Clase 27 Transmi-I

Estreptococos: Generalidades y Características

The speaker introduces the topic of streptococci, focusing on general characteristics and details that will aid in understanding the mechanisms of virulence.

Streptococcus Genus Creation

• Streptococcus genus created by Billroth in 1877, using Greek terminations to describe easily foldable and elongated structures.

• Current genus comprises over 50 species, all being Gram-positive cocci forming pairs or chains.

Chain Formation Characteristics

• Streptococci exhibit incomplete cell division, forming short or long chains due to incomplete cellular division.

• Cellular rearrangement during division leaves a scar at the center of each cell, marking the point for future divisions.

Cell Division and Growth

• Division occurs perpendicular to the chain axis, leading to new cell formation in central parts rather than ends.

• Observation not visible in Gram staining; streptococci are facultative anaerobes capable of growth without oxygen.

Virulence Factors and Classification

Discussion on virulence factors exhibited by streptococci along with their classification based on physiological characteristics.

Physiological Characteristics

• Streptococci are capnophilic, inhabiting human skin and tissues while some found in animals.

• They ferment carbohydrates into lactic acid and require enriched media due to fastidious nature.

Enzymatic Features

• Catalase-negative organisms distinguishing them from other important streptococcus genera.

• Non-motile, non-sporulating bacteria exhibiting pathogenicity through pyogenic processes leading to pus formation.

Pathogenicity and Classification Challenges

Exploration of streptococcus' pathogenic nature as pyogenic agents and challenges in their classification systems over time.

Pathogenicity Insights

• Streptococci commonly manifest as pyogenic pathogens causing purulent infections characterized by pus formation.

• While not exclusive pus producers, they are well-known for such infections compared to other bacterial species.

Classification Complexity

• Various classification systems have been attempted but face challenges with evolving research tools uncovering more sophisticated identification methods.

Classification of Streptococci Based on Hemolytic Patterns

In this section, the speaker discusses the classification of streptococci based on their hemolytic patterns using agar blood plates.

First Classification System - Hemolytic Patterns

• Blood agar preparation involves adding 5% sheep blood to a liquefied agar base at a temperature suitable for hand tolerance.

• The atmosphere in which streptococci grow on agar is crucial; a capnograph provides the necessary gas mixture.

Hemolytic Categories

• Streptococci produce substances that partially or completely destroy red blood cells, leading to categorization as alpha-hemolytic or beta-hemolytic based on the extent of destruction.

• Alpha-hemolytic streptococci produce pneumolysin, resulting in partial destruction and formation of biliverdin pigment around colonies.

Beta-Hemolytic Streptococci

• Beta-hemolytic streptococci produce streptolysins, with two types: S (produced in serum presence) and O (oxygen-labile).

• Beta-hemolytic streptococci appear yellow due to red cell destruction around colonies, indicating complete lysis.

Rebecca Lancefield's Contribution to Streptococcus Classification

This part delves into Rebecca Lancefield's system for classifying streptococcus species based on carbohydrate molecules' conformations.

Lancefield's Classification System

• Lancefield identified different carbohydrate conformations in Gram-positive cocci and used them for classification.

• She produced antisera by inoculating purified carbohydrate chains into animals to create specific antibodies against these antigens.

Antigen Specificity

• Antisera with specific antibodies react with laboratory antigens derived from the original carbohydrates, aiding in identification through agglutination tests.

• Antigen A is specific to Streptococcus pyogenes, while antigen B belongs to Streptococcus agalactiae due to distinct rhamnose residues' spatial arrangement.

Importance and Limitations

Classification of Streptococci

The speaker discusses the challenges in classifying streptococci and how advancements in technology have led to a better understanding of different species within this group.

Challenges in Classification

• New technologies revealed that Streptococcus anginosus could be classified into at least three groups (F, G, L), indicating previous classifications might have been incorrect.

Cross-Reactivity and Caution

• Cross-reactivity was observed due to identification by various antisera, emphasizing the need for caution in classification.

Importance of Pathogens

• Key pathogens like Streptococcus pyogenes (Group A beta-hemolytic streptococcus) are highlighted as crucial, marked in blue on a list of identified species.

Changes in Nomenclature and Classification

The discussion shifts towards changes in nomenclature impacting the classification of streptococci, leading to potential confusion but retaining some validity for laboratory reports.

Nomenclature Changes

• Changes in genus nomenclature affected previously known streptococci groups like Enterococcus and Lactococcus.

