Podcast
Questions and Answers
Which type of media is recommended for cultivating Francisella tularensis?
Which type of media is recommended for cultivating Francisella tularensis?
What is the primary reason that biochemical tests are not recommended for identifying Francisella tularensis?
What is the primary reason that biochemical tests are not recommended for identifying Francisella tularensis?
What are the growth characteristics of Francisella tularensis on agar media?
What are the growth characteristics of Francisella tularensis on agar media?
Which of the following statements is true regarding the infectious dose of Francisella tularensis?
Which of the following statements is true regarding the infectious dose of Francisella tularensis?
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Which biosafety level precautions are required for handling Francisella tularensis?
Which biosafety level precautions are required for handling Francisella tularensis?
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What is the primary cause of whooping cough in humans?
What is the primary cause of whooping cough in humans?
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Which stage of whooping cough is characterized by a mild cough and sneezing?
Which stage of whooping cough is characterized by a mild cough and sneezing?
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What is NOT involved in the attachment of Bordetella pertussis to the respiratory tract?
What is NOT involved in the attachment of Bordetella pertussis to the respiratory tract?
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Which toxin is primarily responsible for the systemic effects observed in pertussis?
Which toxin is primarily responsible for the systemic effects observed in pertussis?
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What is the incubation period for whooping cough?
What is the incubation period for whooping cough?
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What is the primary mechanism through which Bordetella pertussis evades host defenses?
What is the primary mechanism through which Bordetella pertussis evades host defenses?
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How is Bordetella pertussis transmitted?
How is Bordetella pertussis transmitted?
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Which stage of whooping cough involves severe coughing and potential for cyanosis?
Which stage of whooping cough involves severe coughing and potential for cyanosis?
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What is the usual manifestation of Cardiobacterium hominis infection?
What is the usual manifestation of Cardiobacterium hominis infection?
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Which characteristic does NOT apply to Cardiobacterium hominis?
Which characteristic does NOT apply to Cardiobacterium hominis?
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What factor enhances the growth of Cardiobacterium hominis in the laboratory?
What factor enhances the growth of Cardiobacterium hominis in the laboratory?
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Which of the following diseases is NOT associated with Eikenella corrodens?
Which of the following diseases is NOT associated with Eikenella corrodens?
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What is the most common clinical form of tularemia?
What is the most common clinical form of tularemia?
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Eikenella corrodens is primarily found in which location of the human body?
Eikenella corrodens is primarily found in which location of the human body?
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Which characteristic differentiates Eikenella corrodens from other HACEK group members?
Which characteristic differentiates Eikenella corrodens from other HACEK group members?
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Which test result is highly suggestive of a tularemia infection?
Which test result is highly suggestive of a tularemia infection?
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Which biotype of F.tularensis is highly virulent and found in North America?
Which biotype of F.tularensis is highly virulent and found in North America?
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What is the Gram stain morphology of Eikenella corrodens?
What is the Gram stain morphology of Eikenella corrodens?
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What are the most common vectors for tularemia transmission?
What are the most common vectors for tularemia transmission?
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Which of the following organisms is associated with fastidious growth on chocolate agar?
Which of the following organisms is associated with fastidious growth on chocolate agar?
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Which of the following routes is NOT a method of transmission for F.tularensis?
Which of the following routes is NOT a method of transmission for F.tularensis?
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What symptoms are most commonly associated with tularemia infection?
What symptoms are most commonly associated with tularemia infection?
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Which antibiotic is commonly considered the drug of choice for treating tularemia?
Which antibiotic is commonly considered the drug of choice for treating tularemia?
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Individuals in which demographic group are at the highest incidence of tularemia?
Individuals in which demographic group are at the highest incidence of tularemia?
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Which organism is primarily associated with severe infections following a dog or cat bite?
Which organism is primarily associated with severe infections following a dog or cat bite?
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What is the drug of choice for treating infections caused by Canimorsus?
What is the drug of choice for treating infections caused by Canimorsus?
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Which of the following Pasteurella species is most commonly isolated from humans?
Which of the following Pasteurella species is most commonly isolated from humans?
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What characteristic is notable for the microscopy of Pasteurella multocida?
What characteristic is notable for the microscopy of Pasteurella multocida?
