Role of aminoglycoside-modifying enzymes and 16S rRNA methylase (ArmA) in resistance of Acinetobacter baumannii clinical isolates against aminoglycosides

Abstract INTRODUCTION: This study aimed to determine the role of genes encoding aminoglycoside-modifying enzymes (AMEs) and 16S rRNA methylase (ArmA) in Acinetobacter baumannii clinical isolates. METHODS: We collected 100 clinical isolates of A. baumannii and identified and confirmed them using microbiological tests and assessment of the OXA-51 gene. Antibiotic susceptibility testing was carried out using disk agar diffusion and micro-broth dilution methods. The presence of AME genes and ArmA was detected by PCR and multiplex PCR. RESULTS: The most and least effective antibiotics in this study were netilmicin and ciprofloxacin with 68% and 100% resistance rates, respectively. According to the minimum inhibitory concentration test, 94% of the isolates were resistant to gentamicin, tobramycin, and streptomycin, while the highest susceptibility (20%) was observed against netilmicin. The proportion of strains harboring the aminoglycoside resistance genes was as follows: APH(3′)-VIa (aphA6) (77%), ANT(2")-Ia (aadB) (73%), ANT(3")-Ia (aadA1) (33%), AAC(6′)-Ib (aacA4) (33%), ArmA (22%), and AAC(3)-IIa (aacC2) (19%). Among the 22 gene profiles detected in this study, the most prevalent profiles included APH(3′)-VIa + ANT(2")-Ia (39 isolates, 100% of which were kanamycin-resistant), and AAC(3)-IIa + AAC(6′)-Ib + ANT(3")-Ia + APH(3′)-VIa + ANT(2")-Ia (14 isolates, all of which were resistant to gentamicin, kanamycin, and streptomycin). CONCLUSIONS: High minimum inhibitory concentration of aminoglycosides in isolates with the simultaneous presence of AME- and ArmA-encoding genes indicated the importance of these genes in resistance to aminoglycosides. However, control of their spread could be effective in the treatment of infections caused by A. baumannii.

Diverse aminoglycoside phosphotransferase types conferring aminoglycoside resistance in Enterobacteriaceae: A single-centre study from Northeast India

The present study investigates the molecular basis of aph-mediated aminoglycoside resistance and their transmission dynamics in a tertiary care hospital of Northeast India. Two hundred forty one isolates (230 Escherichia coli and 11 Klebsiella pneumoniae) were collected and screened for aminoglycoside resistance genes. Various aph types were amplified using polymerase chain reaction (PCR) assay. Plasmid incompatibilty, horizontal transferability and ERIC-PCR based typing were carried out for all the positive isolates. Among them, 67 isolates showed the presence of aph gene. Aph (3“)-IIIa and aph (3')-Via were predominant and horizontally transferable. All the plasmids were of incompatibility I1 group. Twenty-eight different haplotypes of E. coli were found harbouring aph gene types. This study was able to identify diverse aph types in a single centre and their corresponding phenotypic trait.

ArmA and RmtB Were the Predominant 16S RMTase Genes Responsible for Aminoglycoside-resistant Isolates in Korea

Pathogenic gram-negatives that produce 16S ribosomal RNA methyltransferases (16S RMTases) have already been distributed all over the world. To investigate the predominance of aminoglycoside resistance associated with 16S RMTases in Korea, we collected a total of 222 amikacin resistant Gram-negative clinical isolates from patient specimens between 1999 and 2015 from three hospital banks across Korea. ArmA and rmtB were the predominant 16S RMTase genes responsible for aminoglycoside-resistant isolates circulating in Korean community settings although only one rmtA-producing isolate was detected in 2006.

