Prevalence and molecular characterization of mycobacterium avium subsp. paratuberculosis in raw milk of dairy herds / Zeinab Ibrahim Ali Ali ; Supervised Adel M. Saudi , Adel M. Talaat

Thesis (Ph.D.) - Cairo University - Faculty of Veterinary Medicine - Department of Food Hygiene and Control

The main objective of the study is to investigate the existence of different members of Non-Tuberculous Mycobacteria (NTM) with special reference to Mycobacterium avium subspecies paratuberculosis (MAP) in raw milk at the farm level and to address a mean of control on M. paratuberculosis in milk and dairy product that is safe for consumer. Interestingly, 5 different NTM species were identified and confirmed genotypically including, M. fortuitum, M. avium ssp. hominissuis,M. abscessus, M. simiae and M. avium ssp. Paratuberculosis. In tank milk, M. fortuitum was the predominant one with 48% predominance compared to M. simiae which detected in only 4% of the samples. On the other hand, M. abscessus and M. fortuitum were obtained from 77% and 23% of the examined milk filters, respectively. Surprisingly, M. avium subsp. hominissuis, Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis) and M. simiae were isolated from 16.7%, 10.4% and 4% of the examined tank milk samples, respectively, but not from milk filters. To investigate the impact of natural bacteriocins on the survival of different strains of M. paratuberculosis in milk, nisin was tested. Surprisingly, nisin had a minimum inhibitory concentration (MIC) that was higher against the laboratory strain (M. paratuberculosis K10) with 500 U/ml compared to other field isolates (e.g. M. paratuberculosis 4B and JTC 1281) with 15 U/ml respectively. In milk, the M. paratuberculosis cultures were inhibited after treatment with permissible levels of nisin at 4oC and 37oC. Using both fluorescent and scanning electron microscopy (SEM), we were able to identify clear defects on bacterial cell walls of treated cultures

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