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Questions and Answers

Explain how the lipases produced by Propionibacterium acnes contribute to the pathogenesis of facial acne.

Lipases produced by P. acnes break down sebum in the sebaceous glands, leading to the release of fatty acids that cause inflammation and contribute to the formation of acne lesions.

Describe the Schick test and its interpretation in assessing immunity to diphtheria.

The Schick test involves injecting diphtheria toxin intradermally. Redness and inflammation indicate a lack of protective immunity, while no reaction suggests immunity due to the presence of neutralizing antibodies.

How does Corynebacterium ulcerans differ from Corynebacterium diphtheriae in terms of disease manifestation?

C. ulcerans causes diphtheria-like throat lesions but typically does not cause toxemia, which is a key feature of C. diphtheriae infections.

Explain why Actinomyces were once considered fungi, and what characteristic confirms they are bacteria.

Actinomyces were initially thought to be fungi due to their long, branching filamentous structures resembling fungal hyphae. However, their true bacterial nature is confirmed by their cell structure, which lacks a nuclear membrane and contains peptidoglycan. Signup and view all the answers

What is the significance of Actinomyces odontolyticus in the development of dental caries?

Actinomyces odontolyticus is associated with the earliest stages of enamel demineralization and the progression of small caries lesions, indicating its role in initiating and advancing tooth decay. Signup and view all the answers

Differentiate between Actinomyces and Nocardia based on their oxygen requirements and typical habitats.

Actinomyces are microaerophilic or anaerobic and are found as commensals in the mouth, while Nocardia are aerobic organisms and are typically found in the soil. Signup and view all the answers

Describe the role of Propionibacteria, specifically Propionibacterium acnes, in the normal skin flora and how it can become pathogenic.

Propionibacterium acnes is a normal component of the skin flora. It becomes pathogenic when it proliferates excessively within hair follicles, leading to inflammation and acne lesions due to the production of lipases and fatty acids. Signup and view all the answers

How do diphtheroids like Corynebacterium hofmannii and Corynebacterium xerosis become opportunistic pathogens?

Diphtheroids are normal inhabitants of the skin and conjunctiva, but they can become opportunistic pathogens in compromised patients, such as causing endocarditis in prosthetic valves. Signup and view all the answers

Why is Actinomyces infection diagnosis challenging, citing specific diagnostic limitations?

Diagnosis is challenging because cultures have poor growth (less than 50% detection rate) and require direct observation of sulfur granules through Gram staining of biopsy or aspiration materials. Signup and view all the answers

How does the presence of an intrauterine device (IUD) increase the risk of actinomycosis, and what specific anatomical area is typically affected?

Long-term IUD use can disrupt the natural flora of the reproductive tract, creating an anaerobic environment that favors Actinomyces growth. This typically affects the female reproductive organs. Signup and view all the answers

Describe the procedure for examining discharges to identify Actinomyces, including the preparation and staining techniques used to visualize the bacteria.

Mix the discharge with sterile saline, allow particles to settle, place between two slides, crush the sample, and perform Gram staining. Look for Gram-positive branching filaments. Signup and view all the answers

Why is long-term antibiotic therapy necessary for treating actinomycosis, and what factors influence the choice of antibiotics?

Long-term therapy is needed because of the slow growth and poor tissue penetration of Actinomyces, requiring extended exposure to antibiotics to eradicate the infection. Choice is influenced by patient allergies and the ability of the antibiotic to penetrate bone, with tetracycline being a common choice. Signup and view all the answers

Explain why actinomycosis is considered an endogenous infection and why this characteristic makes prevention strategies particularly difficult to implement.

Actinomycosis is endogenous because Actinomyces species are normal flora in the body (e.g., mouth and GI tract). Prevention is difficult because the bacteria are already present, and infection arises from opportunistic overgrowth or entry into sterile sites, not external exposure. Signup and view all the answers

Why is isolating Actinomyces israelii from clinical specimens considered difficult, especially in pus specimens?

