Micro Exam 4- LabCE
Agar plates on a positive blood culture are incubated for 48 hours and no growth is visible on the agar plates. The tech reviews the initial Gram stain from the blood culture bottle, which reveals tiny pleomorphic Gram-negative coccobacilli. What organism should the tech suspect and what should the tech do next? -Campylobacter jejuni; Set up a CVA plate in the 42ºC incubator -Francisella tularensis; Sub blood culture bottle to a media with cysteine for optimal growth -Yersinia pestis; Sub blood culture bottle to media at room temperature incubation -Streptococcus pneumoniae; Organism has autolysed in blood culture bottle
Francisella tularensis is a slow-growing, pleomorphic Gram-negative coccobacilli. The most common clinical presentation is ulceroglandular disease where the organism is transported to the lymph nodes and then disseminated in the bloodstream. Blood cultures that grow poorly or fail to grow on blood agar and show Gram-negative coccobacilli in the Gram stain, should have the organism subcultured to a media that contains cysteine (such as chocolate agar, modified Thayer Martin agar, cysteine heart agar, or buffered charcoal-yeast extract agar) to enhance the growth of the organism. Growth may also be increased with additional CO2 incubation.
Illustrated in this photograph is the surface of a 5% sheep blood agar plate on which are growing colonies of yellow-pigmented Staphylococcus species. Note the tiny semi-translucent colonies that satellite around some of the colonies. Pleomorphic gram-negative bacilli were seen on gram stain. The most likely identification is: Neisseria elongata Moraxella catarrhalis Haemophilus influenzae Granulicatella species
Haemophilus influenzae
A pediatric patient arrived at the doctor complaining of itching eyes that appeared red and slightly purulent. When a sample was submitted to the laboratory, the sample grew only on the chocolate plate as seen in the upper image. When performing a satellite test, the image on the bottom is observed. What is the most likely identity of the organism causing this patient's symptoms? Moraxella catarrhalis Haemophilus influenzae Streptococcus pneumoniae Listeria monocytogenes
Haemophilus influenzae will grow on the chocolate plate as observed in the upper image. It will also exhibit growth on the satellite test as observed in the lower image. In pediatric patients, it is the leading cause of conjunctivitis, which is the condition described in the question above. Moraxella catarrhalis and Streptococcus pneumoniae would grow on sheep blood agar in addition to the chocolate agar, thus it would not be necessary to perform a satellite test, as the organisms would not grow in a satellite formation. Both organisms are common causes of conjunctivitis, but would not grow as described above.
The fastidious gram-negative bacillus, often producing pitting of the agar around the colonies growing on blood agar, as illustrated in this photograph, producing a bleach-like odor is most commonly associated with one or more of the following conditions: "Clenched fist" infections of the hand Juvenile periodontitis Pneumonia Dog bite cellulitis
"Clenched fist" infections of the hand
An 18-year-old student was seen in the college health center with a sudden onset of headache, fever, and stiff neck. A gram stain of the cerebral spinal fluid sediment is shown in the photograph (intracellular bacteria). The MOST likely cause of this patient's acute meningitis is: Haemophilus influenzae Escherichia coli Neisseria meningitidis Streptococcus pneumoniae
-The correct answer is Neisseria meningitidis -Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae are the three most common causes of bacterial meningitis. The gram stain shown in the photograph illustrates numerous segmented neutrophils, one of which includes tiny, gram-negative cocci (tip of the arrow). The bacterial cells of S. pneumoniae are gram-positive, therefore ruled out by the gram stain. N. meningitidis is the most likely possibility, based both on the gram stain morphology and the age of the patient, where this agent has its highest incidence. H. influenzae is a possibility, although the bacterial cells are usually more bacillary and pleomorphic than seen here and infections are more common in neonates and younger children. E. coli meningitis is generally limited to the newborn period. The bacterial cells of E. coli are gram-negative but are distinctly bacillary.
