Plastic is linked to every aspect of our daily lives and has become indispensable to humans. However, due to mismanagement, large amounts of plastic waste end up in our oceans, where they get rapidly colonized by marine microbes. This new human-made marine microbial ecosystem is known as the plastisphere. Research efforts to identify the plastic microbial community have been focused mostly in the Northern Hemisphere, and the Southern Hemisphere plastisphere is often overlooked. Here, in the first plastisphere study conducted in Southern Australia, we characterise the marine bacterial diversity of polypropylene, a highly littered plastic polymer, using high-throughput 16S rRNA gene sequencing. The sampling sites ranged along the South Australian metropolitan coastline, covering urban jetties, metropolitan beaches, an estuarine river, with mangrove systems and a wastewater treatment plant. Results identify clear spatial variation of the plastisphere throughout the coastline and indicate the presence of potential marine pathogens (e.g. Vibrio genus) and bacterial families associated with antibiotic resistance (e.g., Sphingomonadacea). Further, bacterial genera that have been previously suggested as plastic degraders (e.g. Alcanivorax) were found, suggesting the possible breakdown of plastic in Australian waters. These results inform pollution management decision makers, on understudied impacts of marine plastic pollution in Australia.