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Colistin is drug of choice for treatment of carbapenem-resistant Acinetobacter baumannii infections. Unfortunately, global increase in clinical outbreaks of colistin and carbapenem resistant A. baumannii infections is on the rise and cause public health concern. In the present study, a total of 187 A. baumannii recovered from specimens of 240 patients admitted to intensive care units (ICUs) of two hospitals in Kerman, Iran during 2017-2018. Among the isolates, we found four extensive drug-resistant (XDR) with Minimum Inhibitory Concentration (MIC) ≥4 μg/mL against colistin. The colistin-resistant (Col-R) isolates harbored blaOXA-51 and blaOXA-23 carbapenemase genes, exhibited resistance to all antibiotic classes except tigecycline and ampicillin-sulbactam. They belonged to clonal complex 2, a new MLST type 1752 and displayed identical RAPD-PCR fingerprints. Phylogenetic tree analysis suggested that, the Col-R A. baumannii emerged by endogenous mutations rather than acquisition of preexisting clones. Expressions of pmrCAB by quantitative real-time PCR (qRT-PCR) revealed 8 and 7 folds increased in the transcription levels of pmrB/C genes in strain 1 grown in presence of 16 μg/mL colistin (p ≤ 0.01). However, no change in the expression of the pmrA was observed. Furthermore, DNA sequencing of Col-R genes illustrated three nonsynonymous substitutions in the LpxA (N136 → K), LpxC (P293 → Q), and PmrB (V21 → F, S28 → R, I149 → F) in the strains 1 and 3, respectively showing MIC 32 μg/mL against colistin. Multiple amino acids alignments demonstrated several substitutions in N-terminal region of PmrB. In conclusion, the above results provide valuable insights into the mechanism of Col-R in A. baumannii and the expressions of relative genes.

Background: Methicillin-resistant (MRSA) Staphylococcus aureus (S. aureus) are responsible for a vast number of nosocomial infections especially in immunocompromised subjects such as cancer patients. The presence of comorbidities including malignancies has been associated, with S. aureus bacteremia mortality. Thus, the detection of MRSA in this patients and the antibiotic susceptibility pattern of the isolates eases the selection of first-line medications and the prevention from further complications in cancer patients. The aim of this study was to determine the prevalence of MRSA infection and antibiotic susceptibility patterns of the isolates in pre and post-chemotherapy course in cancer patients.Materials and Methods: From May 2011 to July 2012, 200 nostril samples of cancerous patients were obtained and cultured on blood agar plates. After isolation and confirmation of S. aureus, antibiotic resistance pattern of the isolates was determined pre-chemotherapy and after the chemotherapy against vancomycin, tigecycline, linezolid, chloramphenicol, and oxacillin using disk diffusion test following CLSI guidelines. Chi-square test was used for data analysis.Results: Among a total number of 200 various cancer patients (64.5% females), 42 (21%) cases were positive for S. aureus and 7 (3.5 %) were MRSA carriers. Mean ages of MSSA and MRSA infected patients were 50.97±15.94 and 53.57±18.28 years old, respectively. In vitro susceptibility pattern of the MRSA and MSSA isolates to the 4 tested agents did not differed significantly after the chemotherapy in contrast with pre-chemotherapy state.Conclusions: This study showed that chemotherapy does not change the susceptibility pattern of MRSA species to antibiotics of choice in cancer patients. However, the importance of controlling methicillin resistant staphylococcal infections in critical cases, specifically cancer cases, necessitates the early detection, further investigations on more effective medications.