Assessment of the Prevalence ofMycobacterium aviumsubsp.paratuberculosisin Commercially Pasteurized Milk

Short communication: Investigation into Mycobacterium avium ssp. paratuberculosis in pasteurized milk in Italy

This study investigated the presence of viable Mycobacterium avium ssp. paratuberculosis (MAP) in pasteurized milk produced by Italian industrial dairy plants to verify the prediction of a previously performed risk assessment. The study analyzed 160 one-liter bottles of pasteurized milk from 2 dairy plants located in 2 different regions. Traditional cultural protocols were applied to 500mL of pasteurized milk for each sample. The investigation focused also on the pasteurization parameters and data on the microbiological characteristics of raw milk (total bacterial count) and pasteurized milk (Enterobacteriaceae and Listeria monocytogenes). No sample was positive for MAP, the pasteurization parameters complied with European Union legislation, and the microbiological analysis of raw and pasteurized milk showed good microbiological quality. The results show that a 7-log (or >7) reduction could be a plausible value for commercial pasteurization. The combination of hygiene practices at farm level and commercial pasteurization yield very low or absent levels of MAP contamination in pasteurized milk, suggesting that pasteurized milk is not a significant source of human exposure to MAP in the dairies investigated.

Thermal Inactivation of Mycobacterium avium subsp. paratuberculosis in Artificially Contaminated Milk by Direct Steam Injection

The efficiency of direct steam injection (DSI) at 105 °C for 3 s to inactivate Mycobacterium avium subsp. paratuberculosis in milk at a pilot-plant scale was investigated. Milk samples were artificially contaminated with M. avium subsp. paratuberculosis and also with cow fecal material naturally infected with M. avium subsp. paratuberculosis. We also tested milk artificially contaminated with Mycobacterium smegmatis as a candidate surrogate to compare thermal inactivation between M. smegmatis and M. avium subsp. paratuberculosis. Following the DSI process, no viable M. avium subsp. paratuberculosis or M. smegmatis was recovered using culture methods for both strains. For pure M. avium subsp. paratuberculosis cultures, a minimum reduction of 5.6 log10 was achieved with DSI, and a minimum reduction of 5.7 log10 was found with M. smegmatis. The minimum log10 reduction for wild-type M. avium subsp. paratuberculosis naturally present in feces was 3.3. In addition, 44 dairy and nondairy powdered infant formula (PIF) ingredients used during the manufacturing process of PIF were tested for an alternate source for M. avium subsp. paratuberculosis and were found to be negative by quantitative PCR (qPCR). In conclusion, the results obtained from this study indicate that a >7-fold-log10 reduction of M. avium subsp. paratuberculosis in milk can be achieved with the applied DSI process.

IMPORTANCE

M. avium subsp. paratuberculosis is widespread in dairy herds in many countries. M. avium subsp. paratuberculosis is the causative agent of Johne's disease in cattle, and infected animals can directly or indirectly (i.e., fecal contamination) contaminate milk. Despite much research and debate, there is no conclusive evidence that M. avium subsp. paratuberculosis is a zoonotic bacterium, i.e., one that causes disease in humans. The presence of M. avium subsp. paratuberculosis or its DNA has been reported in dairy products, including pasteurized milk, cheese, and infant formula. In light of this, it is appropriate to evaluate existing mitigation measures to inactivate M. avium subsp. paratuberculosis in dairy products. The work conducted in this study describes the efficacy of direct steam injection, a thermal process commonly used in the dairy industry, to eliminate M. avium subsp. paratuberculosis and a surrogate bacterium in milk, thus ensuring the absence of M. avium subsp. paratuberculosis in dairy products subject to these process conditions.

Evaluation of methods for Mycobacterium avium ssp. paratuberculosis detection in milk samples from the cattle herd showing low seroprevalence of Johne's disease

Mycobacterium avium ssp. paratuberculosis (MAP) is the cause of chronic gastroenteritis in cattle called the Johne's disease (JD). The disease causes significant economic losses in cattle production. MAP is also supposed to be involved in the Crohn's disease and inflammatory bowel disease (IBD) in people. The detection of the cattle infection based on investigations of milk samples and evaluation of the capacity of the methods used to detect the disease was the objective of the present study. Following methods were applied for milk samples testing: detection of MAP in bacterial culture, detection of the specific IS-900 fragment of MAP in the genetic material isolated directly and detection of MAP antibodies. The results obtained were compared with the "golden standard" results, i.e. the isolation of MAP from the faeces. PQStat-the program for diagnostic reliability estimation, was used for evaluation of the sensitivity, specificity and predictive value. The method based on detection of the specific IS-900 fragment of MAP in the genetic material isolated directly from milk samples was found to possess the highest sensitivity. Detection of anti-MAP antibodies on the other hand showed the lowest sensitivity. The method of detecting anti-MAP antibodies in milk was the most specific while detection of the IS-900 fragment in the genetic material was the least specific method. These results obtained may serve as a guide to choose the most appropriate method for diagnosis of MAP infections by milk sample testing.

