03/09/2026
๐๐๐ ๐ซ๐๐ฌ๐๐๐ซ๐๐ก๐๐ซ๐ฌ ๐๐จ๐๐ฎ๐ฆ๐๐ง๐ญ ๐๐ง๐ญ๐ข๐๐ข๐จ๐ญ๐ข๐-๐ซ๐๐ฌ๐ข๐ฌ๐ญ๐๐ง๐ญ ๐๐๐๐ญ๐๐ซ๐ข๐ ๐ข๐ง ๐๐๐ฅ๐๐ฃ๐ฎ๐ง๐๐ง ๐ฅ๐๐ง๐๐๐ข๐ฅ๐ฅ ๐ฌ๐๐๐ข๐ฆ๐๐ง๐ญ๐ฌ
Sediments at the Calajunan Sanitary Landfill in Iloilo City may serve as environmental reservoirs of antibiotic-resistant bacteria, according to a study led by researchers from Central Philippine University and partner institutions.
The study, titled โOccurrence and Antibiotic Resistance Profiles of Bacterial Isolates from Sediments of the Calajunan Sanitary Landfill, Iloilo, Philippines,โ examined the bacterial communities found in different areas of the landfill, their antimicrobial resistance profiles, virulence-associated characteristics, and the relationship between bacterial distribution and sediment conditions. The research involved CPU researchers Ted Rudi Aurelio and Rolando Pakingking Jr., from College of Medical Laboratory Science together with researchers from partner institutions.
Researchers collected sediment samples from five areas of the 24-hectare landfill: an organic waste and composting area, a medical waste disposal zone, two active landfill cells receiving mixed and unsorted waste, and a leachate-impacted area. Samples were collected during June and July 2025 and examined for their physicochemical properties and bacterial communities.
The study recovered a total of 489 bacterial isolates from the landfill sediments. The bacterial community was dominated by Bacillus species, which accounted for 51.3% of the isolates. Among the most abundant were Bacillus subtilis at 14% and Bacillus proteolyticus at 13%. The researchers also recovered diverse Gram-negative bacteria, including Aeromonas, Citrobacter, Enterobacter, Klebsiella, Morganella, Proteus, Providencia, and Pseudomonas.
The organic-rich area also recorded the highest bacterial counts. Total heterotrophic plate counts across the sampling stations ranged from 7.05 to 7.89 log10 CFU/g, with the highest counts consistently observed at the organic waste station. The researchers found that sediment conditions varied significantly across the landfill, with organic carbon, total nitrogen, pH, and calcium emerging as the physicochemical properties most closely associated with the distribution of bacterial taxa.
Some of the recovered bacteria also displayed characteristics associated with opportunistic microorganisms. Aeromonas species consistently exhibited DNase and gelatinase activities, and most also showed hemolytic activity. However, the researchers emphasized that these traits alone do not establish pathogenicity, since pathogenic potential depends on multiple genetic and environmental factors that were not examined in the study.
More notably, the study found widespread antimicrobial resistance among the bacterial isolates. After excluding resistance considered intrinsic to particular bacterial species under current EUCAST recommendations, acquired resistance was particularly frequent against ฮฒ-lactams, macrolides, aminoglycosides, nitrofurans, and tetracyclines. At the level of bacterial taxa, resistance was most frequently observed for neomycin, followed by amoxicillin, erythromycin, and oxytetracycline.
The researchers also calculated the Multiple Antibiotic Resistance (MAR) index using acquired resistance profiles. MAR values ranged from 0.1 to 0.8, with isolates having values of 0.2 or higher predominating among most bacterial species. Some of the highest values were observed in Pseudomonas guariconensis and Pseudomonas putida at 0.7, Providencia vermicola at 0.6, and Citrobacter europaeus and Aeromonas taiwanensis at 0.8.
The findings are significant because the study provides what the researchers describe as the first baseline characterization of the cultivable bacterial community in landfill sediments in Western Visayas and one of the few integrated investigations of landfill-associated bacteria in the Philippines. It brings together sediment analysis, bacterial identification, virulence-associated testing, antimicrobial susceptibility testing, and MAR index analysis to provide site-specific evidence on environmental antimicrobial resistance.
The researchers stressed that the results should be viewed within a One Health perspective, in which human, animal, agricultural, and environmental health are interconnected. While the study did not investigate actual transmission pathways, landfill environments may provide opportunities for resistant bacteria to persist and potentially disseminate through pathways such as leachate, surface runoff, wildlife, domestic animals, or occupational exposure.
At the same time, the researchers noted important limitations. The study examined only cultivable bacteria, assessed antimicrobial resistance phenotypically rather than through resistance genes, and did not measure environmental factors such as heavy metals and antibiotic residues. Only representative isolates underwent 16S rRNA gene sequencing. The researchers therefore recommend future studies using approaches such as metagenomics, whole-genome sequencing, resistome analysis, mobile genetic element characterization, and environmental contaminant measurements.
The study demonstrates that sediments of the Calajunan Sanitary Landfill harbor diverse cultivable bacteria, including organisms exhibiting acquired antimicrobial resistance and virulence-associated phenotypes. The researchers conclude that landfill sediments represent important environmental reservoirs with ecological and public health relevance and should be considered in broader One Health-based antimicrobial resistance surveillance in the Philippines.
The study was published in the June 2026 issue of the Journal of Bacteriology and Virology, providing a significant contribution to the limited body of Philippine research on environmental antimicrobial resistance.
