Elimination of experimentally induced bovine intramammary infection assessed by multiplex real-time PCR and bacterial culture

Current and Emerging Diagnostic Approaches to Bacterial Diseases of Ruminants

The diagnostic approaches and methods to detect bacterial pathogens in ruminants are discussed, with a focus on cattle. Conventional diagnostic methods using culture, isolation, and characterization are being replaced or supplemented with new methods. These include molecular diagnostics such as real-time polymerase chain reaction and whole-genome sequencing. In addition, methods such as matrix-assisted laser desorption ionization-time-of-flight mass spectrometry enable rapid identification and enhanced pathogen characterization. These emerging diagnostic tools can greatly enhance the ability to detect and characterize pathogens, but performance and interpretation vary greatly across sample and pathogen types, disease syndromes, assay performance, and other factors.

Rapid Staphylococcus aureus Detection From Clinical Mastitis Milk by Colloidal Gold Nanoparticle-Based Immunochromatographic Strips

Rapid diagnostic technologies for bovine mastitis caused by Staphylococcus aureus (S. aureus) are urgently needed. In the current study, we generated an anti-ribosomal protein-L7/L12 antibody to detect S. aureus and an anti-ribosomal protein-L7/L12 antibody-coated immune-chromatographic strip (ICS) test. Moreover, we determined the ability of the ICS test to detect S. aureus from milk samples collected from cows with clinical mastitis. The developed ICS reacted to S. aureus in a bacteria load-dependent manner with a detection limit of ~10⁴ CFU/mL. In the evaluation of possible cross-reactivity of the ICS test, six strains of coagulase-negative Staphylococci showed slightly positive reactions, although at a lower level; however, other bacteria were completely negative. Next, we investigated the sensitivity and specificity of the ICS test compared with the bacteriological culture method using milk samples from clinical bovine mastitis. The results of the experiments demonstrated that the ICS test had high sensitivity [100%, 95% confidence interval (CI): 91.3–100%] and specificity (91.9%, CI: 90.5–91.9%) compared with culture tests. In addition, the kappa statistic demonstrated that ICS tests showed substantial agreement (k = 0.77, CI: 0.66–0.87) with culture tests. Positive correlations were observed for the statistical analysis between S. aureus (nuc gene) copy numbers and ICS test scores in mastitic milk infected by S. aureus. Therefore, we assume that this new detection method using ICS may be useful as a highly sensitive S. aureus-screening method for the diagnosis of bovine mastitis. Our findings support the ongoing effort to develop an ICS method for bovine S. aureus-induced mastitis, which can contribute to the rapid diagnosis of this disease.

Fluorescence immunoassay through histone-ds-poly(AT)-templated copper nanoparticles as signal transductors for the sensitive detection of Salmonella choleraesuis in milk

The rapid and sensitive detection of foodborne pathogens is one of the most important issues in food safety control. In this work, we developed a novel fluorescence immunoassay method for the sensitive detection of Salmonella choleraesuis. The method uses the fluorescent signals of histone-ds-poly(AT)-templated copper nanoparticles (His-pAT CuNP) as signal transducers and glucose oxidase as an alternative for horseradish peroxidase for the generation of hydrogen peroxide (H₂O₂) through the catalysis of glucose. The H₂O₂ is then further converted into hydroxyl radical (·OH) by Fenton reagents. Owing to the ultrahigh sensitivity of His-pAT CuNP synthesis toward ·OH, the proposed fluorescence immunoassay method exhibited excellent sensitivity for S. choleraesuis, with a limit of detection of 8.04 × 10¹ cfu/mL, which is 3 orders of magnitude lower than that of the tetramethylbenzidine-based traditional immunoassay. The reliability of the proposed method was evaluated by using spiked milk samples with S. choleraesuis concentration ranging from 8.8 × 10¹ to 8.8 × 10⁴ cfu/mL. The average recoveries for the intra- and inter-assay ranged from 73.52 to 96.59% and from 66.99 to 98.24% with a coefficient of variation from 6.85 to 31.26% and 5.46 to 17.99%, respectively. These results indicated that the proposed fluorescence immunoassay possesses a great potential for ultra-sensitive detection of foodborne pathogens in food safety control.

Expert evaluation of different infection types in dairy cow quarters naturally infected with Staphylococcus aureus or Streptococcus agalactiae

The purpose of this study was to improve the diagnostic recommendations for Staphylococcus aureus and Streptococcus agalactiae control using bacterial culture (BC), polymerase chain reaction (PCR) and somatic cell count (SCC) as diagnostic methods. The study was carried out in three steps: firstly, diagnostic test patterns for naturally infected quarters with Staph. aureus (24 quarters) and Strep. agalactiae (16 quarters) were created by sampling the quarters each day for 21 days and analysing the daily quarter milk samples using BC, PCR and SCC. Secondly, 30 mastitis experts were asked to group and describe the diagnostic test patterns and to establish a diagnosis for each group. The experts' statements regarding the groups they established were subsequently examined using qualitative content analysis to assign "infection types" to the statements. Lastly, the test performance was estimated for BC, PCR and SCC using generalised logistic regression models with the interpreted statements as a reference for infection. The experts mainly identified the Staph. aureus quarter-patterns as persistent infections, while some had more dynamic patterns. Strep. agalactiae quarter-patterns mainly involved persistent infection, yet some appeared hard to diagnose and were assigned to almost all different infection types, while experts did not agree on the interpretation. Estimates of Se for detection of Staph. aureus infection were 95.9% [93.7; 97.3] for BC, 99.5% [98.3; 99.8] for PCR, and 96.1% [94.0; 97.5] for SCC. The corresponding Sp estimates were 74.5% [65.7; 81.7], 66% [57.2; 73.8] and 43.7% [36.2; 51.5] for BC, PCR and SCC, respectively. The Se estimates of BC and PCR for Strep. agalactiae infection were 100% [83.5; 100] and 99.9% [99.6; 100], respectively, whereas the Se of SCC detecting Strep. agalactiae infection was only 34.3% [26.4; 43.3]. This indicated that Strep. agalactiae-positive BC and PCR test results were more important than SCC results to the experts when diagnosing a quarter as infected. The Sp estimates of BC, PCR and SCC for Strep. agalactiae infection were 99% [72.8; 100], 97.7% [62.1; 99.9], and 65.7% [56.7; 73.7], respectively. We conclude that PCR and BC are highly sensitive in the detection of persistent and new infections as defined by the experts, although the Se was not always 100%. An accepted lower Sp suggests that experts place less emphasis on false-positive results. We recommend that efforts are made to develop consistent terminology to characterise intramammary infections over time so that the course of infection can be taken into account at diagnosis.