Gram-Negative Cocci: Medically Relevant Diagnosis PDF

Gram-Negative Cocci: Medically Relevant Diagnosis by Heba Rashed  Introduction to Gram Negative Cocci Defining Characteristics Varied Cell Arrangements Culturing Requirements Gram negative cocci are a group Gram negative cocci can appear i...

Gram-Negative Cocci: Medically Relevant Diagnosis by Heba Rashed  Introduction to Gram Negative Cocci Defining Characteristics Varied Cell Arrangements Culturing Requirements Gram negative cocci are a group Gram negative cocci can appear in Gram negative cocci are of spherical bacteria that stain pink pairs (diplococci), tetrads, or fastidious organisms that irregular clusters, depending on or red when subjected to the Gram require specialized culture the species. This morphological staining procedure. This indicates media and growth conditions to diversity aids in their identification. they have a thin thrive in the laboratory setting. peptidoglycan layer and an On which medium should a nasopharyngeal swab be cultured to diagnose Neisseria meningitidis carriers? A. Chocolate agar B. Thayer-Martin medium C. Blood agar D. MacConkey agar ANSWER: B  Epidemiology and Clinical Significance Gram-negative cocci are widely distributed in nature and can colonize various sites in the human body. They are clinically significant as they can cause serious infections, particularly in immunocompromised individuals and hospital settings. Certain species, such as Neisseria gonorrhoeae and Neisseria meningitidis, are known to cause gonorrhea and meningitis, respectively, which are major public health concerns. Other species, like Moraxella catarrhalis, are common respiratory pathogens that can lead to sinusitis, bronchitis, and pneumonia.  Morphological Characteristics Gram-negative cocci are small, spherical bacteria that typically occur in pairs or clusters. They have a characteristic bean-shaped or coffee bean-like appearance under the microscope. These bacteria have a thin peptidoglycan layer in their cell wall and an outer membrane with lipopolysaccharides, which gives them their gram-negative staining properties. Staining Properties Gram-negative cocci exhibit characteristic staining properties when subjected to the Gram staining technique. They are classified as gram-negative due to their thin peptidoglycan layer and the ability of the gram-negative stain to penetrate their cell wall. Upon Gram staining, gram-negative cocci appear as pink or red-colored cells, in contrast to the purple-stained gram-positive bacteria. Culture Requirements Aerobic Growth Gram-negative cocci generally require aerobic conditions for optimal growth and cultivation. Incubation Conditions Incubation at 35-37°C with 5-10% CO2 is commonly required to support the growth of these fastidious organisms. Enriched Media They typically grow well on blood agar, chocolate agar, or other nutrient-rich media that provide essential growth factors. Selective Media Selective media, such as Thayer-Martin agar, can be used to isolate and differentiate specific Gram-negative cocci species. Biochemical Tests Oxidase Test Determines the presence of the Carbohydrate Utilization enzyme cytochrome c oxidase, which is a key characteristic of many Gram- Evaluates the bacteria's ability to negative cocci, including Neisseria and ferment or oxidize different Moraxella species. carbohydrates, providing insights into their metabolic profiles and species  Serological Tests Antigen Detection Serological tests can detect bacterial antigens, providing rapid diagnosis of infections. Antibody Detection Measuring the body's immune response by detecting specific antibodies can aid diagnosis. Which test is NOT typically performed to confirm the species identification of Neisseria? A. Fermentation of glucose B. Lactose fermentation C. Oxidase test D. Gram staining ANSWER: B  Medically Important Gram Negative Cocci Species Neisseria Moraxella Includes N. gonorrhoeae and N. Opportunistic pathogens like M. meningitidis, which cause catarrhalis that can cause serious infections like gonorrhea respiratory infections, especially in and meningococcal disease. immunocompromised individuals. Acinetobacter Multidrug-resistant species like A. baumannii that are major causes of nosocomial infections in healthcare settings. Neisseria Species 1 Pathogenic Neisseria Key pathogenic Neisseria species include N. gonorrhoeae, the causative agent of gonorrhea, and N. meningitidis, responsible for meningococcal disease. 