Colony Information and Courses from MediaLab, Inc.
These are the MediaLab courses that cover Colony and links to relevant pages within the course.
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| The patient was admitted to the hospital. The sputum specimen was inoculated to sheep blood agar. Based on the colony morphology and the alpha hemolysis seen in the image to the right, the most likely identification is: | View Page |
| Colony Morphology The growth observed on the anaerobic blood agar plate after 48 hours incubation (see upper image), revealed a spreading colony. The spreading nature of the colony is better observed in the lower image. No growth was observed on subcultures incubated aerobically indicating that this isolate is truly an anaerobe (although aerotolerance studies would be needed for confirmation). The spreading nature of the colony and the lack of hemolysis are highly suggestive of Clostridium septicum. However, biochemical confirmation is necessary. | View Page |
| The bacterial cells shown in the image were observed in a smear prepared from the colony shown before. Which of the following tests will help to affirm the identification of Staphylococcus aureus? | View Page |
| Illustrated in the upper image are tiny pinpoint 24-hour colonies recovered from one of the splenic abscesses. The wide zones of beta hemolysis are better seen in the close-in view of the 36 hour culture shown in the lower image. Streptococcus anginosus ("milleri" ) can be suspected if one of the following odors is detected: | View Page |
| Shown in the image is a close-in view of the colony growth after 48 hours incubation. What are the possible presumptive identifications suggested by the colonies observed? (Choose all that apply) | View Page |
| Colony Morphology Image of the surface of blood agar after 24 hours incubation at 35C in 10% CO2, on which are growing tiny, translucent, gray colonies surrounded by a narrow zone of "soft" beta hemolysis. There was no growth on the MacConkey plate. | View Page |
| Shown in theimage are three tubes: (1) motility agar (note subsurface flare shown by arrows); (2) esculin hydrolysis (+), and (3) VP (+). The reactions illustrated here are sufficient to rule out Erysipelothrix rhusiopathiae. | View Page |
| Which of the following is the proper designation for the pluripotential stem cell that is a precursor for both myeloid and lymphoid cell lines: | View Page |
| Investigative Therapies Short chain fatty acids that increase levels of butyrate analogues inhibit the switching of hemoglobin chain production from gamma (HbF) to beta (HbA). Use of these compounds in the treatment of sickle cell is still under investigation.In clinical trials, cells containing HbF have been found to increase in number with the use of decitabine, a DNA hypomethilation agent. Also needing further investigation is the use of erythropoietin for treating sickle cell disease. Various colony stimulating factors have been found to increase the production of HbF. | View Page |
| The indole test may be used to differentiate members of which of the following species: | View Page |
| Match the description with the appropriate illustration of colony elevations: | View Page |
| Match the illustrations with the corresponding description of colony edges: | View Page |
| Assume you perform microbiology for an institution submitting surveillance cultures for MRSA. Which isolate should receive further workup to rule out methicillin (oxacillin) resistance? | View Page |
| Stool Culture Stool culture is very effective in detecting C. difficile. Unfortunately, non-toxigenic strains will also grow, requiring strains to be tested for toxin production. The greatest disadvantage to culture is the length of time that is needed before results are available, which may be up to four days. However, antibiotic sensitivity testing following culture is useful for strain-typing that would provide necessary epidemiological information during nosocomial outbreaks.Colonies of C. difficile will appear white, flat, and spreading on blood agar (see top image on the right). Cycloserin- cefoxitin-fructose agar(CCFA) is a selective media that is used for isolation of C. difficile. There is however, no distinction between pathogenic and commensal strains, which all produce yellow colonies with a characteristic "ground glass" appearance. as shown in the bottom image on the right. The characteristic odor of "horse manure" aids in identification of C. difficile. Stool samples are directly inoculated onto CCFA and incubated in an anaerobic atmosphere at 37°C for 48 hours. Large, thin, gram-positive bacilli with spores will be observed on a Gram stain of a typical colony, as shown below. | View Page |
| Susceptibility testing of Enterococci All susceptibility testing for Enterococci should follow the standards defined by CLSI. Selection of drugs for testing will follow the same criteria defined previously. Because the Enterococci posses many intrinisic resistance factors, there are many antibiotics that should not be tested (or if tested, suppressed from the final report). CLSI document M100 defines all applicable criteria. Both Disk Diffusion (Kirby Bauer) and broth dilution (MIC) methods are commonly employed, utilizing the following testing conditions: Medium: MHA for disk diffusion; CAMHB for broth dilution(supplemented to 50 ug/ml for daptomycin) Inoculum: Growth method or direct colony suspension, equivalent to a 0.5 McFarland standard Incubation: 35 + 2o C; ambient air. Disk diffusion; 16 to 18 hours; Dilution methods; 16 to 20 hours. All methods: 24 hours for vancomycin. | View Page |
