Classification of Pathogenic bacteria Flashcards
Be familiar with the nomenclature of clinically significant Gram positive bacteria.
Gram-positive cocci include Staphylococcus (catalase-positive), which grows clusters, and Streptococcus (catalase-negative), which grows in chains. The staphylococci further subdivide into coagulase-positive (S. aureus) and coagulase-negative (S. epidermidis and S.
Describe where they may colonise and/or infect (body or environment) (Gram positive)
- Staphylococcus
Staphylococcus aureus:
Colonization: Nasal passages, skin.
Infection: Skin and soft tissue infections (like abscesses), pneumonia, osteomyelitis, endocarditis, and sepsis.
Staphylococcus epidermidis:
Colonization: Skin, mucous membranes.
Infection: Associated with device-related infections (e.g., catheters, prosthetic devices) and opportunistic infections in immunocompromised patients.
Staphylococcus saprophyticus:
Colonization: Urinary tract.
Infection: Urinary tract infections, particularly in young women. - Streptococcus
Streptococcus pyogenes:
Colonization: Throat, skin.
Infection: Pharyngitis (strep throat), cellulitis, impetigo, and can lead to systemic conditions like rheumatic fever and scarlet fever.
Streptococcus agalactiae:
Colonization: Gastrointestinal tract, urogenital tract.
Infection: Neonatal sepsis and meningitis, infections in pregnant women.
Streptococcus pneumoniae:
Colonization: Nasopharynx.
Infection: Pneumonia, meningitis, otitis media, sinusitis.
Viridans group streptococci:
Colonization: Oral cavity, gastrointestinal tract.
Infection: Endocarditis, dental infections. - Enterococcus
Enterococcus faecalis and Enterococcus faecium:
Colonization: Gastrointestinal tract.
Infection: Urinary tract infections, bacteremia, endocarditis, and infections associated with indwelling catheters. - Listeria
Listeria monocytogenes:
Colonization: Environment (commonly found in soil, water, and contaminated food).
Infection: Meningitis and sepsis, particularly in pregnant women, newborns, and immunocompromised individuals. - Corynebacterium
Corynebacterium diphtheriae:
Colonization: Throat, skin.
Infection: Diphtheria (primarily in the throat). - Bacillus
Bacillus anthracis:
Colonization: Environment (found in soil).
Infection: Anthrax (cutaneous, inhalational, or gastrointestinal).
Bacillus cereus:
Colonization: Environment (commonly found in rice, vegetables).
Infection: Food poisoning (emetic and diarrheal syndromes). - Clostridium
Clostridium perfringens:
Colonization: Gastrointestinal tract.
Infection: Gas gangrene, food poisoning.
Clostridium difficile:
Colonization: Gastrointestinal tract (after antibiotic use).
Infection: Antibiotic-associated diarrhea and pseudomembranous colitis.
Clostridium botulinum:
Colonization: Environment (found in soil and improperly canned foods).
Infection: Botulism (foodborne, wound, or infant botulism). - Actinomyces
Actinomyces israelii:
Colonization: Oral cavity, gastrointestinal tract.
Infection: Chronic infections, often in the jaw (actinomycosis) and other tissues. - Nocardia
Nocardia species:
Colonization: Environment (soil).
Infection: Pulmonary infections, skin infections, and opportunistic infections in immunocompromised patients.
These bacteria can thrive in various environments, and their ability to colonize different parts of the body contributes to their pathogenicity.
Understand the terms colonisation versus infection.
Colonization
Definition: Colonization refers to the presence of bacteria in or on a host without causing disease. The bacteria can multiply and establish themselves in specific locations, such as the skin, mucous membranes, or gastrointestinal tract.
Characteristics:
Asymptomatic: The host does not show symptoms of illness.
Non-invasive: The bacteria typically do not invade host tissues or cells.
Normal Flora: Many colonizing bacteria are part of the normal microbiota, contributing to health by preventing the growth of pathogenic organisms.