Study on the aminoglycoside resistance gene of nosocomial multidrug-resistant Acinetobacter baumannii / 国际检验医学杂志

Objective To investigate the prevalence of aminoglycoside resistance gene in multidrug-resistant Acinetobacter bau-mannii isolated in clinical at a certain time,and to provide the basis for the control of nosocomial infection.Methods 9 strains of multidrug-resistant Acinetobacter baumannii were isolated in First People′Hospital of Weifang from November 26,2013 to Decem-ber 12,2013.Identification of bacteria and susceptibility testing were conducted by VITEK2,and partial antimicrobial drug suscepti-bility tests were performed by the disk diffusion method.Aminoglycoside resistance genes were detected by PCR and the positive genes were partly sequenced.Results Among the 9 stains of multidrug-resistant Acinetobacter baumannii,2 strains carried aac(3)-Ⅰ gene,3 carried ant(3″)-Ⅰ gene,3 carried aac(6′)-Ⅰ gene.AndarmA gene was positive in 9 strains.All strains were resistant to aminoglycosides,such as amikacin,gentamicin and tobramycin.There were 5 specien issolated in ICU,while 3 specimens were isola-ted in neurosurgery ward.All specimens were separated from sputum.Conclusion Antimicrobial resistance to aminoglycosides of Acinetobacter baumannii isolated in the hospital during this time was related to aminoglycoside resistance gene.Nosocomial infec-tion caused by multidrug-resistant Acinetobacter baumanniiin,ICU and neurosurgery ward should be vigorously monitored.

The prevalence of aminoglycoside-modifying enzyme and virulence genes among enterococci with high-level aminoglycoside resistance in Inner Mongolia, China

ABSTRACT This study highlights the prevalence of aminoglycoside-modifying enzyme genes and virulence determinants among clinical enterococci with high-level aminoglycoside resistance in Inner Mongolia, China. Screening for high-level aminoglycoside resistance against 117 enterococcal clinical isolates was performed using the agar-screening method. Out of the 117 enterococcal isolates, 46 were selected for further detection and determination of the distribution of aminoglycoside-modifying enzyme-encoding genes and virulence determinants using polymerase chain reaction -based methods. Enterococcus faecium and Enterococcus faecalis were identified as the species of greatest clinical importance. The aac(6')-Ie-aph(2")-Ia and ant(6')-Ia genes were found to be the most common aminoglycoside-modifying enzyme genes among high-level gentamicin resistance and high-level streptomycin resistance isolates, respectively. Moreover, gelE was the most common virulence gene among high-level aminoglycoside resistance isolates. Compared to Enterococcus faecium, Enterococcus faecalis harbored multiple virulence determinants. The results further indicated no correlation between aminoglycoside-modifying enzyme gene profiles and the distribution of virulence genes among the enterococcal isolates with high-level gentamicin resistance or high-level streptomycin resistance evaluated in our study.

Epidemiological study of the genes conferring aminoglycoside resistance in 36 strains of multidrug-resistant Acinetobacter baumannii / 中国感染与化疗杂志

Objective To investigate the prevalence of genes conferring aminoglycoside resistance in multidrug-resistant strains of Acinetobacter baumannii (MDR-ABA).Methods Multidrug-resistant A.baumannii strains were isolated during the period from August to November 2012 from patients in the affiliated hospital of Jiangsu University and the First Hospital of Zhen-jiang.Kirby-Bauer diffusion method was used to determine the susceptibility of these strains to antimicrobial agents.PCR was performed to detect the aminoglycoside resistance genes.Results The 36 MDR-ABA strains showed high resistance rates to most antimicrobial agents except cefoperazone-sulbactam.The prevalence of the genes conferring aminoglycoside resistance, aac (3)-I,aac (6’)-Ib,aph (3’)-I and armA,was 72.2% (26/36),72.2% (26/36),80.6% (29/36)and 80.6% (29/36), respectively.Conclusions The MDR-ABA strains in this study are highly resistant to antimicrobial agents,which is closely as-sociated with the genes conferring aminoglycoside resistance.

