Abstract
The origin of bacteria resistance to antibiotics can either be chromosomal or extra-chromosomal (plasmid mediated) and one way of determining the origin of bacterial drug resistance is by plasmid elimination. In this study, the antibiotic susceptibility of seven Escherichia coli isolates (numbered 1-7) from urine and stool samples, were assessed using the disk diffusion method. The 10 antibiotics used were: nitrofurantoin (100 µg), ciprofloxacin (5 µg), tetracycline (50 µg), norfloxacin (10 µg), amoxycillin (20 µg), ofloxacin (5 µg), chloramphenicol (10 µg), cefuroxime (30 µg), ampicillin (10 µg) and gentamicin (10 µg). All isolates (100%) were observed to have shown resistance to ampicillin. Isolate No 6 was resistant to 70% of the antibiotics while isolate No 7 was observed to be resistant to 30% of the antibiotics. In order to determine if the resistance is plasmid mediated or chromosomal-borne, two of the isolates (29%) that showed resistance to more than one antibiotic were subjected to acridine orange mediated plasmid elimination. Isolate No 6 lost its resistance to 5 out of the 7 antibiotics (71%) while isolate number 7 lost its resistance to 2 out of the 3 antibiotics (67%) after the curing. Loss of resistance after the plasmid curing was an indication that the resistance was plasmid-mediated while the resistance mechanism for those that retained their resistance after plasmid curing was chromosomal-borne. It was suggested that further studies be done for the characterization of resistance plasmids on E. coli and policies be set that will minimize the indiscriminate use of antibiotics. Key words: Antibiotics, chromosomal, Escherichia coli, plasmid, resistance, sensitivity, susceptibility.
Highlights
Escherichia coli is a rod-shaped, Gram-negative facultative aerobic, coliform bacterium of the genus Escherichia which is classified as member of Enterobacteriaceae within the Gamma Proteobacteria class, found in the lower intestine of warm blooded organisms (Tenaillon et al, 2010)
The two isolates (29%); isolate no. 6 and 7 with resistance to more than one antibiotic were subjected to plasmid curing
Resistance to ampicillin was still retained by isolate no. 6, zone of inhibition of diameter 13 mm was observed as against none that was observed before the curing which may be an indication that the ampicillin resistant was being mediated by both the plasmid and the bacterial chromosome (Jesús et al, 2014). This is a preliminary study showing the susceptibility and resistance of E. coli to the various tested antibiotics, where resistance to the most used antibiotic like ampicillin, nitrofurantoin, amoxycillin and tetracycline were observed
Summary
Escherichia coli is a rod-shaped, Gram-negative facultative aerobic, coliform bacterium of the genus Escherichia which is classified as member of Enterobacteriaceae within the Gamma Proteobacteria class, found in the lower intestine of warm blooded organisms (Tenaillon et al, 2010). Despite most strains being commensal inhabitants of the intestine, there are some extraintestinal pathogenic E. coli (ExPEC) bacteria which have the ability to cause diverse and serious diseases, such as urinary tract infections (UTIs) and bacteremia (Wiles et al, 2008; Ron, 2010; Kanayama et al, 2015). The plasmids which are extra-chromosomal materials allow the movement of genetic materials, including antimicrobial resistant genes between bacterial species and genera through gene exchange processes thereby causing a rapid increase in antibiotic resistance (Carattoli, 2013)
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