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Which of the following characteristics is NOT true about Pasteurella species?
Which of the following characteristics is NOT true about Pasteurella species?
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What is the common clinical manifestation of infections caused by Pasteurella multocida?
What is the common clinical manifestation of infections caused by Pasteurella multocida?
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What type of appearance do colonies of Pasteurella multocida have on blood agar?
What type of appearance do colonies of Pasteurella multocida have on blood agar?
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Which Pasteurella species is known to be isolated from genital specimens and placenta?
Which Pasteurella species is known to be isolated from genital specimens and placenta?
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What is the most common cause of disease in humans from the Legionella genus?
What is the most common cause of disease in humans from the Legionella genus?
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Which serogroup of Legionella pneumophila was responsible for the 1976 outbreak?
Which serogroup of Legionella pneumophila was responsible for the 1976 outbreak?
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What incubation condition is optimal for the growth of Legionella pneumophila?
What incubation condition is optimal for the growth of Legionella pneumophila?
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Which of the following is NOT a characteristic of Legionella pneumophila?
Which of the following is NOT a characteristic of Legionella pneumophila?
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What is the primary mode of transmission for Legionella pneumophila?
What is the primary mode of transmission for Legionella pneumophila?
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What initial symptoms characterize Pontiac fever caused by Legionella pneumophila?
What initial symptoms characterize Pontiac fever caused by Legionella pneumophila?
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For what length of time should blood cultures be incubated to detect Legionella pneumophila?
For what length of time should blood cultures be incubated to detect Legionella pneumophila?
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Which of the following tests is least useful for the rapid diagnosis of Bordetella pertussis?
Which of the following tests is least useful for the rapid diagnosis of Bordetella pertussis?
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What is one distinguishing feature of Bordetella pertussis?
What is one distinguishing feature of Bordetella pertussis?
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What type of medium is optimal for isolating Bordetella pertussis?
What type of medium is optimal for isolating Bordetella pertussis?
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Which antibiotic is often considered the drug of choice for treating infections caused by Legionella pneumophila?
Which antibiotic is often considered the drug of choice for treating infections caused by Legionella pneumophila?
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In order to be considered positive for Legionella pneumophila, what titer must the indirect FAT show?
In order to be considered positive for Legionella pneumophila, what titer must the indirect FAT show?
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What is a common environmental condition where Legionella pneumophila can thrive?
What is a common environmental condition where Legionella pneumophila can thrive?
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What is a characteristic appearance of visible colonies of Legionella pneumophila on culture?
What is a characteristic appearance of visible colonies of Legionella pneumophila on culture?
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Study Notes
Fastidious Gram Negative Rods
- These bacteria are difficult to cultivate on standard laboratory media.
- Facultative anaerobes (some are aerobic or microaerophilic).
- Human infections with these bacteria are relatively uncommon.
- Examples include Haemophilus, Francisella, Legionella, Bordetella, and Brucella. The HACEK group (Haemophilus parainfluenzae, Aggregatibacter, Cardiobacterium, Eikenella, and Kingella) causes Subacute Bacterial Endocarditis (SBE).
Haemophilus
- Facultative anaerobes requiring enriched media (fresh blood or heme/NAD).
- Require X (heme) and V factor (NAD) in fresh blood for growth.
- Growth requires 5-10% CO2.
- Relatively short, pleomorphic (variable shape), non-motile gram-negative rods that sometimes form coccobacillary shapes.
- Often have a polysaccharide capsule, with serotyping (categorizing by capsule antigen) significant in clinical contexts, especially for Haemophilus influenzae type b.
Useful Tests
- ALA or Porphyrin test: Some Haemophilus use δ-aminolevulinic acid (ALA) to synthesize heme factor, producing porphyrins that fluoresce under UV light.
- This test is more accurate than X and V factor disks at determining X factor requirements.
Horse Blood Agar
- Hemolysis is observed on HBA, as it does not hemolyze sheep's blood.
- Hemolysis is best viewed from behind the agar plate.
- Stabbing the inoculation area enhances the hemolytic reaction.
X and V Factor Requirement
- X factor is heme, hematin, or hemichrome required for catalase, peroxidase and cytochrome electron transport system.
