Department of Biology, California State University Northridge, Northridge, CA, USA.
Microbiologyopen. 2020 Jun;9(6):1247-1263. doi: 10.1002/mbo3.1034. Epub 2020 Apr 3.
Carbapenems are last-resort β-lactam antibiotics used in healthcare facilities to treat multidrug-resistant infections. Thus, most studies on identifying and characterizing carbapenem-resistant bacteria (CRB) have focused on clinical settings. Relatively, little is still known about the distribution and characteristics of CRBs in the environment, and the role of soil as a potential reservoir of CRB in the United States remains unknown. Here, we have surveyed 11 soil samples from 9 different urban or agricultural locations in the Los Angeles-Southern California area to determine the prevalence and characteristics of CRB in these soils. All samples tested contained CRB with a frequency of <10 to 1.3 × 10 cfu per gram of soil, with most agricultural soil samples having a much higher relative frequency of CRB than urban soil samples. Identification and characterization of 40 CRB from these soil samples revealed that most of them were members of the genera Cupriavidus, Pseudomonas, and Stenotrophomonas. Other less prevalent genera identified among our isolated CRB, especially from agricultural soils, included the genera Enterococcus, Bradyrhizobium, Achromobacter, and Planomicrobium. Interestingly, all of these carbapenem-resistant isolates were also intermediate or resistant to at least 1 noncarbapenem antibiotic. Further characterization of our isolated CRB revealed that 11 Stenotrophomonas, 3 Pseudomonas, 1 Enterococcus, and 1 Bradyrhizobium isolates were carbapenemase producers. Our findings show for the first time that both urban and agricultural soils in Southern California are an underappreciated reservoir of bacteria resistant to carbapenems and other antibiotics, including carbapenemase-producing CRB.
碳青霉烯类抗生素是医疗保健机构中用于治疗多重耐药感染的最后手段β-内酰胺类抗生素。因此，大多数关于鉴定和表征耐碳青霉烯类细菌（CRB）的研究都集中在临床环境上。相对而言，人们对环境中 CRB 的分布和特征以及土壤作为美国 CRB 潜在储库的作用知之甚少。在这里，我们调查了洛杉矶-南加州地区 9 个不同城市或农业地点的 11 个土壤样本，以确定这些土壤中 CRB 的流行率和特征。所有测试的样本都含有 CRB，频率为每克土壤<10 至 1.3×10 cfu，大多数农业土壤样本中的 CRB 相对频率高于城市土壤样本。对这些土壤样本中的 40 株 CRB 进行鉴定和表征发现，它们大多数是 Cupriavidus、Pseudomonas 和 Stenotrophomonas 属的成员。在我们分离的 CRB 中鉴定出的其他不太常见的属，特别是来自农业土壤的属，包括 Enterococcus、Bradyrhizobium、Achromobacter 和 Planomicrobium。有趣的是，所有这些耐碳青霉烯类抗生素的分离株对至少 1 种非碳青霉烯类抗生素也具有中度或耐药性。对我们分离的 CRB 的进一步表征表明，11 株 Stenotrophomonas、3 株 Pseudomonas、1 株 Enterococcus 和 1 株 Bradyrhizobium 分离株是碳青霉烯酶产生菌。我们的研究结果首次表明，南加州的城市和农业土壤都是耐碳青霉烯类和其他抗生素的细菌的未被充分认识的储库，包括产碳青霉烯酶的 CRB。
