Epidemiological characterization of bacterial pathogens and antimicrobial resistance profiles in porcine respiratory disease complex in Jiangxi Province, China
This study characterizes the epidemiology and antimicrobial resistance of bacterial pathogens in porcine respiratory disease complex across Jiangxi Province, China, identifying *Escherichia coli* and *Streptococcus suis* as dominant agents with distinct age-related infection patterns and severe multidrug resistance, particularly in *E. coli*, to inform evidence-based control strategies.
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Pigs, like all farm animals, are susceptible to a complex web of illnesses that can stall their growth and threaten the food supply. Among the most persistent challenges is a condition known as the porcine respiratory disease complex. This is not a single sickness caused by one germ, but rather a tangled mix of viral and bacterial infections that attack the lungs. While viruses often start the trouble by damaging the lung tissue, bacteria frequently move in to make the situation much worse, leading to severe pneumonia. For farmers, this means sick animals that eat less, grow slower, and sometimes die, resulting in significant financial loss. For the broader community, the way these bacteria respond to medicine matters deeply. When bacteria become resistant to the drugs used to treat them, the infections become harder to cure in the animals, and there is a risk that these tough germs could pass to people, making human infections difficult to treat as well.
In the Jiangxi Province of China, a major center for pig farming, scientists recently set out to map exactly which bacteria are causing these lung infections and how they are reacting to antibiotics. For years, researchers had a general idea of the culprits, but they lacked a detailed, up-to-date picture of what was happening specifically in the lungs of sick pigs in this region. To fill this gap, a team from the Jiangxi Academy of Agricultural Sciences and the Hubei Academy of Agricultural Sciences collected lung tissue from 372 pigs that were either sick or had died from pneumonia across eleven different cities. The collection period spanned from January 2022 to February 2026, covering a wide range of pig ages, from tiny newborns to fully grown adults. The researchers carefully processed these samples in a laboratory, growing the bacteria present in the lungs to identify them and then testing them against a variety of common medicines to see which ones still worked.
The investigation revealed a bacterial landscape that was somewhat different from what has been seen in other parts of the world. While many international studies often point to other bacteria as the primary cause of pig pneumonia, this study found that two specific types of bacteria were the dominant troublemakers in Jiangxi. The most common was Escherichia coli, a germ often associated with the gut but found here in the lungs, accounting for nearly 29 percent of all the bacterial strains isolated. The second most frequent was Streptococcus suis, making up about 25 percent of the findings. Together, these two species caused more than half of the bacterial infections identified. The researchers also noted that the age of the pig mattered greatly. A germ called Glaesserella parasuis tended to infect the youngest piglets, while another bacterium, Pasteurella multocida, and a third type, Enterococcus faecalis, were more likely to be found in older pigs. This suggests that the risk of infection changes as the animal grows, requiring different prevention strategies at different stages of life.
Perhaps the most critical finding of the study concerned how these bacteria respond to antibiotics, the medicines used to kill them. The team tested the bacteria against twenty different drugs, including common treatments and some powerful, last-resort medicines. The results showed a worrying pattern of resistance, particularly with the Escherichia coli. This bacterium proved to be highly resistant to many standard drugs, including amoxicillin, tetracyclines, macrolides, and sulfonamides. Even more concerning, a portion of these E. coli strains were resistant to carbapenems, a class of antibiotics that doctors reserve for their most serious human infections. This suggests that the pigs in this region are carrying bacteria that could potentially pass these difficult-to-treat traits to humans. In contrast, the Streptococcus suis bacteria were still vulnerable to beta-lactam antibiotics, a group that includes penicillin and amoxicillin, but they had become almost completely immune to macrolides and tetracyclines. The third major bacterium, Pasteurella multocida, was the most cooperative, remaining sensitive to most of the drugs tested.
The study also highlighted the severity of multidrug resistance, a situation where a single bacterium can shrug off three or more different types of antibiotics. The E. coli strains were the worst offenders in this regard, with nearly 43 percent of them resistant to nine different classes of drugs. Some of these super-resistant strains could even withstand ten or eleven different types of antibiotics. The Streptococcus suis showed a moderate level of resistance, while Pasteurella multocida remained relatively easy to treat. These findings paint a clear picture of a region where the bacteria causing pig pneumonia have evolved to survive many common treatments. The researchers conclude that relying on old methods of disease control is no longer enough. They emphasize the need for age-specific prevention measures, such as protecting young piglets from the germs that target them, and urge for a more careful, scientific approach to using antibiotics. By understanding exactly which germs are present and how they resist medicine, farmers and veterinarians can make better decisions to protect the health of the pigs and reduce the risk to public health.
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