A rapid detection method combining immunomagnetic separation (IMS), PCR and slot blot detection was developed for the detection of Salmonella and Listeria monocytogenes in milk. Bacteria were first isolated and concentrated from phosphate-buffered saline (PBS) or milk by IMS. After extraction from diluted bacteria culture with the extraction buffer, bacterial DNA was subjected to PCR. Slot blot assay was optimized and used to measure PCR products. The lowest level of detection by this method was 40 cfu/ml in PBS or milk for both pathogens. The whole detection procedure could be completed within 7 h. Moreover, this detection method is simple and easy to handle for a large number of samples. Using multiplex PCR (amplification of two different bacterial DNA in the same PCR tube) and slot blot, simultaneous detection of both bacteria was also assessed. The detection sensitivities of 103 cfu/ml for both bacteria were the same as when PCR and slot blot were used for each bacterium separately. The combination of IMS, PCR and slot blot seems to give a highly sensitive and time-efficient procedure, which could be used for routine detection of Salmonella and L. monocytogenes in milk.

Heat resistant sporeforming psychrotrophic bacteria were isolated from raw milk samples from 59 Grade A farms in Oregon. Forty-nine of the 59 (83%) raw milk samples in this survey contained sporeforming psychrotrophic bacteria; isolates from twenty-four (40%) of the samples exhibited proteolytic properties. Populations of sporeforming psychrotrophic bacteria ranged from <10 to >10,000 CFU/mL for all samples. One hundred-two isolates were identified as Bacillus species. Twelve different Bacillus species were identified with B. licheniformis being the most predominate (18% of the samples) and B. laterosporus the least frequently isolated species, (2%). Fifty-eight percent of the bacilli isolates produced a bitter off-flavor and putrid odor, while 42% produced a fruity and/or rancid off-flavor when inoculated into sterile whole milk. Based on biochemical activity tests, 83% of the thermoduric isolates hydrolysed casein while 56% were proteolytic (in litmus milk), 57% demonstrated lipolytic activity and 31% produced acid in litmus milk. Forty-eight isolates that tested positive for proteolysis were evaluated quantitatively for activity, which ranged from 0.93 to 1.93 units (expressed as mM of alanine). Isolates of Bacillus cereus var. mycoides demonstrated significantly higher (p>0.05) proteolytic activity than other Bacillus species isolated. / Graduation date: 1988

No description available.

No description available.

M.S.

Work on the isolation of Bacillus albolactis from milk, and studies of it in pure culture, indicated the presence of two main colonial varieties. / Master of Science

M.S.

The causes of acid liquefaction in a high grade pasteurized milk were investigated. 1. Liquefying milk produced much less acid and had a much lower plate count than normal milk. 2. <i>Bacillus albolactis</i> was found regularly in the milk. It made up a much larger percentage of the total flora in liquefying than in normal milk. 3. Associated growth experiments showed that <i>Strep. lactis</i> could control the liquefying activities of <i>Bacillus albolactis</i>. 4. Pasteurization experiments showed that milk heated for 20 minutes at temperatures higher than 61°C. would undergo acid liquefaction. This appeared to be due to the increase in the percentage of <i>Bacillus albolactis</i>. 5. Inoculation of pasteurized samples with <i>Strep. lactis</i> prevented acid liquefaction. 6. Comparison with a type species showed that the strains of <i>Strep. lactis</i> repeatedly isolated from the milk studied were of the <i>tardus</i> variety. 7. The liquefaction was probably primarily due to an increased percentage of <i>Bacillus albolactis</i> brought about by pasteurization; the lack of the type of species of <i>Strep. lactis</i> and the absence of lactobacilli might also have been contributing factors. / Master of Science

This study has consisted primarily of the addition of varying amounts of chloral hydrate to nutrient agar plates and the determination of the definite effects thereof upon the colony plate counts of various samples of milk.

