Abstract:
Indiscriminate use of antibiotics in poultry production is among the factors responsible for antibiotic
resistance by microorganisms. Large amounts of poultry droppings are generated annually which
are used in fish feeding and as manure in agricultural farms. However, there is a dearth of
information on the antibiotic resistance profile of Enterobacter species, a member of pathogens on
the priority list of the World Health Organisation for developing new antibiotics: Enterococcus
faecium- Staphylococcus aureus- Klebsiella pneumoniae- Acinetobacter baumannii- Pseudomonas
aeruginosa- Enterobacter species, from poultry origin. Therefore, the aim of this study was to
determine the antibiotic resistance pattern of Enterobacter species isolated from poultry droppings
of selected farms in southwest Nigeria.
Poultry dropping samples from layer chickens (24), broiler chickens (16), cockerels (8) and Noilers
(4) were aseptically collected from 27 farms across the six states of southwest, Nigeria. Total
Heterotrophic Bacterial Count (THBC) was done using pour plate method, while the isolation of
Enterobacter species was carried out using standard method. The isolates were identified using the
conventional method and Matrix-Assisted Laser Desorption Ionization-Time of Flight-Mass
Spectrometry (MALDI-TOF-MS). Antibiotic susceptibility of the isolates on 20 antibiotics was
determined using Kirby-Bauer’s disc diffusion method. Extended Spectrum Beta-Lactamase
(ESBL) production of the isolates was determined using phenotypic methods. The ESBL and
Antibiotic Resistance (AR) genes were detected with specific primers using polymerase chain
reaction. Selected multiple antibiotic resistant isolates from chicken droppings were genome
sequenced using Illumnia technology (Mi-Seq). Pathosystems Resource Integration and Centre for
Genomic Epidemiology Database were used for genomic analysis. Data were analysed using
descriptive statistics.
The THBC ranged 8.8×106 ±0.3 (Noilers) to 9.6×106±2.1 CFU/g (layer chickens), while the 72
Enterobacter spp. isolated comprised E. cloacae (52), E. asburiae (12), E. kobei (7) and E. ludwigii
(1). The resistance patterns of the Enterobacter spp. showed that all the isolates were resistant to
cefpodoxime, cefixime and amoxicillin across the states, while the least resistance was to
ciprofloxacin (8.3%). Forty-two of the Enterobacter spp. were ESBL producers out of which 71.4%
haboured at least one of the ESBL genes (blaCTX-M, blaTEM and blaSHV). The ampC, qnrB, dfrA1 and
ermB, were detected in 52.8% of the Enterobacter species, which are of public health importance.
Enterobacter cloacae (ILB8) genome revealed a close relationship with the pathogenic E.
hormaechei and E. mori from humans and plants, respectively and contained virulence genes of
clinical importance. Forty AR genes were detected in the E. cloacae (ILB8). A class C betalactamase gene (blaACT-16_AB737978) had been identified in another E cloacae strain from a
septicaemic neonate, while fosfomycin gene (fosA) had also been identified in E. mori from a
diseased Morus alba plant. There is the possibility of the spread of AR genes from bacteria present
in poultry droppings to humans and plants through contact with the environment.
Enterobacter species from poultry droppings in the southwest Nigeria were multiple antibiotic
resistant. Extended Spectrum Beta-Lactamase-producing Enterobacter species had antibiotic
resistance genes.
