Michael S. Osato

Baylor College of Medicine, Houston, Texas, United States

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Publications (128)1181.84 Total impact

  • Rita Reddy · Rebecca L Penland · Michael S Osato · David Y Graham ·

    Helicobacter 06/2011; 16(3):252-3. DOI:10.1111/j.1523-5378.2011.00836.x · 4.11 Impact Factor
  • Jan P.G. Bergmanson · Eva Wang · Anisa I Gire · Michael S Osato ·
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    ABSTRACT: The environment preferred by Acanthamoeba trophozoites and the mechanism by which the amebae enters the cornea are not yet fully understood. A better understanding of the pathogenesis of this disease may help with prevention and treatment. To define the preferred environments for Acanthamoeba survival and proliferation in vitro by examining the effect of tonicity, nutrient concentration, and free chlorine content on Acanthamoeba. Human corneal isolates of Acanthamoeba castellanii and Acanthamoeba polyphaga trophozoites were cultured at 22°C (room temperature) in PYG (peptone-yeast extract-glucose) medium. The effect of tonicity on amebae was determined by incubating trophozoites in sodium chloride solutions in concentrations ranging from 0% to 10% for 19 days. Two different sets of media were prepared-one with and the other without added nutrients. The tonicity varied from 50 to 3438 mOsm/L while the pH was maintained at 6.7-6.8. Aliquots were recovered to determine the number and morphologic type of the amebae. To test the effect of chlorine, Acanthamoeba trophozoites were incubated for 7 days in buffered solutions with free chlorine concentrations varying from 0 to 5 mg/L free chlorine at 22°C. The pH was maintained at 7.2 and the tonicity varied from 88 to 92 mOsm/L. Trophozoites were enumerated by hemocytometer. Low tonicity solutions (<300 mOsm/L) favored the trophozoite stage, but elevating tonicity encouraged encystment. Only 3.3-3.9% of the trophozoites remained in 10% NaCl, while 46-58% of the trophozoites were present in distilled water. Increasing osmolality yielded a smaller number of Acanthamoeba with a greater proportion of cysts. Nutrients improved the replication rate at lower concentrations, increased the number of trophozoites and reduced the percentage of cysts. Chlorine completely inhibited both species of Acanthamoeba at free chlorine levels of 5mg/L, while lesser concentrations were less inhibitory. Acanthamoeba prefer hypotonic environments. Nutrients merely slowed the conversion of trophozoites to cysts at higher tonicity levels. Chlorine concentrations less than 5 mg/L, ocular irritation level, did not effectively convert trophozoites into cysts. We conclude that contact lens patients should avoid hypotonic ocular exposures, especially tap water and stagnant media such as lake water, and water from poorly maintained swimming pools and hot-tubs.
    Contact lens & anterior eye: the journal of the British Contact Lens Association 04/2011; 34(4):164-8. DOI:10.1016/j.clae.2011.02.003 · 1.37 Impact Factor
  • Francisco C Ramirez · Michael S Osato · David Y Graham · Karen L Woods ·
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    ABSTRACT: Bacteremia and sepsis are serious complications of endoscopic retrograde cholangiopancreatography (ERCP) and occur in between 0.5 and 3% of cases. Patients with obstructed bile ducts are at highest risk of developing septic complications. The purpose of this investigation was to determine whether the addition of gentamicin to the ERCP contrast medium prevents or reduces the growth of Pseudomonas aeruginosa in vitro. Artificial bile ducts were fashioned out of dialysis tubing and suspended in flasks containing brain heart infusion (BHI) broth. The tubing contained BHI broth alone, with or without contrast medium or with contrast medium plus gentamicin. The artificial ducts were inoculated with gentamicin-sensitive or gentamicin-resistant P. aeruginosa and quantitative cultures were performed. The contrast medium alone was bacteriostatic to both sensitive and resistant P. aeruginosa isolates. The addition of gentamicin to the contrast medium eliminated the sensitive strain after 2 h and resulted in a reduction in the number of gentamicin-resistant P. aeruginosa after 4 h. Incubation of the resistant isolate in the presence of contrast and gentamicin for an additional 4 h led to a further reduction in viable bacteria but did not completely eliminate the organisms. These results support the use of gentamicin in the contrast medium injected into the biliary system as an ancillary method to prevent post-ERCP sepsis.
