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1.
BACKGROUND: Both various virulence factors of Helicobacter pylori and host factors influence the clinical outcome of H. pylori infection. In animal experiments with Helicobacter felis, large variations in the severity of disease have been observed between different mouse strains infected with a single isolate of H. felis. C57BL/6 J mouse strain that lacks the expression of group IIA phospholipase A2 has been shown to develop more severe gastric inflammation than other mouse strains. Thus, group IIA phospholipase A2 has been suggested to play a role in regulating inflammation in gastric mucosa. The aim of this study was to examine the possible role of group IIA phospholipase A2 in experimental Helicobacter infection. MATERIALS AND METHODS: Transgenic mice expressing human group IIA phospholipase A2 and their group IIA phospholipase A2 deficient nontransgenic C57BL/6 J littermates were infected with H. felis. The mice were killed 3, 8, and 19 weeks after inoculation of bacteria to determine the histopathological changes in gastric mucosa. RESULTS: The infected mice developed chronic inflammation in gastric mucosa. We found no differences in the colonization of bacteria between transgenic and nontransgenic mice. At 3 and 8 weeks, no difference was found in the severity of inflammation between the two groups. Nineteen weeks after the administration of bacteria the inflammation was more marked in nontransgenic than transgenic mice. Group IIA phospholipase A2 was expressed by in situ hybridization in the neck cells of the glandular stomach in transgenic mice. CONCLUSIONS: The results of the present study suggest that the endogenous expression of group IIA phospholipase A2 diminishes chronic inflammation in gastric mucosa in experimental H. felis infection in mice.  相似文献   

2.
BACKGROUND: The development of a vaccine against Helicobacter pylori has become a priority to prevent major morbidity and mortality associated with this infection. Our goal was to prepare and evaluate a DNA vaccine based on the urease B gene (ureB). METHODS: The ureB gene of H. pylori was amplified and cloned into the eukaryotic expression vector pcDNA3.1/TOPO. Plasmid DNA was purified from transformed Escherichia coli cells and used to immunize mice by the intragastric, intramuscular, intrarectal (40 micro g each) and intranasal (16 micro g) route, three doses every 2 weeks, with CpG oligodeoxynucleotide (ODN) as adjuvant. Four weeks after the third dose, animals were orally challenged with Helicobacter felis and were sacrificed 6 weeks later. The stomach was stained to detect the presence of infection. RESULTS: Despite in vitro confirmation of successful cloning and functionality of the ureB gene with expression of a protein morphologically and antigenically identical to urease B, the DNA vaccine did not perform well in vivo. Immunization of mice produced a weak immune response. Overall, intrarectal and intranasal administration seemed more immunogenic than other routes. Protection against challenge was modest and nonsignificant, and slightly better on animals immunized by the intramuscular and intranasal route. CONCLUSION: A DNA vaccine based on H. pylori urease B was poorly immunogenic and nonprotective at the conditions evaluated. Higher doses, better adjuvants or a prime-boost approach may circumvent these limitations.  相似文献   

3.
BACKGROUND: We previously REPORTED that mice with diabetes and short-term Helicobacter felis infection had an increase in glycated hemoglobin (HbA1c). Here we report the effect of long-term infection. MATERIALS AND METHODS: Six-week-old C57BL/6 mice were injected with streptozotocin to induce diabetes and started on daily insulin. Following streptozotocin injection, animals were paired according to their HbA1c values and randomized to orally receive either H. felis or culture medium alone. Weight and HbA1c were monitored monthly for 6 months. RESULTS: Thirty animals corresponding to 15 pairs were included in the study. H. felis-infected diabetic mice developed significantly more gastritis than uninfected animals. Sixteen mice died during the observation period. As compared to uninfected animals, infected mice died more frequently (40% versus 67%, p = .14) and earlier (160 versus 61 days, p = .20); both variables combined showed that H. felis infection significantly decreased the chances of survival during the study period (p = .045). In addition, infected mice showed a trend for higher increase in their HbA1c (0.97 +/- 2.5% versus - 0.22 +/- 3.0%; p = .21) and lower weight gain (2.0 +/- 3.4 g versus 2.9 +/- 2.0 g; p = .15) than uninfected mice. CONCLUSION: Long-term H. felis infection had a deleterious effect in mice with streptozotocin-induced diabetes resulting in increased mortality. If the same phenomenon occurs in humans this could lead to interventions to improve the long-term outcome of patients with diabetes.  相似文献   

