Podcast
Questions and Answers
What organism is primarily associated with decubitus ulcers?
What organism is primarily associated with decubitus ulcers?
Which bacteria is NOT typically associated with diabetic foot ulcers?
Which bacteria is NOT typically associated with diabetic foot ulcers?
What type of infections are associated with the collection of sinus aspirates?
What type of infections are associated with the collection of sinus aspirates?
Which organism is known to cause nodular lymphangitis?
Which organism is known to cause nodular lymphangitis?
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Which methods are used to culture sinus aspirates?
Which methods are used to culture sinus aspirates?
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Which test is least desirable for specimen collection?
Which test is least desirable for specimen collection?
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What type of specimen collection bypasses the oral cavity for anaerobic cultures?
What type of specimen collection bypasses the oral cavity for anaerobic cultures?
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What type of specimens are preferred for culturing anaerobic infections?
What type of specimens are preferred for culturing anaerobic infections?
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Which of the following is NOT a method for specimen microscopic examination?
Which of the following is NOT a method for specimen microscopic examination?
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What defines 'overt' bioterrorism?
What defines 'overt' bioterrorism?
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In what year did the Oregon Salmonella incident occur, representing bioterrorism?
In what year did the Oregon Salmonella incident occur, representing bioterrorism?
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Which organism is associated with rashes seen in dermatologic manifestations of systemic infections?
Which organism is associated with rashes seen in dermatologic manifestations of systemic infections?
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Which bacteria is NOT commonly associated with routine cultures for cystic fibrosis patients?
Which bacteria is NOT commonly associated with routine cultures for cystic fibrosis patients?
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For what temperature and atmosphere should routine cultures be incubated?
For what temperature and atmosphere should routine cultures be incubated?
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For children with Otitis Media, what is recorded under oil immersion?
For children with Otitis Media, what is recorded under oil immersion?
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What is the importance of Gram stain evaluation in the work-up process?
What is the importance of Gram stain evaluation in the work-up process?
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Which organisms are commonly associated with acute sinusitis?
Which organisms are commonly associated with acute sinusitis?
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What is the almost exclusive causative agent of epiglottitis in children aged 2-6 years?
What is the almost exclusive causative agent of epiglottitis in children aged 2-6 years?
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Which method is NOT typically used for specimen collection in upper respiratory tract infections?
Which method is NOT typically used for specimen collection in upper respiratory tract infections?
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What type of media is Bordetella pertussis cultured on?
What type of media is Bordetella pertussis cultured on?
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Which pathogen is predominantly sought in throat culture?
Which pathogen is predominantly sought in throat culture?
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Which characteristic is true about Gram staining in upper respiratory tract infections?
Which characteristic is true about Gram staining in upper respiratory tract infections?
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What is a common cause of chronic sinusitis in adults?
What is a common cause of chronic sinusitis in adults?
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Which condition is NOT typically caused by upper respiratory tract pathogens?
Which condition is NOT typically caused by upper respiratory tract pathogens?
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What is the outermost layer of the skin called?
What is the outermost layer of the skin called?
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Which organism is associated with the infection called Erysipelas?
Which organism is associated with the infection called Erysipelas?
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Which type of infection is characterized by a collection of pus in the skin and subcutaneous tissue?
Which type of infection is characterized by a collection of pus in the skin and subcutaneous tissue?
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Which organism is often responsible for surgical wound infections?
Which organism is often responsible for surgical wound infections?
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Which skin infection is often triggered by the obstruction of oil or sweat glands?
Which skin infection is often triggered by the obstruction of oil or sweat glands?
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What severe infection is associated with the organism Clostridium perfringens?
What severe infection is associated with the organism Clostridium perfringens?
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What condition is characterized by inflammation of hair follicles?
What condition is characterized by inflammation of hair follicles?
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Which organism is commonly found in animal bites?
Which organism is commonly found in animal bites?
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What is the incubation period for Tularemia?
What is the incubation period for Tularemia?
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Which illness is characterized by adenopathy without lesions?
Which illness is characterized by adenopathy without lesions?
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What is the infective dose of Francisella tularensis?
What is the infective dose of Francisella tularensis?
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Which of the following clinical presentations has a higher associated mortality if left untreated?
Which of the following clinical presentations has a higher associated mortality if left untreated?
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How long can Francisella tularensis persist in moist soil?
How long can Francisella tularensis persist in moist soil?
