摘要

衣原体是最近被发现引起人眼，咽和胃肠道动物传染病的猪病原体。许多菌株含有赋予四环素抗性的四环素C类基因[tet（C）]盒。在50年代将四环素引入动物饲料之后，该盒最初可能通过来自革兰氏阴性供体的水平基因转移获得。各种研究小组已经描述了不同衣原体物种通过同源重组交换DNA的能力。由于90％以上的猪链球菌菌株对四环素具有抗性，因此它们代表了衣原体科内和之间抗生素抗性传播的潜在来源。在这里，我们研究了猪链球菌菌株之间tet（C）转运的遗传学。四环素敏感的梭状芽孢杆菌菌株S45在McCoy细胞中同时或顺序地与四环素抗性梭菌菌株共感染。可能的重组体通过源自经典噬菌斑测定的收获测定进行克隆纯化。缺乏转座酶IS200和IS605的C.suis品系Rogers132是最有效的供体，在筛选的56个（5.4％）克隆中的三个中产生两种独特的重组体。发现重组体对四环素具有8-16μg/ mL的最小抑制浓度（MIC）。只要重组体在S45（0.032μg/ mL）的MIC的两倍时开始在四环素中生长，抗性保持稳定超过10代。基因组分析揭示tet（C）通过同源重组整合到S45基因组中，取决于重组：nrqF和pckG之间的55kb交换，以及kdsA和cysQ之间的175kb交换。这两个位点都与反向重复序列或与重组热点相关的基序有关。我们的研究结果表明，转入S45的盒子转移频率较低，不需要IS200 / IS605转座酶，如果最初在四环素中生长则稳定，并导致多基因组配置。我们提供了稳定盒式转移的模型，以更好地了解衣原体感染人类的衣原体物种的能力，这是公共卫生重要性的问题。

Chlamydia suis is a swine pathogen that has also recently been found to cause zoonotic infections of the human eye, pharynx, and gastrointestinal tract. Many strains contain a tetracycline class C gene [tet(C)] cassette that confers tetracycline resistance. The cassette was likely originally acquired by horizontal gene transfer from a Gram-negative donor after the introduction of tetracycline into animal feed in the 1950s. Various research groups have described the capacity for different Chlamydia species to exchange DNA by homologous recombination. Since over 90% of C. suis strains are tetracycline resistant, they represent a potential source for antibiotic-resistance spread within and between Chlamydiaceae species. Here, we examined the genetics of tet(C)-transfer among C. suis strains. Tetracycline-sensitiveC. suis strain S45 was simultaneously or sequentially co-infected with tetracycline-resistant C. suis strains in McCoy cells. Potential recombinants were clonally purified by a harvest assay derived from the classic plaque assay. C. suis strain Rogers132, lacking transposases IS200 and IS605, was the most efficient donor, producing two unique recombinants detected in three of the 56 (5.4%) clones screened. Recombinants were found to have a minimal inhibitory concentration (MIC) of 8-16 μg/mL for tetracycline. Resistance remained stable over 10 passages as long as recombinants were initially grown in tetracycline at twice the MIC of S45 (0.032 μg/mL). Genomic analysis revealed that tet(C) had integrated into the S45 genome by homologous recombination at two unique sites depending on the recombinant: a 55 kb exchange between nrqF and pckG, and a 175 kb exchange between kdsA and cysQ. Neither site was associated with inverted repeats or motifs associated with recombination hotspots. Our findings show that cassette transfer into S45 has low frequency, does not require IS200/IS605transposases, is stable if initially grown in tetracycline, and results in multiple genomic configurations. We provide a model for stable cassette transfer to better understand the capability for cassette acquisition by Chlamydiaceae species that infect humans, a matter of public health importance.

https://www.frontiersin.org/articles/10.3389/fmicb.2017.00156/full