Organism Information and Courses from MediaLab, Inc.

This test is sensitive to 0.06-0.1 mg/dL nitrite ion in urines with a low specific gravity and ascorbic acid concentrations of less than 25 mg/dL. Pink spots or pink edges should not be interpreted as a positive result because some medications can color urine red or turn red in an acid environment. Any degree of uniform pink color should be considered positive, suggesting the presence of 105 organisms/mL. Detection of low levels of nitrite ion may be enhanced by comparing the activated test strip to a white background. It is important to note that color development is NOT proportional to the number of bacteria present. The test is specific for nitrites and does not react with any other substances normally present in urine. Negative results do not necessarily rule out a urinary tract infection because yeasts or gram-positive bacteria unable to reduce nitrites may be the causative agent.

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.

Citron DM. Appelbaum PC.: How far should a clinical laboratory go in identifying anaerobic isolates, and who should pay? Clinical Infectious Diseases. 16 Suppl 4:S435-8, 1993Identification of anaerobic bacteria in specimens from sites of infection due to mixed organisms can be time-consuming and expensive. Laboratories should limit anaerobic workups by testing only those specimens that have been properly collected and transported to the laboratory.Use of selective and differential media for initial processing can provide rapid and relevant information to the clinician. Anaerobes isolated from normally sterile sites and sites of serious infection should always be completely identified. Group-or genus-level identifications may suffice in other instances.The Bacteroides fragilis group of organisms should always be identified because of their virulence and resistance to many antimicrobial agents.Some of the other organisms that warrant identification include Clostridium septicum (associated with gastrointestinal malignancy); Clostridium ramosum, Clostridium innocuum, and Clostridium clostridioforme (which are resistant to antibiotics); Clostridium perfringens (a cause of myonecrosis and gas gangrene,potentially serious infection); anaerobic cocci (which may be resistant to metronidazole and clindamycin); and fusobacteria (which may be virulent and resistant to clindamycin and penicillin).

Piscitelli SC., Shwed J., Schreckenberger P., Danziger LH. Streptococcus milleri group: renewed interest in an elusive pathogen. European Journal of Clinical Microbiology & Infectious Diseases.11:491-8, 1992The following review examines the bacteriological characteristics, epidemiology, pathogenicity and antimicrobial susceptibility of the "Streptococcus milleri group". "Streptococcus milleri group" is a term for a large group of streptococci which includes Streptococcus intermedius, Streptococcus constellatus and Streptococcus anginosus.Usually considered commensals, these organisms are often associated with various pyogenic infections including cardiac, intra-abdominal, subcutaneous and central nervous system infections, particularly with the formation of abscesses.Organisms of the "Streptococcus milleri group" are often unrecognized pathogens due to the lack of uniformity in classifications and difficulties in microbiological identification. Penicillin G, cephalosporins, clindamycin and vancomycin all possess activity against these streptococci.Use of agents with poor activity may promote infections with "Streptococcus milleri group" and allow it to exhibit its pathogenicity. An understanding of these organisms may aid in their recognition and proper treatment.

The prototype history for this organism is either a still birth or a neonate with death ensuing within 2 or 3 days post-partem due to high fever, sepsis, and respiratory distress. The mother usually experienced a flu-like illness late in the third trimester of pregnancy, characterized by low-grade fever, myalgias, malaise and backache. In this case, biopsy material of brain tissue obtained at autopsy was submitted to the pathology laboratory for tissue diagnosis and fluid from the pia-arachnoid was sent to the microbiology laboratory for culture.

Photomicrograph of a gram stain prepared from an 18 hour old broth culture.The organism is a small, non-spore-forming bacillus measuring between 0.4 to 0.5um by 1.0 to 3.5um.Coccobacillary forms, diplobacilli, and bacilli in short chains or in diphtheroidal clusters (upper right in photograph) may all be observed in gram stain preparations.When found in the CSF, the organism may be found both intracellularly and extracellulary.

Griego RD. Rosen T. Orengo IF. Wolf JE.: Dog, cat, and human bites: a review. Journal of the American Academy of Dermatology. 33:1019-29, 1995It is estimated that half of all Americans will be bitten by an animal or another human being during their lifetimes. The vast majority of the estimated 2 million annual mammalian bite wounds are minor, and the victims never seek medical attention. Nonetheless, bite wounds account for approximately 1% of all emergency department visits and more than $30 million in annual health care costs.Infection is the most common bite-associated complication; the relative risk is determined by the species of the inflicting animal, bite location, host factors, and local wound care. Most infections caused by mammalian bites are polymicrobial, with mixed aerobic and anaerobic species.The clinical presentation and appropriate treatment of infected bite wounds vary according to the causative organisms. Human bite wounds have long had a bad reputation for severe infection and frequent complication. However, recent data demonstrate that human bites occurring anywhere other than the hand present no more of a risk for infection than any other type of mammalian bite.The increased incidence of serious infections and complications associated with human bites to the hand warrants their consideration and management in three different categories: occlusional/simple, clenched fist injuries, and occlusional bites to the hand. This article reviews dogs, cat, and human bite wounds, risk factors for complications, evaluation components, bacteriology, antimicrobial susceptibility patterns, and recommended treatments. Epidemiology, clinical presentation, and treatment of infections caused by Pasteurella multocida, Capnocytophaga canimorsus, Eikenella corrodens, and rhabdovirus (rabies only) receive particular emphasis.