4.
BACKGROUND: The role of Helicobacter pylori infection in iron deficiency during pregnancy is limited. The aim of the present study was to assess the relationship between Helicobacter infection and levels of iron stores in pregnant mice. MATERIALS AND METHODS: Female C57BL/6 mice were either inoculated with 10(8) H. pylori, Helicobacter felis or water. In the nonpregnant study, 15 mice from each group were sacrificed after 4 and 20 weeks of infection. In the pregnancy study, after 6 weeks of infection all female mice were mated and approximately 2 weeks after mating, half of the pregnant mice (n = 9/group) from each group were sacrificed. The remaining mice were allowed to give birth, and approximately 4 weeks after birth, mice were asphyxiated with CO2, followed by heart puncture, and killed by cervical dislocation. Serum ferritin and iron were determined with a micro-particle enzyme immunoassay method and by a timed-endpoint method. RESULTS: Serum iron levels in mice infected with H. felis were significantly (p < .05) lowered compared to control (24%) and H. pylori (27%)-infected mice at 4 weeks of infection. Serum iron in the control, H. pylori and H. felis groups were significantly (p < .05) elevated at 20 weeks by 39, 26 and 77%, respectively, compared to 4 weeks of infection. H. felis-infected mice had a significantly (p < .05) decreased serum ferritin level during pregnancy (61%) compared to H. pylori-infected mice. CONCLUSION: These results suggest that H. felis but not H. pylori infection causes an acute iron deficiency in normal and pregnant mice.  相似文献   

5.
目的研究不同浓度抗坏血酸(ascorbic acid)溶液对幽门螺杆菌(Helicobacter pylori,H.pylori)相关萎缩性胃炎小鼠模型的作用。方法将C57BL/6小鼠随机分为5组,每组10只。组1为空白对照组,余4组小鼠用幽门螺杆菌悉尼菌株(Helicobacter pylori-Sydney strain 1,H.pylori-SS1)感染2周,快速尿素酶法和免疫组织化学法检测H.pylori-SS1的定植;组3、组4和组5小鼠分别给予抗坏血酸低倍剂量(0.1 g/L)、中倍剂量(0.5 g/L)和高倍剂量(1.0 g/L)灌胃22周。灌胃结束后,处死所有小鼠取胃组织和血清,H&E染色观察组织学变化,ELISA检测血清胃泌素(gastrin)和白介素8(IL-8)水平。结果与H.pylori组相比,抗坏血酸干预组胃组织萎缩程度减轻、血清胃泌素水平升高、炎症因子水平降低(组2 vs组3:F=21.730,P=0.029;组2 vs组3:F=42.781,P=0.015;组2 vs组3:F=35.720,P=0.021),中倍剂量组较低倍剂量组有更显著的作用(组3 vs组4:F=21.730,P=0.041;组3 vs组4:F=42.781,P=0.034;组3 vs组4:F=35.720,P=0.043),但高倍剂量组与中倍剂量组差异无统计学意义(组4 vs组5:F=21.730,P=0.125;组4 vs组5:F=42.781,P=0.391;组4 vs组5:F=35.720,P=0.450)。结论抗坏血酸干预可减轻小鼠H.pylori相关萎缩性胃炎症状,高剂量抗坏血酸与中低剂量比无显著差异。  相似文献   

6.
Background. In murine Helicobacter infection it has been demonstrated that the degree of gastric mucosal inflammation is determined by mouse strain. This is a valuable tool for investigating genetic, immunological or bacterial determinants for the outcome of human Helicobacter infection. This study aims to devise a robust method to facilitate these investigations. Materials and Methods. C57BL/6, BALB/c and (C57BL/6 × BALB/c) F1 mice were given 108H. felis by gavage on days 1, 3 and 5 of the experiment Sections of the lesser and greater curve of stomach were examined at 12 weeks to assess active gastritis using a semi‐quantitative and a quantitative method by counting neutrophils in glands in four zones of the mucosa. Results. Semi‐quantitative scoring for active inflammation, based on the Sydney System, was inadequate with little discrimination between strains. Quantifying the level of active inflammation, counting the number of neutrophils in inflamed gastric glands and taking the total number of neutrophils in three inflamed pits within each zone (cardia, body, transitional zone and antrum) showed clear differences between the two parental strains for the degree of active gastritis and furthermore, using this system the phenotype of the (C57BL/6 × BALB/c) F1 was found to be between the two parental extremes. Conclusions. This novel method provides a numerical value for active inflammation in the stomach that is accurate, reproducible and discriminatory.  相似文献   

