Gram-Positive and Negative Bacteria PDF

Gram-positive bacteria are classified based on their shape (cocci or bacilli) and their ability to retain the crystal violet stain in the Gram staining process. Below is a detailed breakdown of **Gram- positive cocci** and **Gram-positive bacilli**, their functions, and the diseases they cause:...

Gram-positive bacteria are classified based on their shape (cocci or bacilli) and their ability to retain the crystal violet stain in the Gram staining process. Below is a detailed breakdown of **Gram- positive cocci** and **Gram-positive bacilli**, their functions, and the diseases they cause: Gram-Positive Cocci These are spherical bacteria that often form clusters or chains. They are divided into two main genera: *Staphylococcus* and *Streptococcus*, with *Enterococcus* also being significant. 1. Staphylococcus** (Cocci in clusters, spherical, non-spore) - Functions: - Part of normal skin and mucosal flora. - Some strains protect against harmful bacteria by competing for resources. - Diseases: - *Staphylococcus aureus*: Causes skin infections (boils, cellulitis), pneumonia, toxic shock syndrome, and food poisoning. - *Staphylococcus epidermidis*: Causes infections in medical devices (e.g., catheters, prosthetics). - *Staphylococcus saprophyticus*: Causes urinary tract infections (UTIs), especially in young women. 2. Streptococcus (Cocci in chains or pairs, spherical, capsulated, non-spore) - Functions: - Some species are part of the normal oral and gut microbiota. - Some contribute to digestive health by breaking down complex carbohydrates. - Diseases: - *Streptococcus pyogenes* (Group A): Causes pharyngitis (strep throat), scarlet fever, rheumatic fever, and necrotizing fasciitis. - *Streptococcus pneumoniae*: Causes pneumonia, meningitis, and otitis media. - *Streptococcus agalactiae* (Group B): Causes neonatal sepsis and meningitis. - *Streptococcus mutans*: Contributes to dental caries (cavities). 3. Enterococcus** (Cocci in pairs or short chains, non-capsulated, no spore, ovoid shape) - Functions: - Part of normal gut flora. - Contribute to carbohydrate fermentation and gut health. - Diseases: - *Enterococcus faecalis* and *Enterococcus faecium*: Cause UTIs, endocarditis, and wound infections, especially in hospitalized patients. Gram-Positive Bacilli These are rod-shaped bacteria and include both spore-forming and non-spore-forming genera. 1. Bacillus (Spore-forming bacilli, Rod shaped with square ends, capsulated) - Functions: - Some species are used in industrial applications (e.g., *Bacillus subtilis* in enzyme production). - Play a role in soil health by decomposing organic matter. - Diseases: - *Bacillus anthracis*: Causes anthrax (cutaneous, pulmonary, and gastrointestinal forms). - *Bacillus cereus*: Causes food poisoning. 2. Clostridium (Spore-forming, obligate anaerobes, long irregular with bulge at terminal ends) - Functions: - Involved in fermentation processes. - Decompose organic material in soil. - Diseases: - *Clostridium tetani*: Causes tetanus (lockjaw). - *Clostridium botulinum*: Causes botulism (a paralytic illness). - *Clostridium difficile*: Causes antibiotic-associated colitis (C. diff infection). - *Clostridium perfringens*: Causes gas gangrene and food poisoning. 3. Corynebacterium (non-spore-forming bacilli, Chinese letters with swollen ends, capsulated) - Functions: - Some species are part of normal skin flora. - Contribute to skin homeostasis. - Diseases: - *Corynebacterium diphtheriae*: Causes diphtheria (a respiratory infection). 4. Listeria (Non-spore-forming bacilli, non-capsulated, vary in size rounded ends, mobile) - Functions: - Rarely part of normal flora; primarily pathogenic. - Diseases: - Listeria monocytogenes: Causes listeriosis, leading to septicemia, meningitis, and stillbirth in pregnant women. 