Aeromonas Species from Nonchlorinated Distribution Systems and Their Competitive Planktonic Growth in Drinking Water

Abstract

Aeromonas is included in the Dutch Drinking Water Decree as an indicator for elevated microbial regrowth in non-chlorinated drinking water distribution systems (DWDS). The temporal and spatial diversity of Aeromonas species in ten DWDS and their planktonic growth characteristics for different carbon sources was investigated. Genotyping of the gyrB gene of isolates showed a non-systematic temporal and spatial variable prevalence of seven different Aeromonas species in these DWDS and no correlation with AOC-P17/NOX and Aeromonas concentrations. Pure cultures of these seven species showed a high affinity to low concentrations (μg/L) of individual amino acids and fatty acids, compounds associated with biomass. Growth occurred at 0.5 μg-C/L of an amino acid mixture. Growth of a mixed community of A. rivuli, A. salmonicida, A. sobria and A. veronii in drinking water occurred in pasteurized samples, however, no growth and decay occurred in competition with the autochthonous bacteria (non-pasteurized samples). This community also failed to grow in non-pasteurized distribution samples from a location with clear increase in planktonic Aeromonas concentrations in the transported drinking water. For competitive planktonic growth of Aeromonas an amino acid concentration of ≥5 μg-C/L is required. AOC-P17/NOX concentrations showed that such concentrations are not expected in Dutch drinking water. Therefore, we suspect that competitive planktonic growth is not the major cause of the observed non-compliance with the Aeromonas standard in non-chlorinated DWSD. Importance The occurrence of the bacterial genus Aeromonas in non-chlorinated drinking water in the Netherlands is regarded as an indication for elevated microbial regrowth in the distribution system. Identification of the prevalent species in ten distribution systems by genotyping yielded seven different species, with A. rivuli, A. veronii and A. sobria as the most dominant ones. Planktonic growth experiments of pure cultures confirmed former published affinity of Aeromonas for certain biomass compounds (amino and fatty acids). In competition with the autochthonous microflora, however, planktonic growth was not observed, only after addition of a threshold amino acid concentration of 5 μg-C/L. Based on our results and further observations we deduced that planktonic growth of Aeromonas in the DWDS is not very likely. Benthic growth in loose deposits and planktonic release is a more plausible explanation for the observed planktonic increase of Aeromonas.

Analysis of global Aeromonas veronii genomes provides novel information on source of infection and virulence in human gastrointestinal diseases

“…A Percentages of virulence factors in different categories. B) Virulence genes in each virulence factor category drinking water and fresh water [2][3][4][5][6]. Human Aeromonas gastrointestinal infections most often occur in warm weather [1,10].…”

“…Aeromonas veronii is a Gram-negative rod-shaped motile bacterium that inhabits mainly freshwater environments such as ground water, lakes and river [1]. It has also been isolated from chlorinated and untreated drinking water [2][3][4][5][6]. Several Aeromonas species including A. veronii are pathogens of aquatic animals, causing diseases such as skin ulceration and systemic hemorrhagic septicemia in fish, which is a great concern in aquaculture globally [7][8][9].…”

Water Lice and Other Macroinvertebrates in Drinking Water Pipes: Diversity, Abundance and Health Risk

“…Additionally, studies of the feces of Asellus aquaticus have indicated that the feces leach organic acids, among other, biopolymers, which seems to support regrowth of bacteria [4,5].…”

“…The support that invertebrates provide for the survival and regrowth of microbes indicates the significance of these organisms to water quality and human health, as well as the need for continuous and quantitative monitoring of invertebrates. Invertebrate occurrence is one of the key parameters influencing microbial regrowth following treatment in addition to raw water quality, e.g., given by microbial growth, development of harmful bacteria as biome of invertebrates and jelly egg masses as substrate for microbe development [5,47,48].…”

“…Water quality is influenced by the development of biofilms embedded with harmful bacteria, as well as species diversity, abundance, biomass, and deposition of water lice feces pellets. Accordingly, large increases in invertebrate abundance leads to increases in crude and fine particulate organic matter (POM; this means living animals and their feces, and dead animals) and increases in microbe abundance [4,5]. Indeed, this influences the biological stability of drinking water [6,7] as well as biological drinking water quality [8].…”