Diagnosis of bacteria from the CMNR group in farm animals

The CMNR group comprises bacteria of the genera Corynebacterium, Mycobacterium, Nocardia, and Rhodococcus and share cell wall and DNA content characteristics. Many pathogenic CMNR bacteria cause diseases such as mastitis, lymphadenitis, and pneumonia in farmed animals, which cause economic losses for breeders and represent a threat to public health. Traditional diagnosis in CMNR involves isolating target bacteria on general or selective media and conducting metabolic analyses with the assistance of laboratory biochemical identification systems. Advanced mass spectrometry may also support diagnosing these bacteria in the clinic's daily routine despite some challenges, such as the need for isolated bacteria. In difficult identification among some CMNR members, molecular methods using polymerase chain reaction (PCR) emerge as reliable options for correct specification that is sometimes achieved directly from clinical samples such as tracheobronchial aspirates and feces. On the other hand, immunological diagnostics such as the skin test or Enzyme-Linked Immunosorbent Assay (ELISA) for Mycobacterium tuberculosis yield promising results in subclinical infections with no bacterial growth involved. In this review, we present the methods most commonly used to diagnose pathogenic CMNR bacteria and discuss their advantages and limitations, as well as challenges and perspectives on adopting new technologies in diagnostics. •Highly sensitive and accurate diagnosis of bacteria of genera Corynebacterium, Mycobacterium, Nocardia, and Rhodococcus (CMNR), which cause significant economic losses in animal husbandry, can be challenging.•Several molecular diagnostic methods have shown increased performance in detecting CMNR bacteria over traditional culturing and biochemical testing.•Serological assays can aid in the diagnosis of subclinical infections, but improvements in the methods are necessary for many CMNR bacteria.•The most widely used diagnostic methods and the perspectives for diagnosing CMNR bacteria are addressed in this review article.