Due to its exacting growth requirements and relatively slow growth rate, it is often obscured by faster-growing bacteria present in pus specimens. Signup and view all the answers

Describe the appearance of Actinomyces israelii colonies on culture media and explain why this morphology is significant for identification.

The colonies resemble breadcrumbs or the surface of 'molar' teeth. This unique colony morphology can aid in preliminary identification of the organism. Signup and view all the answers

How does Actinomyces israelii typically gain access to deeper tissues to cause infection, and what predisposing factors are often involved?

Actinomyces israelii gains access through breaks in mucosal barriers caused by injury, coincident infection, trauma, or surgery. These factors allow the bacteria to penetrate deeper tissues. Signup and view all the answers

What are 'sulfur granules', how are they formed in actinomycosis, and why are they significant for diagnosis?

Sulfur granules are clumps of Actinomyces israelii organisms seen in pus discharging from sinus tracts. They are significant because they are a key diagnostic clue for actinomycosis; when crushed and Gram-stained, they reveal Gram-positive, branching filaments. Signup and view all the answers

Explain why actinomycosis is often described as an endogenous infection and how the commensal nature of Actinomyces israelii contributes to this.

Actinomycosis is described as an endogenous infection because Actinomyces israelii is a commensal organism found in the normal oral flora. It becomes pathogenic when it takes advantage of injury to penetrate mucosal barriers. Signup and view all the answers

How can polymicrobial infections involving Actinomyces israelii influence the pathogenesis and clinical presentation of actinomycosis?

Polymicrobial infections can alter the typical disease presentation and potentially worsen the infection due to synergistic effects among different bacterial species. This can complicate diagnosis and treatment. Signup and view all the answers

In the context of diagnosing actinomycosis, what is the preferred method for analyzing clinical specimens to identify Actinomyces israelii directly, and why is it favored?

The preferred method is to crush and Gram-stain sulfur granules, followed by observation for Gram-positive, branching filaments, and also culture the granules. It's favored because granules contain a high concentration of the organism, increasing the likelihood of identification. Signup and view all the answers

Describe the typical clinical presentation of orofacial actinomycosis, including common locations and associated patient history.

Orofacial actinomycosis typically presents as a chronic abscess, often at the angle of the lower jaw, with multiple external sinuses. Patients usually have a history of trauma, such as tooth extraction or a blow to the jaw. Signup and view all the answers

Explain why a test that measures lactobacilli levels might be useful for monitoring a patient's dietary profile, even if the test itself is not highly reliable.

Even if unreliable on its own, the correlation between lactobacilli levels and dietary carbohydrate intake allows it to serve as an indicator of the dietary profile. Signup and view all the answers

Describe the mechanism by which Corynebacterium diphtheriae causes harm to the human body, referencing the specific type of molecule involved.

Corynebacterium diphtheriae produces an exotoxin that mediates the disease. This toxin is responsible for the virulence of the bacteria. Signup and view all the answers

How does the method of transmission for Corynebacterium diphtheriae influence strategies for preventing its spread?

Since transmission primarily occurs through respiratory droplets, prevention strategies should focus on respiratory hygiene, such as covering coughs and sneezes, and potentially using masks. Isolation of infected individuals also helps. Signup and view all the answers

Explain the significance of 'snapping fission' in the context of identifying Corynebacterium under a microscope.

Snapping fission causes the bacteria to arrange at angles to each other resembling Chinese characters, which is a key identifying characteristic. Signup and view all the answers

Describe how metachromatic staining reveals information about the internal composition of Corynebacterium diphtheriae.

Metachromatic staining causes intracellular granules of polymerized phosphate to stain a different color (red) than the rest of the cell (blue). Signup and view all the answers

In the Elek test, why is it crucial that the filter paper is soaked in diphtheria antitoxin, and how does this directly contribute to the test's ability to identify toxigenic strains of C. diphtheriae?

