The use of spiral plating and microscopic colony counting for the rapid quantitation of Mycobacterium paratuberculosis

Enumeration of Mycobacterium avium subsp. paratuberculosis by quantitative real-time PCR, culture on solid media and optical densitometry

Background

Different approaches are used for determining the number of Mycobacterium avium subsp. paratuberculosis (MAP) cells in a suspension. The majority of them are based upon culture (determination of CFU) or visual/instrumental direct counting of MAP cells. In this study, we have compared the culture method with a previously published F57 based quantitative real-time PCR (F57qPCR) method, to determine their relative abilities to count the number of three different MAP isolates in suspensions with the same optical densities (OD). McFarland turbidity standards were also compared with F57qPCR and culture, due to its frequent inclusion and use in MAP studies.

Findings

The numbers of MAP in two-fold serial dilutions of isolates with respective OD measurements were determined by F57qPCR and culture. It was found that culture provided lower MAP CFU counts by approximately two log₁₀, compared to F57qPCR. The McFarland standards (as defined for E. coli) showed an almost perfect fit with the enumeration of MAP performed by F57qPCR.

Conclusions

It is recommended to use culture and/or qPCR estimations of MAP numbers in experiments where all subsequent counts are performed using the same method. It is certainly not recommended the use of culture as the standard for qPCR experiments and vice versa.

Occurrence of Mycobacterium avium subsp. paratuberculosis in milk at dairy cattle farms: a systematic review and meta-analysis

Presence of Mycobacterium avium subsp. paratuberculosis (MAP) in milk for human consumption is a concern due to its possible relationship with Crohn's disease in humans. Pasteurization effectively reduces the MAP load by four to five logs, but the efficacy depends on the MAP concentration, which depends on the prevalence among contributing herds and individuals. Considerable variation of MAP in bulk tank milk (BTM) and individual cow's milk (IM) is reported, but factors associated with MAP occurrence in milk at farm level have not been described. This study systematically reviewed published studies aiming at estimating the occurrence of MAP in on-farm BTM and IM by meta-analysis. A total of 692 articles were identified through electronic databases and initially screened using title and abstract. The quality of the 61 potentially relevant articles was assessed using full text and 31 articles were eventually included in the meta-analysis. The apparent prevalence (AP) of MAP in BTM and IM on farm were summarized in relation to strata defined by the test used to identify MAP and the infection status of the herds/animals. There was considerable inconsistency in the reporting, resulting in missing information potentially explaining the dispersion in the estimated AP. The overall AP and 95% confidence intervals based on PCR and culture of MAP were summarized to 0.10 (0.04-0.22) in BTM and 0.20 (0.12-0.32) in IM. Quantifying the MAP load in test-positive milk samples was not possible because very few articles provided quantitative information on individual samples.

Modified Culture Protocol for Isolation ofMycobacterium aviumsubsp.paratuberculosisfrom Raw Milk

A modified culture method using C18-carboxypropylbetaine (CB-18) and microscopic screening was evaluated for time to and limit of detection of Mycobacterium avium subsp. paratuberculosis (MAP) in raw milk. Bulk-tank milk samples were spiked with six different concentrations (10(1) to 10(6) CFU/mL) of MAP. Samples were processed using two different protocols. The first protocol involved specimen processing with the zwitterionic detergent C18-carboxypropylbetaine (CB-18) and lytic enzymes followed by culture on modified Middlebrook 7H10 agar plates with microscopic screening. The second protocol used 0.75% hexadecylpyridinium chloride (HPC) for specimen processing, followed by culture on Herrold's egg yolk medium (HEYM). Both protocols were repeated eight independent times, and the detection limit and time to detection were compared. The presence of MAP in spiked milk samples was detected between 14 and 45 days (N [number of samples], 46; mean, 22.7; median, 19.5) using the CB-18 and microscopic screening method, and between 21 and 63 days (N, 47; mean, 31; median, 28) using HEYM (P < 0.001). Time to detection also varied with MAP concentration (P < 0.001). Higher concentrations of MAP were detected earlier than lower concentrations and this finding was independent of the method used (P = 0.479). The two methods had similar detection limits but the modified culture method reduced the time to detect MAP in raw milk for the majority of concentrations.

