Date of Award
Master of Public Health
School of Medical and Health Sciences
Professor Jacques Oosthuizen
Dr Megan Lloyd
Field of Research Code
11, 1117, 111705
Background Information The global misuse and overuse of antibiotics in human medicine and the animal production industry is contributing to the development of antibiotic resistance in bacteria. This is a serious threat to modern medicine and public health. Antibiotic resistant organisms can cause severe infections in humans which are difficult to treat, and in some cases impossible to resolve which can lead to premature death. Several studies have been conducted across the globe to assess the use of antibiotics in the seafood industry and the associated health risks, however, limited studies have recently explored this risk in an Australian setting.
Aims This thesis aimed to investigate the presence of antibiotic residues in seafood sold in Western Australia. Furthermore, the occurrence of antibiotic resistance in Gram negative bacteria isolated from fish sold in Perth, Western Australia was assessed. The impact of country of origin on the presence of antibiotic residues and antibiotic resistant bacteria in seafood samples has also been considered.
Methodology Historical data was accessed from the Local Health Authorities Analytical Committee regarding the presence of eight antibiotic types in 253 seafood samples purchased throughout Western Australia between May and June 2017. Forty-four fish samples, a mix of local and imported from Asian countries, were sourced from retail shops located in the metropolitan area of Perth between September and November 2017. Gram negative bacteria were isolated by homogenisation of the fish with a Luria Bertani Broth and incubation on media selective for Gram negative bacteria. A series of preliminary microbial identification tests were conducted on selected bacterial isolates. Matrix Assisted Laser Desorption Ionization-Time of Flight confirmed the identification of the bacteria to species level. The identified bacteria (n = 35) were analysed for antibiotic susceptibility to eight antibiotic types using the standard disc diffusion method.
Results The majority of seafood samples were free from antibiotic residue contamination and compliant with Australian legislation. A single non-compliant sample contained antibiotic residues below the level required to pose an immediate health risk to the consumer. This result suggests the Australian consumer has limited risk of consuming antibiotic residues in seafood.
Thirty-five Gram negative bacterial isolates from ten genera were identified. The majority of the antibiotic resistance observed in the bacteria was either explained by intrinsic resistance or was similar to previous reports. Potential acquired antibiotic resistance was observed in four Acinetobacter species and a Rhizobium isolate which were isolated from commonly farmed fish from Australia (n = 1), China (n = 1) and Vietnam (n = 3). It is possible the fish may have been exposed to antibiotics during the production cycle. However, this result must be read with caution since there are limited standardised breakpoint guidelines for these particular species and, therefore the results were inferred using guidelines for other, similar, bacterial species.
From these results, it appears that there is limited risk to consumer health from exposure to antibiotic resistant bacteria via consumption of seafood, however, only a limited number of samples were assessed, and Gram positive bacteria were not evaluated in this study. These results are reassuring but suggest that vigilance is required to ensure that the risk to consumers is minimised. Where antibiotics are used inappropriately in environmental settings, the risk of environmental bacteria developing further antibiotic resistance will remain. Routine surveillance of antibiotic resistance in pathogenic bacteria in domestic and imported food of animal origin is recommended to monitor this potential risk to human public health.
Robinson, H. K. (2018). Antibiotic resistance in Gram negative bacteria isolated from fish sold in Western Australia. Retrieved from https://ro.ecu.edu.au/theses/2161
Available for download on Tuesday, July 07, 2020