Survival of MAP During Dairy Processing

Numerous pasteurization studies involving MAP have been reported in the scientific literature. Space does not permit the listing of all these studies here, so readers are directed to a review and critique of these studies by Robertson et al.

(2017). The studies involved different types of heating apparatus, different MAP strains prepared in different ways and different culture methodologies after heating. Consequently, it is very difficult to compare the studies or to reach a consensus opinion on the effect of commercial high-temperature, short-time (HTST) pasteurization conditions (72°C for 15 s) on MAP viability. The findings can best be described as conflicting: some researchers report inactivation of more than seven log₁₀ MAP, whereas others consistently report a more modest four- log₁₀ reduction (Cerf et al., 2007). Hammer et al. (2014) reported that homogenization applied before, during or after HTST pasteurization did not impact MAP inactivation significantly, which is contrary to a previous report by Grant et al. (2005), which found that homogenization before or during HTST pasteurization led to greater MAP inactivation.

A recently published review by Mullan (2019) concluded that there are at least eight possible reasons why viable MAP is being reported to be present in retail pasteurized milk. These are as follows: (i) the remarkable heat resistance of MAP; (ii) the potential existence of a heat-resistant subpopulation; (iii) the location of MAP cells in somatic cells in milk affording protection during heating; (iv) the non-homogeneous distribution of MAP in milk; (v) leakage within, or incorrect operation of, pasteurizers; (vi) poorly designed pasteurizing systems without over-pressure or differential pressure systems; (vii) high concentrations of MAP in raw milk and clumping of MAP cells; and (viii) possible false positive results with the newer phage-based assays.

Two pasteurization process modelling studies, which specifically considered survival of MAP, should also make interesting reading for dairy processors. Salgado et al. (2011, p. E500) suggested that there is ‘68.4% probability that the 15 s HTST pasteurization process would not achieve at least five decimal reductions in MAP counts'. Chandrakash and Davey (2017, p. 11) concluded that ‘any pasteurization process is a mix of failure and success, with around 5.7% failure events suggested, equating to ~21 pasteurization failures, with unwanted MAP survival, each year averaged over an extended period of daily batch-continuous operations'.

In view of the fact that studies have suggested that HTST pasteurization may not completely eliminate viable MAP, the effect of novel milk processing techniques has been studied. The use of pulsed electric fields to destroy pathogenic bacteria, due to electrical breakdown of the cell membrane and electroporation, has been investigated for MAP inactivation. Rowan et al. (2001) observed a 5.9-log₁₀ reduction in viable MAP when spiked cow's milk was subjected to 2500 pulses at 30 kV/cm in a 25-min period, which represented a greater kill than was achieved by laboratory pasteurization (2.4 log₁₀). Stabel et al. (2001) reported that application of 5, 10 or 15 kGy of gamma radiation achieved a six-log₁₀ reduction in MAP in raw milk. In contrast, ultraviolet light treatment of MAP in milk had minimal effect on viability (0.5-1.0-log₁₀ reduction per 1000 mJ/ml; Altic et al., 2007). Treatment of MAP-spiked milk with high hydrostatic pressure (500 MPa for 10 min) achieved a four- to six-log₁₀ kill (Lopez-Pedemonte et al., 2006; Donaghy et al., 2007), a similar reduction to HTST pasteurization. Peterz et al. (2016) studied the effect of direct steam injection at 105°C for 3s using pilot-scale equipment and were unable to recover viable MAP from spiked milk (10^5-6 CFU/ ml) after treatment.

None of the alternative processes investigated to date appears to offer a viable alternative to HTST pasteurization, with the possible exception of direct steam injection. However, more research on the latter dairy processing technology is required.

Limited research on MAP survival during production of other dairy products is available. During cheesemaking there is an approximately ten-fold concentration of any MAP present in the milk upon curd formation (Donaghy et al., 2004). During the subsequent ripening period, some inactivation of MAP occurs, principally dictated by pH, salt concentration, length of ripening period and presence of lactic acid cultures (Sung and Collins, 2000; Spahr and Schafroth, 2001; Donaghy et al., 2004; Hanifian, 2014). During yoghurt production, numbers of viable MAP remained unchanged in two studies (Van Brandt et al., 2011; Klanicova et al., 2012). However, during storage of fermented or probiotic-containing products (e.g. kefir, acidophilus milk and yoghurt), longer exposure to pH 1,000,000 CFU/g faeces. Hovingh et al. (2006) found that 10-15% of animals in four infected herds were supershedders. They calculated that a single supershedder would shed more MAP than 2000 moderate or 20,000 light shedders. Okura et al. (2013) and Rani et al. (2019) concluded the same about the relative contribution of faecal shedding by supershedders to levels of MAP contamination of raw milk at farm level. This situation has major implications for levels of MAP contamination in bulk tank milk of infected farms, and potential for environmental transmission of paratuberculosis within either dairy or beef herds.

