Alexander Govaris

Review of Shiga-toxin-producing Escherichia coli (STEC) and their significance in dairy production

The involvement of the pathogenic Shiga-toxin-producing Escherichia coli (STEC; also called verocytotoxic-producing E. coli or VTEC) in sporadic cases and disease outbreaks is presently increasing. Infrequent cases are due to ingestion of milk and dairy products. As ruminants are healthy carriers of STEC and most dairy products may provide these bacteria with favourable conditions for their growth, milk and dairy products are a potential source of STEC. But not all STEC serotypes are pathogens; only relatively small numbers in the entire family of STEC are pathogenic. This review focuses on the recent advances in understanding of STEC and their significance in milk and dairy products. It is intended to gather the information that is needed to understand how these bacteria are described, detected and characterised, how they contaminate milk and grow in dairy products, and how the dairy industry can prevent them from affecting the consumer.

Lipid and protein oxidation of α-linolenic acid-enriched pork during refrigerated storage as influenced by diet supplementation with olive leaves (Olea europea L.) or α-tocopheryl acetate.

The objective of this study was to evaluate the effect of diet supplementation with olive leaves or α-tocopheryl acetate on lipid and protein oxidation of raw and cooked n-3 enriched-pork during refrigerated storage. Enrichment of pork with α-linolenic acid through diet supplementation with linseed oil enhanced (p≤0.05) lipid oxidation in both raw and cooked chops but had no effect (p>0.05) on protein oxidation during refrigerated storage while decreasing (p≤0.05) the sensory attributes of cooked pork. Diet supplementation with olive leaves or α-tocopheryl acetate had no effect (p>0.05) on the fatty acid composition of pork but decreased (p≤0.05) lipid oxidation while exerting no effect (p>0.05) on protein oxidation in both raw and cooked α-linolenic acid-enriched chops stored and chilled for 9 days. Moreover, olive leaves and α-tocopheryl acetate supplemented at 10 g/kg and 200mg/kg diet, respectively, exerted (p≤0.05) a beneficial effect on the sensory attributes of cooked α-linolenic acid-enriched pork chops.

Effect of olive leaf (Olea europea L.) extracts on protein and lipid oxidation of long-term frozen n-3 fatty acids-enriched pork patties.

Our previous study has demonstrated the protective effects of olive leaf extracts on the oxidation of pork patties from n-3 fatty acid-enriched meat during refrigerated storage. The target of the present study was to examine these effects during frozen storage. Results showed that frozen storage accelerated (P=0.05) both lipid and protein oxidation in pork patties, but an addition of olive leaf extract at 200mg gallic acid equivalent/kg improved sensory attributes by delaying oxidation of lipids (reduction (P=0.05) of conjugated dienes, hydroperoxides and malondialdehyde), and of proteins (reduction (P=0.05) of protein carbonyls and inhibition (P=0.05) of the decrease of protein sulfhydryls).

The induction of lymphoid follicle-like structures in the ovine teat duct following experimental infection with Mannheimia haemolytica.

The objectives of this study were to investigate the early stages of experimental infection of the ovine mammary gland with Mannheimia haemolytica and to identify the lymphocyte subsets accumulating at the teat duct. M. haemolytica was inoculated into one teat of each of 25 ewes and clinical, bacteriological, cytological, haematological, physicochemical, gross pathological, histopathological and immunohistochemical examinations were carried out. Clinical signs of inflammation were evident by 8 h but had subsided 2 days after challenge. Polymorphonuclear neutrophils (PMN) predominated in milk films up to 1 day following challenge, but the proportion of lymphocytes and macrophages progressively increased thereafter. Total blood leucocyte counts decreased immediately after challenge and then rose until 1 day after challenge with immature PMNs comprising >3% of the total. The pH of the mammary secretions from the challenged side was increased (>7.0). Focal lymphoid accumulations were observed in the lamina propria at the junction of the teat duct and cistern, including CD79(+), CD3(+) and gammadelta T cells, CD68(+) and MHC-II(+) cells with a particular increase in the numbers of CD8(+) T cells from days 3 to 5 after challenge. The findings suggest that these organised lymphoid structures are inducible and contribute to the defence of the infected teat when the PMN-macrophage response is overwhelmed.

Effects of experimental challenge of ewes with Mannheimia haemolytica on subsequent milk composition

The objective was to describe the physicochemical changes during the early phase of subclinical mastitis and to associate them with pathological findings. A Mannheimia haemolytica strain was deposited into one teat duct of 25 ewes and the clinical, bacteriological, cytological, physicochemical (pH, milk composition), gross-pathological and histological findings were subsequently recorded. The organism was consistently isolated from samples of teat duct material (140/150) but not from mammary secretion (50/150). California Mastitis Test (CMT) scores increased (>1) and remained high (143/150 samples) after challenge; polymorphonuclear neutrophils (PMN) predominated in milk films, but the proportion of lymphocytes and macrophages progressively increased. Increased pH values (>7.0) were recorded in the mammary secretion from the challenged side. Furthermore, content of fat, total proteins and lactose therein decreased markedly. Histological changes (leucocytic infiltration, destruction of epithelial cells) were observed in the mammary parenchyma of the ewes. The present results confirm that the reduction of milk constituents is the effect of cellular damage and can occur soon after infection.