Legionella pneumophila infection-mediated regulation of RICTOR via miR-218 in U937 macrophage cells.

BACKGROUND: Inhalation of aerosolized Legionella pneumophila, a Gram-negative bacterium, can cause severe pneumonia. During infection, L. pneumophila replicates intracellularly in macrophages. The involvement of host microRNAs (miRNAs) in L. pneumophila infection is not fully understood. METHODS: The human macrophage-like cell line U937 was infected with L. pneumophila. The levels of miRNA and messenger RNA (mRNA) were measured using reverse transcriptase polymerase chain reaction. Release of lactate dehydrogenase was used to evaluate cytotoxicity. The expression of RICTOR and related proteins was examined by western blotting of cell lysates. RESULTS: L. pneumophila infection upregulated the expression of miR-218 and the host genes SLIT2 and SLIT3 in U937 cells. The expression of RICTOR, a component of the mechanistic target of rapamycin complex 2 (mTORC2), decreased during L. pneumophila infection. RICTOR protein expression was inhibited by the overexpression of miR-218, whereas knockdown of miR-218 restored the downregulation of RICTOR by L. pneumophila. L. pneumophila infection induced the expression of the proinflammatory cytokines IL-6 and TNF-alpha, which was modulated by knockdown of miR-218 or RICTOR. CONCLUSIONS: Our study revealed the involvement of miR-218 in regulating the inflammatory response of macrophages against L. pneumophila infection. These findings suggest potential novel roles for miR-218 and RICTOR as therapeutic targets of L. pneumophila infection.

Prevalence of Legionella pneumophila in water distribution systems in hospitals and public buildings of the Lublin region of eastern Poland.

OBJECTIVE: The aim of this study was to determine the prevalence of L. pneumophila in water supply systems, hospitals and public buildings in the Lublin region of eastern Poland. MATERIAL AND METHODS: The study was carried out in 26 different objects in the Lublin region. The number of Legionella bacteria in water samples was determined by the membrane filtration method and/or by surface inoculation in accordance with the standards. RESULTS: The study showed the presence of L. pneumophila in 166 hot water samples (74.77%). In 34.33% (n=57) of water samples the count of tested bacteria exceeded the acceptable level of >100 CFU/100 ml. Of the samples where an acceptable level of bacteria was exceeded, 49 samples had an average level of L. pneumophila (100-1,000 CFU/100 ml), and the level in 8 samples was high (>1,000 CFU/100 ml). CONCLUSIONS: The water samples collected form the hot water supply system of hospitals and public buildings showed exceeded counts of L. pneumophila, indicating the risk of infection. The constant monitoring of water distribution systems is an important element of the control of infections caused by these organisms.

Bacterial pneumonia in HIV-infected patients: use of the pneumonia severity index and impact of current management on incidence, aetiology and outcome.

OBJECTIVES: Despite a recent decrease, bacterial pneumonia (BP) is still the most common admission diagnosis in HIV patients. We analyse BP incidence, characteristics and prevention measures. METHODS: Observational study of all patients hospitalized for BP in a tertiary hospital in Barcelona, Spain, from January 2000 to December 2005. Demographic and HIV-related data, BP risk factors, characteristics of BP and outcomes are analysed. RESULTS: One hundred and eighty-six BP episodes in 161 patients were included; patients were mainly male (73.7%) and intravenous drug users (73.7%). A decrease in BP incidence was seen during the study period, especially in vaccinated patients. The most commonly isolated microorganism was Streptococcus pneumoniae (31.7%), followed by Legionella pneumophila (5.9%). Legionella pneumophila was more likely in patients with undetectable viral load, higher CD4 cell counts or prior vaccination. Highly active antiretroviral therapy, cotrimoxazole prophylaxis and pneumococcal vaccination did not have a significant influence on bacteraemia rate, in-hospital complications or BP mortality. High Pneumonia Severity Index (PSI) predicted mortality accurately [relative risk 15.2, 95% confidence interval 3.2-71.7; P=0.001]. Mortality was 9.1%, but was significantly higher in patients with CD4 counts under 200 cells/microL (P=0.022). CONCLUSIONS: A decline in BP incidence was seen during the study period. Combining CD4 cell count and PSI score could become a good strategy in deciding which patients have to be hospitalized.