The antitoxin in the filter paper binds to the toxin produced by toxigenic strains. The visible precipitation line forms where the antitoxin and toxin combine, confirming toxin production. Signup and view all the answers

What is the critical distinction between toxigenic and commensal corynebacteria, and why is this distinction clinically important?

Toxigenic corynebacteria produce a harmful toxin, while commensal species do not. This distinction is clinically important because only toxigenic strains cause the severe disease diphtheria. Signup and view all the answers

Explain why both in vitro (Elek test) and in vivo (animal inoculation) methods are sometimes used to confirm exotoxin production by Corynebacterium diphtheriae.

While the Elek test detects toxin production, animal inoculation confirms the toxin's virulence and effects in a living organism, offering a more complete assessment. Signup and view all the answers

Explain the mechanism by which diphtheria toxin inhibits protein synthesis in eukaryotic cells, detailing the specific roles of Subunits A and B.

Subunit B of diphtheria toxin binds to a receptor on the eukaryotic cell surface, facilitating the entry of Subunit A into the cell. Subunit A then catalyzes the ADP-ribosylation of elongation factor 2 (EF2), which is essential for protein synthesis, thereby halting protein production. Signup and view all the answers

Describe the composition of the pseudomembrane formed in the respiratory mucosa due to diphtheria infection, and explain how it contributes to the pathology of the disease.

The pseudomembrane consists of bacteria, fibrin, epithelial cells, and phagocytic cells. It obstructs the airway, leading to asphyxiation and potentially death, marking a critical stage in the disease's progression. Signup and view all the answers

Explain the process by which diphtheria toxin is converted into a toxoid, and why this conversion is crucial for prophylactic immunization.

Diphtheria toxin is treated with formaldehyde to convert it into a toxoid. This process renders the toxin nontoxic while preserving its antigenicity, enabling it to stimulate an immune response without causing disease, which is essential for safe and effective immunization. Signup and view all the answers

Outline the steps involved in the systemic spread and effects of diphtheria toxin, focusing on the target organs and the resulting clinical manifestations.

After permeating into the bloodstream, diphtheria toxin affects motor nerves of the myocardium and the nervous system. This can lead to myocarditis, neurological damage, and other systemic complications, illustrating the far-reaching impact of the toxin. Signup and view all the answers

Compare and contrast the mechanisms of action of antitoxin and antibiotics in the treatment of diphtheria.

Antitoxin neutralizes the diphtheria toxin, preventing it from binding to and damaging cells, while antibiotics such as penicillin or erythromycin kill the Corynebacterium diphtheriae bacteria, thus stopping further toxin production. They target different aspects of the disease. Signup and view all the answers

Describe the methodology and purpose of the Schick test in assessing immunity to diphtheria.

The Schick test involves inoculating a standardized dose of diphtheria toxin into the skin to assess the level of circulating antibodies. A positive reaction (inflammation) indicates a lack of immunity, while no reaction suggests sufficient antibody levels due to prior immunization or infection. Signup and view all the answers

Explain why cutaneous diphtheria infections are often mixed infections, and identify the common bacterial species involved in these cases.

Cutaneous diphtheria infections are often mixed due to compromised skin barriers, which allow for co-infection. Common bacterial species involved include Staphylococcus aureus and Streptococcus pyogenes, alongside Corynebacterium diphtheriae. Signup and view all the answers

Describe the role and mechanism of ADP-ribosyl transferase and Elongation Factor 2 (EF2) in the pathogenesis of Diphtheria Toxin.

ADP-ribosyl transferase is an enzymatic component of Diphtheria Toxin that catalyzes the transfer of an ADP-ribose moiety to Elongation Factor 2 (EF2), in the host cell. EF2 is crucial for protein synthesis during translation. By modifying EF2, the toxin inhibits its function, thereby halting protein synthesis in eukaryotic cells. Signup and view all the answers

Explain, using your understanding of microbial metabolism, why Lactobacillus species are able to thrive in acidic environments.