Examples:
Staphylococcus epidermidis colonizing the skin.
Streptococcus pneumoniae colonizing the nasopharynx without causing pneumonia.
Infection
Definition: Infection occurs when bacteria invade the host’s tissues, leading to disease. This involves the bacteria overcoming the host’s defenses and causing symptoms.
Characteristics:
Symptomatic: Infections typically produce observable signs and symptoms, such as fever, inflammation, pain, or pus.
Invasive: The bacteria may enter the bloodstream, tissues, or organs and disrupt normal function.
Pathogenicity: The bacteria often produce toxins or have mechanisms that damage host cells and tissues.
Examples:
Staphylococcus aureus causing a skin abscess.
Clostridium difficile leading to colitis.
Key Differences
Presence vs. Impact: Colonization can exist without disease, whereas infection implies a detrimental effect on the host.
Host Response: In colonization, the host immune system may recognize the bacteria but does not mount a significant response; in infection, the immune system is actively responding to eliminate the invading pathogens.
Describe common infections due to Gram positive bacteria.
- Staphylococcus aureus
Skin and Soft Tissue Infections: Such as abscesses, cellulitis, and impetigo.
Pneumonia: Can occur, particularly in patients with underlying lung disease or after influenza.
Endocarditis: Infection of the heart valves, especially in individuals with heart conditions.
Osteomyelitis: Bone infections, often following a skin infection or trauma.
Sepsis: A serious bloodstream infection that can lead to systemic inflammatory response syndrome (SIRS). - Staphylococcus epidermidis
Device-Related Infections: Infections associated with indwelling catheters, prosthetic devices, and pacemakers due to biofilm formation.
Endocarditis: Particularly in patients with prosthetic heart valves. - Staphylococcus saprophyticus
Urinary Tract Infections (UTIs): Commonly associated with young women, often after sexual activity. - Streptococcus pyogenes (Group A Streptococcus)
Pharyngitis: Commonly known as strep throat.
Skin Infections: Such as impetigo and cellulitis.
Scarlet Fever: Characterized by a red rash, often following strep throat.
Rheumatic Fever: A complication that can occur after untreated strep throat, affecting the heart and joints. - Streptococcus agalactiae (Group B Streptococcus)
Neonatal Infections: Such as sepsis and meningitis in newborns, often transmitted from the mother during delivery.
Infections in Pregnant Women: Can cause urinary tract infections and other complications. - Streptococcus pneumoniae
Pneumonia: A leading cause of community-acquired pneumonia.
Meningitis: Can cause bacterial meningitis, especially in children and the elderly.
Otitis Media: Middle ear infections, especially in children. - Enterococcus faecalis and Enterococcus faecium
Urinary Tract Infections: Common in hospitalized patients, particularly those with catheters.
Endocarditis: Can infect heart valves, especially in individuals with pre-existing heart conditions.
Bacteremia: Infection in the bloodstream, particularly in immunocompromised patients. - Listeria monocytogenes
Listeriosis: Foodborne illness that can cause fever and muscle aches, and may lead to meningitis or sepsis, especially in pregnant women, newborns, and immunocompromised individuals. - Corynebacterium diphtheriae
Diphtheria: A respiratory infection characterized by a thick membrane in the throat, leading to breathing difficulties. - Bacillus anthracis
Anthrax: Can cause cutaneous (skin), inhalational (lungs), or gastrointestinal infections, depending on the route of exposure. - Clostridium perfringens
Gas Gangrene: A severe soft tissue infection that produces gas in tissues, often following trauma or surgery.
Food Poisoning: Typically from contaminated meat products. - Clostridium difficile
C. difficile Infection (CDI): Often occurs after antibiotic use, leading to severe diarrhea and colitis. - Actinomyces israelii
Actinomycosis: A chronic infection that often presents as a jaw or facial infection, but can affect other body areas. - Nocardia species
Nocardiosis: Can cause pulmonary infections or disseminated disease, especially in immunocompromised individuals.