2 Morphology and Staining Neisseria are Gram-negative diplococci, often described as "coffee bean" or "kidney bean" 3 Growth Requirements shaped. 4 Virulence Factors Neisseria species are fastidious, Pili, outer membrane proteins, and requiring enriched media like blood capsular polysaccharides contribute to agar or chocolate agar for the virulence and pathogenicity of optimal growth. Diagnosis of Neisseria Meningitidis 1 Sample Collection Collect samples from the nasopharynx or cerebrospinal fluid for diagnosis of Neisseria meningitidis Gram Staining 2 Perform Gram staining to observe the characteristic Gram-negative diplococci with the typical "coffee bean" appearance. 3 Culture-Based Identification Grow the bacteria on selective media like modified Thayer-Martin agar and perform biochemical tests to confirm the species. Specimens are CSF and blood Blood sample for blood culture 1- CSF: is withdrawn by lumber puncture ( invasive procedure ) under complete aseptic conditions. Divided into 3 tubes The CSF is turbid, and contain high number of cells mainly polymorphs Tube 1 CSF for microbiological analysis Tube 2 CSF for chemical analysis for protein and glucose Tube 3 CSF for white cells count The tube (1) CSF is centrifuged What does the first tube of CSF collected for microbiological analysis typically contain? A. High levels of sugar B. Exclusively lymphocytes C. High number of cells mainly polymorphs D. No cellular debris ANSWER: C The tube (1) CSF is centrifuged Aspirate the supernatant and is used for Detection of capsular antigen using latex agglutination Deposit is used for preparation of smear stained with Gram to demonstrate gram negative diplococci intracellular and extracellular. Culture on chocolate agar or Thayer Martin medium and incubate at 37C for 24 hours 5-10% CO2 conditions (candle jar). The colonies are identified by morphology, gram stain (oxidase test, fermentation of glucose and maltose with acid only Diagnosis of N. meningitidis carriers: The specimen used is a nasopharyngeal swab (West swab) that is cultured on Thayer martin medium and incubate at 37C for 24 hours 5- 10% CO2 conditions. The oxidase test is a biochemical test used to identify bacteria that produce the enzyme cytochrome c oxidase, an important component of the electron transport chain in certain bacteria. This enzyme enables the bacteria to use oxygen as the terminal electron acceptor, a process important for aerobic respiration. Purpose The test is commonly used to differentiate between various groups of Gram-negative bacteria: Oxidase-positive bacteria include species such as Neisseria, Pseudomonas, and Vibrio.  N.meningitidis N.gonorrhoeae Morphology Capsule No capsule chemical Glucose and maltose Glucose Fermentation Virulence factors Capsule No capsule Pili Pili Disease Meningitis Gonorrhoeae Mode of Droplet Sexually transmission Which mode of transmission is associated with Neisseria gonorrhoeae? A. Contact with infected surfaces B. Sexually C. Aerosol D. Droplet spread ANSWER: B Which pathogenic species is responsible for gonorrhea? A. Moraxella catarrhalis B. Acinetobacter baumannii C. Neisseria meningitidis D. Neisseria gonorrhoeae ANSWER: D Certain species, such as Neisseria gonorrhoeae and Neisseria meningitidis, are known to cause ______ and meningitis, respectively. ANSWER: gonorrhea Moraxella Species Gram-Negative Cocci Medically Relevant Moraxella species are aerobic, Species gram-negative cocci that often The most clinically appear in pairs or tetrads. significant Moraxella species are M. Opportunistic Pathogens catarrhalis and M. Moraxella can cause respiratory tract lacunata. infections, conjunctivitis, and rarely, more invasive infections. Moraxella catarrhalis is a common pathogen that can lead to respiratory tract infections A. True B. False ANSWER: A Diagnosis of Moraxella Catarrhalis Culture Grow M. catarrhalis on blood agar or chocolate agar. Colonies are smooth, grayish, and non-hemolytic. Staining Gram-negative diplococci with characteristic "coffee bean" morphology under the microscope. Biochemical Tests Positive for catalase, oxidase, and DNase. Distinguish from Neisseria based on nitrate reduction and carbohydrate utilization. Which is a characteristic morphological feature of Moraxella catarrhalis? A. Diplococci with 'coffee bean' morphology B. Gram-positive cocci C. Spherical clusters D. Filamentous rods ANSWER: A Which culture medium is appropriate for growing Moraxella catarrhalis? A. Blood or chocolate agar B. Sabouraud agar C. Nutrient agar D. MacConkey agar ANSWER: A