Lactobacillus species are aciduric, meaning they can survive and thrive in acidic environments. They achieve this through mechanisms that maintain internal pH homeostasis, such as proton pumps to expel excess protons, and alterations in their membrane lipids to reduce proton permeability. Signup and view all the answers

Contrast the metabolic processes of homofermentative and heterofermentative Lactobacillus species, detailing the end products and their implications in different environments.

Homofermentative Lactobacillus produce primarily lactic acid from glucose fermentation, leading to a significant decrease in pH. Heterofermentative Lactobacillus produce lactic acid, acetate, ethanol, and carbon dioxide; the production of multiple end products results in a smaller pH decrease compared to homofermenters. Signup and view all the answers

Discuss the potential mechanisms by which Lactobacillus oris, a newly described species in the oral cavity, contributes to or inhibits the development of dental caries, considering its unique metabolic characteristics.

As a newly described species, the exact mechanisms of L. oris are still under investigation. However, based on its metabolic characteristics, it could potentially contribute to caries through acid production if it's highly acidogenic. Conversely, it might inhibit caries by producing bacteriocins, competing with other cariogenic bacteria, or contributing to a more balanced oral microbiome. Signup and view all the answers

Evaluate the historical perspective of Lactobacillus as the primary cariogenic agent and explain why this view has evolved, referencing specific research or findings.

Early research considered Lactobacillus the main cariogenic agent, using lactobacillus counts to indicate caries activity. This view evolved as studies demonstrated that Streptococcus mutans initiates caries formation more effectively through its ability to produce copious amounts of extracellular polysaccharides for biofilm formation. Lactobacillus is now considered important in caries progression. Signup and view all the answers

Considering the facultative anaerobic nature of Lactobacillus, how might changes in the oxygen tension within a deep carious lesion affect its metabolism and contribution to the lesion's progression?

In deep carious lesions, reduced oxygen tension favors the growth of facultative anaerobes like Lactobacillus. This shift can enhance their fermentative metabolism, leading to increased acid production. The increased acidity demineralizes tooth structure and contributes to lesion progression. Signup and view all the answers

Propose a strategy to selectively inhibit the acid production of Lactobacillus in the oral cavity without disrupting the overall balance of the oral microbiome. What are the potential challenges and benefits of this approach?

A potential strategy involves using specific enzyme inhibitors targeting the fermentative pathways of Lactobacillus, or bacteriophages that selectively target acid-producing strains. Challenges include ensuring specificity to avoid off-target effects on beneficial bacteria and preventing resistance development. The benefit includes minimizing pH drop without broad-spectrum disruption. Signup and view all the answers

Compare and contrast the roles of Lactobacillus in the oral cavity, gastrointestinal tract, and female genital tract, highlighting how their metabolic activities contribute to the local environment and overall health in each location.

In the oral cavity, Lactobacillus contributes to caries progression through acid production. In the gastrointestinal tract, they aid in maintaining gut homeostasis and nutrient absorption. In the female genital tract, they produce lactic acid, maintaining a low pH that inhibits pathogen growth. The metabolic activities of Lactobacillus are crucial for the health of each environment. Signup and view all the answers

Based on the characteristics of Lactobacillus, how would the presence of Corynebacterium or Propionibacteria influence the micro-environmental conditions (e.g., pH, nutrient availability) within a dental biofilm, and what implications might this have for caries development?

Corynebacterium and Propionibacteria can contribute to pH changes and nutrient competition within a biofilm. Propionibacteria produce propionic acid, potentially lowering the pH, while Corynebacterium may utilize different substrates, altering nutrient availability. These interactions can either promote or inhibit Lactobacillus growth and acid production, thereby influencing caries development. Signup and view all the answers

Flashcards

Lactobacilli

Saprophytes found in vegetable and animal matter, some are commensals in the human body.

Homofermenters

Lactobacilli that produce mainly lactic acid (65%) from glucose fermentation.