microbiology review

Name this species of Aspergillus: Aspergillus fumigatus Aspergillus flavus Aspergillus niger

A. flavus. A. flavus produces yellow-green to olive colonies with a light-colored reverse. Circumferential phialides are seen microscopically. Some strains are uniseriate while others are biseriate. The conidiophores of A. flavus are also often times spiny or rough.

The hyaline septate molds found in soil, decaying organic matter or as plant pathogens. We all regularly breathe in the conidia of this mould, but those with weakened immune systems and lung disease are at risk for disease. The typical hyphae of it are 3 to 6 µm in width, septate, and dichotomously branched at 45 degree angles. The invasive hyphae are often oriented in parallel arrays as grow throughout tissues. Much of the tissue damage that occurs in invasive aspergillosis results from infarction consequent to vascular invasion and thrombosis. Fruiting heads (vesicles covered with phialides and conidia) may be seen in air filled tissue pockets.

Aspergillus Aspergillus fumigatus, Aspergillus flavus and Aspergillus niger account for the majority of cases of human aspergillosis.

Name this species of Aspergillus: Aspergillus fumigatus Aspergillus flavus Aspergillus niger

Aspergillus fumigatus A. fumigatus colonies are blue-green with a distinct white apron and a light-colored or white reverse. Microscopically, the conidiophores terminate in a swollen vesicle with a single row of phialides (uniseriate) that cover only the top 2/3 of the vesicle. Each phialide gives rise to a chain of small (2-4 µm) round conidia.

This species of Aspergillus have a dark brown to black surface due to the dark pigmentation of the conidia, but the reverse side is light-colored or white. Vesicles with two rows of phialides (biseriate) that cover the entire surface of the vesicle are seen microscopically. Phialides produce chains of rough, round dark conidia.

Aspergillus niger

What is a distinguishing feature of Aspergillus spp. in tissue identification? Tendency to be invasive Pseudohyphae Septate and dichotomous 45 degree branching angle Broad and ribbon like branching

Aspergillus spp. has a distinguishing feature in tissue of acute angle, septate and dichotomous branching. Many species of fungi can be invasive and is thus not a distinguishing feature. Pseudohyphae are most commonly associated with Candida albicans. Broad and ribbon-like branching is a feature associated with the Mucor spp.

Commonly found in the environment and may be recovered from the skin, gastrointestinal tract, and respiratory tract of heatlh humans. The genus is characterized by production of true hyphae, pseudohyphae, annelloconidia resembling arthroconidia, and the lack of blastoconidia. Invasive disease can occur in the immunocompromised. Those with hematologic malignancies are at most risk. Infection with B. capitatus presents similarly to that of invasive candidiasis in neutropenic patients. Most patients have fungemia and many develop deep organ involvement.

Blastoschizomyces capitatus (Geotrichum capitatum) Strange that it is named Blastoshizomyces but the species lacks blastoconidia.

Which features distinguishes Candida glabrata from other infectious Candida species? The ability to produce hyphae or pseudohyphae Encapsulation Larger size Germ tube production

C. glabrata are smaller, ranging from 2 - 4 µm in diameter, and cannot produce hyphae or pseudohyphae. C. glabrata is not encapsulated. An example of an encapsulated yeast is Cryptococcus. C. glabrata is actually smaller in size than the other Candida species. Germ tube production is a confirmatory test used to identify C. albicans.

Candida species other than this particular one are generally moderately sized yeasts, ranging in size from 5 - 7 µm that may produce pseudohyphae and/or hyaline septate hyphae, depending on the species. Deep infections can produce true hyphae, but the detection of budding yeast help aid in the diagnosis of candida. This particular type of Candida is smaller, ranging from 2 - 4 µm in diameter, and cannot produce hyphae or pseudohyph. The presence of a predominately neutrophilic inflammatory response to --- is helpful in distinguishing infection with this organism from H. capsulatum. Is it Candida albicans, C. glabrata, C. tropicalis, C. parapsilosis complex, or C. krusei?

C. glabrata. While Candia albicans is the most commonly encountered pathogenic Candida sp., glabrata is the only one that can be differentiated from others by morphology (smaller size) alone. All other Candida species are roughly the same size as a red blood cell.

