Mycobacterium（Mycobacterium）It is a kind of slender and slightly curved, sometimes with branches or filaments.Mycobacterium has been classified as actinomycetes in taxonomy.Actinomycetes that are pathogenic to humans can be divided into two categories: mycotic acid containing and mycotic acid free.Mycobacterium belongs to mycotic acid group.[1]
The main characteristics of this genus of bacteria arecell wallContains a lot oflipid, mainlyMycotic acid。This is closely related to its dyeing, growth characteristics, pathogenicity and resistance.Generally, it is not easy to stain. If it can resist the decolorization of strong decolorizing agent hydrochloric acid ethanol after being heated or prolonged, it is also calledAcid fast bacilli(acid-fast bacilli)。It has no flagella, spores, and produces neither exotoxin nor endotoxin. Its pathogenicity is related to its composition.The diseases caused were all chronic, accompanied by granuloma.[1]
Mycobacterium is a kind of slender and slightly curved bacteria that can grow as branches.[2]
Salient characteristic
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Mycobacterium
Mycobacterium（Mycobacterium）It is a kind of slender and slightly curved bacilli, named after the tendency of branching growth.The remarkable characteristics of this genus are:
④ The resulting infection is mostly a chronic process, with long-term persistence and destructive tissue lesions.[3]
Distribution range
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Non tuberculous mycobacteria are widely distributed in the external environment, human and animal organisms.Human isLeprosy bacillusThe only host of.[4]
Mycobacterium tuberculosis（M.tuberculosis）, commonly known asMycobacterium tuberculosisOr tubercle bacillus, which is the pathogen causing tuberculosis.It can invade all organs of the body, but most of them are pulmonary tuberculosis (because of its aerobic nature).Tuberculosis is an infectious disease.[1]
Mycobacterium tuberculosis is a slender and slightly curved bacterium with a size of 1-4 μ mX0.4 μ m.Mycobacterium bovis is thicker and shorter.MycobacteriumOfBacterial cell wallThe lipid content is high, accounting for about 60% of the dry weight. In particular, there is a large amount of mycotic acid surrounded byPeptidoglycanThe outside of the layer can affect the penetration of dyes.Mycobacterium generally uses Ziehl NeelsenAcid fast stainingIt can be dyed with 5% carbolic acid fuchsin after heating, but it is not easy to decolorize with 3% hydrochloric acid ethanol.If methylene blue is used for re staining, mycobacteria will be red, while other bacteria and substances in the background will be blue.[1]
In recent years, it was found that Mycobacterium tuberculosiscell wallThere is another layerCapsule。It is not easy to see because of the damage during production.If gelatin is used before fixing the prepared electron microscope specimen, dehydration and contraction of capsule can be prevented.Under the electron microscope, we can see that there is a thick transparent area outside the bacteria, namely the capsule, which has a certain protective effect on Mycobacterium tuberculosis.[1]
Specific oxygen demand.The optimum temperature is 37 ℃, and no growth occurs below 30 ℃.Mycobacterium tuberculosis cell wall has a high lipid content, which affects the absorption of nutrients, so it grows slowly.In general medium, it takes 18-24 hours for each generation of division, and only 5 hours for nutrient enrichment.[1]
The first separation requires nutrient rich medium.Commonly used are Lowenstein JensenSolid mediumIt contains egg yolk, glycerin, potato, inorganic salt, malachite green, etc.Malachite green can inhibithybrid bacteriumGrowth, easy to separate and long-term culture.Egg yolk contains lipid growth factor, which can stimulate growth.According to the number of inoculated bacteria, it can be seen in 2-4 weekscolony of bacteriaGrowth.The colony is granular, nodular or cauliflower shaped, milky white or beige, opaque.stayLiquid mediumIt is possible that the bacteria grow rapidly due to the large nutrient contact surface.Generally, it can grow in 1-2 weeks.Clinical specimen examinationliquid cultureThe positive rate was several times higher than that of solid culture.[1]
Mycobacterium tuberculosis does not ferment sugars.The difference with Mycobacterium bovis is that Mycobacterium tuberculosis can synthesize nicotinic acid and reduce nitrate, while Mycobacterium bovis cannot.heatEnzyme contact testIt is of great significance to distinguish mycobacterium tuberculosis from non mycobacterium tuberculosis.Most of mycobacterium tuberculosis were positive in enzyme contact test, but negative in heat enzyme test;Most of the two tests were positive for nontuberculous mycobacteria.[1]
Mycobacterium tuberculosis can formcolony of bacteria, virulence, immunogenicity andDrug resistanceEquivariant.Bacillus Calmette and Guerin (1908) used the Bacillus Calmette and Guerin vaccine toculture mediumThe attenuated live vaccine strain obtained through 230 generations in 13 years in China is now widely used for vaccination.[1]
Mycobacterium tuberculosis[1]
Mycobacterium tuberculosis does not produce internal and external toxins.Its pathogenicity may be related to theHistiocyteInflammation caused by internal mass reproduction, the toxicity of cell components and metabolic substances, and the immune damage caused by the body to the cell components are related.
