Legionella pneumophila Grows Adherent to Surfaces in vitro and in situ

Abstract

Legionella pneumophila continues to play a role in both community- and nosocomially-acquired pneumonia. We investigated the ability of L pneumophila to adhere to various types of materials such as those found in the hospital air-cooling and portable water distribution systems. Through the use of a unique sampling apparatus, we were able to regularly acquire planktonic and sessile samples and determine the numbers of bacteria present in both populations, in vitro and in situ. Portions of these apparatuses could be aseptically removed for examination by scanning electron microscopy, or for the determination of the number of viable adherent L pneumophila. The number of bacteria present in each sample was determined by direct plate count, with presumptive L pneumophila colonies being positively identified by direct fluorescent antibody staining techniques. The results demonstrated that not only are legionellae capable of colonizing various metallic and nonmetallic surfaces but that they are preferentially found on surfaces. Surface-adherent bacteria may play a profound role as a reservoir of these potential pathogens in aquatic environments. Furthermore, these results suggest that any comprehensive legionella monitoring program must include not only water samples but also an examination of the adherent populations.

Necrotrophic Growth of Legionella pneumophila

“…Protozoan hosts are supposed to be crucial for replication of L. pneumophila in aquatic environments (10,12,15,16), although alternative pathways have been suggested (5,18,20,21,27,32). This paper demonstrates that L. pneumophila is able to thrive on heat-killed microbial cells present in biofilms or heattreated water systems.…”

“…On the one hand, it is supposed that L. pneumophila grows within protozoan hosts in aquatic environments and that this interaction is central to the pathogenesis and ecology of L. pneumophila (10,12,15,16). Conversely, a number of studies suggested the protozoon-independent survival and growth of L. pneumophila (18,21,27,32), in which case the bacterium uses biofilm matrices as a shelter and source of nutrients. Although scarce, there is evidence that a number of microorganisms in the proximity of L. pneumophila may favor its growth by excreting extracellular compounds as carbon and energy sources (1,23,29).…”

Each water outlet is a unique ecological niche forLegionella pneumophila

“…Once in the system the temperature of the water, < 60°C [11], presence of amoebae [12], turbidity, organic carbon, zinc, copper and algae [13] are all important factors in maintaining growth. Various components of plumbing systems are more readily colonized by legionella than others [14,15].…”

Role of biofilms in the survival of Legionella pneumophila in a model potable-water system

“…An extensive study by Kuchta et al (1998) examined interactions between L. pneumophila and Hartmannella vermiformis, and the efficacy of several disinfectants, and strongly suggested the requirement of protozoan organisms as a ' growth factor ' for the cell replication of Legionella. Some investigators (Wright et al, 1989) have carried out in vitro studies of Legionella biofilm formation and have observed biomass accumulation on the substrata in the absence of protozoan cells. These studies have referred to the biomass as ' growth ' ; however, they failed to address whether those Legionella cells were actually dividing in the absence of protozoa or merely surviving, which, in our view, is a more relevant question.…”