Colistin-resistant multidrug-resistant (MDR), extensively drug-resistant (XDR), and pan-drug-resistant (PDR) bacteria are highly lethal and many researchers have tried hard to combat these microorganisms around the world. Infections caused by these bacteria are resistant to the last resort of antibiotic therapy and have posed a major challenge in clinical and public health. Since the production of new antibiotics is very expensive and also very slow compared to the increasing rate of antibiotic resistance, researchers are suggesting the use of natural substances with high antibacterial potential. Bacteriophages are one of the most effective therapeutic measures that are known to exist for use for incurable and highly resistant infections. Phages are highly taken into consideration due to the lack of side effects, potential spread to various body organs, distinct modes of action from antibiotics, and proliferation at the site of infection. Although the effects of phages on MDR and XDR bacteria have been demonstrated in various studies, only a few have investigated the effect of phage therapy on colistin-resistant isolates. Therefore, in this review, we discuss the problems caused by colistin-resistant MDR and XDR bacteria in the clinics, explain the different mechanisms associated with colistin resistance, introduce bacteriophage therapy as a powerful remedy, and finally present new studies that have used bacteriophages against colistin-resistant isolates.

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Background: Nosocomial infection caused by Acinetobacter baumannii has emerged as a world-wide serious problem in the emergence of multidrug-resistant (MDR). Infections caused by antibiotic-resistant strains of A. baumannii cannot be completely eliminated among the infected patients. This study aimed to monitor antibiotic resistance among A. baumannii strains isolated from burnt children.Methods: After performing biochemical identification tests on 115 isolates, 62 were detected as A. baumannii. Minimum inhibitory concentration (MIC) was used to test susceptibility to colistin, and disk agar diffusion was used for the susceptibility of the isolates to the antibiotics Ciprofloxacin, Amikacin, Gentamicin, Cefepime, Meropenem, Imipenem, Ceftazidime, Levofloxacin and Piperacillin/Tazobactam. Bacterial species were isolated and identified as multidrug-resistant (MDR), extensively drug-resistant (XDR) and pan drug-resistant (PDR), based on the susceptibility patterns to elected antibiotics, deputing different classes of antimicrobial.Results: The antibiotic susceptibility pattern out of a total of 62 bacterial strains used in this study. Thirty-six (58%) strains were categorized as MDR, 17 (27.5%) as XDR, and nine (14.5%) as PDR. Conclusion:To reduce the threat of antimicrobial resistance, MDR, XDR and PDR A. baumannii strains must be evaluated by all clinical microbiology laboratories.

The aim of this study was to investigate the effect of zinc oxide nanoparticles (ZnO‐NPs) on the expression of genes involved in toxin–antitoxin (TA) systems in multidrug‐resistant (MDR) Acinetobacter baumannii. Seventy clinical isolates of A. baumannii were collected from variuos clinical samples. Antimicrobial susceptibility test was determined by disk diffusion. Type II TA system‐related genes including GNAT, XRE‐like, hipA, hipB, hicA, hicB were screened using polymerase chain reaction (PCR). ZnO‐NPs prepared and characterized by field emission scanning electron microscopy and X‐ray diffraction. MIC of ZnO‐NPs of A. baumannii isolates was performed using the microdilution method. The expression of type II TA systems‐related genes were assessed with and without exposure to ZnO‐NPs using real‐time PCR. The highest rate of resistance and sensitivity was observed against cefepime (77.14%), and ampicillin/sulbactam (42.85%), respectively. All A. baumannii isolates were considered as MDR. In this study, three TA loci were identified for A. baumannii including GNAT/XRE‐like, HicA/HicB, and HipA/HipB and their prevalence was 100%, 42%, and 27.1%, respectively. There was no significant relationship between the prevalence of these systems and the origin of A. baumannii. Our data showed significant correlations between the presence of HicA/HicB system and resistance to ceftazidime, meropenem, imipenem, and cefepime (p < 0.05), and the presence of HipA/HipB system and resistance to ceftazidime, meropenem, imipenem, and cefepime (p < 0.05). In presence of ZnO‐NPs, the expression of all studied genes decreased. GNAT and hicB showed the highest and lowest expression changes by 2.4 folds (p < 0.001) and 1.3 folds (p < 0.05), respectively. This study demonstrates the promising potential of nanoparticles to impact the expression of the genes involved in TA Systems. So, the application of ZnO‐NPs may be helpful to design target‐based strategies towards MDRs pathogens for empowered clinical applications by microbiologists and nanotechnologists.

Acinetobacter baumannii is an important nosocomial pathogen which causes a wide range of infections. In this study, we addressed the role of class 1 integron, ISAba1 and ISAba125 associated with antimicrobial resistance in 72 clinical isolates of A. baumannii collected from clinical settings in Tehran, Iran. Moreover, to study the clonal relatedness of strains, repetitive extragenic palindromic-PCR (rep-PCR) assay was carried out. PCR revealed that bla-like, bla-like, bla-like, bla-like, bla, integrase gene (intI1), ISAba1, and ISAba125 were present in 86.11% (62/72), 84.72% (61/72), 30.55% (22/72), 0% (0/72), 0% (0/72), 58.33% (42/72), 97.22% (70/72), and 65.27% (47/72) of the strains, respectively. Sequencing of 39 internal variable regions of class 1 integrons showed seven gene cassette arrays, including aadA4-catB8-aadA1 (2.77%), aadA1-aadA4 (1.38%), aacC4-aadA1 (2.77%), aacC4 (22.22%), aadA1 (13.88%), aadA4 (5.55%), and catB8 (5.55%). We detected ISAba1 in the upstream of bla-like, bla-like, and bla in 54.16% (39/72), 9.72% (7/72), and 56.94% (41/72) of the strains, respectively. Whereas, there was a low frequency of disruptions in carO and dacD genes: 5.55% (4/72) and 4.16% (3/72). Rep-PCR analysis revealed that the isolates were genetically diverse. However, Cl-12 and Cl-15 were the largest clusters and they were recovered from various hospitals. Our analysis showed the high rates of class 1 integrons as a repertoire of aminoglycoside-modifying enzymes. It seems that linkages of ISAba1-bla-like and ISAba1-bla, and disruptions in carO or dacD can develop resistance to carbapenems among clinical isolates of A. baumannii.