Case Study for Clinical Microbiology A Model Enteric Pathogen

Question: 1. Based on the information presented, what is the primary diagnosis?2. Which of the biochemical tests presented is MOST distinctive for this organism? Why?3. Which of the above test results is most selective/differential for this diagnosis? Why?4. Differentiate between Vi and H serotyping. What is being tested (antibody or antigen) and identify the location of each on the microorganism. Answer: Case study 1-Mariya 1. Ova and parasite analysis of Marias stool revealed the presence of trophozoites with centrally located bands and two eccentrically located nuclei. The cysts were thin-walled, smooth and 8-12 m wide. From this description, it can be interpreted that Maria had a Giardia lambia infection. 2. Marias report shown that that there was absence of C. difficile, the cyst were definitely belongs to some parasitic group. The cysts were oval shaped and the length was also similar to the Giardia cysts, 8-12 m approximately. The distinct nature of the centrally located bands with eccentrically located nuclei and prominent central karyosome showed similarity with Giardia parasite. In addition, her history identified that she had fieldwork in Colorado, where she worked with animals and contaminated water. Giardia lamblia is a water-borne pathogen. Usually, symptoms of giardiasis appear after one to three weeks of infection. The time scaled mached with her externship. 3. The centrally located bands often seen in the identified parasite Giardia lambia, are known as Axostyle. It helps the parasite by providing support and helps in motility. 4. Physician could suspect Cryptosporidium parvum, which is one of the major causes of water-borne disease in US. Cyclospora cayetanensis and Entamoeba histolytica have very similar symptoms, which could be suspected, but these are mainly acquired during travelling to tropical areas. 5. Recommended timing for the diagnosis of intestinal parasites usually varies according to different diagnostic kits. Three specimens are usually collected for increasing the chance of detecting correct parasite, as parasites shed intermittently. However, the procedures should be completed on separate days, separate times (Cheng, 2012). 6. In ova and parasite analysis, both concentrate and permanent stained slides are required. It is because, concentrate wet mount exhibits motility of the parasites, but unable to identify the features of cysts and trophozoites. Wet mounts are easy to perform and faster procedure. On the other hand, the trichrome stained slides help to examine parasitic ova and cyst morphology and allow to preserve the specimen. It also gives the confirmation of parasites identity. 7. When the physician ordered C. difficile, he suspected that the pathogen might passed in feces and transmitted through fecal oral route. Maria was likely to live in an unhygienic environment, when she was working with animals in the sanctuary. On the other hand, C. difficile infection is usually caused because antibiotics destroy normal flora and allows this organism to overgrow. 8. Marias history showed her practice of consuming old antibiotics. In spite of having little stomach ache a diarrhea, however, the antibiotics could have killed the normal flora, which helped the overgrowth of C. difficile. 9. The C. difficile toxin assay is based on the polymerase chain reaction or PCR reaction. In the first step, increasing heat to 95 C, the DNA in the sample are denatured and the strands are separated. In the next step, primers are added at lowered temperature, these primers bind to the specific genes of interest. Then, with heat resistant DNA polymerase enzyme, sequences are copied on each half of the helix (Cheng, 2012). The process is then repeated for 30 to 40 cycles to produce billions of DNA copies. 10. The C. difficile toxin assay is favored over culture, as a method of diagnosing this disease because the culture required 2-3 days to grow. Cutlture method cannot distinguish between colonization and overgrowth of a microorganism. On the other hand, PCR method is faster and provides accurate results. This process is very sensitive towards the toxin B. However, the assay is much costly compared to the conventional culture technique (Wensaas et al., 2012). Case study 2: 22 years old male 1. Based on the information presented in the case study, the primary diagnosis was that the patient was suffering from an enteric disease. The patient revealed that when he was bin India, he experienced watery diarrhea. Other vital signs were normal. His present symptoms were intermittent and generalized sweating with chills, fatigue, myalgia, left parietal headache and malaise. The test results suggested that the organism was a gram-negative non-fecal coliform bacterium. The differential diagnosis, biochemical results and serotyping tests confirmed the presence of S. typhimurium. 2. Within the biochemical tests done for identifying the microorganism in the patients feces, the SIM or the Sulfide-Indole-Motility medium is the best for differentiating the organism from the others similar organisms. It is because, this tests is performed for distinguishing between E. coli and S. enterica. Three distinctive characteristics can be analyzed through this test, the ability to produce sulfide, indole and mortility. E. coli is fecal coliform, thus produce indole, but S. enterica, being a non-fecal coliform, does not produce indole, which is a distinctive feature (Broz, Ohlson Monack, 2012).. On the other hand, Salmonella sp. has the ability to produce H2S, which E. coli cannot. Therefore, this is the most distinctive test. In contrast, TSI gives positive results for Salmonella and Shigella. 3. Within all the tests, including the biochemical, serotyping and susceptibility tests, the most selective or differential test is the setotyping test, the slide agglutination test with Salmonella polyvalent O antigen antiserum and Vi antigen antigen antiserum. It is the test, which can precisely indentify the presence of S. typhi within its other serotypes. As the patients sample showed a negative oxidase, urease and indole test, the sample was tested for agglutination with polyvalent O and Vi antiserum. The agglunitation is seen due to the interaction within specific antigen and antibody, thereby specifiying the organism. The agglutination of the sample O antigen indicates the somatic antigens are present in the antisera (Khan et al., 2012). On the other hand, the agglutination with Vi antiserum indicates the presence of heat sensitive capsule present in S. typhi species. Thus, it is the most distinctive test. 4. The serotyping characterization is done on the basis of immunologic reactivity of two surface structures; the O antigen is the lipopolysaccharide and the H antigen is the flagellin protein. The O antigen is a carbohydrate antigen; it is the most important one for determining serotype. This antigen is found in the LPS of the organism (Khan et al., 2012). On the other hand, H antigen is a protein antigen, found in the flagella of the organism. In both cases, antigen is tested. Reference List Broz, P., Ohlson, M. B., Monack, D. M. (2012). Innate immune response to Salmonella typhimurium, a model enteric pathogen.Gut microbes,3(2), 62-70. Cheng, T. C. (2012).General parasitology. Elsevier. Khan, S., Harish, B. N., Menezes, G. A., Acharya, N. S., Parija, S. C. (2012). Early diagnosis of typhoid fever by nested PCR for flagellin gene of Salmonella enterica serotype Typhi.The Indian journal of medical research,136(5), 850. Wensaas, K. A., Langeland, N., Hanevik, K., Mrch, K., Eide, G. E., Rortveit, G. (2012). Irritable bowel syndrome and chronic fatigue 3 years after acute giardiasis: historic cohort study.Gut,61(2), 214-219.