Characteristics of microbiomes of the saliva, duodenal bulb, and descending portion of superficial nonampullary duodenal epithelial tumors.

INTRODUCTION: Nonampullary duodenal epithelial tumors are rare, but their prevalence is increasing. Various gastrointestinal cancers have been associated with microbiomes. We evaluated the characteristics of the salivary and duodenal microbiomes of patients with nonampullary duodenal epithelial tumors. METHODS: Saliva and biopsy samples from the duodenal bulb and descending portion were obtained from 15 patients with nonampullary duodenal epithelial tumors and 10 controls. Next-generation sequencing was performed to identify bacteria for comparison. RESULTS: Saliva samples had higher Amplicon Sequence Variants (ASVs) and more observed species than duodenal samples. Saliva samples from patients with nonampullary duodenal epithelial tumor were dominated by Bacteroidetes and Prevotella, whereas Proteobacteria and Neisseria were dominant in the control samples. The relative abundance of bacteria was higher in patients with nonampullary duodenal epithelial tumors. Most bacteria were classified as bacteria of oral origin. Oribacterium and Stomatobaculum were significantly higher in the saliva, duodenal bulb, and descending portion of patients with nonampullary duodenal epithelial tumors. CONCLUSION: Patients with nonampullary duodenal epithelial tumors had different salivary and duodenal microbiomes than controls. Bacteria types differed between groups at each site, and most bacteria of oral origin were more abundant in patients with nonampullary duodenal epithelial tumors.

The Impact of KRAS Mutation in Patients With Sporadic Nonampullary Duodenal Epithelial Tumors.

INTRODUCTION: The genomic characterization of primary nonampullary duodenal adenocarcinoma indicates a genetic resemblance to gastric and colorectal cancers. However, a correlation between the clinical and molecular characteristics of these cancers has not been established. This study aimed to elucidate the clinicopathological features of sporadic nonampullary duodenal epithelial tumors, including their molecular characteristics and prognostic factors. METHODS: One hundred forty-eight patients with sporadic nonampullary duodenal epithelial tumors were examined in this study. Patient sex, age, TNM stage, tumor location, treatment methods, histology, KRAS mutation, BRAF mutation, Fusobacterium nucleatum, mucin phenotype, and programmed death-ligand 1 (PD-L1) status were evaluated. KRAS and BRAF mutations, Fusobacterium nucleatum, mucin phenotype, and PD-L1 status were analyzed by direct sequencing, quantitative polymerase chain reaction, and immunochemical staining. RESULTS: The median follow-up duration was 119.4 months. There were no deaths from duodenal adenoma (the primary disease). Kaplan-Meier analysis for duodenal adenocarcinoma showed a significant effect of TNM stage (P < 0.01). In univariate analysis of primary deaths from duodenal adenocarcinoma, TNM stage II or higher, undifferentiated, KRAS mutations, gastric phenotype, intestinal phenotype, and PD-L1 status were significant factors. In multivariate analysis, TNM stage II or higher (hazard ratio: 1.63 × 1010, 95% confidence interval: 18.66-6.69 × 1036) and KRAS mutation (hazard ratio: 3.49, confidence interval: 1.52-7.91) were significant factors. DISCUSSION: Only KRAS mutation was a significant prognostic factor in primary sporadic nonampullary duodenal adenocarcinoma in cases in which TNM stage was considered.

Molecular profiling and identification of prognostic factors in Chinese patients with small bowel adenocarcinoma.

Small bowel adenocarcinoma (SBA) is a rare malignancy with a poor prognosis and limited treatment options. Despite prior studies, molecular characterization of this disease is not well defined, and little is known regarding Chinese SBA patients. In this study, we conducted multigene next-generation sequencing and 16S ribosomal RNA gene sequencing on samples from 76 Chinese patients with surgically resected primary SBA. Compared with colorectal cancer and Western SBA cohorts, a distinctive genomic profile was revealed in Chinese SBA cohorts. According to the levels of clinical actionability to targetable alterations stratified by OncoKB system, 75% of patients harbored targetable alterations, of which ERBB2, BRCA1/2, and C-KIT mutations were the most common targets of highest-level actionable alterations. In DNA mismatch repair-proficient (pMMR) patients, significant associations between high tumor mutational burden and specific genetic alterations were identified. Moreover, KRAS mutations/TP53 wild-type/nondisruptive mutations (KRASmut /TP53wt/non-dis ) were independently associated with an inferior recurrence-free survival (hazard ratio [HR] = 4.21, 95% confidence interval [CI] = 1.94-9.14, P < .001). The bacterial profile revealed Proteobacteia, Actinobacteria, Firmicutes, Bacteroidetes, Fusobacteria, and Cyanobacteria were the most common phyla in SBA. Furthermore, patients were clustered into three subgroups based on the relative abundance of bacterial phyla, and the distributions of the subgroups were significantly associated with the risk of recurrence stratified by TP53 and KRAS mutations. In conclusion, these findings provided a comprehensive molecular basis for understanding SBA, which will be of great significance in improving the treatment strategies and clinical management of this population.