Which organisms/conditions would be classified as Biosafety Level 3 agents? Mycobacterium tuberculosis and Coxiella burnetti Marburg virus and Congo-Crimean hemorrhagic fever Bacillus subtilis and Naegleria gruberi HIV and hepatitis B virus
Biosafety Level 3 (BSL-3) procedures are recommended to handle material suspected of harboring organisms unlikely to be encountered in the clinical laboratory, such as Mycobacterium tuberculosis and Coxiella burnetti.
Tiny Gram-negative coccobacilli were isolated on chocolate agar from a wound on a man who had been hunting wild boar. The microbiologist performed the following test: Oxidase Positive Urease Positive Motility Nonmotile Colony morphology Small, nonhemolytic Which of the following species is most probable? Bacillus anthracis Brucella species Francisella tularensis Yersinia pestis
Brucella species is the correct answer. Brucella species can be found in wild boars and is also considered a bioterrorist agent, but can cause infections in game hunters. Brucella are tiny Gram-negative coccobacilli that tend to stain lightly; in addition, growth is best observed on chocolate and can take 48 hours before growth can be seen.
The recovery of this bacterial species from diarrhea stool specimens requires the use of selective culture media such as Butzler selective media or Skirrow blood agar incubated at 42° C in an atmosphere of 5% oxygen, 10% CO2, and 85% nitrogen. Growth on Skirrow blood agar as illustrated in the upper image are confluent smooth non-hemolytic colonies growing along the streak line with lateral extensions (arrows). Slender, long branching, S-shaped Gram negative rods are observed on Gram stain, as observed in the lower image. Positive reactions for oxidase, indoxyl, and hippurate provide for a more definitive identification. With these observations, select the name of this isolate. Campylobacter coli Campylobacter jejuni Helicobacter cinaedi Cardiobacterium hominis
Campylobacter jejuni
Eikenella corrodens is associated with which of the following? Localized juvenile periodontitis Aortic valve infection Clenched fist infection Juvenile osteomyelitis
Clenched fist infection All HACEK members are known to cause endocarditis. Three of the HACEK members are: -Eikenella corrodens is a normal inhabitant of the oropharynx. Most infections with this organism are a result of trauma especially human bite wounds or fistfights. Inflammation of the knuckles following fistfights may occur and are known as clenched fist wounds or infections. -Aggregatibacter (formerly Actinobacillus) actinomycetemcomitans is a member of the normal oral flora and is a major cause of juvenile periodontitis. -Cardiobacterium hominis infects the aortic valve more frequently than other HACEK organisms. -Kingella kingae has a particular predilection for causing infections of the bones and joints, particularly of young children, and is associated with juvenile osteomyelitis.
The following organism is an anaerobic organism that produces spores and a double-zone of beta-hemolysis. Pseudomonas aeruginosa Clostridium perfringens Enterobacter aerogenes Cutibacterium (Propionibacterium) acnes
Clostridium perfringens is an anaerobic organism that is known to cause gas gangrene, food poisoning, and necrotizing enteritis. The identification of this organism begins with the appearance of a Gram-positive, spore-forming bacillus that produces a double-zone of beta-hemolysis on blood agar.
A sample from a wound infection, suspected case of gas gangrene, was cultured and showed anaerobic colonies that are small, smooth, light gray-yellow, and surrounded by a distinctive double zone of beta hemolysis (arrows). Gram stain, as illustrated in the lower photomicrograph, are large, non-spore forming, "box-car" shaped gram-positive bacilli. What is this organism that is also related to outbreaks of food-borne diarrhea following ingestion of contaminated meat products? Actinomyces israeli Bifidobacterium species Cutibacterium (Propionibacterium) acnes Clostridium perfringens
Clostridium perfringens is an immediate presumptive identification because the colonies growing on blood agar after anaerobic incubation show a double zone of hemolysis. The distinct, large, narrow elongated "box-car" shaped gram positive bacilli seen in gram stains prepared from one of the colonies confirms this identification. Immediate reporting of this presumptive identification should be made so that selective antibiotic therapy can be administered for treatment of infections presenting as gas gangrene and serious food poisoning.