- V factor is NAD, a coenzyme that transfers electrons in reactions.
- Both are found in red blood cells (RBCs).
X and V Factors Test
- Diagnostic tests where culture media contains X and V factors.
Species Characteristics
- A table listing growth results on X, V, and combined X/V factors for Haemophilus influenzae, H. aegypticus, H. parainfluenzae, H. haemolyticus, and H. parahaemolyticus.
H. influenzae and H. aegyptius
- Appear as coccobacilli, thread-like rods with significant pleomorphism.
- Usually encapsulate, but capsules can be lost during subculture.
- Colonies are generally round, small, and convex, and are non-hemolytic.
- H. influenzae usually ferments glucose and xylose but not lactose or sucrose.
H. Influenzae and H. aegyptius
- Variable urease and indole reactions distinguish H. aegyptius from H. influenzae.
- H. influenzae, especially in young patients (<15 years), should be serotyped.
- The organism can produce six different capsular antigen types (a-e).
- Latex agglutination tests rapidly detect capsular antigens.
Clinical Significance
- Also known as Pfeiffer bacillus, named after Richard Friedrich Johannes Pfeiffer who identified it during the 1892 influenza pandemic.
- It doesn't cause influenza, but has been a secondary invader when combined with the Influenza A virus.
- Adherence is mediated by pili (especially in the case of Hib).
- Transmitted person-to-person via respiratory droplets, causing sinusitis and middle ear infections.
- Hib causes pneumonia, empyema, epiglottitis, cellulitis, septic arthritis, as well.
- Treatment with β-lactam antibiotics (e.g., Ceftriaxone, Fluoroquinolones) is helpful if the bacteria does not produce β-lactamase.
- There was and still are 4 conjugated vaccines available today for Hib.
- Can be carried in the URT (approximately 2–4% of healthy individuals). Carrier rate is significantly higher (up to 80%) for non-typable strains.
- Non-encapsulated strains are non-invasive, primarily causing issues in patients with underlying chronic conditions (bronchitis, emphysema, COPD).
- H. aegyptius is a common cause of conjunctivitis and is sometimes isolated from blood cultures.
Antibiogram Pattern
- Common Haemophilus strains are typically susceptible to ampicillin.
- A minority (25-30%) are β-lactamase-positive and less susceptible.
- These strains are generally susceptible to newer cephalosporins, such as cefotaxime and ceftriaxone.
H. parainfluenzae
- Resembles H. influenzae, both microscopically and in colony morphology.
- In blood cultures, H. parainfluenzae may form filamentous clumps.
- ALA positive requires only NAD.
- Non-hemolytic on horse blood agar.
- Produces acid and gas from glucose and sucrose but does not utilize lactose or xylose.
- Urease/catalase status is variable, and indole negative.
Clinical Significance (HACEK and Capnocytophaga)
- Part of the normal microbiota of the human respiratory tract.
- May cause endocarditis, urethritis, and URT infection.
- Potential pathogens in patients with compromised immune systems.
Francisella
- Two species: F. tularensis (pathogenic) and F. philomiragia.
- F. tularensis has four subspecies (biovars): tularensis, holarctica, mediasiatica, and novicida.
- F. tularensis is a Category A biological agent.
- Appears as non-motile, non-spore-forming, strictly aerobic, gram-negative bacilli or coccobacilli.
- Facultative intracellular pathogen.
- Requires nutritional supplements like cysteine, cystine, or thiosulfate..
Francisella tularensis
- Does not grow well on routine lab media.
- Best growth on cysteine-supplemented agar (incubation at 37°C, with aerobic conditions).
- Good growth occurs on blood-cysteine-glucose, enriched chocolate, or Thayer-Martin agar, and on BCYE media containing cysteine.
- Highly infectious; handled in BSL-3 safety practices.
- Extremely small, intracellular GNCB; stains poorly with Gram's stain and exhibits high pleomorphism.
Identification
- Francisella are difficult to identify biochemically.
- Usually missed in tissue smears with gram staining due to their small size, intracellular state, and pale staining.
- They possess a thin capsule composed of lipid, proteins, and carbohydrates.
Francisella
- Use chocolate agar, MTM, BCYE, and TSB broth to culture.