The association between cagL and cagA, vacAs-m, babA genes in patients with gastric cancer, duodenal ulcer, and non-ulcer dyspepsia related to Helicobacter pylori.

INTRODUCTION: As a component of the cag T4SS, the cagL gene is involved in the translocation of CagA into host cells and is essential for the formation of cag PAI-associated pili between H. pylori and gastric epithelial cells. AIM: We aimed to investigate the clinical association of the cagL gene with other virulence factors (VacA, CagA, EPIYA-C, and BabA protein) of H. pylori strains isolated from GC, duodenal ulcer (DU), and non-ulcer dyspepsia (NUD) cases. METHODS: The patient group (PG), including 47 patients (22 GC and 25 DU) and a 25 control group (CG= NUD) were included. Amplification of the H. pylori cagL, cagA, vacA, and babA2 genes and typing of EPIYA motifs were performed by PCR methods. RESULTS: Sixty-one (84.7%) H. pylori strains were detected with cagL (93.6% in SG, 68% in CG). We detected a significant difference between SG and CG for the presence of cagL (p=0.012) but no statistical comparison was done for (≥2) EPIYA-C repeats In the comparison of H. pylori strains with cagA/vacAs1m1 and cagA/ vacAs1m2 and babA2 for the presence of cagL, we could not detect a significant difference (p=1). CONCLUSION: We detected a significant difference between groups for the presence of cagL genotype (p=0.012). The vacAs1m1 (OR: 2.829), genotypes increased the GC and DU risk by 2.8 times, while multiple (≥2) EPIYA-C repeats incresed the GC and DU risk by 3.524 times. Gender (to be female) (OR: 0.454) decreased the GC and DU risk by inversly decreased in the multivariate analysis.

Benign and malignant gastroduodenal diseases associated with Helicobacter pylori: a narrative review and personal remarks in 2018.

The subject of Helicobacter pylori continues to elicit worldwide interest in many research fields. Epidemiological data suggest that the prevalence of the infection is decreasing in Western/developed countries and even in some developing regions, but this is masked by the high prevalence in the most populous regions. Chronic gastritis, caused invariably by the bacterium, was again classified in Kyoto and Helicobacter pylori-associated gastritis was included as a distinct entity. The prevalence of peptic ulcers is decreasing, but bleeding ulcers are a challenging problem, with stable mortality levels even in the endoscopic era. With the extended use of endoscopy, gastric polyps (GP) have become more prevalent: some are associated with the infection, some are not. Autoimmune and Helicobacter-induced gastritis can share common pathogenetic mechanisms. Gastric cancer (GC) is ranked highly on mortality lists worldwide. Its surgical treatment has registered some progress though. Little, if any improvement has been achieved in the medical treatment of advanced GC. With proper organization, GC seems a preventable disease. In spite of many guidelines, the Pan-European registry of Helicobacter pylori management shows that eradication rates obtained in many places are suboptimal. A new therapeutic regimen was compiled with promising pilot results. The results obtained with vonaprazan are limited to Asia. New avenues of both antibiotic and non-antibiotic treatments are expected to accelerate the eradication of this ulcerogenic and carcinogenic bacterium.

Helicobacter pylori VacA, acting through receptor protein tyrosine phosphatase α, is crucial for CagA phosphorylation in human duodenum carcinoma cell line AZ-521.