Can grow on bacteriological media (sheep blood agar and chocolate agar). They may appear as small, creamy or white colonies that are somewhat more raised than staphylococcal colonies. A presumptive identification can be made by observing pasty, yellow-white colonies from which "feet" extend out from the margins into the surrounding agar. This pathogen causes thrush, vulvovaginitis, and esophagitis in immunocompromised.

Candida species

The distinctly mucoid appearance of the colonies in image B provides for a presumptive identification of this encapsulated yeast with its production of abundant polysaccharide capsular material. Common in bird excrement and can cause infections including meningitis in humans.

Cryptococcus species

This pathogen keratinophilic, which means that they are able to digest keratin as a nutrient source using keratinases. This special ability is the source of their pathogenicity and thus most infections are limited to superficial keratinized structures such as hair, nails, and the stratum corneum of skin. They are uniformly resistant to cyclohexamide. The rapid diagnosis of dermatophytosis can be made with a bedside KOH or calcofluor white preparation of skin scrapings. Microscopy cannot be used to distinguish. Infections can take many forms, including tinea capitis (scalp ringworm), tinea corporis (ringworm), tinea cruris (jock itch), tinea pedis (athlete's foot), and tinea unguium (onychomycosis).

Dermatophytes (Epidermophyton, Microsporum, Trichophyton)

Ubiquitous soil saprophytes and occasional plant pathogens. They are responsible for a variety of superficial and invasive human infectious disease. These pathogens produce characteristic fusoid or sickle-shaped macroconidia when cultured on synthetic media, but the tissue forms of these fungi are purely hyphal. Conidia can also be seen in smears from blood cultures growing these organisms. 3 to 8 µm in width, are septate, branched and haphazardly dispersed throughout the lesions. The hyphal branches characteristically arise at right angles from parent hyphae. The hyphae cannot be reliably distinguished from those of Aspergillus spp. Definitive diagnosis requires isolation in culture. Opportunistic infections frequently begin as cutaneous infections which manifest clinically as painful, erythematous or necrotic nodules that enlarge and ulcerate. The fungi can disseminate to the lungs, kidneys, and other organs.

Fusarium

This pathogen is a commensal of the skin. Some species are lipid-dependent. It can cause Tinea versicolor is a common infection of the superficial epidermis . It is one of the most common cutaneous infections in the tropics and subtropics worldwide. It may rarely cause bloodstream infections; these are usually associated with an indwelling intravascular catheter and the administration of hyperalimentation that contains lipids. The organisms appear as very small yeasts about 2 µm in diameter with unipolar broad-based budding. Budding yeasts are described as resembling bowling pins, while the daughter cell budding from the parent cell is sometimes likened to a turtle head coming out of its shell.

Malassezia spp.

This yeast that produce a carotenoid pigment ranging from yellowish to red that can be visualized with individual colonies. It can produce multilateral budding yeast cells, and occasional production of true hyphae or pseudohyphae. The budding yeast are 5-8 µm and are narrow-based. It can be isolated from soil, water, fruit juices, milk products, shower curtains, and toothbrushes. Immunocompromised patients, especially those with central venous catheters or other indwelling catheters, are at high risk for infections, most commonly presenting as fungemia. Other types of infection include endocarditis, meningitis, peritonitis, and ocular infection. Prophylaxis or treatment with fluconazole has been recognized as a risk factor for fungemia.

Rhodotorula

This potential pathogen is a colonizer of mucosal surfaces and is part of the normal flora of the gastrointestinal tract, the respiratory tract, and the vagina. The most important disease caused by it is fungemia. It occurs in immunocompromised and critically ill patients. Its infection is clinically indistinguishable from invasive candidiasis. Fever is common and chorioretinitis may occur. The yeast is characterized by round to oval multilateral budding yeast cells and short, rudimentary pseudohyphae. It is also the yeast used in brewing beer :)

Saccharomyces cerevisiae

What shape is commonly associated with the description of the macroconidia of Fusarium spp.? Please select the single best answer Sword-like Sickle-shaped Ovoid Oblong

Sickle-shaped. Fusarium species produce septate, curved to crescent or sickle-shaped conidia, called macroconidia which are, to some extent, characteristic of species (Figure 3). The macroconidia are slightly curved and tapered towards each end (fusiform) and are sometimes also referred to as boat-shaped.