Mycobacterium tuberculosis can invade susceptible organism through respiratory tract, digestive tract or skin injury, causing tuberculosis of many tissues and organs, among which pulmonary tuberculosis is caused most by respiratory tract.Because there are a large number of normal flora living in the intestinal tract, Mycobacterium tuberculosis must compete to survive and adhere to susceptible cells.There is no normal flora in the alveoli. Mycobacterium tuberculosis can be inhaled through droplets or dust containing bacteria, so pulmonary tuberculosis is more common.
In some patients, Mycobacterium tuberculosis can enter the blood circulation and cause intrapulmonary and extrapulmonary spread, such as cerebral and renal tuberculosis,Sputum bacteriumBeing swallowed into the digestive tract can also cause intestinal tuberculosisTuberculous peritonitisEtc.[1]
Immune mechanism: Mycobacterium tuberculosis is an intracellular infection bacterium, and its immunity is mainly cellular immunity based on T cells.T cells cannot directly interact with intracellular bacteria. They must first react with infected cells, leading to cell collapse and the release of Mycobacterium tuberculosis.Although the body can produce antibodies against Mycobacterium tuberculosis, the antibodies can only play an auxiliary role in contact with the released bacteria.After mycobacterium tuberculosis invades the respiratory tract, 80% - 90% of the alveoli aremacrophage, 10% islymphocyte(T cells predominate);The inactive macrophages in the original alveoli have weak antibacterial activity, which can not prevent the growth of the swallowed Mycobacterium tuberculosis, but can take the Mycobacterium tuberculosis to other places.But canPresenting antigenT lymphocytesSensitization.Sensitized lymphocyteCan produce a variety ofLymphokine, such as IL-2, IL-6, INF - γ, which can kill Mycobacterium tuberculosis in the focus by their combined action with TNF - α.[1]
The main methods to control tuberculosis are: ① discovery and treatmentSputum bacteriumPositive person; ②Newborns are vaccinated with BCG vaccine.[1]
nontuberculosis mycobacteria
Nontuberculous mycobacteria refers to mycobacteria other than Mycobacterium tuberculosis, Mycobacterium bovis and Mycobacterium leprae.Formerly known asAtypical mycobacterium(atypical mycobacterium), its characteristics are different from that of mycobacterium tuberculosis, for example, it is sensitive to acid and alkali;It is resistant to commonly used anti tuberculous drugs;The growth temperature is not as strict as that of Mycobacterium tuberculosis;Most exist in the environment;It is a conditional pathogen.It can cause tuberculous lesions and attract attention.Antigens cross with Mycobacterium tuberculosis.[1]
Runyon according tocolony of bacteriaNon tuberculous mycobacteria were divided into 4 groups by pigment and growth rate.[1]
Group I
Photochromogen
The bacteria in this group are cream colored in the dark, and they will become orange after being exposed for 1 hour.Slow growth,colony of bacteriaSmooth.Mycobacterium kansas is a human pathogen（M. kansas）, causing human pulmonary tuberculosis like lesions, often cavity formation;Mycobacterium marinum（M. marinum）, can pass through in waterSkin abrasionsIt is easy to be mistaken for Mycobacterium leprae because of the presence of acid fast bacteria in pathological examination.[1]
Group II
Scotochromogen
thisBacteroidWhen cultivating in the darkcolony of bacteriaIt is orange.It grows slowly at 37 ℃ with smooth colonies.M. scrofulaceum, which is pathogenic to human beings, causes childrenlymphadenitis。[1]
Group III
Nonphotochromogen
Usually no pigment is produced.It grows slowly at 40-42 ℃.The colony is smooth.Birds-Intracellular Mycobacterium（M.avium-intracellulare）It can cause tuberculous lesions, mostly in the lungs and kidneys.[1]
Group IV
Rapid growth bacteria
