Highly antibiotic-resistant strain of MRSA that arose in pigs can jump to humans

jg533 — Tue, 28 Jun 2022 07:00:00 +0000

̽��ֱ��strain, called CC398, has become the dominant type of MRSA in European livestock in the past fifty years. It is also a growing cause of human MRSA infections.

̽��ֱ��study found that CC398 has maintained its antibiotic resistance over decades in pigs and other livestock. And it is capable of rapidly adapting to human hosts while maintaining this antibiotic resistance.

̽��ֱ��results highlight the potential threat that this strain of MRSA poses to public health. It has been associated with increasing numbers of human infections, in people who have and have not had direct contact with livestock.

“Historically high levels of antibiotic use may have led to the evolution of this highly antibiotic resistant strain of MRSA on pig farms,” said Dr Gemma Murray, a lead author of the study, previously in the ̽��ֱ�� of Cambridge’s Department of Veterinary Medicine and now at the Wellcome Sanger Institute.

She added: “We found that the antibiotic resistance in this livestock-associated MRSA is extremely stable – it has persisted over several decades, and also as the bacteria has spread across different livestock species.”

Antibiotic use in European livestock is much lower than it has been in the past. But the researchers say that ongoing reductions in antibiotic use on pig farms - due to recent policy changes - are likely to have a limited impact on the presence of this strain of MRSA in pigs because it is so stable.

While livestock-associated CC398 is found across a broad range of livestock species, it is most commonly associated with pigs. Its rise has been particularly evident in Danish pig farms where the proportion of MRSA-positive herds has increased from less than 5% in 2008 to 90% in 2018. MRSA doesn’t cause disease in pigs.

“Understanding the emergence and success of CC398 in European livestock - and its capacity to infect humans - is vitally important in managing the risk it poses to public health,” said Dr Lucy Weinert in the ̽��ֱ�� of Cambridge’s Department of Veterinary Medicine, senior author of the paper.

̽��ֱ��success of CC398 in livestock and its ability to infect humans is linked to three mobile genetic elements in the MRSA genome. These are chunks of genetic material that give the MRSA certain characteristics, including its resistance to antibiotics and its ability to evade the human immune system.

̽��ֱ��researchers reconstructed the evolutionary history of two particular mobile genetic elements called Tn916 and SCCmec that confer antibiotic resistance in MRSA, and found they have persisted in a stable way in CC398 in pigs over decades. They also persist when CC398 jumps to humans – carrying with them high levels of resistance to antibiotics commonly used in farming.

In contrast, a third mobile genetic element called φSa3 – which enables the CC398 strain of MRSA to evade the human immune system – was found to have frequently disappeared and reappeared over time, in both human-associated and livestock-associated CC398. This suggests that CC398 can rapidly adapt to human hosts.

“Cases of livestock-associated MRSA in humans are still only a small fraction of all MRSA cases in human populations, but the fact that they’re increasing is a worrying sign,” said Weinert.

Intensification of farming, combined with high levels of antibiotic use in livestock, has led to particular concerns about livestock as reservoirs of antibiotic-resistant human infections.

Zinc oxide has been used for many years on pig farms to prevent diarrhoea in piglets. Due to concerns about its environmental impact and its potential promotion of antibiotic resistance in livestock, the European Union will ban its use from this month. But the authors say this ban may not help reduce the prevalence of CC398 because the genes conferring antibiotic resistance are not always linked to the genes that confer resistance to zinc treatment.

MRSA was first identified in human patients in 1960. Due to its resistance to antibiotics it is much harder to treat than other bacterial infections. ̽��ֱ��World Health Organisation now considers MRSA one of the world’s greatest threats to human health.

̽��ֱ��findings are published today in the journal eLife.

̽��ֱ��research was funded by Wellcome, the Medical Research Council and the Raymond and Beverly Sackler Fund.

Reference

Matuszewska, M, Murray, GGR et al: ‘Stable antibiotic resistance and rapid human adaptation in livestock-associated MRSA.’ ELife, June 2022. DOI: 10.7554/eLife.74819

A new study has found that a highly antibiotic-resistant strain of the superbug MRSA – methicillin resistant Staphylococcus aureus – has emerged in livestock in the last 50 years, probably due to widespread antibiotic use in pig farming.

Cases of livestock-associated MRSA in humans are still only a small fraction of all MRSA cases in human populations, but the fact that they’re increasing is a worrying sign.

Lucy Weinert

Mark Holmes

Pig farm

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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Pig-borne disease jumped into humans when rearing practices changed

cjb250 — Tue, 31 Mar 2015 09:00:00 +0000

Almost every pig carries harmless strains of the S. suis bacterium – such strains are known as ‘commensal’ strains. However, a more virulent group of strains of the bacteria also exist, which cause disease in pigs worldwide and are a major driver of antibiotic use for prevention. Increasingly, this group of strains is also implicated in serious human diseases such as meningitis and septicaemia.

In order to understand the genetic basis of disease in S. suis, an international study, led by the Bacterial Respiratory Diseases of Pigs-1 Technology (BRaDP1T) consortium, examined the genomes of 375 clinical samples from pigs and humans from the UK and Vietnam and combined these with data already published on 15 S. suis genome sequences and draft genomes from around the world. They found that the commensal strains and disease-causing strains differed genetically; in particular, the disease-causing strains have between 50 and 100 fewer genes than the commensal strains.

Dr Lucy Weinert from the Department of Veterinary Medicine at the ̽��ֱ�� of Cambridge, first author of the study, says: “It seems that the loss of genes is associated with causing disease. This is something we see quite often in bacteria, but for reasons that are unclear. One possibility is that the missing genes are those that hinder the function of newly-acquired virulence factors in the genomes.”

By examining the S. suis’s ‘tree of life’ – which looks at how the bacteria have evolved over time – the researchers were able to show that the emergence of a group of strains causing meningitis in pigs and the human form of the disease dates back to the 1920s, when pig production was intensified with the introduction of wide-scale indoor rearing of meat-producing pigs in larger groups, supported by government schemes that favoured larger producers with regular throughput. However, despite having jumped the species barrier from pig to human, the bacteria do not appear to have adapted to infect humans.

“A group of more virulent strains seem to have emerged at around the time the pig industry changed, and it is these strains that mostly cause disease in pigs and humans,” says Professor Duncan Maskell, Head of the School of the Biological Sciences at Cambridge.

“Human S. suis disease in the West is extremely rare, but is seen more frequently in south east Asia. It is most likely spread to humans through poor food hygiene practices or other environmental factors. This emphasises the importance of monitoring such practices and putting policies in place to reduce the risk of the spread of infections between species.”

̽��ֱ��study was primarily funded by the Biotechnology and Biological Sciences Research Council.

Reference
Weinert, LA et al. Genomic signatures of human and animal disease in the zoonotic pathogen Streptococcus suis. Nature Communications; 31 March 2015

̽��ֱ��most virulent strains of Streptococcus suis, the leading cause of bacterial meningitis in adult humans in parts of southeast Asia and in pigs around the world, are likely to have evolved and become widespread in pigs at the same time as changes in rearing practices, according to research from an international consortium published today in the journal Nature Communications.

A group of more virulent strains seem to have emerged at around the time the pig industry changed, and it is these strains that mostly cause disease in pigs and humans

Duncan Maskell

Balint Földesi

Pig Head

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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̽��ֱ�� of Cambridge - Lucy Weinert

Highly antibiotic-resistant strain of MRSA that arose in pigs can jump to humans

Pig-borne disease jumped into humans when rearing practices changed