    Journal of Digestive Diseases 08/2010; 11(4):237-43. DOI:10.1111/j.1751-2980.2010.00444.x · 1.96 Impact Factor
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    ABSTRACT: The acute antibody and T-cell immune response to Helicobacter pylori infection in humans has not been studied systematically. Serum from H. pylori-naive volunteers challenged with H. pylori and cured after 4 or 12 weeks was tested by enzyme-linked immunosorbent assays for anti-H. pylori-specific immunoglobulin M (IgM) and IgA established using bacterial lysates from homologous (the infecting strain) and heterologous H. pylori. Proteins recognized by IgM antibody were identified by mass spectrometry of immunoreactive bands separated by two-dimensional gel electrophoresis. Mucosal T-cell subsets (CD4, CD8, CD3, and CD30 cells) were assessed by immunohistochemistry. All 18 infected volunteers developed H. pylori-specific IgM responses to both homologous or heterologous H. pylori antigens. H. pylori antigens reacted with IgM antibody at 4 weeks postinfection. IgM Western blotting showed immunoreactivity of postinfection serum samples to multiple H. pylori proteins with molecular weights ranging between 9,000 (9K) to 150K with homologous strains but only a 70K band using heterologous antigens. Two-dimensional electrophoresis demonstrated that production of H. pylori-specific IgM antibodies was elicited by H. pylori flagellins A and B, urease B, ABC transporter binding protein, heat shock protein 70 (DnaK), and alkyl hydroperoxide reductase. Mucosal CD3, CD4, and CD8 T-cell numbers increased following infection. IgM antibody responses were detected to a range of homologous H. pylori antigens 2 to 4 weeks postchallenge. The majority of H. pylori proteins were those involved in motility and colonization and may represent targets for vaccine development.
    Infection and Immunity 06/2005; 73(5):2999-3006. DOI:10.1128/IAI.73.5.2999-3006.2005 · 3.73 Impact Factor
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    ABSTRACT: The aim of this study was to evaluate the effectiveness of the Calijing disinfection kit (an endoscope disinfection method used in Chinese hospitals) in eradicating Helicobacter pylori and assess whether use of the kit in 1994 during endoscopies in the Shandong Intervention Trial (SIT), Shandong, China, could have resulted in iatrogenic transmission of H pylori . Bacterial culture studies at the Veterans Affairs Medical Center, Houston, Texas, using endoscopes and forceps from 49 H pylori -positive patients were performed on contaminated endoscopes before and after disinfection with the Calijing kit. At least 1 endoscope culture site was H pylori positive in 39 of 49 (79.6%) specimens predisinfection, whereas H pylori was not isolated from any endoscopic culture site postdisinfection. Non- H pylori bacteria and fungi were recovered from 22.6% of the postdisinfection cultures. Although no viable H pylori were recovered following the disinfection procedures, levels of H pylori below the detection threshold of the bacteriologic assay may have contributed to an increase in H pylori seroprevalence noted in the SIT. In addition, the kit was unable to provide disinfection against non- H pylori organisms, suggesting the need to adhere to internationally accepted disinfection procedures for endoscope reprocessing.
    American Journal of Infection Control 06/2005; 33(4):197-201. DOI:10.1016/j.ajic.2004.11.002 · 2.21 Impact Factor
  • M. S. Osato · D. Y. Graham ·

