Bacteroidales markers for microbial source tracking in Southeast Asia.

Area of Science:

• Environmental microbiology
• Molecular biology
• Public health

Background:

• Fecal pollution in urban tropical environments poses a significant public health challenge.
• Host-associated microbial markers are crucial for tracing pollution sources.
• Previous studies have focused on different geographical regions, necessitating local validation.

Purpose of the Study:

• To validate host-associated Bacteroidales 16S rRNA gene marker assays for identifying fecal pollution sources in Singapore's urban tropical environment.
• To compare the performance of various human- and animal-associated assays.
• To assess the cross-reactivity of assays with different animal species.

Main Methods:

• Collection of 295 samples from sewage, humans, domesticated animals, and wild animals in Singapore.
• Analysis using real-time PCR with specific human-associated (e.g., B. theta), canine-associated (BacCan), and total Bacteroidales (BacUni) assays.
• Evaluation of diagnostic sensitivity and specificity for each assay.

Main Results:

• B. theta demonstrated high sensitivity (69% in stool, 100% in sewage) and specificity (98%) for human fecal pollution.
• BacCan assay was validated for tracking canine fecal pollution with >80% sensitivity and specificity.
• BacUni showed 100% sensitivity and specificity for mammals, confirming its utility for total Bacteroidales detection.
• Rabbit fecal samples exhibited cross-reactivity with several human and canine assays.

Conclusions:

• B. theta is a reliable marker for human fecal pollution in Singapore, differing from preferred assays in South Asia.
• BacCan and BacUni assays are effective for tracking canine and total mammalian fecal pollution, respectively.
• Identified cross-reactivity highlights the need for careful assay selection in diverse environments.