7.
To determine whether a protective immune response could be elicited by oral delivery of a recombinant live bacterial vaccine, Helicobacter pylori urease subunit B (UreB) was expressed for extracellular expression in food-grade bacterium Lactococcus lactis . The UreB-producing strains were then administered orally to mice, and the immune response to UreB was examined. Orally vaccinated mice produced a significant UreB-specific serum immunoglobulin G (IgG) response. Specific anti-UreB IgA responses could be detected in the feces of mice immunized with the secreting lactococcal strain. Mice vaccinated orally were significantly protected against gastric Helicobacter infection following a challenge with H. pylori strain SS1. In conclusion, mucosal vaccination with L. lactis expressing UreB produced serum IgG and UreB-specific fecal IgA, and prevented gastric infection with H. pylori .  相似文献   

8.
Helicobacter pylori is a human pathogen, whereas the natural hosts for 'Gastrospirillum hominis' and Helicobacter felis are animals. 'G. hominis' is occasionally found to cause infection in humans, whereas H. felis only rarely infects humans. The pathogenesis of H. pylori infection is not completely understood and in order to reveal differences in immune response to the three Helicobacter species, the upregulation of adherence molecule CD11b/CD18, chemotactic activity and oxidative burst response of neutrophils after stimulation with H. pylori, 'G. hominis' and H. felis sonicates, were compared. Like H. pylori, 'G. hominis' and H. felis induced upregulation of CD11b/CD18 and chemotaxis of neutrophils. 'G. hominis' demonstrated a more pronounced upregulation of CD11b/CD18, whereas H. felis was the strongest stimulant of neutrophil chemotaxis. H. felis was unable to stimulate neutrophils to oxidative burst response, whereas 'G. hominis' activated neutrophils in a dose-dependent way similar to H. pylori. 'G. hominis' and H. felis were both able to prime neutrophils for oxidative burst response similar to H. pylori. In conclusion, we observed clear differences in neutrophil responses to different Helicobacter species, which indicates that bacterial virulence factors may be important for the diversity in the pathogenetic outcome of Helicobacter infections.  相似文献   

9.
Background. The ammonia‐monochloramine system plays an important role in Helicobacter pylori‐associated gastric mucosal injury. Polaprezinc, a new antiulcer agent, has a scavenging action against monochloramine. The aim of the experiment was to investigate the inhibitory effects of polaprezinc on the H. pylori‐induced gastritis in Mongolian gerbils. Materials and Methods. Mongolian gerbils fasting for 24 hours were orally given culture broth containing 2–4 × 108 colony‐forming units of H. pylori ATCC 43054 per milliliter. From 4 hours after inoculation until the end of the experiment, gerbils were given chow pellets with or without 0.02% polaprezinc. All gerbils were killed 12 weeks later. The grades of H. pylori density and histologic features of gastritis were evaluated in accordance with the Updated Sydney System. The scavenging effect of polaprezinc on monochloramine was investigated spectrophotometrically. Results. Polaprezinc had little or no influence on the H. pylori density in both pyloric and fundic mucosae. However, it significantly attenuated the development of polymorphonuclear neutrophil activity, mononuclear infiltration, and surface epithelial erosion in both pyloric and fundic mucosae compared with those of the control group. H. pylori inoculation significantly increased the heights of both pyloric and fundic mucosae (mainly due to the increased height of foveolar hyperplasia), but polaprezinc inhibited the increase of mucosal thickness in both pyloric and fundic mucasae. No intestinal metaplasia was detected in this study. Spectrophotometric examination revealed that polaprezinc scavenged monochloramine. Conclusions. Polaprezinc inhibited the development of H. pylori‐induced gastritis through its scavenging action against monochloramine.  相似文献   

