Detection of <i>Acinetobacter baumannii</i>in the Oropharynx of Long-Term Hospitalized Patients and the Expression of <i>IntI</i>Gene Induced by Different Antibiotics

Acinetobacter baumannii is the main drug resistant bacteria in clinic at present, and its drug resistance is still rising rapidly. Integrons play an important role in bacterial acquisition of exogenous drug resistance genes. This study investigated A. baumannii colonization in oropharynx and the integron gene carrying, and the expressions of integrase gene were determined when exposed to the different concentrations of antibiotics. 64 hospitalized patients were collected during January 2019 to June in respiratory department of our hospital (the hospitalized time more than 14 days) in our experiment. All throat swab collections were used for DNA extraction, and A. baumannii identification and integron gene detection were done by PCR assay. A. baumannii strains isolated from the oropharynx were identified by MALD-TOF-MS technology and the drug resistance was also analyzed. When expose to a series of ceftazidime and imipenem (10 μg/mL, 5 μg/mL, 1 μg/mL, 0.1 μg/mL, 0.01 μg/mL), the expressions of integron gene in the strains originated from oropharynx were determined by qRT-PCR assay. The results of the PCR showed that 60 patients had detected the A. baumannii Ab-ITS gene and rA gene in throat swabs, wherein 43 patients with symptoms of infection and 17 without symptoms of infection. There was no significant difference in Ab-ITS gene and rA gene detection rates in the symptoms of infection and no symptoms of infection (P > 0.05). In total 60 cases of samples, 29 cases had detected the IntI genes. 6 strains of A. baumannii isolated from the throat swabs of hospitalized patients were multi-drug resistant bacteria with IntI gene and variable region genes. Gene sequencing analysis revealed that the variable region gene cassettes were aacA4-catB8-aadA1-qacEdelta1. When exposed to the concentration of 1 μg/mL and 5 μg/mL ceftazidime, the mRNA expression of IntI had significantly increase compared to the negative control (P < 0.05). When exposed to the concentration of 0.1 μg/mL, 1 μg/mL and 5 μg/mL imipenem, the mRNA expression of IntI had significantly increase compared to the negative control (P < 0.05). The results indicated that oropharyngeal microflora includes multidrug-resistant A. baumannii and carries ingegron genes in long-term hospitalized patients. The improper use of ceftazidime and imipenem might also contribute to the up-regulation of the integrase genes expression and the enhancement of bacterial resistance, which requires more attention in clinical work.