Helicobacter pylori, a major cause of gastroduodenal diseases, produces vacuolating cytotoxin (VacA) and cytotoxin-associated gene A (CagA), which seem to be involved in virulence. VacA exhibits pleiotropic actions in gastroduodenal disorders via its specific receptors. Recently, we found that VacA induced the phosphorylation of cellular Src kinase (Src) at Tyr418 in AZ-521 cells. Silencing of receptor protein tyrosine phosphatase (RPTP)α, a VacA receptor, reduced VacA-induced Src phosphorylation. Src is responsible for tyrosine phosphorylation of CagA at its Glu-Pro-Ile-Tyr-Ala (EPIYA) variant C (EPIYA-C) motif in Helicobacter pylori-infected gastric epithelial cells, resulting in binding of CagA to SHP-2 phosphatase. Challenging AZ-521 cells with wild-type H. pylori induced phosphorylation of CagA, but this did not occur when challenged with a vacA gene-disrupted mutant strain. CagA phosphorylation was observed in cells infected with a vacA gene-disrupted mutant strain after addition of purified VacA, suggesting that VacA is required for H. pylori-induced CagA phosphorylation. Following siRNA-mediated RPTPα knockdown in AZ-521 cells, infection with wild-type H. pylori and treatment with VacA did not induce CagA phosphorylation. Taken together, these results support our conclusion that VacA mediates CagA phosphorylation through RPTPα in AZ-521 cells. These data indicate the possibility that Src phosphorylation induced by VacA is mediated through RPTPα, resulting in activation of Src, leading to CagA phosphorylation at Tyr972 in AZ-521 cells.

Duodenal gastrinoma with multiple gastric neuroendocrine tumors secondary to chronic Helicobacter pylori gastritis.

Helicobacter pylori (HP) has been associated with neuroendocrine tumors of the stomach and duodenum. Gastric enterochromaffin-like (ECL) cell tumors and duodenal gastrinomas have also been associated with HP gastritis in separate series but have not been reported together. With other possible causes excluded, we present a patient with HP-associated atrophy of the oxyntic mucosa that ultimately resulted in stimulation and reactive hyperplasia of gastrin-producing cells in both the antrum and proximal duodenum, the latter progressing to formation of a gastrin-producing cell nodule (gastrinoma). Both of these sources of gastrin resulted in ECL hyperplasia in the atrophied oxyntic mucosa with progression to microcarcinoids and well-differentiated neuroendocrine tumors, along with hypertrophy of residual proximal gastric parietal cells. As atrophy tends to spread from the antrum proximally, residual oxyntic mucosa was still infected with HP and offers 1 explanation for the apparent paradox of atrophic gastritis with ECL hyperplasia and neoplasia in the distal oxyntic mucosa, with proximal oxyntic mucosa showing mild hypertrophic changes in a background of typical HP gastritis.

[Progress in application of near infrared reflectance spectroscopy to the study of ruminant nutrition].

The near infrared reflectance spectroscopy (NIRS) technique has been widely used in the study of ruminant nutrition with many of its operational merits such as facility, shortcut and accuracy, etc. Study suggested that the standard error of cross-validation (SECV) ranges from 1.6% to 2.8% in predicting organic matter digestion of ruminant diet by using the NIRS technique; the chemical and biological compositions and the microbial protein proportion in the duodenal digesta can be predicted accurately using the NIRS. However, the kinetic parameters of degradation are not well predicted; The prediction of intake of stall feeding animals by using NIRS is similar to the determination of in vivo method, but the standard error of prediction is about 14% when using the NIRS to predict intake of grazing animals. All of the studies suggest that big progress has been made in using NIRS technique to predict feed digestion and evaluate the diet quality and intake of ruminant animals, which also suggest that the NIRS technique has a wide prospect in the study of ruminant nutrition.

Serum antibodies positivity to 12 Helicobacter pylori virulence antigens in patients with benign or malignant gastroduodenal diseases--cross-sectional study.