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    ABSTRACT: A reliable challenge model is needed to evaluate Helicobacter pylori vaccine candidates. A cag pathogenicity island negative, OipA positive, multiple antibiotic susceptible strain of H pylori obtained from an individual with mild gastritis (Baylor strain 100) was used to challenge volunteers. Volunteers received 40 mg of famotidine at bedtime and 10(4)-10(10) cfu of H pylori in beef broth the next morning. Infection was confirmed by (13)C urea breath test ((13)C-UBT), culture, and histology. Eradication therapy was given four or 12 weeks post challenge and eradication was confirmed by at least two separate UBTs, as well as culture and histology. Twenty subjects (nine women and 11 men; aged 23-33 years) received a H pylori challenge. Eighteen (90%) became infected. Mild to moderate dyspeptic symptoms occurred, peaked between days 9 and 12, and resolved. Vomitus from one subject contained >10(3) viable/ml H pylori. By two weeks post challenge gastric histology showed typical chronic H pylori gastritis with intense acute and chronic inflammation. The density of H pylori (as assessed by cfu/biopsy) was similarly independent of the challenge dose. A minimal infectious dose was not found. Gastric mucosal interleukin 8 levels increased more than 20-fold by two weeks after the challenge. Challenge reliably resulted in H pylori infection. Infection was associated with typical H pylori gastritis with intense polymorphonuclear cell infiltration and interleukin 8 induction in gastric mucosa, despite absence of the cag pathogenicity island. Experimental H pylori infection is one of the viable approaches to evaluate vaccine candidates.
    Gut 10/2004; 53(9):1235-43. DOI:10.1136/gut.2003.037499 · 14.66 Impact Factor
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    ABSTRACT: Quadruple therapy provided inadequate eradication rate when given twice-a-day at breakfast and evening meals. To test twice daily (mid-day and evening) quadruple therapy for Helicobacter pylori eradication. This was a single-centre pilot study in which H. pylori-infected (positive histology and culture and RUT) patients were given 2 x 250 mg of metronidazole and 2 x 250 mg of tetracycline, two Pepto-Bismol tablets, plus one 20 mg rabeprazole tablet twice-a-day for 14 days. H. pylori status was confirmed 4 or more weeks after the end of therapy. Thirty-seven patients including 3 with peptic ulcer disease, 19 asymptomatic infected, 4 GERD, and 11 with NUD. Mid-day quadruple therapy was successful in 92.3% (95% CI: 79-98%) including 96.2% of those with metronidazole-susceptible strains, and in 83.3% (10/12) of those with metronidazole-resistant H. pylori. Compliance was 100% by pill count except in one individual who stopped medication after 12 days because of side-effects and who failed therapy. Moderate or greater side-effects were experienced by five patients. Twice-a-day, mid-day, quadruple therapy proved effective using the combination of bismuth subsalicylate and rabeprazole instead of bismuth subcitrate and omeprazole. Detailed studies of different formulations (e.g. 2 x 250 mg versus 1 x 500 mg of metronidazole or tetracycline) and timing of administration (breakfast and evening meal versus mid-day and evening meals) may result in significant improvements in H. pylori eradication regimens.
    Digestive and Liver Disease 07/2004; 36(6):384-7. DOI:10.1016/j.dld.2004.01.019 · 2.96 Impact Factor
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    Michael S Osato · David Y Graham ·