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Which statement regarding Brucellosis is true?
Which statement regarding Brucellosis is true?
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What is one characteristic of anthrax as a bioterror agent?
What is one characteristic of anthrax as a bioterror agent?
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What is the vaccine efficacy for Tularemia?
What is the vaccine efficacy for Tularemia?
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What may be the first sign of a bioterror attack involving anthrax?
What may be the first sign of a bioterror attack involving anthrax?
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Which arthropod is primarily associated with the transmission of Tularemia?
Which arthropod is primarily associated with the transmission of Tularemia?
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Which delivery method is NOT commonly associated with bioterror agents?
Which delivery method is NOT commonly associated with bioterror agents?
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What does the Laboratory Response Network (LRN) primarily focus on?
What does the Laboratory Response Network (LRN) primarily focus on?
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What is a characteristic of Category A bioterror agents?
What is a characteristic of Category A bioterror agents?
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Which of the following is NOT a biological delivery method mentioned?
Which of the following is NOT a biological delivery method mentioned?
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What is the particle size range for successful aerosol dispersion of anthrax?
What is the particle size range for successful aerosol dispersion of anthrax?
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What is a common feature of bioterrorism agents like anthrax?
What is a common feature of bioterrorism agents like anthrax?
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Which laboratory level is responsible for confirmatory testing of pathogens?
Which laboratory level is responsible for confirmatory testing of pathogens?
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What is NOT a feature of agents categorized as Category B?
What is NOT a feature of agents categorized as Category B?
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Study Notes
Skin and Soft Tissue Infections
- Skin is the outermost layer, consisting of epidermis (outermost), dermis (contains hair follicles, sebaceous glands, sweat glands), and subcutaneous layer (fat).
- Fascia (fibrous tissue) and muscles are also associated with skin.
- Wound infections are caused by trauma (minor or severe), obstruction of oil/sweat glands, or inflammation of hair follicles.
- Infecting organisms can be endogenous (normal flora) or exogenous (outside the body).
- Common skin flora includes Staphylococci (S. epidermidis & S. aureus), diptheroids (Corynebacterium), micrococci, streptococci (non-hemolytic), Propionibacterium acnes, anaerobes, and yeast.
- Dermatitis is inflammation of the skin, which can be caused by Candida spp., S. aureus, coliforms, Corynebacterium spp., and molds (dermatophytes)
- Pyoderma is inflammation of skin with pus. Examples include: Impetigo (blister-like superficial skin infection caused by Group A streptococci & S. aureus); Erysipelas (superficial, painful skin infection caused by Group A streptococci & S. aureus); Anthrax (rare, caused by Bacillus anthracis).
- Erysipeloid is a superficial soft skin infection, associated with animal/meat/hides, caused by Erysipelothrix rhusiopathiae.
- Cellulitis, a diffuse infection of deep epidermis and subcutaneous tissue, is caused by Group A streptococci and S. aureus.
- S. aureus and MRSA can cause folliculitis (infected hair follicle, sometimes due to contaminated hot water tubs), furuncles (boils), and carbuncles (involve multiple hair follicles).
- Abscesses are collections of pus in skin and subcutaneous tissue.
- Soft tissue (wound) infections can be caused by many organisms, including S. aureus, streptococci, and anaerobes, common causes in surgical wounds and burns, and animal/human bites (e.g., Pasteurella multocida).
- Myonecrosis is a serious muscle infection causing gas gangrene, commonly caused by C. perfringens.
- Necrotizing fasciitis is a severe fascia infection, typically caused by Group A strep and S. aureus.
- Decubitus ulcers (bed sores or pressure sores) are caused by bacteria near the rectum, commonly Enterobacteriaceae, Pseudomonas, and Enterococci.
- Diabetic foot ulcers are slow-healing injuries caused by S. aureus, streptococci, Enterobacteriaceae, Pseudomonas aeruginosa, and anaerobes.
- Nodular lymphangitis is characterized by Sporothrix schenckii, Nocardia spp., Actinomyces spp., and Mycobacteria.
- Dermatologic manifestations of systemic infections can result from various pathogens including Borrelia burgdorferi, T. pallidum, Rickettsiae, Leptospira, and Mycobacterium leprae, resulting in erythema migrans, rashes.
- Viral infections leading to dermatologic manifestations include measles (Rubeola and Rubella), Chickenpox/Shingles (Varicella-Zoster Virus), Herpes Simplex Virus, Warts (HPV).
