Decay of Mycobacterium bovis in whole milk submitted to pasteurization parameters

Abstract

Parameters for milk pasteurization were established a long time ago, considering the thermal resistance of Mycobacterium bovis, and the systematic adoption of this process has drastically reduced the incidence of human tuberculosis caused by this pathogen. However, more recently, molecular methods have allowed the identification of genetic variations in this bacterium that may lead to greater thermal resistance. The aim of this study was to investigate whether genetic variation leads to variation in the death pattern of this bacterium during the milk pasteurization process. Samples of UHT (ultrahigh temperature)-treated whole milk were artificially contaminated with four different Mycobacterium bovis spoligotypes and were subjected to pasteurization by low-temperature long-time (LTLT) and high-temperature short-time (HTST) treatments. The M. bovis spoligotypes were quantified (Colony Forming Unit per milliliter of milk) before and during the thermal process. The decay of the pathogen was quantified by calculating the difference between the measurements at the beginning and at the end of the thermal treatment. The data demonstrated that the LTLT and HTST pasteurization processes considerably reduced the M. bovis load in the milk; however, the bacterium was not eliminated. There was no difference in the thermal resistance of the spoligotypes tested or in the efficiency of pasteurization processes (LTLT versus HTST). However, heating phase was more effective in reducing the M. bovis load than the target temperature maintenance phase. Key words: Batch pasteurization. Bovine tuberculosis. Flow pasteurization. Mycobacterium bovis. Thermal death. ResumoOs parâmetros para a pasteurização do leite foram estabelecidos há muito tempo, considerando a resistência térmica de Mycobacterium bovis e a adoção sistemática deste processo reduziu drasticamente a incidência de tuberculose humana causada por este patógeno. Entretanto, mais recentemente, métodos moleculares permitiram a identificação de variações genéticas nesta bactéria que podem levar a uma maior resistência térmica. O objetivo deste estudo foi investigar se a variação genética apresenta modificação no padrão de morte da bactéria durante o processo de pasteurização do leite. Amostras de leite tratadas por UHT (ultra-alta temperatura) integral foram contaminadas com quatro diferentes espoligotipos de Mycobacterium bovis e foram submetidos ao tratamento por temperatura baixa e tempo longo (LTLT) e temperatura alta e tempo curto (HTST). Os espoligotipos M. bovis foram quantificados (Unidades Formadoras de colônias por mililitro de leite) antes e durante o processo térmico. A diminuição do patógeno foi quantificada através do cálculo da diferença entre as medições no início e no fim do tratamento térmico. Os dados demonstraram que os processos de pasteurização HTST e LTLT reduziram consideravelmente a carga de M. bovis no leite; no entanto, a bactéria não foi eliminada. Não houve diferença na resistência térmica dos espoligotipos testados nem na eficiência dos pr...

Effect of pasteurization on the decay of Mycobacterium bovis in milk cream

“…The heating step was the most efficient in inactivating the microorganism (Figure 1), which is consistent with the result obtained by Ribeiro et al (2016a). Grant et al (1996) evaluated the resistance of Mycobacterium paratuberculosis under conditions of slow pasteurization and observed a significant decrease in bacterial load in the first third of the process followed by a slight reduction in the bacterial load.…”

“…Ribeiro et al (2016a) evaluated the survival of the same spoligotype (SB1141) at 72°C for 20 s in UHT whole milk and the results obtained were similar to the ones we obtained for the treatment combination of 75°C and 15 s. This finding is of particular interest because milk cream contains approximately 10 times the fat content that is usually found in UHT whole milk. In addition, the heating time needed for the sample to reach the target temperature was similar in both studies [1 min 45 sec (WB at 85°C), Ribeiro et al (2016a); 1 min and 41 sec (WB at 95°C), present study]. This result indicates that the penetration of heat in milk cream is similar to that in whole milk and suggests that the effect of this process is similar in both substrates.…”

“…The IL was 8.0 log CFU mL -1 and the bacterial load ranged between 7.8 and 8.3 log CFU mL *: when samples reached the target temperature **: after 5 seconds on target temperature **: after 15 seconds on target temperature. Ribeiro et al (2016a) evaluated the survival of the same spoligotype (SB1141) at 72°C for 20 s in *: when samples reached the target temperature **: after 5 seconds on target temperature **: after 15 seconds on target temperature. Ribeiro et al (2016a) evaluated the survival of the same spoligotype (SB1141) at 72°C for 20 s in UHT whole milk and the results obtained were similar to the ones we obtained for the treatment combination of 75°C and 15 s. This finding is of particular interest because milk cream contains approximately 10 times the fat content that is usually found in UHT whole milk.…”

“…Ribeiro et al (2016a) evaluated the survival of the same spoligotype (SB1141) at 72°C for 20 s in *: when samples reached the target temperature **: after 5 seconds on target temperature **: after 15 seconds on target temperature. Ribeiro et al (2016a) evaluated the survival of the same spoligotype (SB1141) at 72°C for 20 s in UHT whole milk and the results obtained were similar to the ones we obtained for the treatment combination of 75°C and 15 s. This finding is of particular interest because milk cream contains approximately 10 times the fat content that is usually found in UHT whole milk. In addition, the heating time needed for the sample to reach the target temperature was similar in both studies [1 min 45 sec (WB at 85°C), Ribeiro et al (2016a); 1 min and 41 sec (WB at 95°C), present study].…”

Whole-Genome SNP Analysis Identifies Putative Mycobacterium bovis Transmission Clusters in Livestock and Wildlife in Catalonia, Spain

“…Within-herd transmission is the most problematic due to the challenges that can pose certain herd-management practices that do not prevent direct contact between infected and non-infected animals, in addition to contaminated soil, feed, and water from infected herd-mates [ 60 ]. Congenital transmission is rare, and transmission via milk is easily preventable by pasteurization [ 61 , 62 ]. Between-herd transmission can be attributed to all clusters in which the most likely explanatory factors were neighborhood, proximity, movement, and shared pasture.…”