Molecular typing, and integron and associated gene cassette analyses in Acinetobacter baumannii strains isolated from clinical samples

Molecular epidemiology and antimicrobial resistance patterns of carbapenem-resistant Acinetobacter baumannii isolates from patients admitted at ICUs of a teaching hospital in Zunyi, China

Background

Carbapenem-resistant Acinetobacter baumannii (CRAB) has emerged as a predominant strain of healthcare-associated infections worldwide, particularly in intensive care units (ICUs). Therefore, it is imperative to study the molecular epidemiology of CRAB in the ICUs using multiple molecular typing methods to lay the foundation for the development of infection prevention and control strategies. This study aimed to determine the antimicrobial susceptibility profile, the molecular epidemiology and conduct homology analysis on CRAB strains isolated from ICUs.

Methods

The sensitivity to various antimicrobials was determined using the minimum inhibitory concentration (MIC) method, Kirby-Bauer disk diffusion (KBDD), and E-test assays. Resistance genes were identified by polymerase chain reaction (PCR). Molecular typing was performed using multilocus sequence typing (MLST) and multiple-locus variable-number tandem repeat analysis (MLVA).

Results

Among the 79 isolates collected, they exhibited high resistance to various antimicrobials but showed low resistance to levofloxacin, trimethoprim-sulfamethoxazole, and tetracyclines. Notably, all isolates of A. baumannii were identified as multidrug-resistant A. baumannii (MDR-AB). The bla OXA-51-like, adeJ, and adeG genes were all detected, while the detection rates of bla OXA-23-like (97.5%), adeB (93.67%), bla ADC (93.67%), qacEΔ1-sul1 (84.81%) were higher; most of the Ambler class A and class B genes were not detected. MLST analysis on the 79 isolates identified five sequence types (STs), which belonged to group 3 clonal complexes 369. ST1145Ox was the most frequently observed ST with a count of 56 out of 79 isolates (70.89%). MLST analysis for non-sensitive tigecycline isolates, which were revealed ST1145Ox and ST1417Ox as well. By using the MLVA assay, the 79 isolates could be grouped into a total of 64 distinct MTs with eleven clusters identified in them. Minimum spanning tree analysis defined seven different MLVA complexes (MCs) labeled MC1 to MC6 along with twenty singletons. The locus MLVA-AB_2396 demonstrated the highest Simpson's diversity index value at 0.829 among all loci tested in this study while also having one of the highest variety of tandem repeat species.

Conclusion

The molecular diversity and clonal affinities within the genomes of the CRAB strains were clearly evident, with the identification of ST1144Ox, ST1658Ox, and ST1646Oxqaq representing novel findings.

Local characteristics of molecular epidemiolgy of Acinetobacter baumannii in Jilin province (northeast China)

A. Baumannii is an opportunistic nosocomial pathogen which has severe antibiotic resistance. However, the epidemiology is less clearly understood in Jilin province and China. Thus, 89 A. baumannii isolates from a single hospital in Jilin province between 2013-2017 were performed by MLST. In order to better understanding of the epidemiology of Jilin isolates, Chinese strains originated from other domestic regions and worldwide isolates in MLST database were analyzed by silico phylogenetic tools together. A total of 22 STs in Jilin were identified, and 10 STs were found to be novel. The top three predominant sequence types are ST195 (n = 34, 38.2%), ST208 (n = 14, 15.7%) and ST540 (n = 13, 14.6%). ST369 is predicted to be group founder and ST195, ST540 are subgroup founders of the majority STs in Jilin Province. Some newly discovered singletons showed close relationship with strains from other countries, which suggest that nation-cross transmission is one of important origin of Jilin strains. The majority of Jilin STs showed clonality and close relationship with the majorities from other regions of China. But occupation of individual STs in Jilin were different from that of other domestic regions. The aggregation trend and genetic relationship proved that predominant Jilin STs continue to mutate during transmission. Drug resistance facilitated transmission of Jilin A.baumannii isolates because more than 94% of isolates are resistant to at least one carbapenem and the STs with strong resistance to carbapenems usually has more isolates. In conclusion, high diversity and different occupation of STs, and occupation of novel STs proved that epidemiology of A. baumannii in Jilin has special regional characteristics, and drug resistance facilitated transmission of domestic strains and foreign strains.