Most likely means of dissemination: AerosolPrimary route of entry: InhalationGeneral signs and symptoms: High fever, chills, headache, coughing up of blood (hemoptysis), and toxemia, progressing rapidly to difficulty in breathing (dyspnea), and bluish discoloration of the skin and mucous membranes (cyanosis).There is another form of the disease called “bubonic plague”. While it is caused by the same organism, it is not transmissible through human contact. Pneumonic plague is transmissible through human contact.

Are used to collect sterile blood samples from patients who may be septic (have bacteria or other organisms growing in their bloodstream). Different blood culture bottles are used for aerobic, anaerobic, and pediatric collections.

Epithelial cells in large numbers within sputum smears means that the specimen is predominantly oral saliva, rather than true sputum from the lung. Epithelial cells in urine smears indicate that the sample has been contaminated by organisms found on the vulva or distal urethra. Bacteria found near or on epithelial cells are usually normal contaminating bacterial flora.White blood cells indicate inflammation and possible infection. The direct smear examination should focus within and around these cells.Red blood cells in a direct smear are not usually significant.Yeast may be present as normal flora in upper respiratory tract or genital tract. They may be significant if they predominate, or if budding yeast forms are seen.Hyphae are more likely to indicate the presence of fungal infection, but this determination requires correlation with clinical findings.Bacteria found in spinal fluid, blood, tissue and specimens from other sterile sites are always significant.Body fluids which are normally sterile must be examined carefully. If only one organism per oil immersion field is identified, then there are about 105 organisms per mL present in the sample! Bacteria observed in specimens from the throat, genital tract and other areas containing normal flora suggest infection only if their composition and type varies significantly from the norm.

Gram negative cocci which occur in pairs with their adjacent sides flattened, giving them a coffee bean appearance, are typical of the genus Neisseria. Neisseria gonorrhea is commonly found within white blood cells; these organisms must be carefully sought within genital tract specimens, and their presence or absence should be specifically noted in the report.The presence of intracellular gram negative diplococci in a purulent male urethral smear is presumptive evidence of gonococci, but this assumption cannot be made in a female.Beware of other organisms which resemble gonococci but are found extracellularly, such as Acinetobacter lwoffi, which must be distinguished biochemically.Direct smears read specifically for the presence of gonococci should include a direct reference to gram negative intracellular diplococci.

Bacteria may be either round (cocci) or rod-shaped (bacilli). Either shape may be Gram positive or Gram negative. A mixture of Gram positive and Gram negative bacteria can occur in the same field. Examples of Gram positive bacilli (rods) are shown on the bottom left, and Gram positive cocci are shown on the bottom right.

The Gram stain provides a fundamental differentiation between types of bacteria. Gram positive bacteria retain the primary stain and are deep violet in color. Gram negative organisms are those that decolorize during the staining process and, after counterstaining, are pink in color. Bacterial organisms occur in two basic shapes: cocci, which are spherical, and bacilli, (also known as rods), which are elongated. Both cocci and rods may be either Gram positive or Gram negative. Examples of Gram positive cocci are shown in the upper image on the right and Gram negative cocci are shown in the lower image.

The culture smear is used to determine the staining characteristic, size, shape and cellular arrangement of the unknown organism. This data helps the microbiologist to decide on additional culture and identification methods. By correlating the Gram stain reaction, size, shape, and cellular arrangement of the organism with colony morphology and growth requirements, the microbiologist may be able to tentatively identify the organism. This information may help the physician to optimize treatment until definitive culture and antibiotic susceptibility results become available. Gram stain reaction and bacterial shape must be included in the report.The cellular arrangement is usually not included in the report since it may vary depending on the culture medium (liquid or solid) used to isolate the organism. The following 12 screens contain additional ungraded practice questions pertinent to the material covered.

Under phase contrast, Trichomonas organisms appear much darker than the surrounding white blood cells.

The Mycobacterium tuberculosis organism is spread through infectious droplet nuclei.When a person infected with pulmonary tuberculosis coughs, sneezes, shouts, or sings, the infectious particles are expelled into the air.The risk of infection is related to both concentration of infectious droplet nuclei and duration of exposure.