- MacConkey and EMB media won't support growth.
- Growth is seen after 48 hours.
- Oxidative, urease, satellite, negative for X and V factors; weakly positive for catalase.
- Infection is possible with just 50 organisms through cutaneous or inhalation routes. Requires BSL 3 precautions
Francisella
- Requires special handling procedures and a bio safety cabinet (BSC).
- Colonies are very small and transparent after extended incubation, sometimes appearing as pinpoint colonies within 24 hours.
- They have a negative oxidase, urease, indole, and ornithine reaction.
- Francisella are weakly positive for catalase and produce β-lactamase.
- These bacteria are facultative anaerobes and require amino acid cysteine
F. tularensis
- Direct fluorescent antibody tests (FAT) are used to detect F. tularensis in tissue and sputum samples.
- A significant antibody titer of 160 in a single sample is strongly suggestive of F. tularensis infection.
- A four-fold increase in antibody titer in paired serum samples taken two weeks apart is very indicative of an active F. tularensis infection.
Clinical Significance (Francisella)
- The agent of tularemia, also called glandular fever, tick fever, or rabbit fever.
- Named after Edward Francis, who extensively studied the organism.
- The species name refers to Tulare County, California, where the organism was first discovered.
- Transmitted by ingestion, inhalation, or an arthropod bite (most common vectors are ticks and deerflies).
Tularemia
- Zoonotic illness (e.g., lemming or water rat).
- Spread through ingestion, inhalation, or arthropod bites.
- Common presentations include pneumonic, glandular, oropharyngeal, oculoglandular, and typhoidal forms; ulceroglandular is the most common.
F. tularensis
- Wide animal reservoir (birds, fish, amphibians, rabbits, muskrats, squirrels).
- Infections can occur from bites, direct contact, or through ingestion of contaminated water or meat.
F. tularensis
- High-risk groups include males and children under 10, and those like hunters, vets, or taxidermists.
- Two biotypes: A (highly prevalent in the US and North America; transmitted by ticks from infected rabbits) and B (more widespread globally and associated with water and rodents).
- Manifestations depend largely on the transmission route.
F. tularensis
- Common symptoms include fever, malaise, headache, and pain in the affected region.
- Infection often starts as minute skin abrasions, leading to enlarged regional lymph nodes that can become necrotic.
Legionella pneumophila
- Discovered after a 1976 outbreak of respiratory illness at an American Legion convention in Philadelphia.
- Pontiac fever is a less severe illness resembling influenza, common during Legionnaire outbreaks in Michigan. L. pneumophila is prevalent in warm, moist environments.
- Water sources are common reservoirs. (Lakes, streams, mud, soil). .
- Of 40+ species, L. pneumophila is the most frequent cause of Legionnaire's disease.
Legionella pneumophila
- Bacteria are aerobic and gram-negative rods.
- Requires iron salts, cysteine, and high humidity for optimal growth (6.9 pH, 37°C, 90% humidity).
- BCYE (buffered charcoal-yeast extract) supplemented with 1% α-ketoglutarate is used for isolation.
Legionella pneumophila
- Stained smears from tissue specimens reveal small, pleomorphic gram-negative bacilli.
- Identification is commonly done with direct FAT.
- Catalase+, gelatinase+, and β-lactamase-positive.
- Produces various enzymes, such as metalloprotease, lipase, DNase, and RNase.
Legionella pneumophila
- Distinguished by oxidase production, hippurate hydrolysis and gram staining.
- Relatively thin (0.5–1.0 μm) rods, ranging in length from 2–50 μm.
- Does not stain well with Gram's stain.
- Basic fuchsin is often used as a counterstain with Gram staining (for 3 minutes).
Legionella pneumophila
- Colonies appear 3-4 days of incubation on proper media.
- Colonies may be round, flat, with entire edges, and glistening, often convex.
- These colonies can have a ground glass-like appearance, giving a speckled or shattered windshield-like effect.
- Pigmentation can vary from colorless to grayish to pale green, to an iridescent pink or blue; colonies may be translucent.
Legionella pneumophila
- Culture specimens include bronchial washings, lung biopsies, pleural fluid, and blood.
- Sputum is not a good culture choice due to the microbiota's presence in the URT.