    The American Journal of Gastroenterology 05/2004; 99(4):769. DOI:10.1111/j.1572-0241.2004.04146.x · 10.76 Impact Factor
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    ABSTRACT: To compare the short-term (7-day) safety and efficacy of two triple-therapy regimens using pantoprazole with those of two dual-therapy regimens (one with pantoprazole and one without), for Helicobacter pylori eradication in patients with peptic ulcer disease. H. pylori infection was identified by rapid urease (CLOtest), and confirmed by histology and culture. Patients were enrolled into one of two randomized, double-blind, multicenter, parallel-group studies. In study A, patients received oral pantoprazole 40 mg, clarithromycin 500 mg, and metronidazole 500 mg (PCM); pantoprazole, clarithromycin and amoxicillin 1000 mg (PCA); or pantoprazole and clarithromycin (PC). In study B, patients received PCM, PCA, PC, or clarithromycin and metronidazole without pantoprazole (CM). Treatments were given twice daily for 7 days. H. pylori status after therapy was assessed by histology and culture at 4 weeks after completing the course of study treatment. Modified intent-to-treat (MITT; each study: n = 424, n = 512) and per-protocol (PP; each study: n = 371, n = 454) populations were analyzed. The MITT population comprised all patients whose positive H. pylori status was confirmed by culture and histology; the PP population comprised patients who also complied with > or = 85% of study medication doses. A total of 1016 patients were enrolled. Cure rates among patients with clarithromycin-susceptible H. pylori strains were 82 and 86% for PCM, and 72 and 71% for PCA, in studies A and B, respectively. Cure rates among patients with metronidazole-susceptible H. pylori strains were 82 and 87% for PCM, and 71 and 69% for PCA, in studies A and B, respectively. The combined eradication rates observed with the PCM regimen were superior to those of all other regimens tested. Side-effects were infrequent and mild. PCM had the highest overall eradication rate in these two studies examining 7-day treatment regimens. All regimens were safe and well tolerated.
    Helicobacter 12/2003; 8(6):626-42. DOI:10.1111/j.1523-5378.2003.00179.x · 4.11 Impact Factor
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    ABSTRACT: Helicobacter pylori infection is the most common cause of gastritis with its associated sequelae. Gastritis secondary to other bacteria is rare. This report describes Enterococcus-associated gastritis in a 59-year-old diabetic man. Nine months after receiving treatment for H. pylori-associated gastritis, he underwent endoscopy to confirm H. pylori eradication and to evaluate the status of previously seen ulcers. Mucosal biopsy specimens revealed severe active but focal gastritis adjacent to gram-positive coccobacilli in short to long chains with no H. pylori. Culture grew an Enterococcus similar to E. hirae and E. durans. No treatment was given, and endoscopy done 2 months later showed complete resolution of the gastritis and absence of H. pylori or enterococci. Our patient's gastritis represents a previously undescribed manifestation of Enterococcus infection. It is possible that the presence of NSAID gastric mucosal injury and diabetes predisposed this individual to the development of transient Enterococcus gastritis.
    Human Pathlogy 10/2003; 34(9):944-5. DOI:10.1016/S0046-8177(03)00287-9 · 2.77 Impact Factor