Impact on Classification

• Due to these changes, classifying streptococci becomes challenging over time, although older terms may still be used in laboratory reports based on reagents used.

Laboratory Identification Methods

Laboratory methods such as catalase testing and biochemical assays play a crucial role in identifying different types of streptococci based on their characteristics.

Catalase Test Significance

• Catalase testing is fundamental for distinguishing between staphylococci (catalase-positive) and streptococci (catalase-negative).

Biochemical Classification System

The speaker introduces the biochemical classification system for partially hemolytic bacteria, outlining specific tests like optochin sensitivity to differentiate between strains.

Optochin Sensitivity Test

• Optochin test involves using a copper salt-soaked disk; inhibition zones indicate positive results. Positive results identify Streptococcus pneumoniae conclusively.

Beta-Hemolytic Streptococcus Classification

Differentiating beta-hemolytic streptococcus strains involves utilizing bacitracin disks to determine susceptibility or resistance, aiding accurate classification.

Bacitracin Disk Test

• Beta-hemolytic streptococcus strains showing growth inhibition around bacitracin disks are classified as Group A (S. pyogenes), while those resistant are categorized as Group B or S. agalactiae.

Enterococcus Identification

Identifying enterococcus involves incubation with sodium chloride-rich broths; growth indicates enterocooci presence while non-growth suggests other species from the list provided earlier.

Enterocooci Identification Method

• Sodium chloride-rich broth incubation aids enterocooci identification; absence indicates other species from the mentioned list or S. bovis.

New Section

In this section, the speaker discusses how individuals can be carriers of certain pathogens due to past infections or immune system control. The focus is on the presence of pathogens in the genitourinary tract and their potential to cause specific conditions.

Understanding Pathogen Carriage

• Individuals may carry pathogens either due to past infections or because their immune system keeps the pathogen in check.

• Pathogens residing in the genitourinary tract can lead to neonatal sepsis or, in severe cases like bacteremia, reach the bloodstream and cause meningitis.

• Certain streptococci take advantage of host predisposing factors, leading to complex clinical conditions when coexisting with other bacteria.

New Section

This segment delves into the implications of pathogen presence in individuals with compromised health conditions, such as cancer patients or those in intensive care units (ICUs), highlighting how specific streptococci strains can lead to severe diseases.

Impact on Vulnerable Populations

• Streptococcus viridans strains, including Streptococcus mutans, can cause significant health issues in immunocompromised individuals beyond typical community-acquired infections.

• Streptococcus mutans is associated with dental caries, while Streptococcus pneumoniae causes serious respiratory tract infections.

New Section

This part focuses on key pathogens within the Streptococcus genus, particularly Streptococcus pyogenes. The discussion covers common characteristics and behaviors of these pathogens.

Characteristics of Streptococcus Pyogenes

• Streptococcus pyogenes typically form small circular white colonies with complete hemolysis halos, indicating beta-hemolytic behavior.

• These bacteria exhibit unique staining properties due to cell death and loss of peptidoglycan components.

New Section

Here, the speaker elaborates on additional features of Streptococcus pyogenes related to carbohydrate fermentation and its implications for disease manifestation.

Disease Manifestation Factors

• Streptococcus pyogenes' ability to ferment carbohydrates contributes to acidity production that complicates disease presentation when interacting with other bacteria.

• The presence of these bacteria in throat and skin tissues can lead to conditions like pharyngitis as a common clinical outcome.

New Section

This section explores how interactions between pathogens like Streptococcus pyogenes and human hosts can result in various clinical manifestations based on virulence factors and environmental conditions.

Clinical Presentation Insights

• Pharyngitis is a prevalent condition caused by direct contact transmission from infected individuals harboring virulent strains like Streptococcus pyogenes.

Understanding Bacterial Virulence Mechanisms

In this section, the discussion revolves around bacterial virulence mechanisms, focusing on how certain factors prevent phagocytosis and complement activation.

Factors Preventing Phagocytosis and Complement Activation

• Bacteria possess receptors on their cell surface that are not recognized by phagocytic cells due to their location outside the capsule.

• The complement system is prevented from being activated, particularly avoiding the formation of the membrane attack complex on the bacterial surface.

• The presence of a capsule inhibits opsonization by blocking necessary molecules like IgA and C3b for identification and activation of the complement system.

Role of Protein M in Streptococcus pyogenes

This part delves into the significance of protein M in Streptococcus pyogenes, highlighting its role in determining bacterial types and serological classification.

Significance of Protein M

• Protein M anchors in the cell membrane and traverses both the cell wall and capsule, with its amino portion being highly variable.

