Gram-negative Information and Courses from MediaLab, Inc.
These are the MediaLab courses that cover Gram-negative and links to relevant pages within the course.
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| Nitrite Test The nitrites portion of the reagent strip provides a rapid screening test for the presence of gram-negative bacteria that are often responsible for urinary tract infections. Although urine cultures are still needed to confirm the diagnosis and monitor any urinary tract or kidney infection, the need for a culture may not be obvious because in some cases of early bladder infection, the symptoms may be vague or the patient may be asymptomatic. Diagnosis and treatment of cystitis (bladder infection) is important because if left untreated it may result in kidney damage, impairment of renal function, hypertension and/or septicemia. | View Page |
| Bladder Infections Bladder infections are usually caused by gram-negative bacteria. These bacteria reduce nitrates derived from food to nitrites when urine remains in the bladder three to four hours, sufficient time for this reaction to occur. Nitrite is not present in urine under normal circumstances. When present, nitrites react with p-arsanilic acid to produce a diazonium compound. The diazonium compound in turn couples with 3-hydroxy-1,2,3,4 tetrahydrobenzo-(h)-quinolin to produce a pink color. A first morning, clean, voided midstream specimen is optimal for detecting nitrites in urine. | View Page |
| Nitrates in urine are reduce to nitrites by: | View Page |
| Which of the following organisms is not an aerobic organism: | View Page |
| Which of the following is the most suitable specimen for the isolation of Bordetella pertussis: | View Page |
| Which of the following is not true about members of the Enterobacteriaceae: | View Page |
| Which of the following best describes the organisms seen in this illustration: | View Page |
| Which of the following best describes the organisms seen in this illustration: | View Page |
| The carbohydrate utilization reaction seen in the QuadFerm system shown in the picture provides a definitive identification of N. gonorrhoeae: | View Page |
| Review 2 Smith KR, Fisher HC III, Hook, EW III: Prevalence of fluorescent monoclonal antibody-nonreactive Neisseria gonorrhoeae in five North American sexually transmitted disease clinics.J Clin Microbiol 34:1551-1552, 1996We compared a direct fluorescent monoclonal antibody (DFA) test with alternative enzymatic and fermention tests for identifying presumptive gonococcal isolates in a systematic sample from patients attending five sexually transmitted disease clinics in five cities.Fourteen (2.5%) of 556 isolates from three clinics were nonreactive with the DFA confirmatory reagent and reactive by both the Quad-Ferm and Rapid NH tests. The prevalence of DFA-nonreactive Neisseria gonorrhoeae isolates varies geographically and is independent of local methods for the identification of possible gonococci.On the basis of our findings, we recommend that for use in medicolegal and other instances in which a diagnosis of gonorrhea has the potential to have far-reaching effects, it is appropriate to test DFA reagent-nonreactive, oxidase-positive, gram-negative diplococci by alternative methods of gonococcal confirmation.Although the prevalence of such isolates could change, the fluorescent monoclonal antibody confirmation reagents remain useful for many clinical situations. Their ease of use and ready applicability for screening large numbers of isolates make them useful for many laboratories. | View Page |
| The recovery of an oxidase-positive, gram-negative diplococcus that tests DFA-nonreactive should be tested by alternative methods when establishing a fool-proof diagnosis of gonorrhea. | View Page |
| Review 1 Garbutt JM. Littenberg B. Evanoff BA. Sahm D. Mundy LM.
Enteric carriage of vancomycin-resistant Enterococcus faecium in patients tested for Clostridium difficile.
Infection Control & Hospital Epidemiology. 20(10):664-70, 1999OBJECTIVE: To identify independent risk factors for enteric carriage of vancomycin-resistant Enterococcus faecium (VREF) in hospitalized patients tested for Clostridium difficile toxin.PATIENTS: Convenience sample of 215 adult inpatients who had stool tested for C. difficile between January 29 and February 25, 1996.RESULTS: 41 (19%) of 215 patients had enteric carriage of VREF. Five independent risk factors for enteric VREF were identified: (1) history of prior C. difficile infection, (2) parenteral treatment with vancomycin for > or = 5 days, (3) treatment with antimicrobials effective against gram-negative organisms, (4) admission from another institution, and (5) age > 60 years. These risk factors for enteric VREF were independent of the patient's current C. difficile status.CONCLUSIONS: Antimicrobial exposures are the most important modifiable independent risk factors for enteric carriage of VREF in hospitalized patients tested for C. difficile. | View Page |
| The gram stain shown in the photograph was prepared from a positive anaerobic blood culture bottle after 36 hours incubation. Based on the morphology of the bacterial cells (some with spores--blue arrows), the most likely identification is: | View Page |
| Eikenella - catalase & oxidase Eikenella corrodens (E) belongs to the HACEK group of miscellaneous gram-negative bacilli which includes Haemophilus aphrophilus (H), Actinobacillus actinomycetemcometans (A), Cardiobacterium hominis (C) and Kingella kingae (K).Cytochrome oxidase and catalase are two rapid tests that help separate the several members of this group.Eikenella corrodens shows cytochrome oxidase activity, but not catalase activity.
The positive oxidase reaction separates E. corrodens from Haemophilus aphrophilus and Actinobacillus actinomycetemcomitans, which are both negative.A. actinomycetemcomitans is also catalase positive, an additional characteristic separating it from E. corrodens, which is negative.As Kingella kingae is also oxidase positive and catalase negative, other tests are needed for differentiation. K. kingae produces acid from glucose and maltose (E. corrodens is asaccharolytic). | View Page |
| Review 1 Newfield RS. Vargas I. Huma Z.:
Eikenella corrodens infections. Case report in two adolescent females with IDDM.
Diabetes Care. 19:1011-3, 1996OBJECTIVE: To alert physicians caring for patients with diabetes to the microorganism Eikenella corrodens and to discuss the appropriate preventive and therapeutic measures to take against this potentially morbid opportunistic Gram-negative bacilli.CASES: We present two cases of extra-oral E. corrodens infections in adolescent females with IDDM. The first patient had diabetes of 4 years' duration, which was moderately well controlled. Chronic finger biting resulted in a complex felon that evolved gradually and worsened while the patient received cephalexin orally. Delay in seeking further intervention resulted in necrosis of her distal fingertip and nail bed. The second patient had poorly controlled diabetes for 5 years. She developed an acute thigh abscess at an insulin injection site that resolved after drainage and intravenous antibiotics.CONCLUSIONS: E. corrodens commonly inhabits the human oral cavity and becomes a pathogen mostly when host defenses are impaired, causing abscesses and infections that are at times fatal. Patients with IDDM are compromised hosts and with daily microtrauma to their skin via glucose monitoring and insulin injections, are prone to develop E. corrodens infections that can be introduced through oral secretions by licking or biting their skin. Educational efforts aimed at preventing exposure of traumatized skin to oral secretions can minimize the risk of E. corrodens infections in compromised hosts.Early intravenous administration of antibiotics, bearing in mind E. corrodens resistance to clindamycin, metronidazole, and other antibiotics, coupled with prompt surgical intervention, is essential in successfully managing E. corrodens infections. | View Page |
| The peripheral blood smear presented here was submitted for morphological/clinical review. Conditions in which this picture may be seen include: | View Page |