Where human and animal sewage
Finding the perfect marker
In human and animal stomachs, many microbes take residence. These microbes are then influenced by the antibiotics being consumed which are then released into the environment through urine and fecal matter.
CrAssphage, a bacteriophage, was identified from human fecal genes. This bacteria-changing virus is found in more abundance than many other phages while being nearly nonexistent in animals. Given this information, crAssphage was the ideal marker for researchers determining human fecal pollution levels in the environment. This marker is also key in distinguishing whether the pollution is due to accumulation in the environment or a genetic selection of resistance.
Interpreting the data
The researchers concluded that the abundance of antibiotic resistant genes correlated with fecal pollution levels rather than the selection of the resistant gene. The highest occurrences of pollution were detected in Indian sediments (due to high levels of pharmaceutical production) as well as hospital and waste water treatment plant effluents throughout the United Kingdom and Singapore.
This study also concluded that wastewater treatment plants were highly effective at removing antibiotics from treated water. This water would then be considered safe for expulsion and no longer a viable carrier of antibiotic- resistant genes. The fecal matter would then be concentrated in sludge that is also eventually released into the environment. These release points appear to be hotspots for antibiotic accumulation resulting in greater antibiotic resistant genes.
Potential for future findings
This study is important beyond the concern for human health. If other fecal phage markers can be identified in livestock, the methods used for human waste could be replicated. This replication could then determine if animals can pass antibiotic resistance on to human or other animals. It may also lead to the determination and regulation of sludge release levels in agriculture.
The full study can be found in the current issue of Nature Communications or through the Nature.com website.