Legionella pneumophila associated with the protozoan Hartmannella vermiformis in a model multi-species biofilm has reduced susceptibility to disinfectants

A Legionella pneumophila peptidyl-prolyl cis-trans isomerase present in culture supernatants is necessary for optimal growth at low temperatures

Several Legionella pneumophila proteins were highly expressed in low-temperature supernatants. One of these proteins was the peptidyl-prolyl isomerase PpiB. Mutants lacking ppiB exhibited reduced growth at 17 degrees C. Since PpiB lacked a signal sequence and was present in 17 degrees C supernatants of type II and type IV secretion mutants, this protein may be secreted by a novel mechanism.

Virulence factor activity relationships: challenges and development approaches

Virulence factor activity relationships (VFAR) is a predictive approach proposed by the National Research Council's Committee on Drinking Water Contaminants (Washington, D.C.) to classify and rank waterborne pathogens. It is based on the presumption that health threats of waterborne pathogens can be predicted from descriptors at different levels of cellular organization. This paper summarizes challenges that need to be addressed while developing VFAR, with a focus on genomics, such as genomic variability among related pathogens and the need to incorporate genetic descriptors for persistence and host susceptibility. Three key components of VFAR development and validation are also presented, including (1) compilation of a comprehensive VFAR database, (2) development of predictive mathematical models relating descriptors to health effects and other microbial responses, and (3) high-throughput molecular monitoring of drinking water supplies and sources. Bayesian approach and on-chip polymerase chain reaction are discussed as examples of mathematical models and molecular monitoring.

Environmental predators as models for bacterial pathogenesis

Environmental bacteria are constantly threatened by bacterivorous predators such as free-living protozoa and nematodes. In the course of their coevolution with environmental predators, some bacteria developed sophisticated defence mechanisms, including the secretion of toxins, or the capacity to avoid lysosomal killing and to replicate intracellularly within protozoa. To analyse the interactions with bacterial pathogens on a molecular, cellular or organismic level, protozoa and other non-mammalian hosts are increasingly used. These include amoebae, as well as genetically tractable hosts, such as the social amoeba Dictyostelium discoideum, the nematode Caenorhabditis elegans and the fruit fly Drosophila melanogaster. Using these hosts, the virulence mechanisms of opportunistic pathogenic bacteria such as Legionella, Mycobacterium, Pseudomonas or Vibrio were found to be not only relevant for the interactions of the bacteria with protozoa, nematodes and insect phagocytes, but also with mammalian hosts including humans. Thus, non-mammalian model hosts provide valuable insight into the pathogenesis of environmental bacteria.

Reducing Legionella colonization in water systems with monochloramine

Monochloramine reduced colonization in building hot water systems.

Monochloramine disinfection of municipal water supplies is associated with decreased risk for Legionnaires' disease. We conducted a 2-year, prospective, environmental study to evaluate whether converting from chlorine to monochloramine for water disinfection would decrease Legionella colonization of hot water systems. Water and biofilm samples from 53 buildings were collected for Legionella culture during 6 intervals. Prevalence ratios (PRs) comparing Legionella colonization before and after monochloramine disinfection were adjusted for water system characteristics. Legionella colonized 60% of the hot water systems before monochloramine versus 4% after conversion (PR 0.07, 95% confidence interval 0.03–0.16). The median number of colonized sites per building decreased with monochloramine disinfection. Increased prevalence of Legionella colonization was associated with water heater temperatures <50°C, buildings taller than 10 stories, and interruptions in water service. Increasing use of monochloramine in water supplies throughout the United States may reduce Legionella transmission and incidence of Legionnaires' disease.

Introduction of monochloramine into a municipal water system: impact on colonization of buildings by Legionella spp

Legionnaires' disease (LD) outbreaks are often traced to colonized potable water systems. We collected water samples from potable water systems of 96 buildings in Pinellas County, Florida, between January and April 2002, during a time when chlorine was the primary residual disinfectant, and from the same buildings between June and September 2002, immediately after monochloramine was introduced into the municipal water system. Samples were cultured for legionellae and amoebae using standard methods. We determined predictors of Legionella colonization of individual buildings and of individual sampling sites. During the chlorine phase, 19 (19.8%) buildings were colonized with legionellae in at least one sampling site. During the monochloramine phase, six (6.2%) buildings were colonized. In the chlorine phase, predictors of Legionella colonization included water source (source B compared to all others, adjusted odds ratio [aOR], 6.7; 95% confidence interval [CI], 2.0 to 23) and the presence of a system with continuously circulating hot water (aOR, 9.8; 95% CI, 1.9 to 51). In the monochloramine phase, there were no predictors of individual building colonization, although we observed a trend toward greater effectiveness of monochloramine in hotels and single-family homes than in county government buildings. The presence of amoebae predicted Legionella colonization at individual sampling sites in both phases (OR ranged from 15 to 46, depending on the phase and sampling site). The routine introduction of monochloramine into a municipal drinking water system appears to have reduced colonization by Legionella spp. in buildings served by the system. Monochloramine may hold promise as community-wide intervention for the prevention of LD.

Bacterial-protozoa interactions; an update on the role these phenomena play towards human illness

The usage of water with poor microbiological quality increases the risk of human illness. This review discusses and updates current thinking on the nature of the interaction between a range of human bacterial pathogens and waterborne protozoa. The importance of protozoa acting as protective environments for pathogenic bacteria from disinfection and of promoting extended survival in otherwise hostile environments is highlighted. The significance of biofilms in water systems, and new relationships between Salmonella and Campylobacter and water-borne protozoa are also discussed. The protection of pathogenic bacteria from disinfection within protozoa and/or biofilms has important implications for water safety.