- L. pneumophila fluoresces under long-wave fluorescence (e.g., Wood's lamp), displaying a pale yellow-green fluorescence.
- 4-fold rise in anti-Legionella antibodies to a titer of 128 or greater is considered a positive test.
Clinical Significance (Legionella)
- Causes Legionnaire's disease (most common in males over 35 with chronic respiratory conditions like smoking or emphysema).
- Acquired via inhalation of aerosols from contaminated water sources (e.g., air-conditioners, showerheads, cooling towers)
- Organisms can reside in the alveolar macrophages.
- Relatively resistant to destruction by PMNs.
- Disease range can be from mild, short-term fever to severe purulent pneumonia
Pontiac fever
- Mild illness resembling influenza.
- Symptoms: sore throat, cough, headache, fever, chills, malaise, myalgia, dizziness, confusion, photophobia, and neck stiffness.
- Erythromycin is the preferred choice as it penetrates WBCs to reach the intracellular pathogen.
- Rifampin can also be used..
Bordetella pertussis
- Strict aerobe, gram-negative, small coccobacillus (singly or in pairs).
- Transmission via aerosolized droplets.
- Strictly a human pathogen, non-invasive.
Bordetella pertussis
- Optimal culture is on media containing charcoal (to neutralize inhibitory effects) Bordet-Gengou medium (potato-sheep blood-glycerol medium that includes Pen G).
- Regan-Lowe medium is commonly used as a transport medium.
- Incubate at 35°C in a moist environment (e.g., sealed plastic bag) for 3-7 days for growth.
Diagnosis (Bordetella pertussis)
- Based on symptoms, cultures of respiratory secretions (Bordet-Gengou medium), direct fluorescent antibody testing (DFA), PCR, and slide agglutination.
Bordetella pertussis
- Biochemical reactions are rarely used for identification.
- Commonly collected specimens are saline nasal washes and nasopharyngeal swabs.
Bordetella pertussis
-
DFA and slide agglutination tests are employed to detect the bacteria in nasopharyngeal aspirates and in cultured colonies.
-
DFA needs to be used with cultures as it’s sensitivity is low.
-
Serologic tests for antibodies are not useful for rapid diagnosis since agglutinating and precipitating properties do not occur until the third week of the illness.
Differentiation of Bordetella Species
- Table showing growth on common media (SBA, MacConkey) and Bordet-Gengou agar, urease, oxidase, and motility for B. pertussis, B. parapertussis, and B. bronchiseptica.
B. pertussis
- Small, transparent, hemolytic colonies on Bordet-Gengou medium.
Clinical Significance (Bordetella pertussis)
- Humans are the only known source.
- Whooping cough (pertussis) is most common in children under 5, and mortality is often high in infants.
- Transmission occurs via inhalation of contaminated aerosols (from individuals in the early stages of the illness).
Pertussis Pathogenesis
- Two stages: Respiratory colonization (7–10 days; no symptoms) and toxin-mediated disease.
Disease Progression (Bordetella pertussis)
- Stages (Catarrhal, Paroxysmal, Convalescent) are outlined over a period of approximately 12 weeks. This includes descriptions of symptoms at each of the three stages.
Stages of Whooping Cough
- Incubation stage (at least two weeks; mild cough, sneezing). Highly infectious, with large numbers of organisms present in respiratory droplets.
- Catarrhal stage (mild cough, sneezing). Highly contagious.
- Paroxysmal stage (severe cough, whooping sound on inhalation; cyanosis, vomiting, and convulsions may occur).
- Convalescent stage (gradual recovery, with eventual cessation of coughing fits).
Colonization (Bordetella pertussis)
- Fimbriae are not involved in colonization. Colonization requires pertussis toxin and filamentous hemagglutinin factors.
Pertussis Toxin (AB-toxin)
- Description of the six protein subunits of the Pertussis toxin (PT).
Pertussis- Disease
- Primarily toxin-mediated, with exotoxins controlled by a central locus. The BvgAS two-component signal transduction system detects environmental signals and regulates gene expression.
Pertussis- Disease
- Inflammation from the toxin inhibits clearance of pulmonary secretions.