It grows at 25-45 ℃.It grows fast and can be seen after 5-7 days of culturecolony of bacteriaThe colony is rough, and some can produce color.The ones that cause disease to people areMycobacterium fortuitum（M.fortuitum）、Mycobacterium chelonensis（M. chelonei）And Mycobacterium ulcers（M.ulcerans）, causing skin diseases.Mycobacterium smegmatis（M.smegmatis）Not pathogenic, but often in the vulvasebumThe presence of mycobacterium tuberculosis in feces and urine should be noted.[1]
Whether nontuberculous mycobacteria have pathogenicity can be distinguished by anti boiling test.The non pathogenic strain loses its acid resistance after boiling for 1 minute, while the pathogenic strain can endure for 10 minutes, even autoclaving does not lose its acid resistance.For the identification of mycobacterium tuberculosis and non mycobacterium tuberculosis, in addition to the heat contact enzyme testLichenGrind the glass slide containing small drops of salt water. The former is not easy to emulsify while the latter is easy to emulsify.[1]
Because many strains of nontuberculous mycobacteriaisoniazid、streptomycinIs resistant to rifampicinsusceptibility；Now it is advocated to use rifampicinEthambutolUsed in combination with isoniazid.Mycobacterium ulcers onlyKanamycinetc.AminoglycosidesAntituberculous drugs are sensitive.But bird intracellular mycobacteriumDrug resistanceStrong;23 strains were reported to be resistant to the above drugs;New erythromycin through structural transformation, such asClarithromycinIt has good anti tuberculous activity in vivo and in vitro, can destroy cell wall and membrane structure, and can be used for blood culture of avian intracellular mycobacteriumClearance rate62% - 98%.
After treatment, nontuberculous mycobacteria often appear L-form, with increased drug resistance, and some do not recover after years of treatment.Moreover, L-type lymphocytes are not easily sensitized due to the lack of cell wall lipids,Tuberculin testIt may be negative, and more attention should be paid to it during diagnosis and treatment.[1]
Mycobacterium leprae
Mycobacterium leprae
Mycobacterium leprae（M.laprae）, commonly known as Leprosy bacilli, which causes leprosy, is a chronic infectious disease.It is widely popular.There are about 12 million cases worldwide, mainly in Asia, Africa and Latin America.Before the founding of the People's Republic of China, the epidemic was serious.[1]
The morphology and staining of Mycobacterium leprae are similar to that of Mycobacterium tuberculosis.Slender, slightly curved, often arranged in bundles.GramAnd acid fast staining were positive.After treatment, it can be short rod, granular or rosaryPolymorphism, which may be L-type variation.Without thorough cure, it can lead to recurrence.[1]
Mycobacterium leprae is a typical intracellular bacterium. A large number of Mycobacterium leprae can be seen in the smear of patient's exudate specimen.The cytoplasm of such cells is foamy, which is called leprosy cell.This is important to distinguish from Mycobacterium tuberculosis.[1]
It has long been believed that Mycobacterium leprae enters the human body mainly through damaged skin and mucosa.In recent years, it has been found that the early nasal mucosa secretion of untreated leprosy patients contains a large number of Mycobacterium leprae, so it is an important way to pass through the respiratory tract.Others such as phlegm, sweat, tears, milk, semen andVaginal dischargeMycobacterium leprae can be found in all cases, so it can also be transmitted by contact.Human resistance to Mycobacterium leprae is strong, mainly relying on cellular immunity.[1]
There is no specific prevention method for leprosy.Since Mycobacterium leprae and Mycobacterium tuberculosis have common antigens, BCG vaccine has been tried to prevent leprosy and achieved certain results.Special attention should be paid to the prevention and treatment of this diseaseClose contactsConduct regular inspection.Early detection and early treatment.The therapeutic drugs mainly include sulfone, rifampicin, chlorphenazine andPropylthioisoniazide。Use two or three kinds of drugs to preventDrug resistanceGenerate.[1]