Be familiar with the nomenclature of clinically significant Gram negative bacteria and
bacteria not readily identified by Gram staining.
> Gram-negative bacteria
1. Enterobacteriaceae Family
Escherichia coli: Common cause of urinary tract infections (UTIs), gastroenteritis, and bacteremia.
Klebsiella pneumoniae: Associated with pneumonia, UTIs, and bloodstream infections, often in hospitalized patients.
Proteus mirabilis: Known for UTIs and kidney stones.
Enterobacter species: Can cause hospital-acquired infections, including UTIs and respiratory infections.
Serratia marcescens: Associated with nosocomial infections, particularly in immunocompromised patients.
Salmonella species: Causes gastroenteritis and typhoid fever.
Shigella species: Known for causing dysentery (shigellosis).
2. Non-Fermenters
Pseudomonas aeruginosa: Common in hospital settings, associated with pneumonia, UTIs, and wound infections, especially in immunocompromised patients.
Acinetobacter baumannii: Associated with severe infections in critically ill patients, especially in intensive care units.
Stenotrophomonas maltophilia: Opportunistic infections in immunocompromised hosts, often resistant to multiple antibiotics.
3. Vibrio
Vibrio cholerae: Causes cholera, characterized by severe diarrhea and dehydration.
Vibrio parahaemolyticus: Associated with gastroenteritis from seafood consumption.
4. Helicobacter
Helicobacter pylori: Linked to peptic ulcers and gastric cancer.
5. Neisseria
Neisseria meningitidis: Causes meningitis and meningococcemia.
Neisseria gonorrhoeae: Causative agent of gonorrhea.
6. Haemophilus
Haemophilus influenzae: Causes respiratory tract infections, meningitis, and is associated with epiglottitis.
7. Francisella
Francisella tularensis: Causative agent of tularemia, often transmitted from animals.
8. Brucella
Brucella species: Cause brucellosis, often acquired from livestock.
9. Campylobacter
Campylobacter jejuni: Leading cause of bacterial gastroenteritis, often from undercooked poultry.
> Bacteria Not Readily Identified by Gram Staining
1. Mycobacteria
Mycobacterium tuberculosis: Causes tuberculosis; detected via acid-fast bacilli staining rather than Gram stain.
Mycobacterium leprae: Causative agent of leprosy, also not visible by Gram staining.
2. Chlamydia
Chlamydia trachomatis: Causes sexually transmitted infections and conjunctivitis, not visible on Gram stain.
3. Rickettsia
Rickettsia species: Cause various typhus and spotted fever diseases; require specialized staining or serological methods for identification.
4. Spirochetes
Treponema pallidum: Causative agent of syphilis; cannot be seen with a Gram stain.
Borrelia burgdorferi: Causes Lyme disease; requires special staining techniques.
5. Legionella
Legionella pneumophila: Causes Legionnaires’ disease; poorly staining and requires special media for growth.
Describe where they may colonise and or/infect (body or environment) (Gram negative)
- Enterobacteriaceae Family
Escherichia coli
Colonization: Gastrointestinal tract (normal flora).
Infection: Urinary tract (UTIs), gastrointestinal infections (diarrhea), bloodstream infections, and meningitis (especially in neonates).
Klebsiella pneumoniae
Colonization: Gastrointestinal tract (normal flora).
Infection: Pneumonia, UTIs, bloodstream infections, and liver abscesses.
Proteus mirabilis
Colonization: Gastrointestinal tract.
Infection: UTIs, often associated with kidney stones.
Enterobacter species
Colonization: Gastrointestinal tract.
Infection: Nosocomial infections, particularly in respiratory and urinary tracts.
Serratia marcescens
Colonization: Environmental sources (water, soil).
Infection: Respiratory infections, UTIs, and bacteremia, particularly in immunocompromised patients.