Thesis (MPA)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: The aim of this thesis was to determine in terms of policy analysis why the bacteriological quality of milk in a particular area did not comply with statutory provisions during production. The policy issue is very complex due to the diversity of conditions that exist during the milking process, which may impact on the levels of bacteria in milk. Considering this diversity, various problematic conditions are likely to cause the bacteriological contamination of milk. Milk is regarded as safe for human consumption when laboratory quality tests indicate its bacteriological suitability. Intervention on the basis of milk control should assure that milk is produced and distributed within acceptable bacteriological levels. The ad hoc milk safety strategy of the West Coast District Municipality (WCDM) was found to be inappropriate for the effective control of hygienic conditions during milk production. The existing strategy does not provide for suitable programmes to deal with this complex issue of policy and the suggestion is that it should be reviewed. Judged on the basis of success factors, a decline in milk bacteriological quality for the WCDM area revealed factors that were not effectively controlled during milk production. During the research period the hygienic quality of milk from the WCDM area was regulated and judged primarily by means of laboratory quality tests. Food safety requires much more than merely relying on quality tests. It is imperative that milk laboratory analyses should in all instances be harmonised by means of an evaluation of hygiene and sanitary conditions during production. How the problem situation with regard to milk quality is approached defines the implementation of strategy. The Environmental Health Practitioners (EHPs) of the WCDM have been implementing the requirements of applicable legislation, but each according to an individual approach. Such modi operandi provide for inconsistency in the execution of any policy. Implementing policy should be relevant, specific and adequate and should be target based. Consequently, the modification of policy is required to the extent of changing the approach when it does not comply with the afore-mentioned criteria, strategy or policy governing milk safety. More could be done by the WCDM to manage problems at milking sheds that is associated with the bacteriological quality of milk. Management control strategy is perceived to be inadequate and coupled with a lack of willingness to tackle the crux of the problem. Implementing legislative policy necessitate an objective approach coupled with an appropriate strategy. The findings of the empirical analysis together with a discussion of the implementation of the WCDM milk control strategy explains the shortcomings that was experienced in that regard. Therefore, an improved policy framework is proposed for controlling milk safety at milking sheds. In addition, a strategic framework is also proposed to administer the milk safety policy by way of programmes. / AFRIKAANSE OPSOMMING: Die doel van hierdie tesis was om, in terme van openbare beleidsanalise, te bepaal waarom die bakteriologiese kwaliteit van melk in ’n spesifieke gebied tydens die produksie daarvan nie aan die wetlike standaarde voldoen het nie. Hierdie beleidsvraagstuk word as kompleks beskou weens die uiteenlopende toestande wat tydens die melkproses ontstaan en wat ‘n impak op die bakterievlakke van melk kan hê. Inaggenome van hierdie diversiteit kan die besmetting van melk waarskynlik deur verskeie probleemtoestande veroorsaak word. Melk word geag veilig te wees vir menslike gebruik wanneer laboratoriumkwaliteittoetse op die bakteriologiese geskiktheid daarvan aandui. Ingryping op grond van melkbeheer moet verseker dat melk binne die aanvaarde bakteriologiese vlakke geproduseer en verskaf word. Die ad hoc melkveiligheidstrategie van die Weskus Distrik se Munisipale (WDM) gebied is onvoldoende bevind vir die effektiewe beheer van higiëniese toestande tydens melkproduksie. Hierdie strategie maak nie voorsiening vir geskikte programme om hierdie komplekse beleidsvraagstuk te hanteer nie en die hersiening daarvan word voorgestel. Geoordeel aan die hand van suksesfaktore, dui ‘n afname in die kwaliteit van melk vir die WDM gebied op faktore wat tydens melkproduksie nie effektief beheer was nie. Die higiëniese kwaliteit van melk binne die WDM gebied was tydens die navorsingstydperk primêr deur middel van laboratoriumkwaliteittoetse gereguleer en geoordeel. Voedselveiligheid vereis dat daar egter op meer as kwaliteittoetse gesteun word. Dit maak dit noodsaaklik dat die laboratoriumanalises van melk in alle gevalle aan die hand van evaluering van higiëniese en sanitêre toestande tydens melkproduksie geharmoniseer word. Die manier waarmee die probleemsituasie met betrekking tot melkkwaliteit benader word, definieer die implementering van strategie. Die Omgewingsgesondheidspraktisyns (OGPs) van die WDM het die voorskrifte van die toepaslike wetgewing geïmplementeer, maar elkeen volgens ‘n eie benadering. ‘n Sodanige modus operandi maak voorsiening vir die inkonsekwente uitvoering van enige beleid. Die implementering van beleid moet relevant, spesifiek, geskik en moet doelgerig wees. Gevolglik waar voornoemde kriteria, strategie of beleid wat melkveiligheid aangaan nie nagekom word nie, noodsaak dit derhalwe ‘n aanpassing van beleid vir soverre die benadering tot strategie vir melkveiligheid geraak word. Die WDM kan meer doen om probleme wat verband hou met die bakteriologiese kwaliteit van melk by melkstalle te bestuur. Die beheerstrategie van die bestuur word as onvanpas beskou en dit gaan gepaard met ‘n gebrek aan ywer om die essensie van die probleem aan te spreek. Die inwerkingstelling van wetgewing noodsaak ’n objektiewe benadering gepaardgaande met ’n geskikte strategie vir die uitvoering van beleid. Die bevindinge van die empiriese analise tesame met ’n bespreking aangaande die implementering van die WDM melkbeheerstrategie bied ’n verduideliking van die tekortkominge in daardie verband aan. Derhalwe word ’n verbeterde beleidsraamwerk voorgestel om die melkveiligheid by melkstalle te beheer. Daarbenewens word ’n strategiese raamwerk om die melkveiligheidbeleid deur middel van programme te uit te voer, ook voorgestel.