Assessing the inactivation of Mycobacterium avium subsp. paratuberculosis during composting of livestock carcasses

Mycobacterium avium subsp. paratuberculosis causes Johne's disease (JD) in ruminants, with substantial economic impacts on the cattle industry. Johne's disease is known for its long latency period, and difficulties in diagnosis are due to insensitivities of current detection methods. Eradication is challenging as M. avium subsp. paratuberculosis can survive for extended periods within the environment, resulting in new infections in naïve animals (W. Xu et al., J. Environ. Qual. 38:437-450, 2009). This study explored the use of a biosecure, static composting structure to inactivate M. avium subsp. paratuberculosis. Mycobacterium smegmatis was also assessed as a surrogate for M. avium subsp. paratuberculosis. Two structures were constructed to hold three cattle carcasses each. Naturally infected tissues and ground beef inoculated with laboratory-cultured M. avium subsp. paratuberculosis and M. smegmatis were placed in nylon and plastic bags to determine effects of temperature and compost environment on viability over 250 days. After removal, samples were cultured and growth of both organisms was assessed after 12 weeks. After 250 days, M. avium subsp. paratuberculosis was still detectable by PCR, while M. smegmatis was not detected after 67 days of composting. Furthermore, M. avium subsp. paratuberculosis remained viable in both implanted nylon and plastic bags over the composting period. As the compost never reached a homogenous thermophilic (55 to 65°C) state throughout each structure, an in vitro experiment was conducted to examine viability of M. avium subsp. paratuberculosis after exposure to 80°C for 90 days. Naturally infected lymph tissues were mixed with and without compost. After 90 days, M. avium subsp. paratuberculosis remained viable despite exposure to temperatures typically higher than that achieved in compost. In conclusion, it is unlikely composting can be used as a means of inactivating M. avium subsp. paratuberculosis associated with cattle mortalities.

Crohn's disease and the mycobacterioses: a quarter century later. Causation or simple association?

It has been more than 25 years since Mycobacterium paratuberculosis was first proposed as an etiologic agent in Crohn's disease based on the isolation of this organism from several patients. Since that time, a great deal of information has been accumulated that clearly establishes an association between M. paratuberculosis and Crohn's disease. However, data are conflicting and difficult to interpret and the field has become divided into committed advocates and confirmed skeptics. This review is an attempt to provide a thorough and objective summary of current knowledge from both basic and clinical research from the views and interpretations of both the antagonists and proponents. The reader is left to draw his or her own conclusions related to the validity of the issues and claims made by the opposing views and data interpretations. Whether M. paratuberculosis is a causative agent in some cases or simply represents an incidental association remains a controversial topic, but current evidence suggests that the notion should not be so readily dismissed. Remaining questions that need to be addressed in defining the role of M. paratuberculosis in Crohn's disease and future implications are discussed.

Modeling the occurrence of Mycobacterium avium subsp. paratuberculosis in bulk raw milk and the impact of management options for exposure mitigation

Mycobacterium avium subsp. paratuberculosis (MAP) is the causal agent of paratuberculosis (Johne's disease) in cattle and other farm ruminants. The potential role of MAP in Crohn's disease in humans and the contribution of dairy products to human exposure to MAP continue to be the subject of scientific debate. The occurrence of MAP in bulk raw milk from dairy herds was assessed using a stochastic modeling approach. Raw milk samples were collected from bulk tanks in dairy plants and tested for the presence of MAP. Results from this analytical screening were used in a Bayesian network to update the model prediction. Of the 83 raw milk samples tested, 4 were positive for MAP by culture and PCR. We estimated that the level of MAP in bulk tanks ranged from 0 CFU/ml for the 2.5th percentile to 65 CFU/ml for the 97.5th percentile, with 95% credibility intervals of [0, 0] and [16, 326], respectively. The model was used to evaluate the effect of measures aimed at reducing the occurrence of MAP in raw milk. Reducing the prevalence of paratuberculosis has less of an effect on the occurrence of MAP in bulk raw milk than does managing clinically infected animals through good farming practices.

