Distribution of 19 major virulence genes in Legionella pneumophila serogroup 1 isolates from patients and water in Queensland, Australia

Abstract

The distribution of 19 major virulence genes and the presence of plasmids were surveyed in 141 Legionella pneumophila serogroup (SG) 1 isolates from patients and water in Queensland, Australia. The results showed that 16 of the virulence genes examined were present in all isolates, suggesting that they are life-essential genes for isolates in the environment and host cells. The 65 kb pathogenicity island identified originally in strain Philadelphia-1 T was detected more frequently in isolates from water (44?2 %) than in those from patients (2?7 %), indicating that the 65 kb DNA fragment may aid the survival of L. pneumophila in the sampled environment. However, the low frequency of the 65 kb fragment in isolates from patients suggests that the pathogenicity island may not be necessary for L. pneumophila to cause disease. Plasmids were not detected in the L. pneumophila SG1 isolates from patients or water studied. There was an association of both lvh and rtxA with the virulent and predominant genotype detected by amplified fragment length polymorphism, termed AF1, whereas the avirulent common isolate from water termed AF16 did not have lvh or rtxA genes, with the exception of one isolate with rtxA. It was found that a PCR detection test strategy with lvh and rtxA as pathogenesis markers would be useful for determining the infection potential of an isolate. INTRODUCTIONLegionellae, the aetiologic agents of legionellosis, are ubiquitous worldwide in rivers and lakes (Fliermans et al., 1981), as well as in man-made water systems such as cooling towers and spas (Fields et al., 2002). The vast majority of cases of legionellosis are caused by Legionella pneumophila, mostly serogroup (SG) 1 strains (Yu et al., 2002). To understand the pathogenicity of L. pneumophila, a number of virulence genes of L. pneumophila have been wellcharacterized and extensively reviewed (Cianciotto, 2001;Dowling et al., 1992). The virulence factors characterized include genes required for the whole infection process, such as bacterial cell attachment to host cells, survival and intracellular replication and cell-to-cell spread. The products of genes involved in the initial attachment to host cells and early stages of intracellular infection include type IV pili, the 60 kDa heat-shock protein Hsp60, the poreformation protein RtxA, the macrophage infectivity potentiator Mip and the macrophage-specific infectivity protein MilA (Cianciotto & Fields, 1992;Cirillo et al., 2001;Garduń o et al., 1998;Harb & Abu Kwaik, 2000). The genes required for bacterial survival and intracellular replication are a group of genes called icm (intracellular multiplication) or dot (defect in organelle trafficking) (Vogel et al., 1998). They form a type IV secretion system to deliver effectors to host cells to control organelle trafficking . A number of effectors have been characterized, including RalF (Nagai et al., 2002), LidA (Conover et al., 2003) and LepA/B (Chen et al., 2004) and other recently identified effectors (Shohdy et al., 2005).In addition, the typ...

Epidemiological Investigation of Legionella pneumophila Serogroup 2 to 14 Isolates from Water Samples by Amplified Fragment Length Polymorphism and Sequence-Based Typing and Detection of Virulence Traits

“…Specific genetic loci lvh and rtxA were chosen because they were suggested as appropriate indicators of L. pneumophila virulence after 19 major virulence genes were studied (42). A genetic element of the lvh locus in the genome of strain Philadelphia 1 (derived from the strain of the first outbreak in Philadelphia, PA) was detected in the genome of an Lp6 strain that has been sequenced in Canada (43).…”

“…rtxA encodes the dot/icm-regulated pore-forming toxin and plays a significant role in the entry of the bacteria into the host cell (17). Rtx toxin consists of two regions; the N-terminal region is responsible for adhesion, and the C-terminal region participates in adhesion and pore formation (42).…”

Molecular depiction of lepA, lidA, ralF, rtxA and lvhB virulence factors of Legionella pneumophila isolated from respiratory tract infections

“…The results of our study showed that the distribution of lepA, lidA, ralF, rtxA and lvhB virulence genes were 11.1% (2/18), 50% (9/18), 27.7% (5/18), 5.5% (1/18) and 16.6% (3/18) with the higher prevalence in male patients with the exception of ralF and lvhB gene. Huang et al (2006) [28] showed that the incidence of lvh and rtxA genes in patients with clinical manifestations of L. pneumophila were 57.6% and 64.4%, respectively. RtxA positive strains of L. pneumophila have been shown to have a high capability to enter to monocytes and epithelial cells, and increased cytotoxicity and intracellular duplication [7].…”

Research advances of Legionella and Legionnaires’ disease

“…The 65 kb pathogenicity island identified originally in strain Philadelphia-1T was detected more frequently in isolates from water (44.2%) than in those from patients (2.7%), indicating that the 65 kb DNA fragment may aid the survival of L. pneumophila in the sampled environment. However, the low frequency of the 65 kb fragment in isolates from patients suggests that the pathogenicity island may not be necessary for L. pneumophila to cause disease [35]. Zhu et al [36] reported the detection of 12 loci of putative pathogenicity island (iraA, iraB, mimP, irvA, ivhB, ivhD, cpxR, cpxA, dotA, rpoB, icmC, and icmD) for The virulence of Legionella may be increased by replication in amoeba.…”