- Toxin-mediated skin diseases include staphylococcal scalded-skin syndrome, toxin shock syndrome (S. aureus), and scarlet fever (S. pyogenes).
- Specimen collection and transport protocols include avoiding surface contamination, decontamination of skin/mucous membranes, preference for tissue/pus aspirates, and maintaining moist tissue.
- Swabs are less desirable in specimen collection.
- For anaerobic infections, the use of anaerobic transport media is required.
- Microscopic examination includes gram stains for detection of clinically significant organisms (evaluation, rejection of specimens with high epithelial quality).
- KOH and calcofluor white mounts, and acid-fast stains may be used for microscopic examination.
- Cultures are conducted using media such as BAP, CHOC, MAC, PEA, with variations based on the suspected organism and the site of infection.
- Anaerobic cultures are particularly important for closed wounds or abscesses.
- Other cultures may involve Lowenstein-Jensen, Middlebrook media, viral culture in shell vials, and Sabouraud's agar for fungi.
Respiratory Tract Infections
- URT infections involve the oral cavity and neck including the nose, mouth, throat, epiglottis, larynx, middle ear and paranasal sinuses.
- LRT infections include the trachea, bronchi, bronchioles, and lung alveoli.
- The area below the larynx is usually sterile.
- Normal flora of the URT includes Staphylococci (including CONS and S. aureus), Streptococci (including viridans and pneumococci), micrococci, diphtheroids, Neisseria spp., Haemophilus, anaerobes, spirochetes and Candida spp.
- URT infections include thrush, laryngitis, epiglottitis, pharyngitis, and tonsillitis. Pathogens include respiratory viruses (influenza, parainfluenza, RSV, adenovirus, rhinovirus, coronavirus, coxsackie A, EBV, CMV), S. pyogenes, B-hemolytic strep groups C, F, and G, and Arcanobacterium haemolyticum, H. influenzae; parainfluenzae; N. gonorrhoeae; Corynebacterium diptheriae; and Bordetella pertussis/parapertussis, yeast.
- URT specimen collection may include swabs, syringes/needles, biopsies. Diphtheria specimens are cultured on BAP, Loeffler, and tellurite media; pertussis specimens are cultured on Bordet-Gengou blood agar.
- Throat cultures often include antigen testing for group A strep followed by confirmation cultures.
- Microscopic examination via gram stain is often not an appropriate diagnostic method due to high numbers of normal flora.
- Cultures for group A strep are common but other potential pathogens may be sought when indicated (e.g., GNR, Arcanobacterium haemolyticum, Corynebacterium diphtheriae).
- Common laboratory procedures for cultures include BAP, CHOC, and MAC, often cultured at 35 °C in CO2. Specific media for cystic fibrosis patients may also be required.
- Methods for sputum collection include expectorated, induced, tracheal aspirates, bronchial washings & brushings, and biopsies. Invasive procedures like bronchoscopy may be reserved for unusual cases
- Processing specimens for gram stains, bacteria, and cultures is generally required, often within 2 hours.
- Evaluation of sputum via gram stain may reveal etiologic agents and sputum suitability for culture, and the presence of contaminants based on number of epithelial cells.
- A good quality sputum sample will show less than 10 epithelial cells per low power field, and greater than 25 PMN per low power field.
- Routine cultures for sputum, tracheal aspirates, bronchial washings, and biopsies (including BAP, CHOC, and MAC) and special media for cystic fibrosis (В. серасіа, MRSA, Pseudomonas) is commonly conducted
- Anaerobic cultures are recommended for particular situations (lung aspirates/ open lung biopsies)
- Bioterrorism agents (including anthrax, plague, Q fever, and tularemia are commonly evaluated from samples.
Other Potential Infection Types
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Anthrax (Bacillus anthracis): three forms (cutaneous, gastrointestinal, inhalation).
- Cutaneous anthrax is the most common form, occurring as a lesion developing into a black eschar.
- Inhalation anthrax presents as flu-like symptoms followed (in ~1-2 days) by respiratory failure. Radiographic findings indicate mediastinal widening. Gastrointestinal anthrax involves ingestion of spores, resulting in bloody diarrhea and vomiting and 50% mortality rate if untreated.