10.
Background. Helicobacter pylori gastritis induces reversible lowering of Ascorbic Acid (AA) intragastric concentrations. No studies have been aimed at determining the gastric juice AA concentration of atrophic body gastritis (ABG) patients. Uric Acid (UA), is another potent hydro‐soluble scavenger of ROS and its possible modification in the gastric juice of patients with H. pylori gastritis have never been investigated. This study was aimed at investigating the levels of AA and UA in the plasma and gastric juice of ABG patients, compared with H. pylori positive patients without corporal atrophy, and with healthy individuals. Materials and Methods. Thirteen ABG patients (Group 1): 32 Chronic non‐atrophic H. pylori gastritis patients (Group 2); and 13 healthy stomach controls (Group 3) attending gastroscopy with gastric biopsies (antrum = 3, corpus = 3) had plasma and intragastric levels of AA and UA measured. Results. Intragastric AA concentration was significantly lower in group 1 (median 0.21 µg/ml, range 0.1–24) compared both with groups 2 (median 5.5 µg/ml, range 0.1–33.2) (p = 0.043) and 3 (median 14.9 µg/ml, range 0.34–44.8) (p = 0.0028). Intragastric UA was not different between the three groups. Intragastric AA concentration resulted negatively correlated with the intragastric pH (Spearman r = ?0.47, p = 0.0003). In patients with gastritis (groups 1 and 2) there was a significant negative correlation between the sum of the Sydney Score variables in the body mucosa, and AA in the gastric juice (Spearman r = ?0.55; p = 0.0001). Conclusion. The study shows that intragastric pH is the key factor for the depletion of gastric juice AA observed in patients with corporal atrophy and to a lower extent with nonatrophic H. pylori gastritis.  相似文献   

11.
目的研究牙斑幽门螺杆菌与慢性胃炎之间的关系。方法对胃炎组、胃炎治疗组分别进行牙斑和胃黏膜幽门螺杆菌培养和比较。结果牙斑细菌培养:胃炎组阳性14例,阳性率为12.8%;治疗组阳性11例,阳性率为10.1%。胃黏膜细菌培养:胃炎组阳性47例,阳性率为43.1%;治疗组阳性19例,阳性率为17.4%。治疗前后比较牙斑标本差异无显著性(P〉0.05),胃黏膜标本差异有非常显著性(P〈0.001)。结论牙斑中确实存在着幽门螺杆菌,而且是胃内反复感染的源泉,以致慢性胃病反复发作,难以治愈。  相似文献   

12.
It has previously been shown that matrix metalloproteinase-9 (MMP-9) levels, originating from macrophages, are considerably increased in human Helicobacter pylori-associated gastritis. Here, the early kinetics of the MMP-9 response resulting from Helicobacter infection in C57BL/6 and MMP-9 knock-out mice using the murine Helicobacter felis model were examined. H. felis infection induced severe gastritis in the murine stomach at just 2 weeks after infection. Before gastritis, an increase was observed in MMP-9-positive cells detected by immunohistochemistry in the basal lamina propria. This finding was corroborated by gelatin zymography of stomach samples. As the gastritis increased so did the concentration of MMP-9 and the incidence of gastric MMP-9-positive cells, their location corresponding to that of macrophages. In contrast, systemic levels of MMP-9 remained unchanged. When MMP-9-deficient mice were infected with H. felis, no significant difference in gastritis development was detected compared with disease development in wild-type animals. We conclude that MMP-9 production is an early event in the response to gastric Helicobacter infection, a feature that may favor the recruitment of immune cells early during infection. At later stages, however, the increased levels of MMP-9 may damage the integrity of the stomach mucosa.  相似文献   

13.
14.
Helicobacter pylori is an important pathogen in gastroduodenal inflammation and ulceration. Several mechanisms have been proposed to explain its role. We studied the cytokine production patterns in situ in gastric mucosal biopsies from H. pylori-positive and H. pylori-negative patients with dyspepsia. Immunohistochemistry with monoclonal antibodies was used. The study showed enhanced expression of interleukin (IL) -8, IL-10 and interferon-gamma (IFN-gamma) in H. pylori infection and a significant association was found between these cytokines and the following parameters: bacteria load, chronic inflammation and activity. These parameters were significantly correlated with the cell markers CD19 and CD56. The study indicates a dual effect of H. pylori on the Th1 response, i.e. a stimulation of the response verified by increased IFN-gamma and a feed-back verified by an increase of the counterinflammatory IL-10, which may dampen the inflammatory and cytotoxic effect of the Th1 response. Furthermore, the study confirms the connection between increase of IL-8 and inflammatory activity in gastric mucosa in H. pylori infection.  相似文献   