The Genetic Characteristics of Multidrug-resistant Acinetobacter baumannii Coproducing 16S rRNA Methylase armA and Carbapenemase OXA-23

Acinetobacter baumannii is a gram-negative organism reported worldwide as a cause of health-care associated infections. Due to its increasing drug resistance, several studies on coproduction of armA and carbapenemase in South Korea and other parts of the world were reported, which can pose significant therapeutic threat. The aim of this study was to investigate genetic characteristics of multidrug-resistant A. baumannii coproducing armA and carbapenemase and its epidemiological relatedness. Forty-five multidrug resistant (MDR) A. baumannii clinical isolates were collected. Antimicrobial susceptibility was determined by agar dilution, Etest and VITEK 2 system. The presence of 16S rRNA methylase and carbapenemase were analyzed by polymerase chain reaction (PCR) and sequencing. Repetitive element palindromic (REP)-PCR was also performed for epidemiologic investigation. All of A. baumannii isolates harbored blaOXA-51 -like gene and 10 isolates showed an upstream ISAba1. 36 isolates (80%) showed amplification of OXA-23, all of which except one had an upstream ISAba1. 16S rRNA methylase armA was found in 44 isolates with high level resistance to aminoglycosides. The rate of coproduction was found in 36 isolates (80%). All isolates showed dominant two patterns in REP-PCR profile. The prevalence of MDR A. baumannii coproducing OXA-23 and armA was high, which the rate of blaOXA-23 coproduction was also high.

Isolation of bacteriophages to multi-drug resistant Enterococci obtained from diabetic foot: A novel antimicrobial agent waiting in the shelf.

Introduction: While foot infections in persons with diabetes are initially treated empirically, therapy directed at known causative organisms may improve the outcome. Many studies have reported on the bacteriology of diabetic foot infections (DFIs), but the results have varied and have often been contradictory. The purpose of the research work is to call attention to a frightening twist in the antibiotic-resistant Enterococci problem in diabetic foot that has not received adequate attention from the medical fraternity and also the pharmaceutical pipeline for new antibiotics is drying up. Materials and Methods: Adult diabetic patients admitted for lower extremity infections from July 2008 to December 2009 in the medical wards and intensive care unit of medical teaching hospitals were included in the study. The extent of the lower extremity infection on admission was assessed based on Wagner's classification from grades I to V. Specimens were collected from the lesions upon admission prior to the initiation of antibiotic therapy or within the first 48 h of admission. Results: During the 18-month prospective study, 32 strains of Enterococcus spp. (26 Enterococcus faecalis and 06 E. faecium) were recovered. Antibiotic sensitivity testing was done by Kirby-Bauer's disk diffusion method. Isolates were screened for high-level aminoglycoside resistance (HLAR). A total of 65.6% of Enterococcus species showed HLAR. Multidrug resistance and concomitant resistance of HLAR strains to other antibiotics were quite high. None of the Enterococcus species was resistant to vancomycin. Conclusion: Multidrug-resistant Enterococci are a real problem and continuous surveillance is necessary. Today, resistance has rendered most of the original antibiotics obsolete for many infections, mandating the development of alternative anti-infection modalities. One of such alternatives stemming up from an old idea is the bacteriophage therapy. In the present study, we could able to demonstrate the viable phages against MDR E. faecalis.

Aminoglycoside Resistance in Gram-negative Bacilli / 대한임상미생물학회지

Aminoglycosides are one of the clinically relevant antibiotics. They kill bacteria by binding to bacterial 30S subunit of ribosome. Resistance to aminoglycosides occurs by three different mechanisms: 1. Production of an enzyme that modifies aminoglycosides, 2. Impaired entry of aminoglycoside into the cell by altering the OMP permeability, decreasing inner membrane transport, or active efflux, 3. The receptor protein on the 30S ribosomal subunit may be deleted or altered as a result of a mutation. By far, enzymatic modification has been the most important mechanism. In this review, the mechanisms of action and resistance, and the prevalence of resistance due to acquisition of enzymes are briefly described.