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. 2022 Aug 25;10(9):1708.
doi: 10.3390/microorganisms10091708.

High Prevalence and Varied Distribution of Antibiotic-Resistant Bacteria in the Rhizosphere and Rhizoplane of Citrus medica

Fang Yang  1   2   3   4 , Yu Wang  1   2   3   4 , Qianwen Liu  1   2   3   4 , Bo Xu  1   2   3   4 , Huan Chen  1   2   3   4 , Yaomen Li  1   2   3   4 , Kun Wang  1   2   3   4 , Guixin Liang  1   2   3   4 , Ruiqi Zhang  1   2   3   4 , Xin'an Jiao  1   2   3   4 , Yunzeng Zhang  1   2   3   4
Affiliations

High Prevalence and Varied Distribution of Antibiotic-Resistant Bacteria in the Rhizosphere and Rhizoplane of Citrus medica

Fang Yang et al. Microorganisms. .

Abstract

The plant-associated bacteria, including that in the rhizosphere and rhizoplane, play important roles in human exposure to antibiotic-resistant bacteria (ARB). The rhizosphere and rhizoplane represent two distinct environments with different selective pressures for bacterial colonization. However, whether the difference in characteristics between the rhizosphere and rhizoplane can affect the abundance and antibiotic resistance profiles of ARB colonizing, the two environments remain largely unknown. In this study, we obtained 174 bacterial isolates from the rhizosphere (113 isolates) and rhizoplane (61 isolates) of Citrus medica trees grown in a park, where humans could easily and frequently contact the trees. A very high proportion of isolates exhibited resistance to several clinically important antibiotics, including β-lactam class antibiotics and polymyxin, with several known antibiotic-resistant opportunistic pathogens, such as Micrococcus luteus, being identified. The prevalence of ARB in the rhizoplane was higher than that in the rhizosphere. While the prevalence of polymyxin-resistant isolates was higher in the rhizoplane, the prevalence of amphenicol-resistant isolates was significantly higher in the rhizosphere. In summary, our findings suggest that the rhizosphere and rhizoplane are important media for the spread of ARB, and the different characteristics between the two environments can affect the distribution of ARB.

Keywords: Citrus medica; antibiotic-resistant bacteria; rhizoplane; rhizosphere.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
The taxonomic distribution of bacterial isolates, obtained from the rhizosphere and rhizoplane of C. medica, shown on Phylum (A), Class (B), Order (C), and Genera (D) level. Items labeled with * are taxa exhibiting significantly higher prevalence in the rhizosphere compared with the rhizoplane, while items with # are those with higher prevalence in the rhizoplane compared with the rhizosphere (Fisher’s exact test, p < 0.05).
Figure 2
Figure 2
Phylogenetic tree, reconstructed based on the 16S rDNA sequences of the 174 isolates. The taxonomic information of the isolates is shown at the family level. The most inner circle is the isolate names. The second circle shows the origin of the isolates (rhizosphere—pink, rhizoplane—blue). The third circle is the taxonomic affiliation of the isolates. The outermost circle is the accumulated amount of antibiotics each isolate is resistant to.
Figure 3
Figure 3
Antibiotic resistance profile differences between the rhizosphere and rhizoplane isolates. The prevalence difference of polymyxin and amphenicol-resistant isolates from the rhizosphere and rhizoplane was shown in the figure. Fisher exact test was used for antibiotic resistance profile comparison between the rhizosphere and rhizoplane isolates, and * denoted p < 0.05.
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