Novel lineage of methicillin-resistant Staphylococcus aureus, Hong Kong

Area of Science:

• Veterinary Microbiology
• Antimicrobial Resistance
• Public Health

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) is a significant pathogen in both human and animal health.
• The prevalence and genetic diversity of MRSA in livestock, particularly pigs, are critical for understanding transmission dynamics.
• Sequence type (ST) 398 is a globally recognized MRSA lineage often associated with pigs.

Purpose of the Study:

• To investigate the spa types and sequence types of MRSA circulating in pigs in Hong Kong.
• To determine if the globally dominant pig-associated MRSA ST398 was present in the Hong Kong pig population.
• To identify any emerging or distinct MRSA lineages within this specific geographic context.

Main Methods:

• Analysis of nasal swabs collected from pig carcasses at Hong Kong markets in 2008.
• Typing of methicillin-resistant Staphylococcus aureus isolates using spa typing.
• Determination of sequence types (STs) for identified MRSA isolates.

Main Results:

• Out of 100 samples analyzed, 16% were positive for MRSA.
• The predominant MRSA identified belonged to spa type t899.
• Genetic analysis revealed that these isolates were predominantly Sequence Type 9 (ST9), not the expected ST398.

Conclusions:

• A distinct MRSA lineage, identified as ST9 (spa type t899), has emerged and is circulating in the pig population in Hong Kong.
• This finding highlights the presence of a unique, non-ST398 MRSA lineage in this region.
• Further surveillance is warranted to understand the epidemiology and public health implications of this emerging pig-associated MRSA strain.