Practical Guidance for Clinical Microbiology Laboratories: Diagnosis of Bacterial Gastroenteritis

Bacterial gastroenteritis is a disease that is pervasive in both the developing and developed worlds. While for the most part bacterial gastroenteritis is self-limiting, identification of an etiological agent by bacterial stool culture is required for the management of patients with severe or prolonged diarrhea, symptoms consistent with invasive disease, or a history that may predict a complicated course of disease. Importantly, characterization of bacterial enteropathogens from stool cultures in clinical laboratories is one of the primary means by which public health officials identify and track outbreaks of bacterial gastroenteritis. This article provides guidance for clinical microbiology laboratories that perform stool cultures. The general characteristics, epidemiology, and clinical manifestations of key bacterial enteropathogens are summarized. Information regarding optimal specimen collection, transport, and processing and current diagnostic tests and testing algorithms is provided. This article is an update of Cumitech 12A (P. H. Gilligan, J. M. Janda, M. A. Karmali, and J. M. Miller, Cumitech 12A, Laboratory diagnosis of bacterial diarrhea, 1992).

Primary amebic meningoencephalitis deaths associated with sinus irrigation using contaminated tap water.

BACKGROUND: Naegleria fowleri is a climate-sensitive, thermophilic ameba found in the environment, including warm, freshwater lakes and rivers. Primary amebic meningoencephalitis (PAM), which is almost universally fatal, occurs when N. fowleri-containing water enters the nose, typically during swimming, and N. fowleri migrates to the brain via the olfactory nerve. In 2011, 2 adults died in Louisiana hospitals of infectious meningoencephalitis after brief illnesses. METHODS: Clinical and environmental testing and case investigations were initiated to determine the cause of death and to identify the exposures. RESULTS: Both patients had diagnoses of PAM. Their only reported water exposures were tap water used for household activities, including regular sinus irrigation with neti pots. Water samples, tap swab samples, and neti pots were collected from both households and tested; N. fowleri were identified in water samples from both homes. CONCLUSIONS: These are the first reported PAM cases in the United States associated with the presence of N. fowleri in household plumbing served by treated municipal water supplies and the first reports of PAM potentially associated with the use of a nasal irrigation device. These cases occurred in the context of an expanding geographic range for PAM beyond southern tier states with recent case reports from Minnesota, Kansas, and Virginia. These infections introduce an additional consideration for physicians recommending nasal irrigation and demonstrate the importance of using appropriate water (distilled, boiled, filtered) for nasal irrigation. Furthermore, the changing epidemiology of PAM highlights the importance of raising awareness about this disease among physicians treating persons showing meningitislike symptoms.

Regulation of dextran sodium sulfate induced colitis by leukocyte beta 2 integrins.

Inflammatory bowel diseases (IBD) are chronic inflammatory disorders whose etiology remains unknown. Reports have shown that infiltration of leukocytes into intestinal tissue is a pathognomonic hallmark for this disease. Leukocyte beta(2) integrins are heterodimeric adhesion membrane proteins that are exclusively expressed on leukocytes and participate in immune cell adhesion and activation. In this study, we examined the pathophysiological role of the beta(2) integrins CD18, CD11a, and CD11b in the pathogenesis of dextran sodium sulfte (DSS)-induced experimental colitis. Disease activity was measured by daily assessment of clinical parameters including stool consistency, weight loss, occult blood, and gross rectal bleeding. Histopathological changes including severity of inflammation, surface epithelial/crypt damage, and depth of injury were also determined. The CD18 null and CD11a null mice had significantly lower disease activity and cumulative histopathological scores compared to wild-type mice. Interestingly, CD11b null mice did not show protection against DSS colitis and displayed increased disease activity compared to wild-type mice. Examination of specific leukocyte populations in the distal colon from various mice revealed significant attenuation of neutrophil and macrophage infiltrates in CD18, CD11a, and CD11b null mice. Surprisingly, the CD11b null mice showed a significant increase in plasma cell infiltration in response to DSS suggesting that this molecule may influence plasma cell function during colitis. This study demonstrates that genetic loss of CD18 or CD11a is protective during experimental colitis and that CD11b may serve a regulatory role during development of disease.

Fever, chills, and weakness in a 61-year-old man.

A 61-year-old man presented to the emergency department of a community hospital with a 2-week history of fever, chills, and sudden extreme weakness of his right arm and lower extremities. He also had a cough, shortness of breath, nausea, abdominal pain, diarrhea, and myalgia. Though initially alert and cooperative, he quickly became unresponsive. In addition, he had hyponatremia, renal insufficiency, and compromised cardiopulmonary function. He was admitted to the intensive care unit for suspected bacterial infection and was started on broad-spectrum antibiotics. Chest radiograph revealed miliary infiltrates consistent with infectious emboli or metastatic carcinoma. Despite intensive resuscitation, the patient died 36 hours after admission. At autopsy multiple nodular lesions were observed on gross examination of the lungs, perihilar and paratracheal lymph nodes, and liver. Microscopic sections of the lung (Figure 1) and brain (Figures 2 and 3) are shown.

Evaluation of four commercially available extended-spectrum beta-lactamase phenotypic confirmation tests.