Infections with Eikenella corrodens is associated with: -Ingestions of food contaminated with saliva -Bites from canines or felines -Trauma associated with human teeth -Inhalation of respiratory droplets
Eikenella corrodens is found in the human mouth and gastrointestinal tract. Infections occur following trauma associated with human teeth including human bites or clench-fist punches to the face. Endocarditis has occurred due to endogenous flora. Eikenella corrodens is part of the normal flora of the human mouth. It is not associated with bites from canines or felines.
All of the following organisms have been linked to causing endocarditis EXCEPT? Aggregatibacter aphrophilus Cardiobacterium hominis Eikenella corrodens Hemophilus influenzae
Hemophilus influenzae is the correct answer because this organism most often causes upper and lower respiratory tract infections and has not been associated with endocarditis.
Blood culture bottles utilized in continuous monitoring systems, such as the BacTec, use resins or charcoal to do which of the following? -Inactivate and absorb out complement -Inactivate and absorb out coagulation factors -Inactivate neutrophils and monocytes -Inactivate and absorb out antimicrobial agents
Inactivate and absorb out antimicrobial agents is the correct answer because resins and charcoal are able to absorb out and inactivate antimicrobial agents, which will enhance the recovery of microorganisms. However, when reading Gram stains from bottles that use charcoal, caution should be used as the charcoal can be misinterpreted as Gram-positive cocci. Inactivates and absorbs out complement, inactivates and absorbs out coagulation factors, and inactivates neutrophils and monocytes are the incorrect answers because resins and charcoal do not have these properties. However, an additive called sodium polyanethol sulfonate (SPS) with a concentration of 0.025% - 0.05% can be found in blood culture bottles. This additive has anticoagulant, anticomplementary, and antiphagocytic properties.
The small beta-hemolytic bacterial colonies growing on blood agar as shown in the upper photograph were recovered from an induced sputum specimen from a young child with pneumonia. The colonies were slow-growing, small, entire, and show soft beta hemolysis. Plump, Gram-negative coccobacilli, lying singly, in pairs and short chains, are seen on gram stain as illustrated in the lower photomicrograph. Most strains are chemically non-reactive except for a positive oxidase reaction and acid produced from dextrose and maltose. What is the name of the isolate? Capnocytophaga species Cardiobacterium hominis Eikenella corrodens Kingella kingae
Kingella kingae is the correct response. Found as normal flora in the upper respiratory tract, particularly of children, this bacterial species may on occasion be the agent of pneumonia. Colonies growing on blood agar are pin-point in size, surrounded by narrow zones of soft beta hemolysis. In Gram stains, short, plump, gram-negative coccobacilli in pairs and short chains are observed. Chemical non-reactivity is evident except for a positive oxidase reaction and the selective carbohydrate utilization of dextrose and maltose. Additional biochemical reactions may be required in certain instances to rule out Neisseria species.
Neisseria species can be traditionally differentiated by their fermentation of sugars. Identify the biochemical reaction that goes with the correct species of Neisseria given. -N. gonorrheae = Glucose +, maltose -, lactose + -N. lactamica =Glucose -, maltose -, lactose - -N. cinera = Glucose +, maltose +, lactose + -N. meningitidis = Glucose +, maltose +, lactose -
N. meningitidis = Glucose +, maltose +, lactose - As a mental reminder, gonorrhoeae = G = glucose; meningitidis = M = maltose; and, lactamica = L = lactose. N. gonorrhoeae is only positive for glucose, while N. meningitidis is positive for maltose and glucose, and N. lactamica is positive for all three sugars.
