Further observations on the problem of isolating Mycoplasma suipneumoniae from field cases of enzootic pneumonia in pigs

Development of a quantitative SYBR Green real-time PCR and microscopic slide culture for in vitro enumeration of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae's slow growth makes enumeration challenging using the traditional colony-forming unit (CFU) method. We introduced an innovative CFU-slide culture (CFU-SC) approach to address this issue. CFU-SC allows accurate counting of M. hyopneumoniae microcolonies, ranging from 7 to 50 µm, using high magnification. While comparing the accuracy of enumeration among CFU, CFU-SC, quantitative polymerase chain reaction (qPCR), and colour change unit (CCU), we found a robust positive correlation between qPCR and CFU-SC with colourCCU method for quantifying M. hyopneumoniae. Newly isolated strains exhibited the lowest Pearson correlation coefficient (r = 0.52) when comparing CFU and real-time PCR, while the highest coefficient (r = 0.86) was observed for the type strain J and new isolates using real-time PCR and CFU-SC. A consensus growth pattern was observed among all quantification methods, except CFU, between newly isolated strains and the type strain J. Notably, new isolates of M. hyopneumoniae showed no senescence phase after 228 h of cultivation, differing from the type strain J. The disparity in growth rate and pattern between new isolates and the type strain J is evident in the smaller agar microcolonies (7-10 µm) of the isolates, contrasting with the larger colonies (100-200 µm) of type strain J.

Improving Mycoplasma hyopneumoniae diagnostic capabilities by harnessing the infection dynamics

Mycoplasma hyopneumoniae remains one of the most problematic bacterial pathogens for pig production. Despite an abundance of observational and laboratory testing capabilities for this organism, diagnostic interpretation of test results can be challenging and ambiguous. This is partly explained by the chronic nature of M. hyopneumoniae infection and its tropism for lower respiratory tract epithelium, which affects diagnostic sensitivities associated with sampling location and stage of infection. A thorough knowledge of the available tools for routine M. hyopneumoniae diagnostic testing, together with a detailed understanding of infection dynamics, are essential for optimizing sampling strategies and providing confidence in the diagnostic process. This study reviewed known information on sampling and diagnostic tools for M. hyopneumoniae and summarized literature reports of the dynamics of key infection outcomes, including clinical signs, lung lesions, pathogen detection, and humoral immune responses. Such knowledge could facilitate better understanding of the performance of different diagnostic approaches at various stages of infection.

Attenuation of Mycoplasma hyopneumoniae Strain ES-2 and Comparative Genomic Analysis of ES-2 and Its Attenuated Form ES-2L

Mycoplasma hyopneumoniae causes swine respiratory disease worldwide. Due to the difficulty of isolating and cultivating M. hyopneumoniae, very few attenuated strains have been successfully isolated, which hampers the development of attenuated vaccines. In order to produce an attenuated M. hyopneumoniae strain, we used the highly virulent M. hyopneumoniae strain ES-2, which was serially passaged in vitro 200 times to produce the attenuated strain ES-2L, and its virulence was evidenced to be low in an animal experiment. In order to elucidate the mechanisms underlying virulence attenuation, we performed whole-genome sequencing of both strains and conducted comparative genomic analyses of strain ES-2 and its attenuated form ES-2L. Strain ES-2L showed three large fragment deletion regions including a total of 18 deleted genes, compared with strain ES-2. Analysis of single-nucleotide polymorphisms (SNPs) and indels indicated that 22 dels were located in 19 predicted coding sequences. In addition to these indels, 348 single-nucleotide variations (SNVs) were identified between strains ES-2L and ES-2. These SNVs mapped to 99 genes where they appeared to induce amino acid substitutions and translation stops. The deleted genes and SNVs may be associated with decreased virulence of strain ES-2L. Our work provides a foundation for further examining virulence factors of M. hyopneumoniae and for the development of attenuated vaccines.

Selective medium for culture of Mycoplasma hyopneumoniae

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Systematic improvements to the medium for growth of Mycoplasma hyopneumoniae.

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Development of selective medium for M. hyopneumoniae inhibitory to M. hyorhinis.

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Improved colony size of M. hyopneumoniae.

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Improved reproducibility of culture for use in genetic manipulations.

The fastidious porcine respiratory pathogen Mycoplasma hyopneumoniae has proven difficult to culture since it was first isolated in 1965. A reliable solid medium has been particularly challenging. Moreover, clinical and pathological samples often contain the fast-growing M. hyorhinis which contaminates and overgrows M. hyopneumoniae in primary culture. The aim of this study was to optimise the culture medium for recovery of M. hyopneumoniae and to devise a medium for selection of M. hyopneumoniae from clinical samples also containing M. hyorhinis. The solid medium devised by Niels Friis was improved by use of Purified agar and incorporation of DEAE-dextran. Addition of glucose or neutralization of acidity in liquid medium with NaOH did not improve the final yield of viable organisms or alter the timing of peak viability. Analysis of the relative susceptibility of M. hyopneumoniae and M. hyorhinis strains to four antimicrobials showed that M. hyopneumoniae is less susceptible than M. hyorhinis to kanamycin. This was consistent in all UK and Danish strains tested. A concentration of 2 μg/ml of kanamycin selectively inhibited the growth of all M. hyorhinis tested, while M. hyopneumoniae was able to grow. This forms the basis of an effective selective culture medium for M. hyopneumoniae.

The passive haemagglutination test for th detection of Mycoplasma suipneumoniae and the possible diagnosis of enzootic pneumonia of pigs

Fourteen cases of enzootic pneumonia, nearly all of which had presented diagnostic difficulties using the metabolic-inhibition test, were re-examined using specific pig antisera in the passive haemagglutination test (PHA). All proved positive for Mycoplasma suipneumoniae, indicating that the test, used in this manner, might be particularly valuable for routine diagnosis.The PHA test was also used to demonstrate antibody to M. suipneumoniae in pneumonic tissue and the associated bronchial lymph nodes.To allay our concern that cross-reactions might interfere with this and other serological tests-the complement-fixation test (CF) and precipitation in agar-gel-the specificity of our reagents and the antigenic relationships of Mycoplasma hyorhinis, Mycoplasma granularum, mycoplasma B3, Mycoplasma hyopneumoniae and three strains of M. suipneumoniae (including cloned and uncloned isolates of the J strain) were studied in various ways. Antibodies to medium constituents occurred in rabbit antiserum but did not present a problem with pig antisera. These antibodies were successfully absorbed from the rabbit antisera but it was not possible to remove medium constituents from the antigens used to produce antisera in rabbits by repeated washing.By all these tests, the main species of mycoplasmas studied seemed to be antigenically distinct. No major antigenic differences between the three strains of M. suipneumoniae were revealed by the PHA test and the CF test; a slight difference in the precipitation lines of one of these strains (MG) in agar-gel might have indicated an antigenic variation or been a measure of some other factor.