Extended-spectrum beta-lactamase (ESBL) production in members of the Enterobacteriaceae can confer resistance to extended-spectrum cephalosporins, aztreonam, and penicillin. As such, the accurate detection of ESBL producers is essential for the appropriate selection of antibiotic therapy. Twenty previously characterized isolates and 49 clinical isolates suspected of ESBL production were tested by four ESBL phenotypic confirmatory methods for accuracy and ease of use. The four ESBL phenotypic confirmation tests included Dried MicroScan ESBL plus ESBL Confirmation panels (Dade Behring, Inc., West Sacramento, Calif.), Etest ESBL (AB BIODISK, Piscataway, N.J.), Vitek GNS-120 (bioMerieux, Inc., Hazelwood, Mo.), and BD BBL Sensi-Disk ESBL Confirmatory Test disks (BD Biosciences, Sparks, Md.). Results were compared to frozen microdilution panels prepared according to NCCLS specifications, and discrepant isolates were sent for molecular testing. The test sensitivities for the ESBL phenotypic confirmatory test methods used in this study were as follows: MicroScan ESBL plus ESBL confirmation panel, 100%; VITEK 1 GNS-120, 99%; Etest ESBL, 97%; and BD BBL Sensi-Disk ESBL Confirmatory Test disks, 96%. The test specificities were as follows: BD BBL Sensi-Disk ESBL Confirmatory Test disks, 100%; MicroScan ESBL plus ESBL confirmation panel and VITEK 1 GNS-120, 98%; and Etest ESBL, 94%. All methods were easy to perform; however, the Etest method required more expertise to interpret the results. All tests offer a feasible solution for confirming ESBL production in the clinical laboratory.

Fatal septicemia due to Clostridium hathewayi and Campylobacter hominis.

Clostridium hathewayi and Campylobacter hominis have not been previously reported in infection. We report a fatal case of septicemia, massive intravascular hemolysis, shock, and disseminated intravascular coagulation; both of these organisms were recovered on blood culture, although it seems likely that the C. hathewayi was responsible for the clinical picture and that the C. hominis was an incidental finding.

Legionella pneumophila serogroup 4 isolated from joint tissue.

We report the isolation of Legionella pneumophila serogroup 4 from synovial tissue obtained from an 80-year-old female with chronic swelling of her right metacarpophalangeal joint. Synovial tissue infections caused by L. pneumophila are rare. Interestingly, this isolate was recovered from chocolate agar after 5 days of incubation.

Spurious automated platelet count. Enumeration of yeast forms as platelets by the cell-DYN 4000.

We recently encountered a patient with thrombocytopenia secondary to multiple drug therapy, disseminated prostatic adenocarcinoma, and sepsis who had a sudden decrease in his platelet count as enumerated by the Cell-DYN 4000 hematology analyzer (Abbott Diagnostics, Santa Clara, CA). A manual platelet count performed thereafter was even lower. The etiology of the spurious platelet count was clarified when numerous yeast forms were observed on routine microscopy of the peripheral blood smear. Subsequently, these organisms were identified as Candida glabrata from a positive blood culture (BACTEC 9240, Becton Dickinson, Cockeysville, MD). To our knowledge, this is the first report of spurious enumeration of yeast forms as platelets in an automated hematology system. The principle underlying platelet enumeration by the Cell-DYN 4000 system and other hematology analyzers and the value of microscopy on peripheral smears with unexpected CBC count results are discussed.

Prevalence study of antibody to ratborne pathogens and other agents among patients using a free clinic in downtown Los Angeles.

Norway rats (Rattus norvegicus) are hosts for various microbes. Homeless people who have contact with rats may be at risk of infection by them. The Los Angeles County Department of Health Services initiated a seroepidemiologic study among patients who used a free clinic in downtown Los Angeles; 200 serum specimens obtained for other routine assays were tested for antibodies to ratborne pathogens and other agents. The seroprevalence of antibody to hepatitis E virus in this population was 13.6%; to Bartonella elizabethae, 12.5%; to B. quintana, 9.5%; to B. henselae, 3.5%; to Seoul virus, 0.5%; and to Rickettsia typhi, 0.0%. This study found that patients and locally trapped rats had antibodies to some of the same agents.

Practical therapeutic application of the oxoid PBP2' latex agglutination test for the rapid identification of methicillin-resistant Staphylococcus aureus in blood cultures.

The Oxoid PBP2' latex agglutination test (OLA; Oxoid, Basingstoke, England) was evaluated in a controlled prospective study examining Staphylococcus aureus from 25 positive blood cultures. Subcultures of positive blood cultures with coagulase-positive, gram-positive cocci in clusters were batched, and the OLA was performed at the end of the working day, once growth was seen on the plate. Results were sent to the infectious disease pharmacist for therapy evaluation, and the 24-hour minimum inhibitory concentration (MIC) was confirmed the next day. Blood culture OLA results correlated 100% with oxacillin MIC results for the patient, and results were available in as little as 3 hours after the blood culture was positive. The mean time difference between the OLA and MIC reports was 19.4 hours. This test allowed same-day resistance marker reporting and was easily incorporated into the work flow of the clinical laboratory.