The most common organism that causes septic arthritis in patients under 30 years of age is: Neisseria gonorrhoeae Staphylococcus aureus Treponema pallidum Chlamydia trachomatis
Neisseria gonorrhoeae
A joint fluid was received in the microbiology laboratory. The specimen was cloudy and many neutrophils with intracellular and extracellular Gram-negative diplococci were seen on the Gram stain. The specimen was inoculated to sheep blood and chocolate agar and grew a small, grayish-white colony on chocolate with no growth observed on the sheep blood. Which of the following is most likely the organism? Neisseria gonorrhoeae Haemophilus influenzae Bacteroides fragilis Streptococcus pyogenes
Neisseria gonorrhoeae is correct based on the Gram stain morphology described. Neisseria gonorrhoeae are Gram-negative diplococci and these organisms may be seen intracellularly or extracellularly within neutrophils. Neisseria gonorrhoeae can cause infectious arthritis in disseminated infections.
The positive oxidase reaction as shown in the image (yellow arrow) rules out which of the following "look-alike" bacteria that resemble N. gonorrhoeae? Moraxella catarrhalis Pastuerella multocida Acinetobacter baumannii Kingella kingae
Neisseria gonorrhoeae is cytochrome oxidase-positive. The only choice given that is oxidase negative is Acinetobacter baumannii. A positive spot oxidase reaction is helpful in ruling out the oxidase-negative Acinetobacter baumannii, which in the Gram stain may simulate Neisseria gonorrhoeae.
Small intracellular gram-negative cocci were observed in a centrifuged spinal fluid sediment as presented in the upper photomicrograph. A clinical diagnosis of meningitis was suspected. Yellow-gray colonies after 24-hour incubation had been observed on blood agar. Based on the carbohydrate utilization tube reactions observed in the lower photograph, what is the presumptive identification of this isolate? (coffee bean shape, ferments glucose and maltose) Neisseria gonorrhoeae Neisseria meningitidis Aeromonas species Kingella kingae
Neisseria meningitidis
Specimen handling from patients with symptoms consistent with tularemia requires work in a biological safety cabinet. Although PCR may confirm infection with Francisella tularensis, the following culture characteristics and tests aid in presumptive identification: -Slow growth on MAC, fast-growth on CHOC; oxidase-positive, negative catalase, X and V factor requirement positive -No growth on MAC, slow growth on CHOC; oxidase negative, positive catalase and ß-lactamase -Fast growth on SBA and MAC; oxidase, catalase, and urease positive - Slow growth on MAC and EMB; oxidase, catalase, and urease negative
No growth on MAC, slow growth on CHOC; oxidase negative, positive catalase and ß-lactamase Francisella tularensis requires cysteine for optimal growth, and therefore, grows best on CHOC or other media containing cysteine. However, colonies may not be visible for 3-4 days.
Various methods have been employed for the detection of Clostridioides difficile disease, which method is the new gold standard for detection? -Culture on cycloserine-cefoxitin-fructose agar (CCFA) -Cell cytotoxicity neutralization assay (CCNA) -Enzyme immunoassays (EIA) detecting toxins -Nucleic acid amplification tests (NAATs)
Nucleic acid amplification tests (NAATs) are becoming the new gold standard for detection. They determine the presence of toxin A and B genes in a stool sample. It is becoming the new gold standard since it does not need confirmation like other test methods. Cell cytotoxicity neutralization assays (CCNA) were considered for a long time the gold standard for Clostridioides difficile detection because they detect the toxins in the stool sample. However, the assay is labor-intensive and requires 48 of incubation for the cells to grow.
Within the genus Campylobacter, the laboratory test most helpful in selectively identifying Campylobacter jejuni is: Indoxyl acetate Hippurate hydrolysis Nitrate reduction Susceptibility to nalidixic acid
Of all the identification characteristics listed in this exercise, only hippurate hydrolysis is 100% specific for Campylobacter jejuni. All other Campylobacter species, including the closely related C. coli and C. fetus, are negative for this characteristic.
