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Indian Journal of Medical Microbiology, Vol. 23, No. 2, April-June, 2005, pp. 92-94 Review Article Multidrug Resistant Salmonella typhi in Asymptomatic Typhoid Carriers among Food Handlers in Namakkal District, Tamil Nadu Senthilkumar B., Prabakaran G. Department of Biotechnology, Centre for Biotechnology, Muthayammal College of Arts and Science, Rasipuram Correspondence Address:Department of Biotechnology, Centre for Biotechnology, Muthayammal College of Arts and Science, Rasipuram - 637 408, senthilmicro@yahoo.co.in Code Number: mb05025 Abstract Purpose: to screen Salmonella typhi in asymptomatic typhoid
carriers and to find out drug resistance and ability of the strains to
transmit drug resistance to other bacteria. Keywords: Asymptomatic typhoid carriers, antibiotics, drug resistance, plasmids, conjugation Typhoid is one of the most wide spread of all bacterial diseases in India. The main source of typhoid is asymptomatic carriers. An individual can asymptomatically carry the typhoid germ for days to years without showing any of symptoms of typhoid fever. In such carriers, the typhoid bacillus continues to multiply in the gall bladder. It reaches the intestine through the bile duct. The silent carriers are the source of typhoid germs for the continued episodes of infections. Women exceed men as carriers by a ratio of 3:1.[1],[2] The rate of resistance development in bacteria has been found to be increasing. Several disease causing bacteria including typhoid causing Salmonella species have now become resistant to one or more antibiotics.[3] The population of multi drug resistant (MDR) Salmonella typhi is steeply increasing in the Indian subcontinent, Southeast Asia and other geographical regions. The emergence of drug resistant pathogens poses a major challenge to the treatment and prevention of typhoid. In particular, the concern is about the spread of these multi drug resistant strains to rural India.[4] The main focus of this study is to determine the ability of the isolates to transfer the drug resistance by conjugation.
Materials and Methods
Antibiotic susceptibility tests were performed by Kirby-Bauer disc diffusion method. Overnight cultures in peptone water were lawned over the Mueller-Hinton agar (Hi-media). The antibiotic discs were used at the following concentration: ampicillin (A) 30 μg, amikacin (Ak) 30 μg, amoxicillin (Am) 25 μg, chloramphenicol (C) 25 μg, ciproflaxacin (Cf) 30 μg, co-trimaxazole (Co) 25 μg, gentamicin (G) 30 μg, nalidixic acid (Na) 30 μg, oflaxacin (O) 30 μg, rifampicin (R) 30 μg, tetracycline (T) 10 μg (Hi-media). Plasmid profile analysis was done as described by Kodo and Liu[6] and chromosomal DNA analysis was done as described by Grimberg et al .[7] Conjugation ability of the isolates was determined by Cappuccino and Shermann procedure.[8]
Results A varying percentage of drug resistance patterns of total isolates against individual antibiotics were observed [Table - 2]. Out of various Salmonella typhi isolates, 83.33% were multidrug resistant and 16.66% were single drug resistant. These multidrug resistant strains were having 120 kb plasmids, which were detected in agarose gel by using Hind III digest of DNA as a marker. The chromosomal DNA alone was encoding for resistance to nalidixic acid and ciprofloxacin that was confirmed in a strain lacking plasmid. In conjugation studies, TR CR strains (isolates) were used as donors against TS CS (E. coli CSH 57) strain as a recipient, 66.66% recipient strains acquired resistance to tetracycline and chloramphenicol [Table - 3]. Discussion The susceptibility to typhoid fever lies between the age 15-25 years.[10] Carrier state of typhoid was observed in the age group 15-45 years in this present investigation. In various Salmonella typhi isolates, 78.4% were resistant to the antibiotics such as ampicillin, chloramphenicol and trimethoprim which are conventionally used to treat typhoid fever.[11] There was a gradual increase in the time period in mean minimum inhibitory concentration of ciprofloxacin.[12] In this study, isolates were least resistant to oflaxacin, ciproflaxacin, gentamicin and nalidixic acid, while high resistance to tetracycline, rifampicin and chloramphenicol was also observed. The isolates were not identical at developing antibiotic resistance. Some isolates of Salmonella typhi showed the resistance to chloramphenicol, ampicillin, streptomycin and tetracycline, while sensitive to gentamicin. Mirza and Hart had also observed similar results.[13] Drug resistance is due to acquisition of plasmid encoded inactivating β-lactamase and chloramphenicol acetyl transferase. Ceftriaxone or fluoroquinolone is highly effective. Ciprofloxacin is effective in treatment of carrier state.[14] However, one of the isolates in this study showed resistance to ciprofloxacin. Plasmid encoded resistance to chloramphenicol, amikacin, ampicillin and chromosome encoded resistance to nalidixic acid and ciprofloxacin have been reported.[15] Plasmid (120 kb) bearing strains were found similar to the study of Karmaker et al.[16] In the present study, 33% of strains showing chromosomal DNA encoded resistance to ciprofloxacin and nalidixic acid were observed. Transferable plasmids have been found in fourteen strains and six of them expressed multiple drug resistance.[15] The plasmids were transferred by 66.66% strains during conjugative recombination in the present study which showed multidrug resistance plasmid. In contrast, the strain-SS-1 showing single antibiotic resistance had no plasmid. The strain SS- 6 has also no plasmid, but its resistance to ciprofloxacin was due to chromosomal DNA. Indiscriminate usage of chemotherapeutic agents in the treatment of various diseases leads to occurrence of drug resistance. From this study it was concluded that drug resistant was found in the isolates from asymptomatic typhoid carrier. In vivo transfer of resistant genes to normal microbial flora pose hazard to human kind. References
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