2.4.1 Spread and survival of MAP in the environment

Cattle are generally not housed all the time, and movement of animals around the farm results in contamination of outdoor areas. Raizman et al. (2004) and Lombard et al. (2006) tested environmental samples from various locations around dairy operations in the USA. Farm locations commonly contaminated by MAP were parlour exits, floors of holding pens, common alleyways, lagoons, manure spreaders and manure pits.

When animals are grazing on pastures, their faeces contaminate soil and grass. Whittington et al. (2004) studied survival in faeces in the Australian environment, and MAP was cultured for up to 55 weeks from dry, fully shaded locations and for much shorter time periods in unshaded conditions. They postulated that diurnal temperature flux due to infrared radiation, rather than ultraviolet inactivation, influenced MAP survival. In a subsequent study of survival of MAP in dam water in shaded or exposed water troughs, Whittington et al. (2005) recorded survival times of up to 48 weeks and 36 weeks, respectively, and for 12-26 weeks longer in the dam sediment. In both studies, Whittington and colleagues obtained results suggestive of dormancy, i.e. MAP detection followed by disappearance and then detection again after a period of time. Numerous invertebrate and protozoal species were observed to be present in the dam water (Whittington et al., 2005). It has been suggested that interaction with nematodes, insects or protozoa (Whan et al., 2006) may enable MAP, an intracellular pathogen, to survive and/or multiply in the environment. Other potential survival mechanisms of MAP in the environment (dormancy, aerosoli- zation and biofilm formation) were reviewed by Rowe and Grant (2006).

MAP on contaminated pasture can run off into watercourses when it rains. Studies by Pickup et al. (2005, 2006) presented evidence of runoff from hills grazed by MAP-infected sheep into the Taff and Tywi rivers in South Wales, UK, especially after periods of high rainfall. More recent studies by the same UK research group (Rhodes et al., 2014; Richardson et al., 2019) reported that aerosols above the Rivers Taff and Tywi contain MAP, and the break of foam bubbles in the water may cause MAP to be aerosolized leading to potential human exposure along these rivers. Richardson et al. (2019) studied these geographic locations over a 10year period and demonstrated persistence of MAP correlating with levels of paratuberculosis in British herds over the same period.

They also reported MAP levels in the river water estimated by qPCR of up to 10⁵ cell equivalents/l (which is equal to 10⁸MAP per m³ of river water). Singh et al. (2012) reported detection of MAP DNA by PCR in 10% of river waters tested in parts of India. The above findings with regard to MAP in raw (untreated) water raise questions about the ability of water treatment processes to remove or inactivate MAP before it reaches the consumer. In laboratory simulations, chlorination of MAP- spiked water at 2 μg∕ml for 30 min resulted in a maximum 2.8-log₁₀ reduction in numbers (Whan et al., 2001), which means that, in common with other mycobacteria, MAP is chlorine resistant. Another water treatment process (COCODAFF) physically removes MAP along with suspended solids (Pickup et al., 2006). However, the contaminated slurry removed may be disposed of back on to the land, creating a cycle of environmental persistence. Waddell et al. (2016) reviewed five untreated water studies and the prevalence of MAP from their meta-analysis was 8.7% by culture (95% CI: 2.5, 7.0) and 42.5% by PCR detection (95% CI: 25.5, 60.4). Similar to milk pasteurization, the efficacy of water treatment processes will depend on the numbers of MAP present in raw waters being treated, which will be influenced by prevalence of MAP infection in animals grazing surrounding land and rainfall patterns leading to runoff into rivers.

Waddell et al. (2016) reported a metaanalysis of six drinking water (i.e. treated water) surveys and reported prevalences of 2.3% by culture (95%CI: 0.0, 66.8) and 35.7% by PCR (95%CI: 21.5, 49.8). Beumer et al. (2008) reported that MAP can frequently be detected in biofilm samples from taps. A study by Sarmento et al. (2018) of drinking water and an untreated domestic water supply in the Porto area of Portugal showed higher levels of MAP contamination in samples of drinking water than in domestic water, and detected MAP DNA at a higher frequency in tap biofilms than in the corresponding collected water, which is in agreement with the US study. A study of water supply systems in the Czech Republic by Klanicova et al. (2013) found no evidence of MAP at any point (watershed, reservoir, drinking water treatment plant, drinking water or household supply) by culture or qPCR, although several other Mycobacterium spp. were cultured and non-tuberculous mycobacteria were detected in 76.7% of water samples by the PCR methods employed.

2.5

<< | >>

↑

Source: Behr Marcel A., Stevenson K., Kapur V. (eds.). Paratuberculosis: Organism, Disease, Control. 2nd edition. — CAB International,2020. — 439 p.. 2020

More medical literature on Medic.Studio

Survival of MAP During Dairy Processing

More on the topic Survival of MAP During Dairy Processing: