Analysis of the Class 1 Integrons, Carbapenemase Genes and Biofilm Formation Genes Occurrence in Acinetobacter baumannii Clinical Isolates

Acinetobacter baumannii is a non-fermentative Gram-negative bacterium that can cause nosocomial infections in critically ill patients. Carbapenem-resistant A. baumannii (CRAB) has spread rapidly in clinical settings and has become a key concern. The main objective of this study was to identify the distribution of integrons and biofilm-formation-related virulence genes in CRAB isolates. A total of 269 A. baumannii isolates (219 isolates of CRAB and 50 isolates of carbapenem-sensitive A. baumannii (CSAB)) were collected. Carbapenemase genes (bla_KPC, bla_VIM, bla_IMP, bla_NDM, and bla_OXA-23-like) and biofilm-formation-related virulence genes (abal, bfms, bap, and cusE) were screened with PCR. Class 1 integron was screened with PCR, and common promoters and gene cassette arrays were determined with restriction pattern analysis combined with primer walking sequencing. Whole-genome sequencing was conducted, and data were analyzed for a bla_OXA-23-like-negative isolate. All 219 CRAB isolates were negative for bla_KPC, bla_VIM, bla_IMP, and bla_NDM, while bla_OXA-23-like was detected in 218 isolates. The detection rates for abal, bfms, bap, and cusE in 219 CRAB were 93.15%, 63.93%, 88.13%, and 77.63%, respectively. Class 1 integron was detected in 75 CRAB (34.25%) and in 3 CSAB. The single gene cassette array aacA4-catB8-aadA1 with relatively strong PcH2 promoter was detected in class 1 integrons. The bla_OXA-23-like-negative CRAB isolate was revealed to be a new sequence type (Oxford 3272, Pasteur 2520) carrying bla_OXA-72, bla_OXA-259, and bla_ADC-26. In conclusion, bla_OXA-23-like was the main reason for CRAB’s resistance to carbapenems. A new (Oxford 3272, Pasteur 2520) CRAB sequence type carrying the bla_OXA-72, bla_OXA-259, and bla_ADC-26 was reported.