| Detecting Vancomycin Resistance All results for vancomycin should be interpreted according to CLSI criteria.Interpretive standards for Enterococcus species against Vancomycin Method Susceptible Intermediate Resistant Disk diffusion >17 mm 15 - 16 mm < 14 mm Broth dilution < 4 µg/mL 8 - 16 µg/mL > 32 µg/mL Screening methodologiesBHI agar with 6 µg/ml vancomycin can be employed as a screen for vancomycin resistance. 1 - 10 µl of a 0.5 McFarland standard suspension is spotted onto the agar surface and incubated at 35 + 2 o C for a full 24 hours. The presence of >1 colony equates to presumptive vancomycin resistance; these isolates would require species identification and a vancomycin MIC.A motility test and documentation of the presence or absence of a yellow pigment can distinguish between the species with intrinisic (VanC) resistance (gallinarum and casseliflavus) and those with acquired (VanA and VanB) resistance (faecium and faecalis). | View Page |
| With regards to identifying resistance in Enterococci, which general statements are true? | View Page |
| Susceptibility Testing When a clinical isolate is presumptively identified as S. aureus, susceptibility testing will be performed by either the Standardized Disk Diffusion (Kirby-Bauer) or Broth Dilution (MIC) methods, using the following testing conditions as recommended by the Clinical and Laboratory Standards Institute (CLSI): Medium: MHA for disk diffusion; CAMHB + 2% NaCL for oxacillin, methicillin, and nafcillin; CAMHB supplemented up to 50 ug/ml calcium for daptomycin Inoculum: Direct colony suspension (0.5 McFarland Standard) Incubation: 35° C (Testing at temperatures above 35° C may not detect MRSA); ambient air; disk diffusion; 16to 18 hours; dilution methods; 16 to 20 hours. All methods: 24 hrs for oxacillin, methicillin, nafcillin, and vancomycin. | View Page |
| Which of the following scenarios represents appropriate detection of MRSA by the Kirby Bauer method? | View Page |
| Illustrated in this photograph is a "green lawn" colony of Gliocladium species. The other hyaline mold that produces this type of colony is: | View Page |
| A dull white fungus, turning mouse gray on maturity, was recovered from material aspirated from a bone cyst in the upper femur. Based on the microscopic appearance as seen in a lactophenol blue mount of a portion of the colony, the most likely identification is: | View Page |
| Match each hyaline mold from the drop-down list to its corresponding colony and microscopic description. The mold colonies are illustrated in the image on the right. | View Page |
| Match each hyaline mold from the drop-down list to its corresponding microscopic and colony description. The microscopic appearance of the molds are illustrated in the image on the right. | View Page |
| Match each hyaline mold from the drop-down list to its corresponding colony and microscopic description. The mold colonies are illustrated in the image on the right. | View Page |
| Match the name of each fungal species listed with its most likely corresponding morphologic features. | View Page |
| The infrequently encountered mold that is represented by the photomicrograph begins as a gray-white colony that blackens with maturity as the hyphae become darkened and single, globose, black conidia are produced. This fungus can be identified as: | View Page |
| Of the following dematiaceous fungi, the black, suede-like colony illustrated here, reaching no larger than the size of a dime after 7 days incubation, most likely can be identified as: | View Page |
| The dematiaceous colony illustrated here grew to a diameter of 3 - 4 cm in 5 days. The dematiaceous fungus that can be ruled out is: | View Page |
| The black yeast colony illustrated in this photograph may represent any of the following dematiaceous molds except: | View Page |
| The dematiaceous conidium illustrated in this photomicrograph was obtained from a tiny portion of dark colony that grew to maturity in six days. Spores incubated in a saline mount for four hours developed germ tubes from both terminal cells. The features observed confirm the identification of: | View Page |
| The etiologic agent of the superficial skin infection tinea niger palmaris (plantaris) is: | View Page |
| The dimorphic fungus that may produce black, yeast-like colonies after prolonged incubation at 37°C is: | View Page |
| The colonies shown in the upper image were obtained on blood agar from a sputum specimen after 10 days incubation at 30°C. The lower image is a photomicrograph of a lactophenol blue mount made from a portion of the colony. The diagnosis is: | View Page |
| The growth of the colonies shown in the upper image was obtained on blood agar from a sputum specimen after 8 days of incubation at 30°C. The lower image is a photomicrograph of a lactophenol blue mount made from a portion of the colony. The diagnosis is: | View Page |
