Enumeration and Detection of Staphylococcus aureus and Other Staphylococcal spp. in Raw Bovine Milk In Soba county of Khartoum State

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Date
2015-06-23
Authors
Mohammed El Hadi Mahgoub El Nazier, El Nazier
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Publisher
UOFK
Abstract
Twenty six bovine raw milk samples were taken from 4 dairy farms in at Soba County of Khartoum State. The principal objective of this investigation was to establish presence, enumeration and the probability of detecting Staphylococcus aureus and other milk staphylococci, bearing in mind that presence of Staph. aureus has always been regarded as an index of sanitation in ready to eat dirty food. Other objectives included comparison of 7 recent selective, differential and general-purpose media for the enumeration of Staph. aureus. These media were Baird-Parker Original Formula (1962) for both surface and pour plates, egg yolk-free Baird-Parker Medium, vogel and Johnson’s agar, Staphylococcus spp. medium Number 110, Mannitol-Salt agar, Brain-Heart Infusion agar plus 1% glucose, International Standards Organization Plate Count Medium (ISO 4883-1978E). The objectives also included identification of the various coagulase-negative Staphylococcal spp. (CNS) in raw milk samples-since CNS rates in human and animal disease production has increased tremendously in the last few years. The investigation of the plasmas of various animal species viz: rabbit, bovine, ovine, caprine and equine for the use of both tube and clumping-factor (CF) tests for identification of Staph. aureus. Evaluation of effectiveness of the various primary and ancillary Staph. aureus tests with regard to local strains of Staph. aureus. Testing whether or not the various batches of the media meet the specifications required for them. The following results were obtained total CFUS of Staph. aureus counts per ml bovine raw milk in the 7 media ranged between nil to less than 2000. Baird-Parker medium (Original Formula) was taken as the control medium against which other media were compared. Values ranged between 80.48% (for VJ, the least selective) and up to 132.39% (the highest count) for Egg yolk-free Baird-Parker medium were obtained. The other 5 media occupied an in–between position. The average score of colonies confirmed as Staph. aureus by the coagulase and Parker (the highest score) to 40% (the lowest score) for BHI+1% glucose. Bacterial genera encountered as contaminants in the 7 media included Bacillus, CNS, Streptococci, Gram-negative rods, fungi and moulds and the least of all was Micrococci. Gram-negative rods were only seen in general purpose media. Bacilli were observed in almost all media. Vogel and Johnson medium was the media capable of contamination and Baird-Parker medium (Original Formula) was the medium most subjected to contamination. The overall incidence of Staph. aureus in the 26 raw milk samples was 42% medium most subjected to contamination. No single test or test criterion by itself suffices as a diagnostic tool for the identification of Staph. aureus and other staphylococci. The identification ground work laid down by Kloos and Schleifer (1975) and later updated in 1986, 1992 and 1980 work by Devriese and Hajek were the 2 monumental frame-works for identification of Staph. aureus and other staphylococci. Staph. aureus and other staphylococci could be incubated at 37oC and at 43oC. Growth at 43oC would prohibit competing microorganisms that cannot grow at 43oC and would reduce the amount of confirmatory tests required. Colonies of Staph. aureus from Baird-Parker medium were most likely, and those from Mannitol-Salt agar are least likely to be confirmed as Staph. aureus. The hyaluronidase test was of considerable importance in confirming identity of local strains of Staph. aureus. Only 36% of local strains of Staph. aureus gave positive results to the egg yolk reaction, i.e. lipovitalinase reaction. Tellurite reduction and haemoysin production were good index markers for identification, while colour of the colony, mannitol fermentation and gelatin hydrolysis were questionable markers for identification of local strains of Staph. aureus. Rabbit plasma was still the plasma of choice for conduction of the coagulase test. Goat plasma was just as good and even more so for conduction of the clumping factor (Cf) test. Next was equine plasma and last was bovine plasma. All these clump bovine Staph. aureus strains, with bovine plasma were the least active in this respect. The 3% KOH test gave results as good as those of the Gram test. About 9 staphylococci other than Staph. aureus were identified. These were Staph. chromogens, Staph. simulans, Staph. epidermidis, Staph. hyicus, Staph. xylosus, Staph. scuri, Staph. cohnii, Staph. carnosus and Staph. lentus. Staph. chromogens, Staph. epidermidis, Staph. simulans, Staph. xylosus and Staph. hyicus were more frequently isolated. All media conformed to the specifications intended for enumeration of Staph. aureus except for the 2 general-purpose media: Brain-Heart Infusion agar (BHI) and ISO.
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Enumeration and Detection of Staphylococcus aureus and Other Staphylococcal spp. in Raw Bovine Milk In Soba county of Khartoum State.
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