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1、Lesson FourteenBrucella SpeciesNew words and phrasesBrucellaCoccobacillaryCoccobacilliDecolouriseZiehl-Neelsen stainCarbol fuchsinAerobicCapnophilicCatalase OxidaseB.ovisSuppurationCaseationPredilectionAllantoicErythritolSteroidHormonePlacentaeUndulantPyrexiaMalaisefatigueOsteomyelitisUreaseMacConke
2、yB.abortus biotype 2VenerealUterusConjunctivaInhalationEndotoxinThoracic ductParenchymatousTextBrucella species are small Gram-negative rods (0.50.7m0.61.5m)that often appear coccobacillary.They are non-motile,non-sporeforming and partially acid-fast in that they are not decolourised by 0.5 per cent
3、 acetic acid(乙酸)in the modified Ziehl-Neelsen(MZN)stain.The carbol fuchsin is retained and the brucellae appear as red-staining coccobacilli.The brucellae are aerobic and capnophilic,catalase-positive,oxidase-positive(except B.ovis and B.neotomae),urease-positive(except B.ovis)and will not grow on M
4、acConkey agar.B.ovis and B.abortus biotype 2 require media enriched with blood or serum.The growth of other brucellae is enhanced on enriched media but they are able to grow on nutrient agar.Brucella species are obligate parasites and each species has a preferred natural host that serves as a reserv
5、oir of infection.Brucellae have a predilection for ungulate(有蹄动物的)placentas,foetal fluids and testes(睾丸)of bulls,rams,boars and dogs.B.abortus is excreted in bovine milk and can remain viable in milk,water and damp soil for up to 4 months.Transmission is by direct or indirect contact with infective
6、excretors（排菌者）.The route of infection is often by ingestion but venereal transmission may occur and is the main route for B.ovis.The brucellae possess an endotoxin that contributes to the pathogenesis,as does a surface cell wall carbohydrate that is responsible for binding to B-lymphocytes.Soon afte
7、r entry into the host the brucellae are engulfed by phagocytic cells in which they survive,multiply and are transported to the regional lymph nodes.The organisms pass to the thoracic duct and then via the blood-stream to parenchymatous(实质的)organs and other tissues such as joints.Granulomatous(肉芽肿)fo
8、ci can develop in tissue with occasional suppuration and caseation.Brucellosis is essentially a disease of the sexually mature animal,the predilection sites being the reproductive tracts of males and females,especially the pregnant uterus.Allantoic factors stimulate the growth of most brucellae.Thes
9、e factors include erythritol,possibly steroid hormones and other substances.Erythritol is present in the placenta and male genital tract of cattle,sheep,goats and pigs but not humans.Erythritol does not stimulate the growth of B.ovis and inhibits B.abortus strain 19,the attenuated vaccinal strain.A
10、pyogranulomatous reaction occurs in affected placentae and abortion occurs from mid-gestation onwards.Apparently normal,but infected neonates can be born but the infection is of limited duration in these animals.Females usually abort only once,after which a degree of immunity develops,and the animal
11、s remain infected and large numbers of brucellae can be excreted in foetal fluids at subsequent parturitions.Permanent infertility may occur in male dogs infected with B.canis.Humans can be infected by all the Brucella species,except B.ovis and the non-pathogenic B.neotomae,and develop undulant feve
12、r.The manifestations are an undulating pyrexia,malaise,fatigue,night sweats,muscle and joint pains,but not abortion.Osteomyelitis is the most common complication.Humans can also develop a hypersensitivity to the antigens of both virulent B.abortus and the vaccinal strain 19.The mycobacteria are thin
13、 rods of varying lengths and sometimes branching filamentous forms occur but these easily fragment into rods.In previously unexposed animals,local multiplication of the mycobacteria occurs and the resistance to phagocytic killing allows continued intracellular and extracellular replication.Infected host cells and mycobacteria can reach local lymph nodes and from there may pass to the thoracic duct with general dissemination.Mycobacterium Species