| The colonies shown in the upper image, obtained from a biopsy of an ulcerating skin lesion of the arm, are growing on agar slants of Sabouraud's dextrose agar. The lower image is a photomicrograph of a lactophenol blue mount made from a portion of the colony growing in the left slant. The diagnosis is: | View Page |
| One of the characteristics common to the dimorphic molds is the ability to convert the mold forms to the yeast forms by incubating subcultures in enriched media at 35°-37°C. The upper image illustrates a subculture of a mold colony suspected of being a dimorphic fungus inoculated to the surface of blood agar and incubated for 3 days at 37°C. Note that the colonies have a prickly appearance, suggesting an intermediate stage of conversion. The lower image is a lactophenol blue mount of a portion of one of the prickly colonies. This fungus can be identified as: | View Page |
| The colonies growing on the surface of this brain-heart infusion with blood agar plate were "converted" from a mold colony suspected of being Histoplasma capsulatum by incubating a subculture at 37°C for 5 days. The yeast forms that must be identified in mounts made from one of these colonies to confirm the identification are: | View Page |
| Match the names of each of the yeast species with its most likely colony morphology as seen in the images on the right. | View Page |
| Match the names of each of the species of yeast listed with its associated phenotypic property that is helpful in establishing a species identification. | View Page |
| Arrange in sequence the steps that should be taken to make a definitive identification of Cryptococcus neoformans. | View Page |
| The growth of the yeast-like colonies shown in the upper image was obtained on blood agar from a skin culture only in the area overlaid by virgin olive oil. The lower image is a photomicrograph of a lactophenol blue mount made from a portion of the colony. The disease associated with this fungus is: | View Page |
| The forms seen in this photomicrograph, produced from a light inoculum of an unknown yeast colony incubated in rabbit plasma at 35°C for 2 hours, leads to the presumptive identification of: | View Page |
| The colony shown in the upper image was recovered from peritoneal fluid of a patient receiving continuous peritoneal dialysis. The lower image is a photomicrograph prepared from a small portion of the colony illustrating the microscopic morphology. Each of the following species of yeast can be eliminated except: | View Page |
| This photomicrograph is an acid-fast stained smear prepared from a yeast colony growing on ascospore agar. A helmet-shaped, red-staining, acid fast yeast cell is seen in the center of view at the tip of the arrow, against the background, blue-staining blastoconidia. The presumptive identification of Hansenula anomala was made. Predisposing conditions that may indicate that this isolate is more than a contaminant include: | View Page |
| Brucella species Culture Characteristics: Slow growth on sheep blood agar (SBA) and chocolate (CHOC) Growth in commercial blood culture systems, but may require extended incubation Enriched atmosphere with CO2may enhance growth of some strains If Brucella is expected or suspected, extend incubation up to seven days Colony Morphology on SBA at 35oC: Visible growth may take 48-72 hours Small, convex, and glistening Non-hemolytic | View Page |
| Burkholderia species Culture Characteristics: B. pseudomallei grows on sheep blood agar (SBA), chocolate (CHOC) agar, and MacConkey (MAC) agar B. mallei grows on very slowly on SBA and CHOC, but little or no growth on MAC Colony Morphology on SBA at 35oC: B. mallei: Smooth, gray, translucent colonies at 48 hours as displayed in the top, right image B. pseudomallei: Smooth, creamy, white colonies at 24 hours as displayed in the lower image on the right B. pseudomallei: May become dry and wrinkled as shown in the image below, often with a purplish hue at 48-72 hours Colony Morphology on MAC at 35oC: B. pseudomallei: Pink colonies at 24-48 hours (may be colorless at 48 hours) B.mallei: No growth or light pink colonies at 72 hours B. pseudomallei on CHOC at 72h image courtesy of CDC | View Page |
| Determine the Quality of a Urine Specimen Submitted for Culture The presence of many squamous epithelial cells (SQEs) also indicates a poorly collected urine specimen. If many SQEs are noted upon microscopic examination, the specimen should be recollected. The patient must be instructed how to collect a midstream, clean catch specimen. A Gram stain of a fresh, midstream urine sample would provide information that could help the physician decide whether to prescribe an antibiotic and the choice of antibiotic based on gram-reaction of the bacteria. Examine a Gram-stained slide made from a drop of uncentrifuged urine under oil immersion (1000X) magnification. If more than one bacterial organism is observed per oil immersion field, it can be determined that the quantity of bacteria is >105 colony forming units (CFU) per mL, and the patient probably has a urinary tract infection (UTI). The Gram stain reaction would also be important. Most bacteria that cause UTIs are gram-negative Enterobacteriaceae. A Gram stain report in this case would be "gram-negative bacilli consistent with quantity >105 CFU/mL." | View Page |
| Culture Smears: Importance and Reporting 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. | View Page |
