ANTIBIOTICS SUSCEPTIBILITY AND MOLECULAR CHARACTERIZATION OF CLINICAL ISOLATES OF E. coli

(A CASE STUDY OF AHMADU BELLO UNIVERSITY TEACHING HOSPITAL SHIKA, ZARIA)

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Department of Pharmaceutical Sciences

ABSTRACT
Antimicrobial drug resistance is a global challenge with the emergence of resistant bacterial strains worldwide. This study was conducted to determine the incidence of E. coli in ABUTH Shika, Zaria (from March 2011 to February 2012), their antibiotics susceptibility pattern, molecular characterization and possible presence of E. coli serotype O157:H7. Clinical isolates of E. coli from inpatients and outpatients were collected and cultured on eosin methylene blue to obtain pure cultures. A retrospective analysis of records of the Medical Microbiology unit for the same period (March 2011 to February 2012) was carried out. The incidence of E. coli isolates in clinical samples was found to be 50% in stool, 26.7% in urine, 13.3% in blood, 6.6% in urogenital and 3.3% in wounds. The retrospective analysis of the prevalence of E. coli associated infections in ABUTH Shika, showed that out of the 751 patients bio-data evaluated, female patients were mostly infected 62.3%(468) compared with male patients 37.4%(281). Of the 751 patients bio-data evaluated, 150 isolates were collected and 60 isolates were confirmed as E. coli. The antibiotic susceptibility profile of clinical isolates of E. coli to fourteen (14) commonly prescribed antibiotics in the treatment of E. coli associated infections showed that 76.7% of the isolates were resistant to ceftazidime, 78.3% to amoxicillin-clavulanic acid, 70% to ampicillinsulbactam, 56.7% to tetracycline, 43.3% to cefalexin, 41.7% to nalidixic acid, 36.7% to amoxicillin and 30% to cefuroxime. The isolates were also found to be sensitive to ceftriaxone (88.3%), gentamicin (78.3%), chloramphenicol (78.3%), ciprofloxacin (71.7%), nitrofurantoin (78.4%), ofloxacin (73.3%). Higher percentage (80%) of the isolates were multidrug resistant (MDR), 11.7% were extensively drug resistant (XDR). Statistical analysis at p value < 0.05, showed a significant difference in the level of resistance expressed by E. coli from different clinical samples. At MARI ≥ 0.3, 71.6% of the patients showed a frequent use of the antibiotics usually prescribed in the hospital for E. coli infections. The high minimum inhibitory concentration (μg/ml) of amoxicillin–clavulanic acid and ceftriaxone to the transconjugants of the multidrug resistant E. coli showed that the resistance exhibited was plasmid encoded. The extended spectrum β-lactamase (ESBLs) using double disc diffusion method showed that of the 10 isolates tested, all were resistant to amoxicillin-clavulanic acid, 7(70%) to ceftazidime, 5(50%) to ceftriazone and cefpodoxime. Seventy percent 7(70%) of the 10 selected multidrug resistant clinical isolates were ESBLs positive; a ≥ 5mm increase in zone diameter for either antibiotics compared to its zone when tested alone, while 30% (3) of the selected isolates showed production of AmpC gene. E. coli serotype O157:H7 was isolated in 11(18.3%) of the 60 confirmed E. coli isolates (that is, 36.7% (11) of the stool isolates (30) were E. coli serotype O157:H7, while other serotypes in stool isolates amounted to 63.3%). Hetero-resistant isolates of E. coli (small colonies variant, found within the diameter of the zone of inhibition of cefoxitin) showed a far higher resistance to some tested antibiotics than that of their parental clinical isolates. Using molecular characterization by polymerase chain reaction (PCR), the ESBLs encoding genes, TEM, SHV and OXA and plasmid bands were detected in the multidrug resistant isolates, and in line with documented works, this suggests that these genes were plasmid encoded. E. coli expressing ESBLs and AmpC enzyme are present in E. coli isolated from ABUTH, Shika, Zaria. These suggest that patients with infections associated with E. coli producing ESBLs and AmpC enzyme may have complication in therapy and limited treatment options, which will lead to higher mortality rate, high economic burden and longer hospital stays.