Water Gene Research Articles

Ultraviolet Disinfection of Antibiotic Resistant Bacteria and Their Antibiotic Resistance Genes in Water and Wastewater

Disinfection of wastewater treatment plant effluent may be an important barrier for limiting the spread of antibiotic-resistant bacteria (ARBs) and antibiotic resistance genes (ARGs). While ideally disinfection should destroy ARGs, to prevent horizontal gene transfer to downstream bacteria, little is known about the effect of conventional water disinfection technologies on ARGs. This study examined the potential of UV disinfection to damage four ARGs, mec(A), van(A), tet(A), and amp(C), both in extracellular form and present within a host ARBs: methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus faecium (VRE), Escherichia coli SMS-3-5, and Pseudomonas aeruginosa 01, respectively. An extended amplicon-length quantitative polymerase chain reaction assay was developed to enhance capture of ARG damage events and also to normalize to an equivalent length of target DNA (∼1000 bp) for comparison. It was found that the two Gram-positive ARBs (MRSA and VRE) were more resistant to UV disinfection than the two Gram-negative ARBs (E. coli and P. aeruginosa). The two Gram-positive organisms also possessed smaller total genome sizes, which could also have reduced their susceptibility to UV because of fewer potential pyrimidine dimer targets. An effect of cell type on damage to ARGs was only observed in VRE and P. aeruginosa, the latter potentially because of extracellular polymeric substances. In general, damage of ARGs required much greater UV doses (200-400 mJ/cm² for 3- to 4-log reduction) than ARB inactivation (10-20 mJ/cm² for 4- to 5-log reduction). The proportion of amplifiable ARGs following UV treatment exhibited a strong negative correlation with the number of adjacent thymines (Pearson r < -0.9; p < 0.0001). ARBs surviving UV treatment were negatively correlated with total genome size (Pearson r < -0.9; p < 0.0001) and adjacent cytosines (Pearson r < -0.88; p < 0.0001) but positively correlated with adjacent thymines (Pearson r > 0.85; p < 0.0001). This suggests that formation of thymine dimers is not the sole mechanism of ARB inactivation. Overall, the results indicate that UV is limited in its potential to damage ARGs and other disinfection technologies should be explored.

Case cluster shifting and contaminant source as determinants of melioidosis in Taiwan

To assess the geographical distribution of melioidosis contamination sources and the association between the location of melioidosis cases and positive sampling sites for Burkholderia pseudomallei in Taiwan. Data on the location of melioidosis cases from 2002 to 2011 were combined with the geographical distribution of B. pseudomallei as indicated by the detection of specific flagella gene products measured from 2005 to 2011. Temporal and spatial analyses were used to determine the incidence, cluster shifts and associations between the two datasets. Melioidosis cases clustered in two 'hot-spot' areas with incidence rates that were significantly higher than in neighbouring towns. The incidence rates in the northern area gradually decreased, while the rates in the southern area increased and were temporally associated with the appearance of B. pseudomallei-specific flagella genes in water samples. Melioidosis hot-spot areas were present in Taiwan. Water contaminated with B. pseudomallei serves as a potential transmission vehicle and is correlated with an increase in melioidosis cases; this correlation was stronger than that for B. pseudomallei-contaminated soil.

Detection of phages carrying the Shiga toxin 1 and 2 genes in waste water and river water samples

To evaluate the occurrence and abundance of phages that carry the stx(1) and stx(2) gene in water samples of different quality. Phages growing on the Shiga toxin-negative Escherichia coli O157:H7 (ATCC 43,888) strain were enumerated by a plaque assay in concentrated raw and treated waste water samples and river water samples. Plaques were investigated for the presence of stx(1) and stx(2) genes by a multiplex/nested PCR procedure. An overall number of 805 plaques were tested for the presence of stx-carrying phages. Stx genes could be demonstrated in 2% (stx(1)) and 16% (stx(2)) of the plaques. Stx-phages were eliminated with approximately the same efficiency in comparison with somatic coliphages during the waste water treatment process. Due to the low numbers of phages carrying the stx genes 1 and 2 in treated waste water and river water, the dilution and inactivation of host bacteria and the unsuitable conditions for the transduction of host organisms in aquatic environments, it is difficult to derive from the data the direct evidence for a public health problem. The results show the quantitative occurrence of stx-carrying phages in waste and river water and confirm the frequent circulation of these viruses in the aquatic environment.

The extent of protist diversity: insights from molecular ecology of freshwater eukaryotes

Classical studies on protist diversity of freshwater environments worldwide have led to the idea that most species of microbial eukaryotes are known. One exemplary case would be constituted by the ciliates, which have been claimed to encompass a few thousands of ubiquitous species, most of them already described. Recently, molecular methods have revealed an unsuspected protist diversity, especially in oceanic as well as some extreme environments, suggesting the occurrence of a hidden diversity of eukaryotic lineages. In order to test if this holds also for freshwater environments, we have carried out a molecular survey of small subunit ribosomal RNA genes in water and sediment samples of two ponds, one oxic and another suboxic, from the same geographic area. Our results show that protist diversity is very high. The majority of phylotypes affiliated within a few well established eukaryotic kingdoms or phyla, including alveolates, cryptophytes, heterokonts, Cercozoa, Centroheliozoa and haptophytes, although a few sequences did not display a clear taxonomic affiliation. The diversity of sequences within groups was very large, particularly that of ciliates, and a number of them were very divergent from known species, which could define new intra-phylum groups. This suggests that, contrary to current ideas, the diversity of freshwater protists is far from being completely described.