Molecular Identification and Antimicrobial Studies of Fluoroquinolone-Resistant Staphylococcus aureus and Escherichia coli from Humans and Farm Animals in Enugu State


Faculty: Pharmaceutical Sciences
Department: Pharmaceutical Microbiology & Biotechnology


Adonu, C.C;
Esimone, C.O;


The increased emergence of fluoroquinolone-resistant Escherichia. coli and Staphylococcus aureus isolates of human and animal origin is a global public health problem. This is because infections caused by these isolates are presently associated with high mortality, morbidity and high drug treatment costs as there are little or no treatment options available. The aim of the study was to isolate, characterize, investigate on the epidemiology and to carry out antimicrobial studies on fluoroquinolone-resistant E. coli (FQREC) and Staph. aureus (FQRSA) isolates from farm animals and human in seven health districts in Enugu State. Specific objectives include: determination of the prevalence and distribution of FQRSA and FQREC as well as some of their resistant genes –Qnr A, gyr A and Nor A genes in the study area; evaluating the contribution of efflux pump inhibitor on fluoroquinolone resistance and evaluation of the antibacterial potentials of Cymbopogon citratus oil and Cocos nucifera essential oils alone and in combination with ciprofloxacin against the test isolates. A total of 7980 specimens of urine, faecal matter, and nasal, wound and skin swabs were collected using sterile containers and swab-sticks by random sampling techniques from humans and farm animals in Enugu State. Eight hundred and forty samples each of urine, faecal matter and nasal swabs were collected from both healthy carriers and patients, and 420 wound swabs were collected from patients alone. Futher, 1680 samples of nasal, vendors table, skin and anal swabs were collected from cattles, pigs and chickens. Isolation of E. coli and Staph. aureus were carried out using MacConkey, mannitol salt and blood agar. Identification was by Gram staining, catalase reaction, coagulase test and polymerase chain reaction. Antimicrobial susceptibility studies were carried out using the Kirby-Bauer disk diffusion technique. All the fluoroquinolone-resistant isolates were evaluated for the presence of plasmid DNA and resistant genes by conventional polymerase chain reaction. In vitro interactions of essential oils of Cymbopogon citratus and Cocos nucifera with ciprofloxacin were done by Checkerboard and thin overlay innoculum susceptibility disc methods respectively. One way ANOVA was used for data analysis using SPSS version 16. A total of 3407 E. coli and Staph. aureus comprising 920 animal isolates and 2487 human isolates were recovered from urine, faecal matter, nasal, wound and skin swabs. The prevalence of ciprofloxacin, ofloxacin, levofloxacin and pefloxacin resistance among E.coli isolates from the subjects were: human (12.5, 12.2, 12.6 and 13.2%), pig (5.7, 6.1, 5.7 and 7.8%), cattle (0, 0, 0 and 0%) and chicken (13.6, 14.3, 11.6 and 17.7%) respectively. The prevalence of ciprofloxacin, ofloxacin, levofloxacin and pefloxacin resistance among Staph. aureus isolates from the subjects were: human (21.1, 21.6, 19.4 and 22.5 %), pig (4.1, 3.4, 2.7 and 4.8 %), cattle (7.5, 7.5, 5.8 and 13.3%) and chicken (13.3 ,13.3, 13.3, and 13.3% ) respectively. The results showed the range of prevalence of genes in both humans and animals to be gyrA, 21.4-63.4% and qnrA, 7.1-22.6% in FQREC and NorA, 0-71.4% in FQRSA. A total of 223 plasmids were detected and cured to the range of 36.4-100%, confirming the contribution of plasmid in mediating fluoroquinolone resistance in these isolates. The presence of efflux pump inhibitor (omeprazole) at 128 μg/ml resulted in a reduction in the ciprofloxacin MIC (2- to 16-fold) for FQRSA, and for FQREC (omeprazole at 64 μg/ml), the MIC values were increased for most of the isolates. Essential oil of Cymbopogon citratus inhibits the growth of FQRSA and FQREC and also exhibit synergism with ciprofloxacin on many of the isolates. This study showed that the sensitivity of FQREC and FQRSA increases in the presence of ciprofloxacin and Cymbopogon citratus essential oil combination. The prevalence of FQRSA and FQREC and their resistant genes are high in Enugu State.