AIM: To investigate the association of gastric histological and endoscopic findings in patients with Helicobacter pylori (H. pylori), according to presence of seropositivity to 12 bacterial virulence antigens. METHODS: This is a cross-sectional single-center study of 360 consecutive outpatients referred in the period of one year to upper gastrointestinal endoscopy because of dyspeptic complaints. Patients sera were tested by Western blot method to determine the presence of serum antibodies to bacterial virulence antigens--p120 (CagA--cytotoxin-associated antigen), p95 (VacA - vacuolating cytotoxin), p67 (FSH--flagellar sheath protein), p66 (UreB--urease enzyme heavy subunit), p57 (HSP homologue--heath shock protein homologue), p54 (flagellin), p33, p30 (OMP--outer membrane protein), p29 (UreA--urease enzyme light subunit), p26, p19, and p17. Upper gastrointestinal endoscopy was performed, endoscopic diagnosis recorded, and 4 mucosal biopsy samples were obtained and assessed according to Updated Sydney protocol. RESULTS: The sera of 207 patients were analyzed. Thirty patients had gastric adenocarcinoma, 126 peptic ulcers, and 51 normal finding. p120 (CagA) seropositivity was significantly more often present in patients with higher activity grade in the antrum (P = 0.025), p30 in patients with greater inflammation in the antrum (P = 0.025) and the corpus (P = 0.010), p33 in patients with greater inflammation in the corpus (P = 0.050), and p19 (OMP) in patients with lower intestinal metaplasia grades in the corpus (P = 0.025). Seroreactivity to all other bacterial proteins showed no association with the histological status of the stomach mucosa. Except for the seropositivity to protein p95 (VacA), which was more often present in patients with duodenal ulcer (P = 0.006), there was no difference in seroreactivity to other bacterial proteins and upper gastrointestinal endoscopic findings. CONCLUSIONS: p120 (CagA), p33, p30 (OMP), and p19 (OMP) seropositivity was more often present in patients with higher grades of the histological parameters of gastritis and seropositivity to protein p95 (VacA) with endoscopic presence of duodenal ulcer. Histological parameters of gastritis are more associated with bacterial virulence than endoscopic findings.

Gastric duodenal metaplasia in duodenal adenomas.

BACKGROUND: In cases of known aetiology, gastric duodenal metaplasia (GMD) is a reversible lesion. In cases of unknown aetiology, the fate of GMD remains elusive. GMD was recently found in a duodenal adenoma. AIM: To audit the frequency of GMD occurring in a cohort of duodenal adenomas. METHODS: Filed H&E-stained sections from 306 consecutive duodenal adenomas were investigated for the presence of GMD. RESULTS: 68% of the adenomas (n = 208) were from patients with familial adenomatous polyposis (FAP), and the remaining 32% (n = 98) were sporadic. GMD was found in 31.7% (66/208) of the duodenal FAP adenomas and in 59.2% (58/98) of the duodenal sporadic adenomas (p<0.05). The causes for this difference are elusive. CONCLUSIONS: As for other metaplasias of the gastrointestinal tract (intestinal metaplasia of the oesophagus and of the stomach, and metaplastic-hyperplastic polyposis of the colon, known to antedate neoplastic transformation), a subset of GMDs of unknown cause might be present in the duodenal mucosa before adenomatous changes ensue. That subset of GMD might have neoplastic proclivity similar to the metaplastic epithelium in other organs of the gastrointestinal tract. The known carcinogenic effect of high concentrations of bile acids and pancreatic juices bathing the duodenal mucosa carrying an irreversible subset of GDM might set aflame the adenomatous neoplastic transformation in these patients.

Detection of serum anti-Helicobacter pylori immunoglobulin G in patients with different digestive malignant tumors.

AIM: To investigate the seroprevalence of Helicobacter pylori infection in patients with different digestive malignant tumors. METHODS: Enzyme linked immunosorbent assay (ELISA) was used to detect serum anti-Helicobacter pylori IgG antibody in 374 patients with different digestive malignant tumors and 310 healthy subjects (normal control group). RESULTS: The seroprevalence of Helicobacter pylori infection was 61.50% (230/374) and 46.77% (145/310), respectively, in patients with digestive tumors and normal controls (P<0.05). The seroprevalence was 52.38% (33/63), 86.60% (84/97), 83.14% (84/101), 45.24 (19/42), 51.13% (18/35) and 44.44% (16/36), respectively in patients with carcinomas of esophagus, stomach, duodenum, rectum, colon and liver (P<0.01). In patients with intestinal and diffuse type gastric cancers, the seroprevalence was 93.75% (60/64) and 72.73% (24/33), respectively (P<0.05). In patients with gastric antral and cardiac cancers, the seroprevalence was 96.43% (54/56) and 73.17% (30/41), respectively (P<0.05). In patients with ulcerous and proliferous type duodenal cancers, the seroprevalence of H pylori infection was 91.04% (61/67) and 52.27% (23/44), respectively (P<0.05). In patients with duodenal bulb and descending cancers, the seroprevalence was 94.20% (65/69) and 45.20% (19/42), respectively (P<0.05). CONCLUSION: H pylori infection is associated with occurrence and development of gastric and duodenal carcinomas. Furthermore, it is also associated with histological type and locations of gastric and duodenal carcinomas.

