What do virulence factors of M. hyo tell us?
by Sebastiaan Theuns
Sample type
Tissue, sick animal, 1 animal in sample
Case discussion
Mesomycoplasma (Mycoplasma) hyopneumoniae was detected at a high load in this respiratory tissue sample, confirming its role in the chronic respiratory disease picture on this farm.
Beyond the mere detection of the pathogen, the metagenomic analysis also read out the virulence factor genes present in this strain: p102 (surface antigen protein P102), p146 (surface antigen protein P146), p65 (surface antigen protein P65) and p97 (surface antigen protein P97). These adhesins are key to the attachment of M. hyopneumoniae to the ciliated epithelium of the airways, the very first step in the pathogenesis of enzootic pneumonia.
Being able to profile these virulence factors directly from the sample, without any culturing of this notoriously slow-growing organism, tells you not only which pathogen is present, but also how dangerous the strain you are dealing with can be.
Getting the most out of a TBS swab
A tracheobronchial swab is only as good as the moment and the animal you take it from. Field-tested tips from a swine vet who has sampled 100+ herds for respiratory work.
⏱️ Sample in the acute phase — Metagenomics on a TBS needs the acute window. Influenza in particular peaks for only a few days; two days too late and a co-infection takes over while the primary virus is already gone. Tell the herd vet to call the moment coughing starts, not after. If the group is already past acute, skip it and sample the next group, roughly four weeks out.
🩺 Pick the right animals — Within the group, swab the animals coughing right now, untreated and actively symptomatic. Walk the pen with two people and a marker spray, tag every cougher you hear so you have enough candidates when it's time to sample. Freshly recovered or not-yet-sick animals won't help you here.
💆🏻 Work calm, let the animal help you — Lay your materials out first and have the catheter in hand before anyone catches the animal. Only then restrain it, so you can swab fast. A squealing, gasping animal is your friend: the open airway lets the catheter slide into the trachea. Don't force it. If the animal goes quiet, or you're not certain you're in the trachea and not the oesophagus, discard that catheter, take a fresh one and move to another animal. Make sure the animal stands square so you reach the trachea cleanly.
🐖 Sows need three people — A sow is big with plenty of room, so the swab itself is easy, but it's not without risk. Work with three: one on the snare, one holding a proper mouth gag to keep the mouth open, one placing the catheter. Trust each other, and if anything goes wrong, drop everything at once. A bite or a head-butt isn't worth it.
🆒 Keep samples cool, move fast — Get the samples cold and to the lab as quickly as possible. Warmth lets unwanted bacteria overgrow and degrades enveloped viruses; both cost you the diagnosis. If you can, sample early in the week to avoid a weekend in transit. The acute window still comes first though: a couple of extra days on a properly cooled sample won't ruin it.
Bonus: TBS isn't the tool for everything. For pathogens like PCV2 (circo), pair the swab with a blood sample.
Exploring the functional microbiome of pigs within the porcine respiratory disease complex: viral-bacterial co-infections and virulence factor profiling
Microbiology Spectrum
Our colleague Adelaide Panattoni has just published in Microbiology Spectrum. Using 225 tracheobronchial swabs from 15 German finisher farms, she and her co-authors mapped the full lower-airway microbiome of pigs with acute respiratory signs, viruses and bacteria together, with nanopore metagenomics.
3 things to remember:
1. PRRSV and swine influenza A were the most common viruses, found in 30% and 23% of samples, the familiar viral drivers of the respiratory complex.
2. On the bacterial side, M. hyopneumoniae, G. parasuis and P. multocida dominated, the disease-associated profile you'd expect in affected lungs, and the virus present shaped which bacteria came up alongside it.
3. The team read virulence factor genes straight from these low-biomass swabs without any culturing, including for M. hyopneumoniae, which is notoriously hard to grow.
The takeaway: a single TBS can tell you not only which pathogens are present, but which of their virulence factors make them dangerous. Open access, links below.