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    ABSTRACT: To compare H2-receptor antagonists and proton pump inhibitors as adjuvants to triple therapy for Helicobacter pylori eradication. H. pylori-infected patients with peptic ulcer were randomized to receive either 300 mg nizatidine or 30 mg lansoprazole plus 1 g amoxicillin and 500 mg clarithromycin taken b.d. for 7 days. H. pylori eradication was assessed 4 weeks after therapy. Using meta-analytical techniques, we combined the results of this study with other randomized controlled comparisons of H2-receptor antagonists and proton pump inhibitors as adjuvants to triple therapy. One hundred and one patients were randomized. H. pylori eradication was 94% (47/50) [95% confidence interval (CI), 83-99%] (intention-to-treat) in the H2-receptor antagonist group vs. 86% (44/51) (95% CI, 74-94%) in the proton pump inhibitor group (P = 0.3). There has been a total of 12 similar studies (1415 patients). The overall efficacy was similar in intention-to-treat analysis: 78% (549/701) with H2-receptor antagonists vs. 81% (575/714) with proton pump inhibitors (odds ratio, 0.86; 95% CI, 0.66-1.12). A non-significant trend favouring H2-receptor antagonist (79% vs. 69%; odds ratio, 1.14; 95% CI, 0.76-1.71; P = 0.5) was seen in the comparison of clarithromycin-containing regimens. In contrast, in non-clarithromycin-containing trials, there was a slight, but significant, advantage with proton pump inhibitors (85% vs. 78%; odds ratio, 0.64; 95% CI, 0.45-0.92; P = 0.02). Overall, proton pump inhibitor and H2-receptor antagonist antisecretory agents appear to be similarly effective as adjuvants for H. pylori triple therapy. It is unlikely that the direct anti-H. pylori effect of proton pump inhibitors is responsible for their ability to enhance anti-H. pylori therapy.
    Alimentary Pharmacology & Therapeutics 06/2003; 17(10):1229-36. DOI:10.1046/j.1365-2036.2003.01583.x · 5.73 Impact Factor
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    ABSTRACT: The mechanism of false negative urea breath tests (UBTs) results among proton pump inhibitor (PPI) users is unknown. We studied the time course of PPI-associated negative UBT, the relation to Helicobacter pylori density, and whether gastric acidification would prevent false negative UBT results. In the UBT experiment, H. pylori-infected volunteers received omeprazole 20 mg b.i.d. for 13.5 days. UBTs with citric acid were done before, after 6.5 days of PPI, and 1, 2, 4, 7, and 14 days after therapy. In the culture and histology experiment, after a wash-out of >5 months, nine of the original subjects were rechallenged with omeprazole for 6.5 days. Antral and corpus biopsies for histology and culture were done before and 1 day after PPI administration. Thirty subjects (mean age 42 yr) were enrolled. UBTs were significantly reduced on day 6.5 (p = 0.031); 10 subjects (33%) developed transient negative UBTs. The UBT recovered in all but one subject by the fourth day post-PPI and in all subjects by day 14. In the culture and histology experiment, upon PPI rechallenge, three of nine subjects (33%) had negative UBTs. H. pylori density, whether measured by culture or histology, decreased with PPI therapy; antral biopsies became histologically negative in five subjects and corpus biopsies in three subjects. PPI-induced negative UBT results were related to the anti-H. pylori effect of the PPI. Acidification of the stomach did not prevent false negative UBT results. Three days is likely the minimum delay from stopping PPI until one should perform a test for active infection. A delay of 14 days is preferred.
    The American Journal of Gastroenterology 05/2003; 98(5):1005-9. DOI:10.1111/j.1572-0241.2003.07426.x · 10.76 Impact Factor