Gastrite associada ao Heliocobacter pylori em adultos e crianças: estudo comparativo / Helicobacter pylori associated gastritis in adults and children: a comparative study

A reaçäo inflamatória da gastrite por H. pylori é pouco estudada em crianças. Objetivos: Analisar a reaçäo inflamatória e imune da gastrite por H. pylori em adultos e crianças, 15 com ulcera duodenal (UD) e 47 adultos, 21 com UD. A análise histológica foi feita, segundo o Sistema Sydney; o exsudato imune foi semi-quantificado; o microrganismo foi pesquisado por cultura, urease e histologia. Os genes ureA e cagA foram pesquisados por Elisa. Resultados: Em crianças, a reaçäo inflamatória predominou nos casos com UD em relaçäo àqueles sem UD (p<0,01). Nos dois grupos, a inflamaçäo predominou no antro (p<0,01), mas a atividade foi semelhante no antro e corpo. A resposta imune foi idêntica no antro e no corpo dos casos com UD. Nos adultos com UD, a inflamaçäo e a atividade foram mais intensas no antro do que no corpo (P<0,0007). A reaçäo imune predominou no antro (p<0,032) em ambos os grupos. Näo houve correlaçäo entre a colonizaçäo bacteriana e a reaçäo inflamatória e imune. Nos casos com UD, isolaram-se predominantemente cepas cagA+, em crianças (93 por cento) e adultos (83 por cento). A infecçäo por cepas cagA+ correlacionou-se com o exsudato plasmocitário (p<0,03) e com a inflamaçäo e a atividade (p<0,04) em crianças. Conclusäo: A resposta inflamatória na gastrite associada ao H. pylori é diferente em adultos e crianças. Conclusäo A resposta inflamatória na gastrite associada ao H. pylori é diferente em adultos e crianças. Conclusäo, o que pode estar relacionado com diferenças na secreçäo ácida e com aspectos evolutivos da infecçäo

[Molecular biology characteristics of Helicobacter pylori]. / A Helicobacter pylori molekuláris biológiai jellemzói.

Attention has been recently adverted to the Helicobacter pylori (H. pylori) by the fact, that its association with occurrence of gastroduodenal ulcer and gastric carcinoma had been justified. Our current understanding about metabolism and physiology of it is still not full, however, great strides have been made as for the methods of investigation during the last 16 years. Complete genome sequence of pathogenic strain of the bacteria have recently became identified, by which certain fundamental aspects of biology of H. pylori have been highlighted. Based on data, infection may presumably act as a cofactor to the development of peptic ulcer disease and carcinogenesis, however, details of pathomechanism are still unclear. Variability and genotype of bacteria, immune reactions and genetic patterns of host organism and mechanisms sustaining the balance of mucosal integrity may have additional influence. This study provides an overview on the current understanding about molecular biology of H. pylori.

Duodenal adenomas in Balb/-c mice monoinfected with Clostridium perfringens.

An outbreak of disease in multiparous females occurred in one isolator in a colony of Balb/-c germ-free mice. The affected isolator had been accidentally contaminated with Copyright Clostridium perfringens. Gross and histological examination of the diseased mice revealed lesions in the lungs, heart and intestinal tract. Lesions in the valvular endocardium and vascular walls were closely associated with bacterial colonies and septic thrombi containing Gram-positive rods. C perfringens type B was recovered in pure culture from the faeces, intestinal contents and atrial thrombi of the sick mice. Intestinal lesions varied, depending on the region of the intestine. The ileum showed shortened villi and ulceration of the mucosa. The duodenum of all the affected mice showed microscopic foci of polypoid adenomatous growth of the crypt epithelium. The significance of these unusual neoplastic lesions is discussed in the context of the growing evidence of an association between cell growth and bacterial cell products.

[Effect of Helicobacter pylori infection on the apoptotic and cell proliferative processes of the gastric mucosa]. / A Helicobacter pylori okozta fertp6és hatása a gyomornyálkahártya apoptotikus és sejtproliferációs folyamataira.

