PREVALENCE AND ANTIMICROBIAL SUSCEPTIBILITY OF SHIGA TOXIN-PRODUCING ESCHERICHIA COLI IN CATTLE IN KADUNA AND SOKOTO STATES, NIGERIA
PREVALENCE AND ANTIMICROBIAL SUSCEPTIBILITY OF SHIGA TOXIN-PRODUCING ESCHERICHIA COLI IN CATTLE IN KADUNA AND SOKOTO STATES, NIGERIA
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Date
2007-08
Authors
LUGA, Igbakura Innocent
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Abstract
A total of 3000 samples comprising of 1800 faecal,400 unpasteurized milk,300 abattoir effluents, 300 water,20 minced meat and 20 cheese were collected and enriched in modified tryptone soya broth (MTSB) supplemented with novobiocin (Oxoid, Basingstoke England) and plated on cefixime sorbitol – MacConkey (CR-SMAC) agar (Oxoid, Basingstoke England). Typical colourless colonies were biochemically tested using standard methods. Isolates biochemically identified as E. coli, were presumptively identified using Remel Wellcolex E. coli O157:H7 kit (Remel Europe, UK) and a reference strain of E. coli O157:H7 (EDL 933). Shiga toxin production was assayed using the Verotoxin E. coli–Reverse Passive Latex Agglutination (VTEC-RPLA) kit (Oxoid, Bassingstoke, England). All STEC O157 strains were tested for haemolytic activity by culturing in brain heart infusion (BHI) agar containing 7% human blood. Molecular assays were carried out using four sets of primers targeting rfbEO157, fliCH7, stx2d and stx1 genes in all the confirmed isolates of E. coli O157:H7 from faecal and bulk milk samples and all E. coli O157:H- from bulk milk and 13 from cattle faeces. Antimicrobial resistance testing was carried out on EHEC STEC O157 by the standardized single disk diffusion method on Mueller – Hinton agar with EHEC EDL 933, as the control organism and a panel of 16 antimicrobial agents (Oxoid Basingstoke, England). The occurrence of enterohaemorrhagic STEC O157:H7 in healthy dairy, nomadic white Fulani cattle and unpasteurized bulk milk was confirmed by multiplex-PCR, duplex-PCR and PCR. The prevalence of faecal excretion of E. coli O157:H7 by multiplex-PCR was 0.6% (10/1800). This prevalence was significantly associated with season (Fisher‟s exact test, p=0.030), age (Fisher‟s exact test, P<0.040) and management type (Fisher‟s exact test,
p=0.034). However the prevalence by multiplex-PCR was not significant for diarrhea (Fisher‟s exact test, p=0.532), breed (Fisher‟s exact test, p=0.440), water quality (Fisher‟s exact test, p=0.627).Twenty one (75%) out of the 28 E. coli O157 strains tested showed resistance to at least one of the antimicrobial agents. Resistance to sulphonamides (64%) was highest in all classes of antimicrobial agents tested, followed by resistance to tetracycline (36%), aminoglycosides (21%), β-lactams (21%) and to quinolones (18%). Among the multiplex – PCR confirmed isolates of faecal origin, resistance by class of antimicrobial agent was highest in sulphonamides (80%), followed by tetracycline and β-lactams (30%), aminoglycosides and quinolones (20%). Twenty-one resistance patterns were detected, including six multi-drug resistant (MDR) phenotypes. This data suggests that selection pressure imposed by the use/misuse of antimicrobial agents in veterinary practice and/or as prophylaxis in the animal production environment in Northwestern Nigeria may have generated a pool of MDR enterohaemorrhagic STEC O157:H7 in the cattle population in this zone. However, the resistance to nalidixic acid suggests a possible role for novel resistance mechanisms in E. coli from cattle in Northwestern Nigeria. To our knowledge, this is the first report of the detection in E. coli of the rfbEO157, fliCH7, stx2d and stx1 genes from bovine isolates in Northwestern Nigeria and the stx2d gene from cattle isolates of E. coli O157:H7.
Description
A DISSERTATION SUBMITTED TO THE POSTGRADUATE SCHOOL AHMADU BELLO UNIVERSITY
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF DOCTOR OF PHILOSOPHY
IN VETERINARY PUBLIC HEALTH AND PREVENTIVE MEDICINE
DEPARTMENT OF VETERINARY PUBLIC HEALTH AND PREVENTIVE MEDICINE,
AHMADU BELLO UNIVERSITY,
ZARIA, NIGERIA
Keywords
PREVALENCE,, ANTIMICROBIAL SUSCEPTIBILITY,, SHIGA TOXIN-PRODUCING ESCHERICHIA COLI,, CATTLE IN KADUNA AND SOKOTO STATES,, NIGERIA.