Acinetobacter baumannii is a Gram-negative opportunistic nosocomial pathogen, which can cause ventilator-related and blood infection in critically ill patients. The resistance of A. baumannii clinical isolates to common antimicrobials and their tolerance to desiccation have emerged as a serious problem to public health. In the process of pathogenesis, bacteria release signals, which regulate virulence and pathogenicity-related genes. Such bacteria coordinate their virulent behavior in a cell density-dependent phenomenon called quorum sensing (QS). In contrast, the two main approaches of QS interference, quorum sensing inhibitors (QSIs) and quorum quenching (QQ) enzymes, have been developed to reduce the virulence of bacteria, thus reducing the pressure to produce bacterial drug resistance. Therefore, QSIs or QQ enzymes, which interfere with these processes, might potentially inhibit bacterial QS and ultimately biofilm formation. In this review, we aim to describe the state-of-art in the QS process in A. baumannii and elaborate on the use of QSIs or QQ enzymes as antimicrobial drugs in various potential sites of the QS pathway.

Objective To investigate the in vitro and in vivo antibacterial activities of tigecycline and other 13 common antimicrobial agents, alone or in combination, against multi-drug resistant Acinetobacter baumannii. Methods An in vitro susceptibility test of 101 Acinetobacter baumannii was used to detect minimal inhibitory concentrations (MICs). A mouse lung infection model of multi-drug resistant Acinetobacter baumannii,established by the ultrasonic atomization method, was used to define in vivo antimicrobial activities. Results Multi-drug resistant Acinetobacter baumannii showed high sensitivity to tigecycline (98% inhibition), polymyxin B (78.2% inhibition), and minocycline (74.2% inhibition). However, the use of these antimicrobial agents in combination with other antimicrobial agents produced synergistic or additive effects. In vivo data showed that white blood cell (WBC) counts in drug combination groups C (minocycline + amikacin) and D (minocycline + rifampicin) were significantly higher than in groups A (tigecycline) and B (polymyxin B) (P < 0.05), after administration of the drugs 24h post-infection. Lung tissue inflammation gradually increased in the model group during the first 24h after ultrasonic atomization infection; vasodilation, congestion with hemorrhage were observed 48h post infection. After three days of anti-infective therapy in groups A, B, C and D, lung tissue inflammation in each group gradually recovered with clear structures. The mortality rates in drug combination groups (groups C and D) were much lower than in groups A and B. Conclusion The combination of minocycline with either rifampicin or amikacin is more effective against multidrug-resistant Acinetobacter baumannii than single-agent tigecycline or polymyxin B. In addition, the mouse lung infection by ultrasonic atomization is a suitable model for drug screening and analysis of infection mechanism.

Background: To analyze the difference of the antibiotic resistance of Acinetobacter baumannii (A. baumannii) isolated from our hospital between 2014 and 2017. Methods: We retrospectively evaluated the patients with a confirmed diagnosis of A. baumannii infection at a tertiary general hospital in Guilin during the period between January 2014 and December 2017. The following clinical and demographic data were collected: age, gender, specimens, microbiology results, and antibiotic resistance patterns of isolates. Bacterial identification and susceptibility testing were performed using MALDI-TOF MS and VITEK 2 COMPACT systems. The results were analyzed according to the Clinical and Laboratory Standards Institute (CLSI) 2018 definitions. Results: From 2014 to 2017, 1,294 strains of A. baumannii were detected, 41.5% of which came from ICU. The sputum separation rate from ICU was significantly higher than those from non-ICU (p < 0.05). Except for amikacin, levofloxacin, and compound sulfamethoxazole, the resistant rates of the others increased year by year. Meanwhile, the resistance rate of carbapenem-resistant A. baumannii in our hospital showed a significant upward trend and exceeded the average of the national level in 2016 - 2017. Conclusions: The drug resistance of A. baumannii has generally increased, and active measures have been taken to develop the combined application of antibiotics. Further studies should focus on the judicious use of available antibiotics and implementation of strict infection control measures to avoid the rapid spread or clonal dissemination of A. baumannii in healthcare facilities.