- Cough progresses from mild to severe and often follows a three-stage progression (Catarrhal, Paroxysmal, Convalescent)
- Slow resolution. Host defenses are evaded.
- Lymphocytosis is a characteristic feature.
Bordetella pertussis Toxins
- Five major toxins.
Systemic Effects of Pertussis Toxin
- Systemic effects include:
- T-cell lymphocytosis with reduced mitogenicity.
- Increased insulin and histamine production.
- Increased IgE production.
- Impaired phagocyte function.
Adenylate Cyclase Toxin
- Both adenylate cyclase and hemolysin are secreted invasive toxins.
Other Toxins
- Dermonecrotic toxin (lethal toxin): strong vasoconstrictor.
- Tracheal cytotoxin: prevents ciliary function of respiratory epithelial cells.
- Lipopolysaccharide (endotoxin): acts as a generalized toxin.
Treatment (Bordetella pertussis)
- Antibiotic treatment (e.g., erythromycin) used to treat.
- Vaccine (e.g., DTaP vaccine): Immunogenicity wanes after 5-10 or more years, necessitating boosters/updated vaccines over time.
- Acellular vaccines are an important alternative.
Brucella
- Intracellular bacteria mainly found in animals; humans are accidental hosts.
- Isolated by Sir David Bruce from the island of Malta, hence the disease's historical name Malta fever, or undulant fever.
- Determined to be a single species,B. melitensis, with additional designations (e.g., B. abortus, B. suis, B. canis) that are used to specify the animal source of the bacteria, though DNA sequencing has confirmed there is only one species.
General Characteristics (Brucella)
- Strictly aerobic, intracellular pathogens with complex growth requirements.
- Require well-defined media containing amino acids, vitamins, salts, and glucose.
- Grow slowly on sheep's or goat's blood agar and or chocolate agar containing 5 to 10% CO2.
- Gram-negative, non-motile rods that stain irregularly and pale with Gram's stain.
- Inactive metabolically, in that they do not produce acid or gas in significant amounts; instead, they reduce nitrates to nitrite.
Brucella
- Small, gram-negative, aerobic, non-motile, non-spore-forming, unencapsulated coccobacilli or bacilli .
- Can be transmitted via aerosolized droplets.
- Should be handled under BSL-3 containment.
- Positive for Oxidase, Catalase, and Urease.
- Can be acquired via laboratory exposure (accidental).
Brucella
- Category B select agents (CDC). Considered a potential bioterrorist agent, with an infectious route through aerosolization, percutaneous penetration, or oral ingestion.
- Includes B. melitensis, B. abortus, B. suis, B. canis, B. ovis, and B. neotomae.
Brucella Identification
- Short coccobacillary or bacilli forms, sometimes with bipolar staining.
- Colonies typically appear after 3–5 days of incubation on enriched media.
- Colonies are small, smooth, convex, appearing transparent and non-hemolytic.
- Colonies tend to become rough on subculture due to capsule loss.
Pathogenesis (Brucella)
- Different biovars have varying amounts of LPS (lipopolysaccharide) antigens (A, M, L). This difference leads to variability in dye susceptibility and H₂S production.
- Brucella localizes in the pregnant uterus of affected animals, utilizing erythritol in allantoic and amniotic fluids.
- Abortion is a substantial clinical presentation.
- Brucella can remain viable in dried soil for up to 60 days, and can be present in animal milk and cheese products.
Stages of Brucellosis
- Acute brucellosis; Non-specific symptoms occurring within 8 weeks of exposure.
- Subchronic stage (undulant form); follows a year-long exposure, marked by undulating fevers, arthritis and epididymoorchitis.
- Chronic stage; after a year of exposure, symptoms including depression, arthritis, and chronic fatigue can occur.
Pathogenesis (Brucella)
- Farmers, vets, and abattoir/slaughterhouse workers are at higher risk.
- Incubation period ranges from 1-6 weeks.
- Slow, insidious onset, disseminated via lymphatics and blood.
- Mononuclear cell proliferation is a key histologic finding.
- Fever often has a daily pattern (rising in the afternoon and falling at night).
- Weakness, malaise, minor aches/pains are associated.
- Immunity strengthens after recovery, although reinfection is possible.