UTILIZAÇÃO DE UMA TÉCNICA RÁPIDA PARA O DIAGNÓSTICO DE MYCOBACTERIUM BOVIS EM AMOSTRAS DE LEITE EXPERIMENTALMENTE INOCULADAS

RESUMO O meio de Middlebrook 7H11 modificado foi comparado ao meio de Stonebrink, a fim de se avaliar a sensibilidade e o tempo de detecção de micobactérias em amostras de leite, experimentalmente inoculadas com Mycobacterium bovis (estirpe AN5), em uma diluição 10-2, e submetidas a duas diferentes técnicas de processamento: gordura (técnica 1) e sedimento (técnica 2), descontaminadas pelo método de Petroff modificado (adicionado de Tween 80), confrontadas com a técnica do leite total submetida ao método de Petroff tradicional. Os resultados destas técnicas (1 e 2) foram comparados entre si pelos testes não paramétricos de Wilcoxon e de MannWhitney e demonstraram que as técnicas 1 e 2 forneceram maior recuperação de micobactérias e proporção de cultivos positivos nos meios de Stonebrink e Middlebrook 7H11; o meio de Middlebrook 7H11 permitiu a visualização precoce das micobactérias, podendo ser utilizado como uma técnica de diagnóstico rápida da tuberculose bovina, em amostras de leite, para fins de vigilância epidemiológica.

Detection ofMycobacterium aviumsubsp.paratuberculosisin Bovine Manure Using Whatman FTA Card Technology and Lightcycler Real-Time PCR

A modified forensic DNA extraction and real-time fluorescent polymerase chain reaction assay has been evaluated for the detection of Mycobacterium avium subsp. paratuberculosis (MAP) in bovine fecal samples using primers and fluorescent resonance energy transfer (FRET) probes targeting the IS900 gene sequence of MAP. DNA was successfully extracted from manure samples by utilizing the Whatman FTA card technology, which allows for simple processing and storage of samples at room temperature. The FTA cards were washed and subjected to a Chelex-100 incubation to remove any remaining polymerase chain reaction (PCR) inhibitors and to elute the DNA from the FTA card. This isolated DNA was then subjected to direct real time fluorescent PCR analysis. Detection of MAP DNA from bovine fecal samples spiked with known concentrations of viable MAP cells was obtained. The detection limits of the assay was consistently found to be between 10(2) and 10(4) colony forming units [CFU]/g, with some samples containing as low as 10 CFU/g, yielding positive assay results. This cost-efficient assay allows reporting of results as early as 4 h after fecal collection, which can be particularly useful in highthroughput herd screening.

Disinfection of Dairy and Animal Farm Wastewater with Radiofrequency Power

Radiofrequency (RF) power was investigated as a new, physical (nonchemical), thermal process to disinfect wastewater from dairy and animal facilities. Samples (n = 38) from 8 dairy, 2 calf, and 3 swine facilities in California were collected over a 3-yr period and characterized for their dielectric properties, chemical composition, and suitability for thermal processing using RF power. To establish efficacy for disinfection, selected samples were inoculated with high levels (10(6) to 10(9) cfu/mL) of bacterial pathogens such as Salmonella sp., Escherichia coli O157:H7, and Mycobacterium avium ssp. paratuberculosis and processed with an RF prototype system. The capabilities of RF power as a method for thermal disinfection of wastewater were demonstrated when bacteria pathogens were completely and rapidly (<1 min) inactivated when temperatures of 60 to 65 degrees C were achieved. Furthermore, RF technology can be used for large-scale, batch or continuous and portable applications, allowing significant improvements in energy-use efficiencies compared with conventional thermal (surface heating) technologies. Therefore, RF power has potential as an alternative to disinfect dairy/animal farm wastewater before recycling.