Mycobacterium avium subsp. paratuberculosis in dairy products, meat, and drinking water

Mycobacterium avium subsp. paratuberculosis (Map) is the cause of Johne's disease, a chronic infection of the gut, in ruminant animals that provide milk and/or meat for human consumption. Map also may be involved in Crohn's disease and type 1 diabetes in humans. Although the role of Map in human diseases has not been established, minimizing the exposure of humans to the organism is considered desirable as a precautionary measure. Infected animals can shed Map in feces and milk, and the organism can become disseminated in tissues remote from the gut and its associated lymph nodes. The presence of at least some Map in raw milk and meat and in natural waters is likely, but the numbers of Map in those foods and waters should be reduced through cooking or purification. The available information relating to Map in milk and dairy products, meats, and drinking water is reviewed here for assessment of the risks of exposure to Map from consumption of such foods and water.

Assessment of food as a source of exposure to Mycobacterium avium subspecies paratuberculosis (MAP)

The National Advisory Committee on Microbiological Criteria for Foods assessed the importance of food as a source of exposure to Mycobacterium avium subspecies paratuberculosis (MAP). MAP is the causative agent of Johne's disease, which affects primarily the small intestine of all ruminants. The significance of MAP as a human pathogen is unknown and is being investigated by several research groups. This document also reviews the efficacy of current detection methods, processing interventions, and MAP inactivation. Research needs related to MAP are provided. The Committee reached the following conclusions: current methods for detection of MAP have significant limitations, and a standard method for the detection of viable MAP cells is needed. Aside from MAP-infected domestic ruminant animals, the organism is found infrequently. If MAP in cattle is controlled, the source of MAP in other animals, food, and water may largely be eliminated. Milk, particularly raw milk, may be a likely food source for human exposure to MAP. Given the prevalence of MAP in U.S. cattle herds, ground beef may be a potential source of MAP. Although humans may be exposed to MAP through a variety of routes, including food and the environment, the frequency and amount of exposure will require additional research.

Rapid assessment of the viability of Mycobacterium avium subsp. paratuberculosis cells after heat treatment, using an optimized phage amplification assay

Thermal inactivation experiments were carried out to assess the utility of a recently optimized phage amplification assay to accurately enumerate viable Mycobacterium avium subsp. paratuberculosis cells in milk. Ultra-heat-treated (UHT) whole milk was spiked with large numbers of M. avium subsp. paratuberculosis organisms (10(6) to 10(7) CFU/ml) and dispensed in 100-microl aliquots in thin-walled 200-microl PCR tubes. A Primus 96 advanced thermal cycler (Peqlab, Erlangen, Germany) was used to achieve the following time and temperature treatments: (i) 63 degrees C for 3, 6, and 9 min; (ii) 68 degrees C for 20, 40, and 60 s; and (iii) 72 degrees C for 5, 10, 15, and 25 s. After thermal stress, the number of surviving M. avium subsp. paratuberculosis cells was assessed by both phage amplification assay and culture on Herrold's egg yolk medium (HEYM). A high correlation between PFU/ml and CFU/ml counts was observed for both unheated (r(2) = 0.943) and heated (r(2) = 0.971) M. avium subsp. paratuberculosis cells. D and z values obtained using the two types of counts were not significantly different (P > 0.05). The D(68 degrees C), mean D(63 degrees C), and D(72 degrees C) for four M. avium subsp. paratuberculosis strains were 81.8, 9.8, and 4.2 s, respectively, yielding a mean z value of 6.9 degrees C. Complete inactivation of 10(6) to 10(7) CFU of M. avium subsp. paratuberculosis/ml milk was not observed for any of the time-temperature combinations studied; 5.2- to 6.6-log(10) reductions in numbers were achieved depending on the temperature and time. Nonlinear thermal inactivation kinetics were consistently observed for this bacterium. This study confirms that the optimized phage assay can be employed in place of conventional culture on HEYM to speed up the acquisition of results (48 h instead of a minimum of 6 weeks) for inactivation experiments involving M. avium subsp. paratuberculosis-spiked samples.

Construction of Mycobacterium abscessus defined glycopeptidolipid mutants: comparison of genetic tools

Mycobacterium abscessus is a rapidly growing mycobacterial species that can be involved in pulmonary and disseminated infections in immunosuppressed or young cystic fibrosis patients. It is an emerging pathogen and has attracted recent attention due to the numerous cases of infection; furthermore, genomic tools have been developed for this species. Nevertheless, the study of this species has until now been limited to spontaneous variants. We report here a comparison of three different mutagenesis systems--the ts-sacB, the phage, and the recombineering systems--and show that there are important differences in their efficiency for the construction of allelic-exchange mutants. We show, using the mmpL4b gene of the glycopeptidolipid pathway as a target, that allelic-exchange mutants can be constructed with a reasonable efficiency (approximately 7%) using the recombineering system. These observations will facilitate genetic and cellular microbiology experiments involving the construction and use of well-defined mutants to study the virulence determinant of this emerging pathogen.