5. Actinomyces (Filamentous, anaerobic bacilli) - Functions: - Part of normal oral flora. - Contribute to oral health by breaking down complex molecules. - Diseases: - Actinomyces israelii: Causes actinomycosis, a chronic infection often involving the jaw, lungs, or abdomen. Summary of Gram-Positive Bacteria - Cocci: *Staphylococcus, Streptococcus, and *Enterococcus are the most clinically significant. - Bacilli: Include Bacillus, Clostridium, Corynebacterium, Listeria, and Actinomyces. - Functions: Many Gram-positive bacteria are part of normal flora, contributing to health by maintaining microbial balance, aiding digestion, and protecting against harmful pathogens. - Diseases: They cause a wide range of infections, from mild skin conditions to severe systemic diseases, often due to opportunistic infections or virulence factors like toxins and enzymes. Gram-negative bacteria are characterized by a thin peptidoglycan layer and an outer membrane containing lipopolysaccharides (LPS), which makes them resistant to many antibiotics. They are classified by their shape: **cocci** (spherical) and **bacilli** (rod-shaped). Below is a detailed breakdown of **Gram-negative cocci** and **bacilli**, their functions, and the diseases they cause: Gram-Negative Cocci These are spherical bacteria that typically occur in pairs (diplococci). The most clinically significant genera are *Neisseria* and *Moraxella*. 1. Neisseria (Diplococci, Kidney shaped, non-spore, non-mobile) - Functions: - Some species are part of the normal flora of the respiratory and urogenital tracts. - Diseases: - Neisseria gonorrhoeae: Causes gonorrhea, a sexually transmitted infection (STI) that can lead to pelvic inflammatory disease (PID) and infertility. - Neisseria meningitidis: Causes meningitis (inflammation of the meninges) and septicemia (meningococcal disease). 2. Moraxella** (Short rods or cocci, non-spore, non-mobile, non-capsulated) - Functions: - Part of the normal flora of the upper respiratory tract. - Diseases: - Moraxella catarrhalis: Causes otitis media (ear infections), sinusitis, and exacerbations of chronic obstructive pulmonary disease (COPD). Gram-Negative Bacilli These are rod-shaped bacteria and include many clinically important pathogens. They are further divided into **Enterobacteriaceae** (intestinal bacteria) and **non-Enterobacteriaceae**. 1. Enterobacteriaceae (Intestinal Gram-Negative Bacilli, round heads, non-spore, non-capsulated, mobile) - Functions: - Many species are part of the normal gut flora and aid in digestion.  - Some participate in nutrient cycling in the environment. - Diseases: - Escherichia coli: Causes UTIs, gastroenteritis (diarrhea), and septicemia. Some strains (e.g., O157:H7) cause hemolytic uremic syndrome (HUS). - Salmonella: Causes salmonellosis (food poisoning) and typhoid fever (*Salmonella typhi*). - Shigella: Causes shigellosis (dysentery), characterized by severe diarrhea. - Klebsiella pneumoniae: Causes pneumonia, UTIs, and wound infections. - Proteus mirabilis: Causes UTIs and kidney stones. - Enterobacter, Citrobacter, and Serratia: Cause opportunistic infections in hospitalized patients. 2. Non-Enterobacteriaceae (Other Gram-Negative Bacilli) - Functions: - Some are environmental bacteria, while others are part of the normal flora. - Disease: - Pseudomonas aeruginosa: Causes hospital-acquired infections (e.g., pneumonia, UTIs, wound infections) and is a major pathogen in cystic fibrosis patients. - Helicobacter pylori: Causes peptic ulcers and gastric cancer. - Haemophilus influenzae: Causes respiratory infections (pneumonia, bronchitis) and meningitis, especially in children. - Bordetella pertussis: Causes whooping cough (pertussis). - Legionella pneumophila: Causes Legionnaires' disease (a severe form of pneumonia). - Vibrio cholerae: Causes cholera, a diarrheal disease. - Campylobacter jejuni: Causes gastroenteritis and Guillain-Barré syndrome (a neurological disorder). - Brucella: Causes brucellosis, a zoonotic disease. - Francisella tularensis: Causes tularemia, a zoonotic infection. - Yersinia pestis: Causes plague (bubonic, pneumonic, and septicemic forms). 