Screening for Antibiotic Resistance Genes in Bacteria and the Presence of Heavy Metals in the Upstream and Downstream Areas of the Wadi Hanifah Valley in Riyadh, Saudi Arabia

Overview

Al-Otaibi and colleagues sampled Wadi Hanifah surface water in Riyadh, Saudi Arabia, for Li, Be, chromium (Cr), Co, total arsenic (As), cadmium (Cd), tin (Sn), total mercury (Hg), lead (Pb), and antibiotic-resistance genes. The source is primary environmental-water evidence and microbiome/AMR context, not food-product or drinking-water occurrence evidence. Its most useful contribution is the paired metal and ARG screening: the paper reports higher ARG burden upstream, while heavy-metal and ARG correlation was weak and not statistically significant.

Key numbers

Heavy metals in surface water

Table 4 reports mean +/- SD concentrations in ug/L for upstream and downstream water samples.

The abstract prints all-site mean concentrations of Li 37.25 ug/L, Be 0.02 ug/L, Cr 0.56 ug/L, Co 0.32 ug/L, As 0.93 ug/L, Cd 0.01 ug/L, Sn 200.4 ug/L, Hg 0.027 ug/L, and Pb 0.26 ug/L across the 18 sites. The stratified Table 4 values above are the routeable record because the paper’s abstract-level all-site means are not fully reconstructable from the upstream/downstream table by a simple 12-upstream/6-downstream site-weighted calculation.

Method performance

Table 3 reports ICP-MS quality-control data for seven of the nine metal targets:

The source does not provide the same QC row for Sn or Hg in Table 3. Several Table 4 means are lower than the printed LOQ values; this page therefore preserves the authors’ table values but flags the issue rather than treating those low-level results as fully quantified without qualification.

Antibiotic-resistance genes

The authors screened 12 ARG targets representing 10 antibiotic classes. Ten targets were detected in at least one site: blaNDM-1, ampC, tet(M), tet(B), erm(B), aac(6’)-Ie-aph(2”)-Ia, sulII, catII, vanA, and dfrA1. mecA and mcr-1 were not detected. Reported site-frequency summaries were 22.2% for blaNDM-1, 61.1% for ampC, 55.5% for tet(M), 55.5% for tet(B), 66.7% for erm(B), 33.3% for aac(6’)-Ie-aph(2”)-Ia, 77.7% for sulII, 72.2% for catII, 50% for vanA, and 55.5% for dfrA1.

ARG levels were significantly higher upstream than downstream (p = 0.002). The paper’s Pearson test for heavy metals versus ARGs was weak and non-significant: R = 0.066, 95% confidence interval -0.41 to 0.5, R2 = 0.004.

Methods (brief)

Water samples were collected in duplicate from 18 Wadi Hanifah sites in September 2022, transported on ice, and filtered through 0.45 um membranes. DNA was extracted from filters and 12 ARGs were screened by PCR with negative controls. Heavy metals were measured by Agilent 7900 ICP-MS with 1500 W reflected power, 15 L/min plasma gas flow, and 1 L/min auxiliary gas flow. The authors used blanks, fresh calibration standards, spiked samples, recovery targets of 70-120%, repeated-measurement RSD targets below 20%, and calibration correlation coefficient r2 above 0.995.

Implications

Certification: This source should not be routed into product or ingredient benchmark pools. It is environmental surface-water evidence for Saudi Arabia and can support context around water quality, microbial co-selection pressure, and the limits of inferring ARG burden from metal concentrations alone.

Courses: Useful example of co-monitoring metals and antibiotic-resistance genes in the same environmental samples, while also showing why method-performance tables matter when reported concentrations are below the printed LOQ.

App: Keep the source visible as context for environmental water and AMR. Do not present the Wadi Hanifah values as drinking-water, bottled-water, or food-product occurrence data without a separate source showing that matrix.

Related evidence

• Microbiome
• Lithium
• Beryllium
• Chromium
• Cobalt
• Arsenic, Total
• Cadmium
• Tin
• Mercury, Total
• Lead

Update history

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