  • Gastroenterology 04/2003; 124(4). DOI:10.1016/S0016-5085(03)81830-9 · 16.72 Impact Factor

  • Gastroenterology 04/2003; 124(4). DOI:10.1016/S0016-5085(03)83005-6 · 16.72 Impact Factor
  • AR Opekun · YW Oh · MS Osato · CW Yeh · DY Graham ·

    Digestive Disease Week 2003 Meeting/104th Annual Meeting of the; 04/2003

  • Gastroenterology 04/2003; 124(4). DOI:10.1016/S0016-5085(03)81814-0 · 16.72 Impact Factor
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    ABSTRACT: This multicenter, randomized, active-controlled trial assessed efficacy of bismuth-based quadruple therapy with omeprazole, bismuth biskalcitrate, metronidazole, and tetracycline (OBMT) using a single-triple capsule of BMT compared with triple therapy with omeprazole, amoxicillin, and clarithromycin (OAC) in treatment of patients with Helicobacter pylori infection and duodenal ulcers. Patients with active duodenal ulcer or diagnosed within the past 5 yr and with infection documented by (13)C-urea breath test plus histology or culture were randomly assigned to 10-day course of OBMT using a single-triple capsule containing bismuth biskalcitrate 140 mg, metronidazole 125 mg, and tetracycline 125 mg given as three capsules q.i.d. with omeprazole 20 mg b.i.d., or a 10-day course of OAC, omeprazole 20 mg plus amoxicillin 1 g plus clarithromycin 500 mg, all b.i.d. Eradication was confirmed by two negative urea breath tests at >1 month and >2 months after therapy. One hundred thirty-eight patients received OBMT and 137 OAC. Modified intent-to-treat eradication rates were 87.7% for OBMT and 83.2% for OAC (95% CI = -3.9%-12.8%; p = 0.29). OBMT eradicated 91.7% metronidazole-sensitive and 80.4% metronidazole-resistant strains (p = 0.06). OAC eradicated 92.1% clarithromycin sensitive and 21.4% clarithromycin-resistant strains (p < 0.001). Adverse events occurred in 58.5% of OBMT patients and 59.0% of OAC patients. OBMT regimen using the single-triple capsule is as efficacious and well-tolerated as the widely used OAC regimen for H. pylori eradication. This OBMT therapy largely overcomes H. pylori metronidazole resistance, present in 40% of patients in this study.
    The American Journal of Gastroenterology 03/2003; 98(3):562-7. DOI:10.1016/S0002-9270(02)06010-0 · 10.76 Impact Factor
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    D Y Graham · A R Opekun · Y Yamaoka · M S Osato · H M T el-Zimaity ·
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    ABSTRACT: Antisecretory therapy may exacerbate Helicobacter pylori corpus gastritis. The rate and mechanism(s) remain unknown. To investigate the early events in proton pump inhibitor therapy on antral and corpus H. pylori gastritis. Nine H. pylori-infected volunteers underwent gastric biopsy with jumbo forceps for culture and histology. Histology was scored in the range 0-5 using a visual analogue scale. The depth of inflammation in gastric pits was scored in the range 1-3 (superficial or less than one-third, one-third to two-thirds and greater than two-thirds of the gastric pit, respectively). Tissue interleukin-1 beta and interleukin-8 levels were measured by enzyme-linked immunoabsorbent assay. Omeprazole, 20 mg b.d., was given for 6.5 days and biopsies were repeated on day 7. Proton pump inhibitor therapy resulted in a fall in H. pylori density in the antrum and corpus. Inflammation and tissue levels of interleukin-8 and interleukin-1 beta decreased in the antrum and increased in the corpus mucosa. There was a significant increase in the depth of inflammation to include the proliferative zone in the corpus. Within 1 week of starting proton pump inhibitor therapy, there was a marked extension of corpus inflammation into the gastric pit and an increase in corpus mucosal interleukin-1 beta and interleukin-8 levels. H. pylori eradication should be considered for all patients receiving long-term antisecretory therapy.
    Alimentary Pharmacology & Therapeutics 02/2003; 17(2):193-200. DOI:10.1046/j.1365-2036.2003.01400.x · 5.73 Impact Factor
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    ABSTRACT: We evaluated a new immunoblot assay (Helicoblot 2.1) for Helicobacter pylori infection and CagA and VacA status by using serum samples from 222 patients. The test accurately detected H. pylori infection and VacA status, but improvements in the interpretation criteria are required before it can be recommended for determination of CagA status.
    Journal of Clinical Microbiology 01/2003; 40(12):4753-6. DOI:10.1128/JCM.40.12.4753-4756.2002 · 3.99 Impact Factor

Publication Stats

3k Citations
1,181.84 Total Impact Points


  • 1996-2011
    • Baylor College of Medicine
      • • Veterans Affairs Medical Center
      • • Department of Medicine
      Houston, Texas, United States
  • 1998-2004
    • United States Department of Veterans Affairs
      Бедфорд, Massachusetts, United States
    • University of Wisconsin - Milwaukee
      Milwaukee, Wisconsin, United States
  • 2003
    • Kangbuk Samsung Hospital
      Sŏul, Seoul, South Korea
  • 1996-2003
    • Minneapolis Veterans Affairs Hospital
      Minneapolis, Minnesota, United States
  • 2002
    • University of Texas MD Anderson Cancer Center
      • Department of Bioimmunotherapy
      Houston, Texas, United States
  • 1999
    • Università degli Studi di Sassari
      • Dipartimento di Scienze Biomediche
      Sassari, Sardinia, Italy