Antibiotic resistance is a growing problem worldwide, with cases of life-threatening diseases such as tuberculosis becoming resistant to even the most powerful drugs. Polymerase chain reaction (PCR) is being used as a tool to find out more about the transmission of antibiotic resistant strains of bacteria, including through contaminated meat.
Researchers based at North Dakota State University looked at methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S aureus (MRSA) in food-producing animals and retail meat in Fargo, North Dakota. In most people, S aureus infection either doesn’t cause any symptoms, or is behind mild illnesses such as skin infections. Around a third of the population carries S aureus on skin or in the throat and nose with no ill effects.However, in people who are already ill, or who have a deficient immune system, infection with S aureus can be very serious.
Starting by isolating the bacteria from the nasal tracts of animals, and from samples of raw meat and deli meat, the team then carried out multiplex PCR in order to identify the 16S rRNA genes (used in bacterial identification), the mecA gene (implicated in methicillin resistance), and the gene for Panton-Valentine leukocidin (a cytotoxin that destroys tissue and white blood cells).
After adding in molecular typing and antimicrobial susceptibility testing, 34.7% of the animals were found to be positive for S aureus, including 50% of pigs and 40.6% of sheep. Almost 48% of the raw meat samples were positive for S aureus (67.6% of chicken and 19.3% of pork), and the bacteria was also found in 13% of the deli meat.
Of the pork samples, a worrying 7% (five samples) were carrying MRSA, and four of these were multidrug resistant. Multidrug resistant isolates were also found ion pigs and sheep, and the strains in pigs and pork were similar enough to suggest to the authors of the paper in Foodborne Pathogens and Disease that it was due to contamination of meat during slaughtering. This could be a source of transmission of MRSA and multidrug-resistant S aureus to humans, with uncooked meat a higher risk.
While MRSA isn’t necessarily a threat to healthy people, and in fact, 1-3% of the general population are asymptomatic MRSA carriers, it’s dangerous if it is passed on to people with compromised immune systems. As more infections become resistant to antibiotics, the role of PCR in tracking the spread of resistance and determining its genetic mechanism will become more important.
Suzanne Elvidge is a freelance science, biopharma, business and health writer with more than 20 years of experience. She has written for a range of online and print publications including FierceBiomarkers, FierceDrugDelivery, European Life Science, the Journal of Life Sciences (now the Burrill Report), In Vivo, Life Science Leader, Nature Biotechnology, New Scientist, PR Week and Start-Up. She specialises in writing on pharmaceuticals, biotechnology, healthcare, science, lifestyle and green living, but can write on any topic given enough tea and chocolate biscuits. She lives just beyond the neck end of nowhere in the Peak District with her second-hand bookseller husband and two second-hand cats.