3. Anaerobic Gram-Negative Bacilli - Functions: - Some are part of the normal flora in the oral cavity, gut, and genital tract.  - Diseases: - Bacteroides fragilis: Causes intra-abdominal infections (e.g., abscesses). - Fusobacterium: Causes dental infections and Lemierre’s syndrome (thrombophlebitis of the jugular vein). Summary of Gram-Negative Bacteria - Cocci: Neisseria and Moraxella are the most clinically significant. - Bacilli: - Enterobacteriaceae: E. coli, Salmonella, Shigella, Klebsiella, etc. - Non-Enterobacteriaceae: Pseudomonas, Helicobacter, Haemophilus, Bordetella, etc. - Anaerobic Bacilli: Bacteroides, Fusobacterium, etc. - Functions: Some Gram-negative bacteria are part of the normal flora and contribute to health, while others are pathogenic or opportunistic. - Diseases: They cause a wide range of infections, including respiratory, gastrointestinal, urinary tract, and systemic infections. Spirochaetes are a unique group of Gram-negative bacteria characterized by their spiral or corkscrew shape and motility. They are classified into three main genera: *Treponema*, *Borrelia*, and *Leptospira*. Below is a synthesis of their **characteristics**, **identification**, **pathogenicity**, and **clinical features** based on the provided context and general knowledge: SPIROCHAETES 1. Characteristics of Spirochaetes - Shape: Spiral or helical (corkscrew-shaped). - Motility: Highly motile due to endoflagella (axial filaments) located between the outer membrane and cell wall. - Gram Stain: Gram-negative (thin peptidoglycan layer and outer membrane). - Oxygen Requirement: Most are anaerobic or microaerophilic. - Habitat: Found in diverse environments, including water, soil, and as pathogens in humans and animals. 2. Identification of Spirochaetes - Microscopy: - Dark-field microscopy or phase-contrast microscopy is used to visualize their spiral shape and motility.  - Gram staining is less effective due to their thin structure; special stains like silver stains (e.g., Warthin-Starry) are often used. - Culture: - Difficult to culture in vitro; some species require specialized media and conditions (e.g., Leptospira* requires serum-enriched media). - Serological Tests: - Antibody detection (e.g., ELISA, FTA-ABS for *Treponema pallidum). - Molecular Methods: - PCR for detecting specific DNA sequences (e.g., Borrelia burgdorferi). 3. Pathogenicity of Spirochaetes - Mechanisms - Endoflagella: Enable penetration into tissues. - Adhesins: Facilitate attachment to host cells. - Immune Evasion: Some species (e.g., Borrelia) can alter surface proteins to evade the immune system. - Toxins: Leptospira produces endotoxins that damage tissues. - Transmission: - Treponema pallidum: Sexual contact or vertical transmission (congenital syphilis). - Borrelia burgdorferi: Tick bites (Lyme disease). - Leptospira: Contact with contaminated water or soil. 4. Clinical Features of Spirochaetes - Treponema pallidum (Syphilis): - Primary Syphilis: Painless chancre at the site of infection. - Secondary Syphilis: Rash, fever, and mucosal lesions. - Tertiary Syphilis: Neurological (neurosyphilis), cardiovascular, and gummatous lesions. - Congenital Syphilis: Stillbirth, neonatal death, or developmental abnormalities. - Borrelia burgdorferi (Lyme Disease) - Early Stage: Erythema migrans (bull’s-eye rash), fever, fatigue. - Late Stage: Arthritis, neurological symptoms (e.g., facial palsy), and carditis. - Leptospira (Leptospirosis) - Mild Form: Fever, headache, muscle pain. - Severe Form (Weil’s Disease): Jaundice, renal failure, hemorrhage, and meningitis.  - Other Spirochaetes: - Borrelia recurrentis: Causes relapsing fever (fever episodes alternating with asymptomatic periods). - Treponema pertenue: Causes yaws (skin, bone, and cartilage lesions). 