Pathogenesis (Brucella)
- Brucella are typically susceptible to tetracycline, streptomycin, and ampicillin but are difficult to eradicate due to their intracellular nature. Extended treatment periods of streptomycin and tetracycline may be necessary.
- Rifampin prophylaxis might be necessary for close exposure in individuals under age 4.
HACEK Group and Capnocytophaga
- HACEK is an acronym encompassing the initial letters of the genera involved: Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, and Kingella.
- Capnocytophaga are also included in this group due to similar criteria.
HACEK Group and Capnocytophaga: General Characteristics
- Gram-negative bacilli.
- Require elevated CO2 (5–10%).
- Usually more dysgonic (slower or poorer growth).
- Key pathogens in endocarditis.
- Often part of the normal mouth flora.
- Opportunistic pathogens, especially in immunocompromised hosts.
- Include both fermentative and non-fermentative gram-negative bacilli.
Aggregatibacter aphrophilus
- "Foam-loving" bacteria needing high CO2 concentrations.
- Commonly found in dental plaque and gingival scrapings.
- A leading cause of endocarditis.
- Clinical presentation includes fever, heart murmur, congestive heart failure, and emboli.
- Colonies on CAP have a convex, granular texture and yellow coloration, often with distinct, opaque central zones.
Aggregatibacter actinomycetemcomitans
- Formerly known as Actinobacillus actinomycetemcomitans.
- Six species are found in humans.
- Gram-negative bacilli to coccobacilli; non-motile.
- Six serotypes based on surface polysaccharides.
- Normal oral microbiota in humans.
- Isolated from blood, lung tissue, mouth/brain abscesses and sinuses. Causes both SBE and periodontitis.
Aggregatibacter actinomycetemcomitans
- Key virulence factors include collagenase, leukotoxin.
- Requires serum for carbohydrate fermentation.
- Star-shaped, with 4–6 points visible at the centre of colonies after 48 hours' growth.
- Catalase+, negative for X and V factors.
- Doesn't grow in McConkey agar, while oxidase status varies; urease-, indole-, esculin-, citrate-, ferments glucose, but not lactose and sucrose.
Cardiobacterium hominis
- Pleomorphic, non-motile, fastidious gram-negative bacilli.
- Normal microbiota of the nose, mouth, and throat; sometimes in the GI tract.
- Common presentation is endocarditis (often with large vegetations but without fever).
- Commonly infects the aortic valve.
- Sometimes associated with meningitis.
- Gram stains sometimes show false-positive reactions in parts of the bacilli.
Cardiobacterium hominis
- On Gram stains, often form rosette swellings, long filaments, or stick-like structures in yeast extract.
- Grows slowly on SBA and CHOC but not on McConkey, with 5% CO2 enhancing growth.
- Ferments glucose, mannitol, sucrose, and maltose when serum is added.
- Positive for oxidase, but negative for catalase, indole, urease, nitrate, gelatin, and esculin.
- Standard therapy includes penicillin and aminoglycosides.
Eikenella corrodens
- Normal microbiota of the oral and intestinal cavities.
- Often associated with human bites and poor oral hygiene.
- Reported as a cause of meningitis, empyema, pneumonia, osteomyelitis, and post-op infections.
- Least predilection for attaching to heart valves among HACEK bacteria.
- Gram-negative coccobacilli, non-motile, oxidase-positive, and saccharolytic.
- Catalase-negative; often produces a yellow pigment.
Eikenella corrodens
- Corrodes (pits) the agar surface.
- Non-hemolytic, but may exhibit greening around colonies on SBA.
- Bleach-like odor from the agar surface is often evident.
- Doesn't grow in MacConkey or EMB broth.
- Forms granules within the tube of broth cultures.
- Positive for lysine and ornithine decarboxylase but negative for arginine dihydrolase.
- Resistant to clindamycin, aminoglycosides, and many β-lactams
- Sensitive to Penicillin, Ampicillin, and cephalosporins in vitro.
Kingella species
- Three known species (K. kingae, K. denitrificans, and K. oralis).
- Coccobacillary to short bacilli with squared ends that commonly develop in pairs or short chains.
- Resist decolorization in Gram staining.
- Often grows on MTM, resembling Neisseria colonies when not pitting agar.
