Rapid Detection and Typing of Actinobacillus pleuropneumoniae Serovars Directly From Clinical Samples: Combining FTA® Card Technology With Multiplex PCR

Detection of Enterotoxigenic Escherichia coli and Clostridia in the Aetiology of Neonatal Piglet Diarrhoea: Important Factors for Their Prevention

This study aimed to research the involvement of enterotoxigenic E. coli (ETEC) and C. difficile or C. perfringens type C in the aetiology of neonatal piglet diarrhoea in Greece and to identify preventive factors for them. A total of 78 pooled faecal samples were collected randomly from 234 suckling piglets (1-4 days of age) with diarrhoea from 26 pig farms (3 piglets × 3 litters × 26 farms = 234 piglets = 78 faecal pool samples). The collected samples were initially screened for the presence of E. coli and C. difficile or C. perfringens via cultivation on MacConkey and anaerobic blood agar, respectively. Subsequently, the samples were pooled on ELUTE cards. From samples tested, 69.23% of those in the farms were ETEC F4-positive, 30.77% were ETEC F5-positive, 61.54% ETEC were F6-positive, 42.31% were ETEC F4- and E. coli enterotoxin LT-positive, 19.23% were ETEC F5- and LT-positive, 42.31% were ETEC F6- and LT-positive, while LT was found in 57.69% of those in the farms. C. difficile was involved in many cases and identified as an emerging neonatal diarrhoea etiological agent. Specifically, Toxin A of C. difficile was found in 84.62% and Toxin B in 88.46% of those in the farms. Antibiotic administration to sows in combination with probiotics or acidifiers was revealed to reduce the detection of antigens of ETEC and the enterotoxin LT of E. coli.

A CRISPR/Cas12a-assisted rapid detection platform by biosensing the apxIVA of Actinobacillus pleuropneumoniae

Actinobacillus pleuropneumoniae is an important respiratory pig pathogen that causes substantial losses in the worldwide swine industry. Chronic or subclinical infection with no apparent clinical symptoms poses a challenge for preventing transmission between herds. Rapid diagnostics is important for the control of epidemic diseases. In this study, we formulated an A. pleuropneumoniae species-specific apxIVA-based CRISPR/Cas12a-assisted rapid detection platform (Card) that combines recombinase polymerase amplification (RPA) of target DNA and subsequent Cas12a ssDNase activation. Card has a detection limit of 10 CFUs of A. pleuropneumoniae, and there is no cross-reactivity with other common swine pathogens. The detection process can be completed in 1 h, and there was 100% agreement between the conventional apxIVA-based PCR and Card in detecting A. pleuropneumoniae in lung samples. Microplate fluorescence readout enables high-throughput use in diagnostic laboratories, and naked eye and lateral flow test readouts enable use at the point of care. We conclude that Card is a versatile, rapid, accurate molecular diagnostic platform suitable for use in both laboratory and low-resource settings.

Rapid Detection of Actinobacillus pleuropneumoniae From Clinical Samples Using Recombinase Polymerase Amplification

Actinobacillus pleuropneumoniae (APP) is the causative agent of porcine pleuropneumonia, resulting in high economic impact worldwide. There are currently 19 known serovars of APP, with different ones being predominant in specific geographic regions. Outbreaks of pleuropneumonia, characterized by sudden respiratory difficulties and high mortality, can occur when infected pigs are brought into naïve herds, or by those carrying different serovars. Good biosecurity measures include regular diagnostic testing for surveillance purposes. Current gold standard diagnostic techniques lack sensitivity (bacterial culture), require expensive thermocycling machinery (PCR) and are time consuming (culture and PCR). Here we describe the development of an isothermal point-of-care diagnostic test - utilizing recombinase polymerase amplification (RPA) for the detection of APP, targeting the species-specific apxIVA gene. Our APP-RPA diagnostic test achieved a sensitivity of 10 copies/μL using a strain of APP serovar 8, which is the most prevalent serovar in the UK. Additionally, our APP-RPA assay achieved a clinical sensitivity and specificity of 84.3 and 100%, respectively, across 61 extracted clinical samples obtained from farms located in England and Portugal. Using a small subset (n = 14) of the lung tissue samples, we achieved a clinical sensitivity and specificity of 76.9 and 100%, respectively) using lung imprints made on FTA cards tested directly in the APP-RPA reaction. Our results demonstrate that our APP-RPA assay enables a suitable rapid and sensitive screening tool for this important veterinary pathogen.

JMM Profile: Actinobacillus pleuropneumoniae: a major cause of lung disease in pigs but difficult to control and eradicate

The Gram-negative bacterium Actinobacillus pleuropneumoniae is the causative agent of pleuropneumonia in pigs, its only known natural host. Typical symptoms of peracute disease include fever, apathy and anorexia, and time from infection to death may only be 6 h. Severe lung lesions result from presence of one or two of the ApxI-III toxins. Control is through good husbandry practice, vaccines and antibiotic use. Culture and presence of the species-specific apxIV gene by PCR confirms diagnosis, and identification of serovar, of which 19 are known, informs on appropriate vaccine use and epidemiology.

Novel DNA Markers for Identification of Actinobacillus pleuropneumoniae

Actinobacillus pleuropneumoniae causes porcine pleuropneumonia, an important disease in the pig industry. Accurate and sensitive diagnostics such as DNA-based diagnostics are essential for preventing or responding to an outbreak. The specificity of DNA-based diagnostics depends on species-specific markers. Previously, an insertion element was found within an A. pleuropneumoniae-specific gene commonly used for A. pleuropneumoniae detection, prompting the need for additional species-specific markers. Herein, 12 marker candidates highly conserved (99 - 100% identity) among 34 A. pleuropneumoniae genomes (covering 13 serovars) were identified to be A. pleuropneumoniae-specific in silico, as these sequences are distinct from 30 genomes of 13 other Actinobacillus and problematic [Actinobacillus] species and more than 1700 genomes of other bacteria in the Pasteurellaceae family. Five marker candidates are within the apxIVA gene, a known A. pleuropneumoniae-specific gene, validating our in silico marker discovery method. Seven other A. pleuropneumoniae-specific marker candidates within the eamA, nusG, sppA, xerD, ybbN, ycfL, and ychJ genes were validated by polymerase chain reaction (PCR) to be specific to 129 isolates of A. pleuropneumoniae (covering all 19 serovars), but not to four closely related Actinobacillus species, four [Actinobacillus] species, or seven other bacterial species. This is the first study to identify A. pleuropneumoniae-specific markers through genome mining. Seven novel A. pleuropneumoniae-specific DNA markers were identified by a combination of in silico and molecular methods and can serve as additional or alternative targets for A. pleuropneumoniae diagnostics, potentially leading to better control of the disease. IMPORTANCE Species-specific markers are crucial for infectious disease diagnostics. Mutations within a marker sequence can lead to false-negative results, inappropriate treatment, and economic loss. The availability of several species-specific markers is therefore desirable. In this study, 12 DNA markers specific to A. pleuropneumoniae, a pig pathogen, were simultaneously identified. Five marker candidates are within a known A. pleuropneumoniae-specific gene. Seven novel markers can be used as additional targets in DNA-based diagnostics, which in turn can expedite disease diagnosis, assist farm management, and lead to better animal health and food security. The marker discovery strategy outlined herein requires less time, effort, and cost, and results in more markers compared with conventional methods. Identification of species-specific markers of other pathogens and corresponding infectious disease diagnostics are possible, conceivably improving health care and the economy.