|Year : 2004 | Volume
| Issue : 3 | Page : 182-184
Plasmid mediated amikacin resistance in clinical isolates of pseudomonas aeruginosa
M Shahid , A Malik
Department of Microbiology, JN Medical College, Aligarh Muslim University, Aligarh - 202 002, India
Department of Microbiology, JN Medical College, Aligarh Muslim University, Aligarh - 202 002, India
Ten multidrug resistant (MDR) isolates of Pseudomonas aeruginosa, obtained from hospitalized burn patients, were selected for plasmid detection, curing and transformation experiments. These isolates were also studied for plasmid mediated resistance. All the isolates were found to harbour R plasmid. Curing and transformation experiments showed that resistance to amikacin was plasmid mediated. -lactamase production was also tested. It is suggested that plasmids should be characterised in all MDR P. aeruginosa strains and a nation wide antibiotic policy should be made to minimise the emergence of drug resistance.
|How to cite this article:|
Shahid M, Malik A. Plasmid mediated amikacin resistance in clinical isolates of pseudomonas aeruginosa . Indian J Med Microbiol 2004;22:182-4
|How to cite this URL:|
Shahid M, Malik A. Plasmid mediated amikacin resistance in clinical isolates of pseudomonas aeruginosa . Indian J Med Microbiol [serial online] 2004 [cited 2019 Oct 22];22:182-4. Available from: http://www.ijmm.org/text.asp?2004/22/3/182/11215
In the past few decades Pseudomonas aeruginosa has been increasingly recognised as a pathogen in a variety of serious infections in hospitalized patients especially with impaired immune defences. This organism is an important opportunistic pathogen with innate resistance to many antibiotics. Despite innate resistance, additional acquired resistance due to plasmids is also found in P.aeruginosa. Plasmid mediated resistance to various antimicrobial drugs have been demonstrated by various workers, and most of them have demonstrated it by plasmid curing experiments alone. In the present study, we have isolated a plasmid responsible for multidrug resistance in P. aeruginosa isolates from burn patients and an attempt was made to demonstrate the drug resistance by plasmid curing experiments as well as by transformation experiments.
| ~ Materials and Methods|| |
The present study was carried out between July 2002 and December 2002. P.aeruginosa isolates were obtained from the pus culture of hospitalized burn patients and were analysed for the presence of drug resistance by the method of Bauer et al on Mueller Hinton agar (HiMedia) by using commercially available paper discs (HiMedia, India). The antibiotic discs and their concentrations used in the present study are shown in [Figure - 1].
Ten multidrug resistant isolates, which were also resistant to amikacin, were selected for plasmid detection, curing and transformation experiments and also for b-lactamase detection. Plasmid isolation was carried out using the large scale alkaline lysis method as described by Davis et al.
Plasmid samples (25 µL) were electrophoresed through 0.8% agarose (type 1; Sigma) in TBE buffer at 150V, 60mA for 5.5 hours by method of Portnoy et al. The gel was stained for 2 hours in 0.5 µg/µL of ethidium bromide solution and destained in water.
| ~ Curing experiments|| |
Ethidium bromide (Sibisco Research Lab. Ltd. India) was used as curing agent. The method described by Guerry and Colwell as adopted in our previous experiments was used. The minimal inhibitory concentration of ethidium bromide was determined for the bacterial isolates in trypticase soy broth (TSB) and the highest concentration permitting growth was used for plasmid curing. Subcultures were initially done on trypticase soy agar and the colonies were tested for antibiotic sensitivity.
| ~ Transformation experiments|| |
Transformation experiments were carried out according to Davis et al as described by us elsewhere by using P. aeruginosa strains as donor and Escherichia More Details coli strain HB101, which was sensitive to all the previously tested drugs, as recipient. The presence of plasmid in transformants was checked through electrophoresis and the transformants were also tested for each drug resistance already recorded for the donor strain.
Beta lactamase production
The iodometric method of Miles et al was used for the detection of b-lactamase production.
| ~ Results|| |
The results of the antimicrobial susceptibility of the P. aeruginosa isolates included in the present study are shown in [Figure - 1]. All 10 MDR P. aeruginosa isolates were examined for the presence of plasmid. All the P. aeruginosa isolates were found to harbour a single and similar plasmid [Figure:2].
Curing and transformation experiments were attempted on these isolates to determine changes in plasmid content associated with antibiotic resistance pattern. After curing experiments the loss of antibiotic resistance was concomitant with the loss of plasmid content [Figure:2]. It was noted that the isolates became sensitive to amikacin while they remained resistant to carbenicillin and clindamycin. Similarly, the transformants (E. coli HB 101) became resistant to amikacin after the transformation experiments while E. coli HB 101 was sensitive to all the drugs prior to the experiments. Agarose gel electrophoresis of the tranformants showed the presence of transforming plasmid [Figure:2]. Out of 10 P. aeruginosa isolates tested, 4 (40%) showed the presence of b-lactamase by the iodometric method.
| ~ Discussion|| |
P. aeruginosa is currently one of the most frequent nosocomial pathogen and the infections due to this organism are often difficult to treat due to antibiotic resistance. The mechanisms of resistance to antibiotics include reduced cell wall permeability, production of chromosomal and plasmid mediated b-lactamases, aminoglycoside-modifying enzymes and an active multidrug efflux mechanism.
An alarming increase in resistance of Pseudomonas spp. to various antimicrobial agents has been reported by many workers  but studies demonstrating the relation of plasmid and drug resistance in clinical isolates of P. aeruginosa by curing and transformation experiments is scanty in our country. In the present study we have isolated a plasmid from MDR P. aeruginosa isolates, which was found responsible for amikacin resistance. An important striking feature found in this study was increased resistance to amikacin and tobramycin whereas the strains were sensitive to gentamicin and netilmicin (80% and 70% respectively). Various workers from our country have reported the opposite i.e., increased sensitivity of P. aeruginosa strains to amikacin and resistance to gentamicin., This might be due to the variations in the usage of antibiotics in different geographical areas.
The fluorinated quinolones, in particular ciprofloxacin, are still active against P. aeruginosa. Resistance may, nevertheless, emerge during long term treatment of chronic infections. Resistance to other antibiotics including cephalosporins and anti-pseudomonal antibiotics may also occur in future. Therefore, to combat this problem, efforts should be made to isolate and characterise plasmids responsible for resistance in MDR P. aeruginosa strains from all over the country and a nation wide antibiotic policy should be defined after evaluating the effectiveness of the regime so that misuse of antibiotics is minimised and also the emergence of multidrug resistant organism can be restricted. This is a preliminary study on plasmid mediated amikacin resistance in P. aeruginosa isolates, however, there is a need for a large scale study to find out the plasmid mediated drug resistance in P. aeruginosa along with isolation and characterisation of the plasmid (s).
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