Quantification of Escherichia coli and Salmonella spp. isolates within the Australian silver gull (Choricocephalus Novaehollandiae) population on Rottnest Island capable of interspecies transmission resulting in human infection

Burton, Michaela Kelly (2021) Quantification of Escherichia coli and Salmonella spp. isolates within the Australian silver gull (Choricocephalus Novaehollandiae) population on Rottnest Island capable of interspecies transmission resulting in human infection. Masters by Research thesis, Murdoch University.

Abstract

Resistance to critically important antimicrobials (CIA) amongst Escherichia coli and Salmonella spp. poses a threat to public health which is complicated by possible interspecies transfer of the antimicrobial-resistant (AMR) bacteria to humans from wildlife reservoirs. A recent national survey of several silver gull populations across Australia identified the carriage of bacteria with resistance to CIA. However, limited studies have identified and quantified AMR transfer potential within a local population. This study emphasised the lack of quantification by previous studies to evaluate the public health risks by CIA resistant E. coli and Salmonella spp. within Chroicocephalus novaehollandiae (Australian silver gull) populations on Rottnest Island. This was achieved through the quantification and susceptibility testing of both Enterobacteriaceae families. From assessment of a sample of the islands silver gull population (n=33), ciprofloxacin resistance amongst E. coli isolates was detected in 54.5% of birds up to 102 CFU/g faeces and ESBL producing E. coli was found in 15.2% of the birds up to 101 CFU/g faeces. The total number of E. coli per sample ranged from 1×104 - 1×105 CFU/g faeces with 269 E. coli isolates demonstrating a large proportion of resistance to trimethoprim/sulfamethoxazole (91.67%), ampicillin (89.22%) and ciprofloxacin (81.86%). AMR was also observed among the isolates to tetracycline (49.61%), ceftriaxone (42.5%) and gentamicin (3.92%), with no resistance observed to meropenem. 36% of the birds tested positive for Salmonella spp. however, none displayed resistance to the test antimicrobials. This study reports that the bacteria within these populations pose a significant One Health risk due to the carriage of CIA-R E. coli, with the risk of interspecies resistance transfer. Additionally, although gulls may pose a zoonotic risk from Salmonella, the risk of AMR is negligible, confirming that first-line antimicrobials are available to treat human infections from seagulls. The findings of this study provide a basis for developing public health mitigation plan that Rottnest Island officials can enforce.

Item Type:	Thesis (Masters by Research)
Murdoch Affiliation(s):	Medical, Molecular and Forensic Sciences
Notes:	Accelerated Research Masters with Training
Supervisor(s):	Abraham, Sam, Abraham, Rebecca and Sahibzada, Shafi
URI:	http://researchrepository.murdoch.edu.au/id/eprint/64997

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