5. Treatment and Prevention - Antibiotics: - Treponema pallidum: Penicillin (drug of choice). - Borrelia burgdorferi: Doxycycline or amoxicillin. - Leptospira: Doxycycline or penicillin. - Prevention: - Safe sexual practices for syphilis. - Tick avoidance for Lyme disease. - Avoiding contaminated water for leptospirosis. Actinomyces is a genus of Gram-positive, facultatively anaerobic, filamentous bacteria that resemble fungi in their growth patterns. These bacteria are known for their role in human and animal infections, as well as their presence in soil and the oral microbiome. 1. (Actinomyces) Morphology & Characteristics Gram-positive Rod-shaped (bacilli) but often form branching filaments Non-motile and non-spore-forming Facultative anaerobes or obligate anaerobes Often part of the normal microbiota of the oral cavity, gastrointestinal tract, and female reproductive tract 2. Notable Species 1. Actinomyces israelii – The most common human pathogen, causes actinomycosis 2. Actinomyces naeslundii – Involved in dental plaque and tooth decay 3. Actinomyces odontolyticus – Associated with oral infections and abscesses 4. Actinomyces viscosus – Found in the oral cavity and linked to periodontal disease 5. Actinomyces bovis – Causes lumpy jaw in cattle 3. Clinical Significance Actinomycosis (Chronic Suppurative Infection) Caused by: A. israelii and related species Symptoms: Chronic, slow-growing abscesses in soft tissues Formation of sulfur granules (yellowish granules in pus) Most commonly affects the face, neck, lungs, and abdomen Transmission: Often follows trauma, dental infections, or surgery Treatment: Penicillin (long-term antibiotic therapy) 4. Role in Dental & Medical Conditions Dental plaque & cavities (A. naeslundii, A. odontolyticus) Periodontal disease (A. viscosus) Endocarditis (rare but possible) Opportunistic infections in immunocompromised individuals 5. Environmental Role Found in soil and plays a role in organic matter decomposition Involved in nitrogen fixation and nutrient cycling Summary Spirochaetes are a distinct group of Gram-negative bacteria with unique spiral shapes and motility. They include pathogens like *Treponema pallidum* (syphilis), *Borrelia burgdorferi* (Lyme disease), and *Leptospira* (leptospirosis). Their identification relies on microscopy, serology, and molecular methods. They cause a range of diseases, from skin lesions to systemic infections, and are treated with antibiotics like penicillin and doxycycline. Chlamydia is a bacterial infection caused by *Chlamydia trachomatis*. Below are its characteristics, culture methods, and diagnostic approaches: Characteristics of Chlamydia 1. Causative Agent: Chlamydia trachomatis Chlamydia pneumoniae (obligate intracellular bacterium). 1. Chlamydia pneumoniae:  Causes respiratory infections, including pneumonia, bronchitis, and sinusitis.  Associated with chronic diseases like asthma and possibly atherosclerosis. 2. Chlamydia psittaci:  Causes psittacosis (also known as parrot fever), a zoonotic disease transmitted from birds to humans.  Leads to flu-like symptoms and atypical pneumonia. 2. Morphology: Chlamydia Trachomatis - Gram-negative. - Lacks a peptidoglycan layer in its cell wall. 3. Life Cycle: - Exists in two forms: - Elementary Body (EB): Infectious, extracellular form.  - Reticulate Body (RB): Non-infectious, intracellular replicative form. 4. Transmission: - Sexual contact (most common). - Vertical transmission (mother to child during childbirth). 5. Clinical Manifestations: - Urogenital infections (e.g., urethritis, cervicitis). - Pelvic inflammatory disease (PID). - Conjunctivitis and pneumonia in neonates. - Lymphogranuloma venereum (LGV) in some cases. Culture of Chlamydia - Chlamydia trachomatis is an obligate intracellular organism, meaning it cannot grow on standard bacterial culture media. - Culture Requirements: - Requires living cells for growth (e.g., McCoy cells, HeLa cells). - Specimens (e.g., cervical, urethral, or conjunctival swabs) are inoculated into cell cultures. - Staining with iodine or fluorescent antibodies is used to detect inclusion bodies in infected cells. - **Limitations**: - Time-consuming and technically demanding. - Less sensitive compared to modern diagnostic methods. Diagnosis of Chlamydia 1. Nucleic Acid Amplification Tests (NAATs): - Gold standard for diagnosis. - Detects *Chlamydia trachomatis* DNA or RNA. - Highly sensitive and specific. - Can be performed on urine samples or swabs (e.g., cervical, vaginal, urethral). 