EXTRACTION AND CHARACTERISATION OF BRUCELLA ABORTUS STRAIN RB51 ROUGH LIPOPOLYSACCHARIDE

Brucellosis is an important zoonotic disease with considerable impacts on human and animal health. Brucella abortus strain RB51 vaccine is used for prevention of bovine brucellosis in Iran. Due to strain roughness, available serological tests cannot detect vaccinated animals. Detection of serological responses to the vaccine is important to monitor accurate vaccination implementation. Rough lipopolysaccharide (RLPS) of RB51 strain was extracted and characterised to develop serological tests for diagnosis of vaccinated animals. RLPS was extracted using phenol-chloroform-petroleum ether and evaluated by limulus amebocyte lysate (LAL) assay, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and agar gel immunodiffusion (AGID). According to our results, the extracted RLPS caused positive reaction in LAL assay. In SDS-PAGE, a band with a molecular weight around 14 kDa was identified after specific staining using silver nitrate. Double AGID of the RLPS with a hyperimmune serum resulted in a precipitation line formation. Our study showed that the method can be successfully used to extract RLPS from Brucella abortus strain RB51 as confirmed by LAL assay, PAGE and AGID. Key words: brucellosis, RB51 vaccine, rough lipopolysaccharid

Frequency of Multi-Drug Resistance and Molecular Characteristics of Resistance to Colistin in Acinetobacter baumannii Collected from Patients in Intensive Care Units with Ventilator-Associated Pneumonia

Background: Acinetobacter baumannii is one of the most common causes of ventilator-associated pneumonia (VAP) in patients hospitalized in ICU. Multiple resistance has resulted in excessive use of Colistin antibiotic, which is the latest treatment option for this bacterium. Therefore, the purpose of this study was to determine the abundance of multi-resistance and molecular characteristics of resistance to colistin among A. baumannii isolated from patients that are infected with VAP and hospitalized in ICU of “Qazvin” and “Masih Daneshvari” hospitals. Materials and Methods: In this study, 200 A. baumannii isolates related to VAP were collected from ICU of “Masih Daneshvari” (2012-2018) and “Qazvin” (2017-2018) hospitals, from bronchoalveolar lavage & tracheal aspirate specimens. Isolates were detected as A. baumannii by PCR with specific primers of the blaOXA-51-like gene. Antibacterial susceptibility of isolates to colistin was determined by the MIC method, and other antibiotics were examined by the disk diffusion method, according to the CLSI criteria. Multi-drug resistance (MDR) and extended–drug resistance (XDR) isolates were determined according to standard definitions of the CLSI. Results: All the isolates were susceptible to colistin. Moreover, they were resistant to piperacillin, piperacillin-tazobactam, ceftazidime, cefotaxime, ceftriaxone, amikacin, gentamycin, levofloxacin, co-trimoxazole, and ciprofloxacin. Antimicrobial resistance rates for tetracycline and ampicillinsulbactam were 8.5% and 20%, respectively. All isolates were MDR and XDR. All isolates were susceptible to colistin (MIC50=1 and MIC90=2 µg/ml). The sequencing results did not show any point mutation in pmr CAB genes, and mcr-1 gene was not detected in any isolates. Conclusion: In this study, all A. baumannii isolates collected from VAP patients were MDR and XDR. Although all isolates were susceptible to colistin, and this agent seems the most appropriate antibiotic for treatment of VAP, colistin resistance can become endemic in the world rapidly due to plasmid-mediated mobile colistin resistance mcr genes