- Laboratory identification commonly includes gram staining (GPR spore-forming bacilli) and aerobic growth, nonhemolytic colonies, with a medusa-head morphology, and catalase-positive, nonmotile characteristics. Specimens for laboratory analysis include sputum, blood, gastrointestinal contents (blood/stool), environment samples, and evidentiary materials.
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Plague (Yersinia pestis): bubonic (infected lymph nodes), septicemic (blood-borne, necrotic changes—referred to as Black Death), and pneumonic (airborne transmission, highest mortality).
- Bubonic plague demonstrates flu-like symptoms with painful buboes; the septicemic form shows no swelling and is similar to the bubonic form; pneumonic plague has the highest mortality rate and presents with flu-like symptoms followed by rapid transmission and hemoptysis (coughing up blood).
- Laboratory identification often involves Gram-staining of specimens (GNR, slow-growth in 2 days, safety-pin appearance, nonmotile, occasionally oxidase, urea, indole negative), testing via SBA, and MAC. Specimen selection is important and specific to the form (bubonic: lymph node aspirate; septicemic: blood; pneumonic: sputum/bronchial wash/aspirate).
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Tularemia (Francisella tularensis): A zoonotic infection spread from animals, showing various clinical presentations and with flu-like symptoms (incubation 1-21 days, mostly 3-5 days; mortality can be low (with treatment to about 10% with no treatment), can last up to 2 weeks, persists in moist soil for months). The three most common presentations include pneumonic (flu-like symptoms over about 3-5 days), typhoidal (initial symptoms), and ulceroglandular (ulcer and adenopathy).
- Laboratory identification may include slow growth of pleomorphic, small GNR that grow on SBA, CHOC, and MTM (buffered charcoal yeast-extract), nonmotile bacteria, catalase-positive and oxidase/urea negative characteristics. Specimens may include serum, blood, tissue samples, lesion/swab specimens, sputum, and environmental samples.
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Brucellosis (Brucella species): transmission occurs with unpasteurized dairy products, direct animal contact, or aerosols. The course of illness can last from weeks to months with fever, profuse sweating, malaise, and headache and muscle/back pain; mortality is typically under 5%.
- Laboratory identification relies on GNCB slow-growth, aerobic growth, but some may grow on MAC, and nonmotile organisms that are catalase, oxidase, and urea positive. Blood or bone marrow, serum, tissue (spleen/liver), and environmental/evidentiary samples may be examined.
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Q Fever (Coxiella burnetii): an infection acquired via inhalation from infected animals. Spore-like bodies are produced. The incubation period is about 2-3 weeks showing flu-like symptoms, and in some cases, pneumonia and hepatitis. Mortality rate is ~2%.
- Laboratory specimens include blood, serum, body fluids, visceral tissue, biopsies, and autopsy materials (stored at 4°C). Isolation testing and direct detection are conducted at reference labs, using BSL level 3 precautions.
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Smallpox (Variola major): a rare, highly contagious disease spread by infected droplets. The incubation period is about 8-16 days. Clinical presentations such as orinary (90% of cases), modified (mild, in previously vaccinated), flat (usually fatal), and hemorrhagic (usually fatal).
- Laboratory identification usually relies on identifying the brick-shaped, DNA Orthopox-virus structure (200 nm). Collection of specimens for testing is often from tissues of the affected skin.
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Other Viral Hemorrhagic Fevers (Filoviruses, Arenaviruses, Bunyaviruses, Flaviviruses): are potentially severe, often life-threatening, viral infections (e.g., Ebola, Marburg, Lassa, Hantavirus, Tick-borne encephalitis, dengue, yellow fever) requiring BSL-3 precautions and testing at dedicated reference labs.
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Other cultures (Eye, Bone, Bone Marrow, External Ear): these infections can involve gram-positive/negative bacteria as normal flora and/or pathogens leading to infection. Special methods for collection via swabs, corneal scrapings, and/or enriched broth and/or media-based cultures, depending on the suspected organism, are needed.
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Botulism (Clostridium botulinum): a neuroparalytic syndrome with seven types of toxin; the most common are types A, B, E and F in humans, and C and D in animals. Presentations include foodborne (infant/non-infant), and wound-associated types. Common specimens for testing include serum, gastric contents, stool, and food/environmental samples.
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Description
Test your knowledge on microbiology regarding infections and specimen collection techniques. This quiz covers various organisms, culture methods, and specific infections such as decubitus ulcers and diabetic foot ulcers. Dive into the specifics of microbial pathogens and their clinical implications.