2. Direct Fluorescent Antibody (DFA) Test: - Detects chlamydial antigens using fluorescent-labeled antibodies. 3. Enzyme-Linked Immunosorbent Assay (ELISA): - Detects chlamydial antigens. - Less sensitive than NAATs. 4. Serology:  - Detects antibodies against *Chlamydia trachomatis*. - Useful for diagnosing chronic infections or LGV. 5. Microscopy: - Staining methods (e.g., Giemsa or iodine staining) to identify inclusion bodies in infected cells. - Rarely used due to low sensitivity. ### **Mycoplasma: Characteristics, Culture, Diagnosis, and Diseases** Characteristics of Mycoplasma 1.General Features: - Smallest free-living bacteria (0.2–0.3 µm in size). - Lack a cell wall, making them resistant to beta-lactam antibiotics (e.g., penicillins, cephalosporins). - Pleomorphic (can change shape) due to the absence of a rigid cell wall. - Gram-negative (but staining is not reliable due to the lack of a cell wall). - Require sterols (e.g., cholesterol) for membrane stability. 2. Genome: - Small genome, highly dependent on the host for nutrients and survival 3. Pathogenic Species: - Mycoplasma pneumoniae: Causes respiratory infections. - Mycoplasma genitalium: Associated with urogenital infections. - Mycoplasma hominis: Linked to pelvic inflammatory disease (PID) and postpartum infections. - Mycoplasma fermentans: Opportunistic pathogen in immunocompromised individuals. Culture of Mycoplasma 1. Growth Requirements: - Mycoplasma are fastidious organisms and require specialized media enriched with sterols (e.g., cholesterol) and other nutrients. - Common media: SP-4 medium, PPLO (Pleuropneumonia-Like Organism) broth or agar. 2. Growth Characteristics: - Slow-growing (may take 1–3 weeks for visible colonies). - Colonies have a characteristic "fried egg" appearance under a microscope. 3. Limitations: - Culturing Mycoplasma is challenging due to their slow growth and specific requirements. - Not routinely performed in clinical settings; molecular methods are preferred.  Diagnosis of Mycoplasma 1. Nucleic Acid Amplification Tests (NAATs): - Most sensitive and specific method. - Detects Mycoplasma DNA or RNA in clinical samples (e.g., respiratory secretions, urogenital swabs). 2. Serology: - Detects antibodies (IgM, IgG) against *Mycoplasma pneumoniae*. - Useful for diagnosing recent or past infections. 3. Culture: - As mentioned, culture is possible but rarely used due to its complexity and time requirements. 4. PCR (Polymerase Chain Reaction): - Rapid and highly sensitive for detecting Mycoplasma species. 5. Microscopy: - Not commonly used due to the small size and lack of a cell wall. Diseases Caused by Mycoplasma 1. Respiratory Infections: - Mycoplasma pneumoniae: - Causes atypical pneumonia ("walking pneumonia"). - Symptoms: Dry cough, fever, headache, sore throat. - Common in children and young adults. 2. Urogenital Infections: - Mycoplasma genitalium - Causes non-gonococcal urethritis (NGU) in men. - Associated with cervicitis, pelvic inflammatory disease (PID), and infertility in women. - *Mycoplasma hominis*: - Linked to postpartum fever, PID, and bacterial vaginosis. 3. Opportunistic Infections: - Mycoplasma fermentans and Mycoplasma hominis: - Can cause systemic infections in immunocompromised individuals. 4. Other Conditions: - *Mycoplasma pneumoniae* has been associated with extrapulmonary manifestations, such as: - Skin rashes (e.g., Stevens-Johnson syndrome). Mycoplasma Overview Mycoplasma is a genus of bacteria that lacks a cell wall, making it unique among prokaryotes. Below are its characteristics, culture methods, diagnostic approaches, and associated diseases.