The role of the Helicobacter pylori in the induction of gastric carcinogenesis seems to be certain. The exact pathomechanism is not yet known, although the special genetic conditions both of the microbe and the host just as the imbalance of the apoptotic and proliferative processes caused by the chronic inflammation are assumed to be involved. The latter one can be proved by the use of different cell proliferative and apoptotic markers. The results are inconsistent whether the eradication therapy causes the regression of premalignant atrophic gastritis. The regression of the MALT-associated lymphoma after the eradication therapy seems to be more convincing. The need of the eradication to prevent gastric cancer can be judged by the follow-up of some biomarkers (e.g. HLA II genotype, PCNA index, anti HP-IgA titer and the serum pepsinogen level), although their diagnostical application could be hardly introduced in the everyday practise so far.

Resolution of a metaplastic duodenal polyp after cure of Helicobacter pylori infection.

Although there have been several reports of hyperplastic gastric polyps associated with persistent Helicobacter pylori gastritis, the association of H. pylori infection with metaplastic polyps in the duodenum has not hitherto been described. After a 52-year-old man had a single episode of hematemesis, endoscopy showed a smooth polyp 1 cm in greatest dimension formed by a proliferation of gastric epithelial cells of fundic and antral type found in the duodenal bulb. The outer surface was entirely covered with a single layer of hyperplastic columnar epithelium with many H. pylori organisms. After administration of metronidazole 500 mg, omeprazole 20 mg for 4 weeks, and clarithromycin 250 mg twice a day for 2 weeks, endoscopy showed a decrease in size of the duodenal polyp. At 12 weeks there was complete regression of the polyp. This report documents a new and unusual finding: resolution of a gastric metaplastic polyp in the duodenum associated with cure of H. pylori.

Aislamiento de Helicobacter pylori de pacientes con trastornos gastroduodenales en San Luis (Argentina) / Helicobacter pylori isolated from patients with gastrointestinal tract diseases in San Luis (Argentina)

Se investigó la presencia de Helicobacter pylori en 50 pacientes con trastornos gastroduodenales que concurrieron a dos centros de salud de la ciudad de San Luis. De cada paciente se tomaron cuatro muestras de biopsia de mucosa de antro gástrico, dos de ellas destinadas al estudio histológico y dos al análisis bacteriológico: observación al Gram, prueba de ureasa y cultivo. Helicobacter pylori se detectó en 38 (76 por ciento) de los pacientes mediante el estudio histológico y en 30 (60 por ciento) por la tinción de Gram. De estos últimos, 28 (93 por ciento) dieron positiva la prueba de ureasa coincidiendo con un número significativo de bacterias. El 80 por ciento (24/30) de las muestras positivas al Gram mostró un buen desarrollo microbiano en los medios de cultivo de Mueller-Hinton y de Skirrow indistintamente. Se recomienda la prueba de ureasa como una alternativa de diagnóstico: rápida, económica y efectiva cuando hay una cantidad suficiente de bacterias.

Aislamiento de Helicobacter pylori de pacientes con trastornos gastroduodenales en San Luis (Argentina) / Helicobacter pylori isolated from patients with gastrointestinal tract diseases in San Luis (Argentina)

Se investigó la presencia de Helicobacter pylori en 50 pacientes con trastornos gastroduodenales que concurrieron a dos centros de salud de la ciudad de San Luis. De cada paciente se tomaron cuatro muestras de biopsia de mucosa de antro gástrico, dos de ellas destinadas al estudio histológico y dos al análisis bacteriológico: observación al Gram, prueba de ureasa y cultivo. Helicobacter pylori se detectó en 38 (76 por ciento) de los pacientes mediante el estudio histológico y en 30 (60 por ciento) por la tinción de Gram. De estos últimos, 28 (93 por ciento) dieron positiva la prueba de ureasa coincidiendo con un número significativo de bacterias. El 80 por ciento (24/30) de las muestras positivas al Gram mostró un buen desarrollo microbiano en los medios de cultivo de Mueller-Hinton y de Skirrow indistintamente. Se recomienda la prueba de ureasa como una alternativa de diagnóstico: rápida, económica y efectiva cuando hay una cantidad suficiente de bacterias. (AU)