Which supplement is necessary to add to culture media to ensure proper growth of Malassezia species? Short chain fatty acid Olive oil KOH Catalase

Some Malassezia spp. require long chain fatty acid supplements such as olive oil or Tween to be added to culture media to ensure growth. Short chain fatty acids are microbial metabolites. KOH (potassium hydroxide) is used to help microscopically visualize fungal elements in hair, skin, and nail specimens. The catalase test is used to help identify isolates of bacteria.

· gram + cocci clusters -coagulase test = negative natural skin flora and submucosal layers, nasal mucosa, newborn umbilicus · Facultative anaerobe Can cause infection of immunocompromised · Hospital acquired (nosocomial) infection of catheters or other surgical implants because it is known to form biofilms that grow on these devices. -common blood culture and catheter culture contaminant

Staph epidermitidis

· gram + cocci in clusters · Catalase positive · Coagulase + used as a distinction between this and other staph -looks like a gold coin on blood agar -frequently found in the upper respiratory tract and on the skin grape-like clusters beta hemolysis

Staphylococcus aureus · Aureus means "gold/yellow coin of ancient Rome"

gram + cocci in chains Catalase = Beta hemolytic on SBA blood agar Causes meningitis in newborns from vaginal canal CAMP factor +

Streptococcus Agilactiae (group B)

· gram + diplococci · Lancet shaped, pairs · respiratory illnesses (ie pneumonia) bile solubility test + optochin (P disc) sensitive

Streptococcus Pneumoniae

· Catalase = · gram positive cocci in chains · common in throat cultures/wounds (strep throat) · Beta hemolytic pattern

Streptococcus pyogenes (group A)

Use what agar to differentiate between cryptococcus neoformans and cryptococcus gattii? A. Mycosel agar B. Tween agar C. BHI agar D. canavanine-glycine-bromthymol blue (CGB) agar

Testing serum (a component of blood) or cerebrospinal fluid for cryptococcal antigen is useful as a first test for cryptococcal infection, but the test doesn't tell the difference between Cryptococcus neoformans and Cryptococcus gattii. Culture is traditionally used to tell if a cryptococcal infection is due to C. neoformans or C. gattii. On canavanine-glycine-bromthymol blue (CGB) agar, C. gattii will turn the culture medium blue, but C. neoformans will leave the color of the medium unaffected (yellow to green). C. neoformans is usually associated with infections in the immunocompromised while C. gattii is associated with infections in the immunocompetent. The most common routes of exposure include contact with contaminated soil and bird droppings.

What is a useful stain for the identification of Cryptococcus? Oil red O Acid fast Mucicarmine Movat pentachrome

The Mucicarmine and Fontana-Masson stains are particularly useful for identification of Cryptococcus although the forms can also be seen on Gomori Methenamine-Silver stain (GMS), Periodic acid-Schiff (PAS), and Hematoxylin and Eosin (H&E). Oil red O is used for staining triglycerides and lipids on frozen section tissue and lipoproteins on paraffin embedded tissue. The Acid fast stain, also known as the Ziehl-Neelsen stain, is used in the identification of mycobacteria as well as the Kinyoun stain, which is also an acid-fast stain. The Movat pentachrome stain is used to highlight various connective tissue.

This fungus is characterized by the production of true hyphae and pseudohyphae, arthroconidia and blastoconidia. There are six species of clinical significance: T. asahii, T. inkin, T. mucoides, T. cutaneum, T. ovoides, and T. asteroides. T. asahii, T. inkin, and T. mucoides are the most commonly isolated of the six species. It was initially recognized as the cause of white piedra, a superficial infection of the hair shaft of the scalp, face, axiallary, or pubic regions, characterized by soft white, yellow, green, or beige nodules composed of hyaline septate hyphae and arthroconidia. The disease occurs worldwide but occurs more commonly in tropical or subtropical regions. Recognized as causing invasive disease in patients who are immunosuppressed in the setting of hematologic or solid organ malignancies or solid organ transplantation. Infections of the immunocompromised are usually disseminated in nature, involve major organs and many are fatal. Pulmonary involvement is the most common site of end-organ disease.

Trichosporon spp. Yeast forms, arthroconidia, and hyphal elements are larger than those of Candida spp. (up to 10 microns). Trichosporon spp. hyphae are often arranged in a radial pattern.

Trichosporon yeast forms arthroconidia and hyphal elements are larger than those of Candida spp. Select true or false?

True. Trichosporon yeast forms arthroconidia and hyphal elements are larger than those of Candida spp. (up to 10 microns). Trichosporon hyphae are often arranged in a radial pattern.