Which strictly human pathogen causes chancroid, a highly contagious, sexually transmitted genital ulcer disease? Treponema pallidum subsp. pallidum Haemophilus ducreyi Chlamydia trachomatis Neisseria gonorrhoeae
Of the sexually transmitted infections listed here, Haemophilus ducreyi is the causative agent of chancroid, or soft chancre. H. ducreyi is the only Haemophilus species that is not part of normal human flora.
Infections of the bone marrow are not only caused by bacteria and fungi, they can be caused by viruses as well. Which of the following viruses can often be isolated from bone marrow specimens? Varicella-Zoster Virus Herpes Simplex Virus Parvovirus B19 Syncytial Virus
Parvovirus B19 is the correct answer because viral replication takes place in human cells and is largely restricted to erythroid progenitor cells, adult bone marrow, and fetal liver cells. Parvovirus B19 is also known as fifth disease and can cause aplastic anemia in patients who have hemoglobinopathies and fetal infections by transplacental inoculation.
A bone biopsy from a jaw sent to a microbiology laboratory for culture grew out an Actinomyces species. What would be the most probable contributing factor to this infection? Poor circulation Poor oral hygiene Break in skin Pelvic infection
Poor oral hygiene
Which of the following is characterized by hypotension due to systemic infection that does not respond to fluid resuscitation (an attempt to replenish body fluid)? Systemic inflammatory response syndrome (SIRS) Sepsis Septic shock Bacteremia
Septic shock is the correct answer. Severe sepsis progresses to septic shock if the hypotension caused by systemic infection does not respond to fluid resuscitation. Septic shock results from the by-products of growing organisms acting on the host body and the host body reacting to the by-products. Gram-negative rods cause the most serious conditions of septic shock. Disseminated intravascular coagulation (DIC) is a complication of septic shock.
Which of the following organisms is the leading cause of bacterial meningitis in infants, young children, and adults in the United States? Haemophilus influenzae Neisseria meningitidis Pediococcus spp. Streptococcus pneumoniae
Streptococcus pneumoniae is the leading cause of bacterial meningitis in the groups listed. Neisseria meningitidis and Haemophilus influenzae are the second and third leading causes, respectively. Pediococcus spp. usually are only capable of causing infections in severely immunocompromised individuals.
Which of the following organisms "pits" the agar, and smells like bleach? Clostridium difficile Eikenella corrodens Proteus vulgaris multocida
The observation of colonies that pit the agar and have a hypochlorite, bleach-like smell is strong evidence for Eikenella corrodens. Clostridium difficile produces a variety of volatile acids, particularly butyric, caproic, and isocaproic acids, that have a distinct fecal smell, simulating a barnyard. The spreading colonies of Proteus vulgaris on chocolate agar have a distinct burned chocolate odor. Pasteurella multocida, which is a strong indole producer, emits an acrid, mothball odor.
A tech working in the laboratory receives a phone call from a doctor who is upset that his patient has a negative urine culture. The doctor indicates that the urinalysis result is positive for leukocyte esterase so the culture should be positive. The doctor feels that the urine culture was not properly handled. How can you explain the discrepancy in the urinalysis and culture to the doctor? -Incorrect agar plates were used for culture -The culture may have been stored incorrectly, causing the organisms to lose viability -The patient could have another infection, such as a sexually transmitted infection (STI) -The culture may have been set up with a 0.01 loop instead of a 0.001 loop
The patient could have another infection, such as a sexually transmitted infection (STI)
A cerebral spinal fluid was collected from a lumbar puncture to evaluate for possible meningitis. Four tubes were collected and sent to the microbiology laboratory for analysis. Which of the four tubes is preferred for microbiology studies? Tube 1 Tube 2 Tube 3 Tube 4
Tube 2 is the correct answer because this tube will be more concentrated and allow for the recovery of low numbers of bacterial organisms causing meningitis. In addition, this specimen will most often be free of blood cells or bacteria introduced by the spinal tap procedure. Tube 1 is incorrect as this tube is used for chemistry studies such as glucose and protein. These tests are least affected by the presence of blood cells and bacteria introduced by the lumbar puncture procedure.