Salmonella species
Colonization: Intestinal tract (primarily in animals).
Infection: Gastroenteritis (foodborne illness), typhoid fever (Salmonella Typhi).
Shigella species
Colonization: Intestinal tract.
Infection: Dysentery (shigellosis), leading to diarrhea with blood and mucus.
2. Non-Fermenters
Pseudomonas aeruginosa
Colonization: Ubiquitous in the environment (soil, water).
Infection: Respiratory tract (especially in cystic fibrosis patients), UTIs, wound infections, and sepsis.
Acinetobacter baumannii
Colonization: Environment (hospital settings).
Infection: Nosocomial infections, particularly in ventilated patients and those with open wounds.
Stenotrophomonas maltophilia
Colonization: Ubiquitous in the environment (soil, water).
Infection: Respiratory tract infections and bloodstream infections, particularly in immunocompromised patients.
3. Vibrio
Vibrio cholerae
Colonization: Aquatic environments (brackish and saltwater).
Infection: Gastroenteritis (cholera), leading to severe diarrhea and dehydration.
Vibrio parahaemolyticus
Colonization: Aquatic environments (associated with seafood).
Infection: Gastroenteritis, typically from consumption of undercooked seafood.
4. Helicobacter
Helicobacter pylori
Colonization: Stomach lining.
Infection: Associated with peptic ulcers and gastric cancer.
5. Neisseria
Neisseria meningitidis
Colonization: Nasopharynx (part of normal flora in some individuals).
Infection: Meningitis and meningococcemia.
Neisseria gonorrhoeae
Colonization: Urogenital tract.
Infection: Gonorrhea, pelvic inflammatory disease, and conjunctivitis.
6. Haemophilus
Haemophilus influenzae
Colonization: Nasopharynx (part of the normal flora).
Infection: Respiratory tract infections, meningitis, and epiglottitis.
7. Francisella
Francisella tularensis
Colonization: Environment (zoonotic).
Infection: Tularemia, often transmitted through contact with infected animals or insect bites.
8. Brucella
Brucella species
Colonization: Environment (zoonotic, associated with livestock).
Infection: Brucellosis, causing systemic disease with flu-like symptoms.
9. Campylobacter
Campylobacter jejuni
Colonization: Intestinal tract of animals (especially poultry).
Infection: Gastroenteritis, often from contaminated food or water.
Describe common infections due to Gram negative and other miscellaneous bacteria.
SUMMARY:
* E. coli
* Salmonella spp.
* Campylobacter spp.
* Pseudomonas spp.
* Helicobacter pylori
* Haemophilus influenzae
* Bacteroides and other anaerobes
Miscellaneous bacteria
* Not all bacteria can be stained with Gram’s method.
* Not all bacteria can be cultured by standard
methods.
– Mycobacterium spp.
– Spirochaetes.
– Chlamydia / Chlamydophila.
> Common Infections Due to Gram-Negative Bacteria
1. Escherichia coli
Urinary Tract Infections (UTIs): One of the most common causes of uncomplicated and complicated UTIs.
Gastroenteritis: Certain strains (like E. coli O157) can cause severe diarrhea and hemolytic uremic syndrome (HUS).
Bacteremia: Can lead to systemic infections and sepsis.
2. Klebsiella pneumoniae
Pneumonia: Especially in patients with underlying conditions, often associated with necrotizing pneumonia.
UTIs: Common in catheterized patients.
Liver Abscesses: Can occur, especially in diabetic patients.
3. Proteus mirabilis
UTIs: Known for urease production, leading to struvite stone formation.
Wound Infections: Can occur, especially in postoperative patients.
4. Pseudomonas aeruginosa
Pneumonia: Particularly in patients with cystic fibrosis or those on ventilators.
Infections in Burns and Wounds: Often causes opportunistic infections in these settings.
UTIs: Common in patients with catheter use.