15.
目的对慢性胃炎患者胃黏膜菌群进行定位及定量分析,探究其与胃炎及幽门螺杆菌(Helicobacter pylori,H.pylori)感染的相关性。方法收集58例慢性胃炎患者胃黏膜标本,提取胃黏膜菌群DNA,行荧光定量PCR定量胃黏膜总细菌及H.pylori,并进行相关性分析;另收集12例慢性胃炎患者胃黏膜标本石蜡包埋切片行荧光原位杂交定位胃黏膜菌群;慢性胃炎、肠化生程度的分类依据新悉尼分类系统。结果慢性胃炎患者胃黏膜细菌主要分布于胃黏膜表面、胃小凹及腺体中,细菌单个散在分布或聚集成团。多元线性回归分析显示胃黏膜总细菌数与性别、年龄、肠化生程度无关,与H.pylori感染、慢性胃炎程度有关(P0.05)。H.pylori阳性组胃黏膜总细菌数与H.pylori细菌数目呈明显正相关(r=0.536,P0.01)。不同胃炎程度之间胃黏膜总细菌数差异有统计学意义(P0.05),其中重度胃炎组胃黏膜总细菌数明显高于轻、中度胃炎组(P0.05、0.01)。不同肠化生程度之间胃黏膜总细菌数差异无统计学意义(P0.05)。H.pylori阳性组胃黏膜总细菌数明显高于阴性组(P0.01)。结论慢性胃炎患者胃黏膜菌群主要分布于胃黏膜表面、胃小凹及腺体中,细菌单个散在分布或聚集成团。胃黏膜菌群与慢性胃炎程度、H.pylori感染有关,与性别、年龄、肠化生程度无关,提示胃黏膜菌群的改变参与慢性胃炎的发展,H.pylori感染可改变胃黏膜菌群。  相似文献   

16.
229例慢性胃炎患者幽门螺杆菌培养及耐药情况   总被引:2,自引:0,他引:2  
目的了解慢性胃炎患者H.pylori感染及其耐药情况,为临床治疗提供参考。方法慢性胃炎患者胃镜活检标本培养分离H.pylori,对分离的H.pylori采用纸片扩散法进行耐药性检测。结果229例患者分离出97株H.pylori;H.pylori分离阳性率为42.36%(97/229),其中男性分离率为43.79%(67/153),女性分离率为39.47(30/76);92株H.pylori对抗生素的耐药性分别为:甲硝唑8.7%,克拉霉素7.6%,阿莫西林1.1%、呋喃唑酮1.1%,阿奇霉素4.4%,左氧氟沙星0%。结论慢性胃炎患者H.pylori感染率较高,但与性别、年龄无关;慢性胃炎H.pylori对常用抗生素敏感,建议采用左氧氟沙星、阿莫西林、呋喃唑酮进行治疗。  相似文献   

17.
BACKGROUND: Infection by Helicobacter pylori has been linked to monoclonal gammopathy of undetermined significance (MGUS). MGUS is thought to develop due to chronic antigenic stimulation in people with a specific genetic predisposition. METHODS AND RESULTS: We describe a patient presenting with dyspepsia associated with H. pylori-related erosive gastritis. Histopathologic findings revealed infiltration with plasma cells containing accumulated condensed intercisternal immunoglobulins, the so-called 'Russell bodies'. In addition, MGUS was present with total immunoglobulins within the normal range but a significantly decreased serum concentration of IgG subtype 3. Molecular analyses demonstrated IgH formation, T-cell receptor gamma rearrangement, and alterations within the IgHG3 gene sequence. Following H. pylori eradication, gastritis and dyspepsia gradually resolved but MGUS persisted for at least 22 months. CONCLUSIONS: This is the first report to demonstrate that upon infection with H. pylori, an impaired secretory capacity of plasma cells due to specific molecular changes can present as Russell body gastritis. The molecular findings question a pathogenetic link between Russell bodies and H. pylori, but suggest genetic alterations in the immunoglobulin locus as the possible cause for both MGUS and Russell body gastritis.  相似文献   

