Relationship between Legionella pneumophila and Acanthamoeba polyphaga: physiological status and susceptibility to chemical inactivation

Abstract

Survival studies were conducted on Legionella pneumophila cells that had been grown intracellularly in Acanthamoeba polyphaga and then exposed to polyhexamethylene biguanide (PHMB), benzisothiazolone (BIT), and 5-chloro-N-methylisothiazolone (CMIT). Susceptibilities were also determined for L. pneumophila grown under iron-sufficient and iron-depleted conditions. BIT was relatively ineffective against cells grown under iron depletion; in contrast, iron-depleted conditions increased the susceptibilities of cells to PHMB and CMIT. The activities of all three biocides were greatly reduced against L. pneumophila grown in amoebae. PHMB (1x MIC) gave 99.99%o reductions in viability for cultures grown in broth within 6 h and no detectable survivors at 24 h but only 90 and 99.9% killing at 6 h and 24 h, respectively, for cells grown in amoebae. The antimicrobial properties of the three biocides against A. polyphaga were also determined. The majority of amoebae recovered from BIT treatment, but few, if any, survived CMIT treatment or exposure to PHMB. This study not only shows the profound effect that intra-amoebal growth has on the physiological status and antimicrobial susceptibility of L. pneumophila but also reveals PHMB to be a potential biocide for effective water treatment. In this respect, PHMB has significant activity, below its recommended use concentrations, against both the host amoeba and L. pneumophila.

Interactions of some common pathogenic bacteria with Acanthamoeba polyphaga

“…It should also be noted that although we found that numbers of L. monocytogenes and S. aureus were greater in the presence of A. polyphaga these data do not compare to that obtained using this amoebal strain and L. pneumpohila serogroup 1, subtype Knoxville (Barker et al, 1992). Barker et al (1992) set up their experiments in exactly the same way as we have in our experiments, except that a MOI of 1 : 1 was used, and they found that bacterial numbers were 2-3 logs higher after 48 h of coculture than in the absence of A. polyphaga.…”

Legionella pneumophila: an aquatic microbe goes astray

“…Post-exponential phase bacteria which are released from a depleted host cell are short, thick, £agellated and highly motile. In addition, this phenotype is more resistant to biocides, antibiotics and it is more invasive and virulent in di¡erent infection models [21,56]. Within the reprogrammed, maturation-blocked vacuole, L. pneumophila alters its physiology and converts to a replicative form (exponential growth phase).…”

Free-living amoebae and their intracellular pathogenic microorganisms: risks for water quality

“…From a public health perspective, amoebae, and notably amoebal cysts, can be highly resistant to various physical and chemical stresses and can thus protect any intracellular microorganism from deleterious environmental conditions that would normally kill them (King et al, 1988;Kilvington & Price, 1990;Barker et al, 1992). This protective effect is of increasing concern because it is speculated that partially efficient biocide treatments might select for FLA together with their intracellular microorganisms.…”