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Concentration (in numbers of copies per milliliter) of ARGs at H1a (black), H1b (diagonal lines), and H2 (gray). Significant differences (P value < 0.05 [Student's t test]) are indicated by different letters (i.e., a and b, a and bc) at the top of each bar. The absence of significant differences is indicated by identical letters (i.e., a and a, a and ab).