5. Acinetobacter baumannii
Nosocomial Infections: Associated with ventilator-associated pneumonia, UTIs, and bloodstream infections in critically ill patients.
6. Salmonella species
Gastroenteritis: Often from contaminated food (poultry, eggs).
Typhoid Fever: Caused by Salmonella Typhi, leading to prolonged fever and systemic illness.
7. Shigella species
Shigellosis: A type of bacillary dysentery characterized by diarrhea (often bloody), abdominal cramps, and fever.
8. Vibrio cholerae
Cholera: Severe diarrhea and dehydration, typically associated with contaminated water or food.
9. Helicobacter pylori
Peptic Ulcer Disease: Associated with chronic gastritis and peptic ulcers; can lead to gastric cancer.
> Common Infections Due to Miscellaneous Bacteria (Not Readily Identified by Gram Staining)
1. Mycobacterium tuberculosis
Tuberculosis (TB): Primarily affects the lungs, causing chronic cough, weight loss, night sweats, and hemoptysis.
2. Chlamydia trachomatis
Chlamydia: A common sexually transmitted infection (STI) causing urethritis, cervicitis, and pelvic inflammatory disease (PID).
3. Rickettsia species
Rickettsial Infections: Includes Rocky Mountain spotted fever and typhus, characterized by fever, rash, and a history of tick exposure.
4. Treponema pallidum
Syphilis: A sexually transmitted infection with stages (primary, secondary, tertiary) that can lead to systemic complications.
5. Borrelia burgdorferi
Lyme Disease: Transmitted by ticks, causing fever, fatigue, joint pain, and characteristic erythema migrans (bull’s-eye rash).
6. Legionella pneumophila
Legionnaires’ Disease: A severe form of pneumonia often associated with contaminated water sources (e.g., cooling towers).
7. Francisella tularensis
Tularemia: Can present with various symptoms based on transmission route (e.g., skin ulcers, respiratory illness).
8. Brucella species
Brucellosis: Causes undulant fever, sweats, and fatigue; often acquired from livestock or unpasteurized dairy.
What are the differences between Gram-Positive and Gram-Negative bacteria?
- Cell Wall Structure
Gram-Positive Bacteria:
Thick Peptidoglycan Layer: The cell wall consists of a thick layer of peptidoglycan, which retains the crystal violet stain used in Gram staining.
Teichoic Acids: These are present in the peptidoglycan layer and contribute to the structural integrity and function of the cell wall.
Gram-Negative Bacteria:
Thin Peptidoglycan Layer: The peptidoglycan layer is much thinner, located between the inner and outer membranes.
Outer Membrane: Contains lipopolysaccharides (LPS), which can act as endotoxins and are important for the structural integrity of the bacteria.
2. Gram Staining
Gram-Positive: Stain purple or blue due to the retention of crystal violet dye during the staining process.
Gram-Negative: Stain pink or red because they do not retain the crystal violet and take up the counterstain (safranin).
3. Permeability
Gram-Positive: The thick peptidoglycan layer makes the cell wall relatively permeable to small molecules but less permeable to larger molecules.
Gram-Negative: The outer membrane acts as a barrier, making them more resistant to certain antibiotics and detergents.
4. Response to Antibiotics
Gram-Positive: Generally more susceptible to antibiotics that target the peptidoglycan layer (e.g., penicillin).
Gram-Negative: Often resistant to many antibiotics due to the protective outer membrane; treatment may require different or more potent antibiotics.
5. Examples
Gram-Positive: Includes bacteria like Staphylococcus aureus, Streptococcus pneumoniae, and Bacillus anthracis.
Gram-Negative: Includes bacteria like Escherichia coli, Salmonella, and Pseudomonas aeruginosa.
6. Clinical Significance
Gram-Positive Infections: Often associated with skin infections, respiratory infections, and some systemic infections.
Gram-Negative Infections: Frequently linked to more severe and systemic infections, especially in immunocompromised patients.