- Non-motile, oxidase+, catalase-, and ferments glucose but not sucrose or other specific carbohydrates.
- Commonly colonizes the upper respiratory tract. Possible association with poor dental hygiene or surgical procedures.
Kingella denitrificans
- Positive for glucose fermentation and nitrate reduction; negative for catalase, superoxide dismutase, urease, indole, esculin, gelatin, and citrate.
Kingella kingae
- Recognized as a major pathogen in children (pediatrics) .
- Weakly ferments glucose and maltose but not sucrose.
- Can produce a yellow pigment.
- Two colony types: spreading or corroding, and smooth, convex, beta-hemolytic.
- Isolated clinically from blood, bone, joint fluid, urine, and wound specimens.
- Major cause of degenerative joint and bone infections in children under three years old.
Kingella kingae
- Causes endocarditis and are generally susceptible to most antibiotics.
HACEK group
- Morphology of Kingella kingae in Gram's stain, a commonly observed characteristic (pleomorphic short rods in chains).
Capnocytophaga
- Member of the family Flavobacteriaceae; includes dysgonic fermenters (DF-1 and DF-2).
- Composed of 7 species, with five commonly residing within the oral cavity.
- Rarely a direct cause of endocarditis, but can cause sepsis in immunocompromised patients (e.g., individuals with neutropenia).
- Fastidious, facultative anaerobic, gram-negative bacilli.
- Thin, often fusiform (pointed ends), resembling Fusobacterium.
- Glide on solid surfaces rather than move by flagella.
Capnocytophaga
- Colonies are normally adherent, showing a yellow-orange pigment, and are mostly non-hemolytic.
- Ferments glucose, maltose, and sucrose (although TSI is negative).
- Indole-negative, and reduces nitrates.
- Negative for the majority of biochemical tests (except esculin hydrolysis).
- Oxidase+ and catalase-negative (except for C. ochracea).
- Isolates are frequently found in dental plaque.
- C. ochracea is a frequent clinical isolate.
Capnocytophaga
- C. canimorsus causes severe, potentially life-threatening infections in humans through dog or cat bites; S to imipenem, erythromycin, clindamycin, tetracycline, quinolones, and β-lactams
- Resistant to aminoglycosides.
- Penicillin is frequently the drug of choice.
Pasteurella species
- Seventeen species based on DNA hybridization.
- P. canis is associated with canines, P. stomatis and P. dagmatis with both dogs, cats, and humans.
- P. multocida has three subspecies: multocida, septica,and gallicida; 5 serogroups (A-F).
Pasteurella species
- Colonizes the upper respiratory and gastrointestinal tracts in mammals/birds.
- Human infections are usually due to animal bites/scrapes.
- P. multocida is the most common isolate.
Pasteurella species
- Gram-negative coccobacilli, ovoid or filamentous, or exhibit bipolar staining and safety-pin appearances.
- Non-motile, facultative anaerobes.
- Ferments glucose without gas production.
- Grows on SBA (non-hemolytic) and CAP; not on McConkey.
- Colonies often exhibit a mucoid appearance with a narrow halo (green-brown).
Pasteurella multocida
- Systemic, pneumonic, and cutaneous forms of infections can occur. Usually, bite wounds or animal scratches are the infection entrance locations.
- Can cause infections such as localized infections, respiratory tract infections, and some life-threatening systemic disorders (meningitis, severe bacteremia).
Pasteurella multocida
- 5% blood or chocolate agar encourages rapid growth; small, smooth, convex colonies; characteristic "musty" smell.
- Does not grow on McConkey agar and is oxidase-positive.
- Microscopic examination reveals very small gram-negative rods exhibiting bipolar staining.
Pasteurella bettyae
- Isolated from many places, including placenta, amniotic fluid, blood, rectal sites, and urogenital specimens.
- Fastidious, capnophilic coccobacilli; facultative anaerobe, non-motile.
- Ferments glucose and fructose.
- Positive for catalase, indole, and variable oxidase activity.
- May grow on McConkey agar under specific conditions.
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Test your knowledge on Francisella tularensis, including its cultivation media, growth characteristics, and biosafety precautions. This quiz covers key aspects of identifying and handling this infectious organism, making it essential for students and professionals in microbiology and public health.