18.
AIM: The persistence of chronic inflammation in gastric mucosa and elevated Helicobacter pylori antibodies after successful eradication therapy are common findings in clinical practice. We studied their possible association with each other and disappearance in long-term follow up, as well as their possible connection with gastric atrophy. PATIENTS AND METHODS: The study population consisted of 108 dyspeptic patients with successful eradication therapy median 6.4 years earlier. The patients underwent gastroscopy, and biopsies from antrum and corpus were evaluated by an experienced pathologist. Serum samples collected from 77 patients were studied for H. pylori antibodies, parietal cell antibodies, as well as for pepsinogen I, pepsinogen II, and gastrin-17 levels. RESULTS: The prevalence of chronic gastric inflammation and elevated H. pylori antibodies after successful eradication therapy decreased by time, but still after 5 years, 17 of 51 (33%) subjects had elevated H. pylori antibodies and 14 of 68 (21%) had a mild inactive chronic inflammation in gastric mucosa. In patients with and without chronic inflammation in gastric mucosa, elevated H. pylori antibodies were detected in three of 10 (30%) and 14 of 41 (34%), elevated parietal cell antibodies in one of 10 (10%) and six of 41 (15%), low pepsinogen I in one of 10 (10%) and none of 41, and elevated gastrin-17 in three of 10 (30%) and six of 41 (15%), respectively. CONCLUSION: More than 5 years after successful H. pylori eradication therapy, mild persistent chronic inflammation may occur in gastric mucosa in up to one-fifth and elevated H. pylori antibodies even in one-third of patients, although these two are independent phenomena.  相似文献   

19.
Background: Helicobacter pylori (H. pylori) is a major cause of chronic gastritis. Statins have several pleotropic effects and their mechanisms of action could be related to anti‐inflammatory, antioxidants, and immunomodulatory effects. Aim: To determine whether statin therapy affects the severity of chronic gastritis. Materials and Methods: In a retrospective study, we evaluated 516 patients who underwent upper endoscopy. One‐hundred and ninety‐eight patients had chronic gastritis, The 198 patients with chronic gastritis were divided into two groups: group 1 comprised patients with a history of statin therapy and group 2 comprised patients with no history of statin therapy. Both groups were compared for age, gender, body mass index (BMI), underlying diseases, drug therapy, alcohol consumption, smoking and the serum levels of C‐reactive protein (CRP). The presence of H. pylori was determined by gastric biopsy and rapid urease test. The grade and severity of gastritis were assessed using the updated Sydney classification system in two gastric biopsy specimens that were taken from each participant in each group. Results: Of the 198 patients with chronic gastritis, 49% of the patients had mild gastritis and 51% had moderate to severe gastritis. From the results of a multiple logistic regression analysis after adjusting for confounding variables that included age, gender, and BMI, we found that elevated serum CRP levels (odds ratio (OR) 2.33; 95% confidence interval (CI) = 0.8–2.6, p = .02), H. pylori (OR 1.99; CI 0.14–2.4, p = .04), and the use of statin (OR 1.64; CI = 0.71–1.77, p = .05) independently predict the severity of chronic gastritis. Conclusion: Long‐standing statin therapy may reduce the severity of chronic gastritis. Mild increased CRP levels in absence of obvious source can predict the severity of chronic gastritis. Further researches are needed to assess the effect of statin in chronic gastritis.  相似文献   

20.
Abstract Immunocompetent and immunodeficient BALB/cA mice were fed orally with 108 colony forming units of 2-day-old spiral or coccoid (12 days old) Helicobacter pylori strain NCTC 11637. Immunocompetent BALB/cA mice were also fed orally with decreasing numbers of spiral or coccoid forms of H. pylori . The gastrointestinal colonisation process was monitored for 34 days post-infection by heparin magnetic separation and subsequent enzyme immunoassay (EIA) for the detection of the H. pylori cells. Both mice types were colonised with H. pylori . The coccoid form of H. pylori gave higher EIA absorbance values and more efficient colonisation in the mice than the spiral form. Immunocompetent BALB/cA mice fed with the coccoid form of H. pylori exhibited an acute inflammation process in histopathological samples from the stomachs. In conclusion, H. pylori can infect both immunocompetent as well as immunodeficient BALB/cA mice and coccoids (viable but non-culturable) obtained after 12 days of culturing can infect BALB/cA mice.  相似文献   

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