• Changes in the amino portion of protein M determine different types of Streptococcus pyogenes based on surface antigen variations crucial for serological typing.

Immunity and Serotype Variability

Discussing immunity conferred by specific serotypes of Streptococcus pyogenes and how variability allows reinfection with different strains.

Immunity and Reinfection

• Infection with one serotype provides protective immunity against future clinical manifestations from that strain but does not prevent infection by other serotypes.

• Individuals can be reinfected with different serotypes due to the vast number (approximately 150) present within Streptococcus pyogenes populations.

Protein M Classification Impact

Exploring how classifying protein M into two classes influences disease outcomes related to Streptococcus pyogenes infections.

Protein M Classification Influence

• Strains with class I protein M are more associated with non-suppurative sequelae following infections, potentially leading to specific consequences under predisposing factors.

Adhesins and Colonization Factors

Detailing adhesins like lipoteichoic acid aiding colonization through attachment mechanisms essential for invasion processes.

Adhesins Functionality

Detailed Explanation of Immune Response Mechanisms

In this section, the speaker delves into the intricate details of immune response mechanisms, focusing on how cells interact and respond to antigens.

The Process of Antigen Presentation and T Cell Activation

• The cell presents molecular receptors involved in antigen presentation. When a T lymphocyte is stimulated by a specific antigen presented by an antigen-presenting cell, it activates and produces a specific response against that antigen.

Activation of B Cells and Production of Antibodies

• Upon activation, the T cell signals the B cell to transform into a plasma cell, producing specific antibodies against the antigen.

Effects of Superantigens on Immune Response

• Superantigens stimulate phagocytic cells and T lymphocytes excessively, leading to uncontrolled secretion of cytokines and proinflammatory substances. This chaotic response results in inflammation and tissue destruction.

Role of Invasins in Tissue Damage

• Invasins like streptokinase degrade plasminogen into plasmin, which breaks down clots and pus, aiding bacterial invasion by evading host defenses.

Impact of Streptolysins on Host Immune System

This section explores how streptolysins contribute to tissue damage and immune evasion by certain bacteria.

Functions of Different Streptolysin Isoforms

• Estreptolisinas are responsible for beta-hemolysis in blood agar. They can lyse phagocytic cells as well as red blood cells and platelets.

Destructive Effects on Phagocytic Cells

• When a phagocytic cell engulfs streptococcus bacteria containing streptolysins, these substances cause cellular destruction within the phagolysosome.

Diagnostic Significance of Streptolysin O

• Streptolysin O acts as an antigenic marker during infection with streptococcus bacteria. Monitoring anti-streptolysin O levels aids in assessing disease severity and treatment efficacy.

New Section

In this section, the discussion revolves around the production of lactic acid by living bacteria in tissues, leading to decreased oxygen supply and tissue necrosis. This acidic environment is exploited by various bacteria, including streptococcus pyogenes.

Production of Lactic Acid and Tissue Necrosis

• Bacteria produce lactic acid as they are alive in tissues, causing acidity that reduces oxygen supply and leads to tissue necrosis.

• Infection and maintenance of acidic microenvironment can result in complete tissue destruction known as streptococcal gangrene.

• Suppurative clinical conditions caused by pyogenic streptococci contrast with non-suppurative conditions like scarlet fever and rheumatic fever affecting joints due to immune responses against similar antigens.

New Section

This section delves into the genetic predisposition to produce antibodies against specific antigens carried by pyogenic streptococci, highlighting the complex interplay between genetic factors and infection outcomes.

Genetic Predisposition and Antibody Production

• Genetic predisposition determines antibody production against certain antigens carried by pyogenic streptococci.

• Glomerulonephritis post-streptococcal infection is associated with type 3 hypersensitivity reactions involving immune complex deposition on glomerular surfaces.

New Section

This segment emphasizes the impact of Streptococcus pyogenes on tissues, showcasing its capabilities through a detailed examination of its effects.

Effects of Streptococcus Pyogenes on Tissues

• Streptococcus pyogenes' actions in tissues demonstrate complexity but not necessarily difficulty, urging further exploration through available resources for a deeper understanding.

New Section

The final part discusses how Streptococcus pyogenes resides in the oral cavity and pharynx, highlighting transmission routes and susceptibility factors for infections.

Transmission Routes and Susceptibility Factors

• Streptococcus pyogenes inhabits the oral cavity and pharynx, with saliva droplets serving as infectious particles for susceptible individuals.