Long-Term Persistence and Leaching of Escherichia coli in Temperate Maritime Soils

c Escherichia coli isolates (n ‫؍‬ 300) collected from six sites in subtropical Brisbane, Australia, prior to and after storm events were tested for the presence of 11 virulence genes (VGs) specific to diarrheagenic pathotypes. The presence of eaeA, stx 1 , stx 2 , and ehxA genes specific for the enterohemorrhagic E. coli (EHEC) pathotype was detected in 56%, 6%, 10%, and 13% of isolates, respectively. The VGs astA (69%) and aggR (29%), carried by enteroaggregative (EAEC) pathotypes, were frequently detected in E. coli isolates. The enteropathogenic E. coli (EPEC) gene bfp was detected in 24% of isolates. In addition, enteroinvasive E. coli (EIEC) VG ipaH was also detected in 14% of isolates. During dry periods, isolates belonging to the EAEC pathotype were most commonly detected (23%), followed by EHEC (11%) and EPEC (11%). Conversely, a more uniform prevalence of pathotypes, EPEC (14%), EAEC (12%), EIEC (10%), EHEC (7%), and ETEC (7%), was observed after the storm events. The results of this study highlight the widespread occurrence of potentially diarrheagenic pathotypes in the urban aquatic ecosystems. While the presence of VGs in E. coli isolates alone is insufficient to determine pathogenicity, the presence of diarrheagenic E. coli pathotypes in high frequency after the storm events could lead to increased health risks if untreated storm water were to be used for nonpotable purposes and recreational activities. Storm events can result in mobilization and transport of fecal contaminants from point sources, such as urban wastewater treatment plants, and nonpoint sources, in particular animal fecal material, to receiving water bodies. The presence of fecal contamination in rivers, lakes, and creeks can lead to the degradation of water quality and subsequently result in the water becoming unfit for potable/nonpotable uses, aquaculture, and recreational activities such as swimming and fishing (1-4).Escherichia coli and Enterococcus spp. commonly found in mammalian feces have been traditionally used as indicators of fecal pollution in fresh and marine waters (5, 6). After storm events, a severalfold increase in the fecal indicator bacteria (FIB) numbers occur in the surface waters (7-9). There may be several sources of E. coli that contribute to sudden increases in numbers of this bacterium in waterways, including sewage overflows, farm animals, pets, and birds. The elevated microbial contaminants in storm runoff (7, 10) and subsequently in receiving water bodies may pose a serious public health risk. Disease outbreaks related to exposure to contaminated freshwater are well documented (11)(12)(13)(14). Exposure to recreational water has been linked to high numbers (21 out of 31) of reported E. coli O157:H7 disease outbreaks in the United States from 1982 to 2002 (15). Despite the significant disease burden linked to contaminated water exposure, the prevalence of E. coli pathotypes in the urban aquatic environment is not well characterized.The majority of E. coli strains are commensal; however, some strains have ...

Section: Discussionsupporting

confidence: 83%

Occurrence of Virulence Genes Associated with Diarrheagenic Pathotypes in Escherichia coli Isolates from Surface Water

Sidhu

Ahmed

Hodgers

et al. 2013

“…Though several authors have isolated E. coli from various natural environments, such as freshwater (4,5), beach water (6, 7), beach sand (7), tropical and subtropical soils (8)(9)(10)(11)(12), coastal temperate forest soils (13), riverine temperate soil (14), and sediments (15), it is difficult to determine unequivocally whether these isolates originated from recent contamination or whether they represent long-term residents in those environments. In 2010, Brennan et al (16) reported the recovery of E. coli populations from intact soil monoliths maintained in lysimeter units (previously described by Ryan and Fanning [17]), which have been protected from fecal contamination since 1998. These long-term soil-persistent E. coli isolates are the subject of the present study.…”

mentioning

confidence: 99%

The General Stress Response Is Conserved in Long-Term Soil-Persistent Strains of Escherichia coli

