95% CI 2.4-11.8, p=0.016), respectively. CONCLUSIONS: The combination of bleach sedimentation and SCA resulted in significantly increased microscopy positivity rates with a case definition of either one or two positive smears. Implementation of bleach sedimentation led to a significant increase in the diagnosis of smear-positive patients. Implementation of SCA did not result in significantly increased diagnosis of tuberculosis, but did result in improved sample quality. Requesting extra sputum samples based on SCA results, combined with bleach sedimentation, could significantly increase the detection of smear-positive patients if routinely implemented in resource-limited settings where gold standard techniques are not available. We recommend that a pilot phase is undertaken before routine implementation to determine the impact in a particular context