Somorin

Abram

Brennan

et al. 2016

Although Escherichia coli is generally considered to be predominantly a commensal of the gastrointestinal tract, a number of recent studies suggest that it is also capable of long-term survival and growth in environments outside the host. As the extraintestinal physical and chemical conditions are often different from those within the host, it is possible that distinct genetic adaptations may be required to enable this transition. Several studies have shown a trade-off between growth and stress resistance in nutrient-poor environments, with lesions in the rpoS locus, which encodes the stress sigma factor RpoS ( S ). In this study, we investigated a unique collection of long-term soil-persistent E. coli isolates to determine whether the RpoS-controlled general stress response is altered during adaptation to a nutrient-poor extraintestinal environment. The sequence of the rpoS locus was found to be highly conserved in these isolates, and no nonsense or frameshift mutations were detected. Known RpoS-dependent phenotypes, including glycogen synthesis and ␥-aminobutyrate production, were found to be conserved in all strains. All strains expressed the full-length RpoS protein, which was fully functional using the RpoS-dependent promoter reporter fusion PgadX:: gfp. RpoS was shown to be essential for long-term soil survival of E. coli, since mutants lacking rpoS lost viability rapidly in soil survival assays. Thus, despite some phenotypic heterogeneity, the soil-persistent strains all retained a fully functional RpoS-regulated general stress response, which we interpret to indicate that the stresses encountered in soil provide a strong selective pressure for maintaining stress resistance, despite limited nutrient availability. IMPORTANCEEscherichia coli has been, and continues to be, used as an important indicator species reflecting potential fecal contamination events in the environment. However, recent studies have questioned the validity of this, since E. coli has been found to be capable of long-term colonization of soils. This study investigated whether long-term soil-persistent E. coli strains have evolved altered stress resistance characteristics. In particular, the study investigated whether the main regulator of genes involved in stress protection, the sigma factor RpoS, has been altered in the soil-persistent strains. The results show that RpoS stress protection is fully conserved in soil-persistent strains of E. coli. They also show that loss of the rpoS gene dramatically reduces the ability of this organism to survive in a soil environment. Overall, the results indicate that soil represents a stressful environment for E. coli, and their survival in it requires that they deploy a full stress protection response. E scherichia coli is a Gram-negative, facultative anaerobe, belonging to the Enterobacteriaceae family, which inhabits the intestinal tracts of humans, warm-blooded animals, and reptiles (1, 2). It can be transferred through water and sediments via feces and is almost universally used as an i...

“…Avery et al (10) observed E. coli persistence in soils amended with cattle, sheep, and swine manure for up to 19 weeks, while Entry et al (11) observed prolonged survival of fecal coliforms and enterococci (at least 42 weeks) in soils amended with dairy manure. Such extended survival in soils can result in the occurrence of indicator organisms in runoff and infiltration waters from sites that have not had prior manure applications for weeks, months, or even years (12,13).…”

mentioning

confidence: 99%

Depth-Dependent Survival of Escherichia coli and Enterococci in Soil after Manure Application and Simulated Rainfall

Stocker

Pachepsky

Hill

et al. 2015

bOnce released, manure-borne bacteria can enter runoff via interaction with the thin mixing layer near the soil surface. The objectives of this work were to document temporal changes in profile distributions of manure-borne Escherichia coli and enterococci in the nearsurface soil layers after simulated rainfalls and to examine differences in survival of the two fecal indicator bacteria. Rainfall simulations were performed in triplicate on soil-filled boxes with grass cover and solid manure application for 1 h with rainfall depths of 30, 60, and 90 mm. Soil samples were collected weekly from depth ranges of 0 to 1, 1 to 2, 2 to 5, and 5 to 10 cm for 1 month. Rainfall intensity was found to have a significant impact on the initial concentrations of fecal indicator bacteria in the soil. While total numbers of enterococci rapidly declined over time, E. coli populations experienced initial growth with concentration increases of 4, 10, and 25 times the initial levels at rainfall treatment depths of 30, 60, and 90 mm, respectively. E. coli populations grew to the approximately the same level in all treatments. The 0-to 1-cm layer contained more indicator bacteria than the layers beneath it, and survival of indicator bacteria was better in this layer, with decimation times between 12 and 18 days after the first week of growth. The proportion of bacteria in the 0-to 1-cm layer grew with time as the total number of bacteria in the 0-to 10-cm layer declined. The results of this work indicate the need to revisit the bacterial survival patterns that are assumed in water quality models. Fecal contamination of soil and water presents a major worldwide health risk. When pathogenic microorganisms enter soil or water, they can infect humans via drinking or recreational activities and through consumption or handling of contaminated produce. The Centers for Disease Control and Prevention (1) estimated in 2011 that each year nearly 1 in 6 Americans (or 46 million people) get sick and roughly 3,000 die from foodborne diseases. Another study performed in the same year estimated that foodborne pathogens resulted in medical care costs in the range from $4.4 billion to $33.0 billion (2). Contamination of soil and water leading to foodborne illness can originate from numerous sources, such as direct deposition by animals, overflow or leakage of faulty septic and sewage systems, or manure application to agricultural fields and pastures (3-5). The potential presence of pathogens that cause foodborne illness can be inferred via the monitoring of fecal indicator bacteria (FIB), such as Escherichia coli and enterococci (6).It has been found that both E. coli and enterococci can survive in the soil for several weeks after deposition, if not longer (7,8). Some studies have found that populations of these organisms can experience initial growth in the soil that can extend their prevalence for longer than previously thought. For example, Lau and Ingham (9) reported that E. coli and enterococci survived in soil following manure incorporation for mo...