21.2 Bacterial Infections of the Skin and Eyes

Pimples are small, inflamed spots on the skin caused by clogged hair follicles, often due to bacteria, dead skin cells, and oil buildup. They are a common symptom of bacterial skin infections.

Folliculitis: Inflammation of hair follicles that can result in red bumps or pustules.

Sebaceous Glands: Glands in the skin that secrete oil (sebum) which can contribute to clogging pores.

Cystic Acne: A severe form of acne involving deep-seated cysts that can cause significant scarring.

Staphylococcus is a genus of Gram-positive bacteria known for their spherical shape and tendency to form clusters resembling grapes. They are commonly found on the skin and in the nasal passages of humans.

Gram-Positive Bacteria: Bacteria that have a thick peptidoglycan layer in their cell walls and retain the crystal violet stain used in Gram's method.

Normal Microbiota: The collection of microorganisms that reside on or within various parts of the human body without causing disease under normal conditions.

Toxic Shock Syndrome: A severe illness caused by staphylococcal toxins characterized by high fever, rash, low blood pressure, and organ failure.

Streptococcus is a genus of Gram-positive bacteria that often occur in chains or pairs. They are known for causing a variety of infections in humans, ranging from mild throat infections to life-threatening diseases.

Hemolysis: The breakdown of red blood cells; used to classify Streptococci.

Gram-Positive Bacteria: Bacteria that have a thick peptidoglycan cell wall which retains the crystal violet stain during the Gram staining process.

Normal Microbiota: The community of microorganisms that reside on or within various parts of the body without causing disease.

S. aureus, or Staphylococcus aureus, is a Gram-positive bacterium known for its ability to cause a wide range of infections, from mild skin conditions to life-threatening diseases. This versatile pathogen is a significant concern in both healthcare and community settings due to its virulence factors and potential for antibiotic resistance. S. aureus is a key topic in the context of Gram-positive bacteria, biochemical identification of microorganisms, and bacterial infections of the skin and eyes. Its unique characteristics and clinical significance make it an important subject of study for students of microbiology.

Coagulase: An enzyme produced by S. aureus that can cause blood clotting, which is used as a diagnostic tool to identify the bacterium.

Staphylococcal Enterotoxins: Potent exotoxins produced by S. aureus that can cause food poisoning and toxic shock syndrome.

Methicillin-Resistant S. aureus (MRSA): A strain of S. aureus that has developed resistance to many antibiotics, including methicillin, making it a significant public health concern.

Impetigo is a highly contagious bacterial skin infection characterized by red sores and blisters, primarily caused by Staphylococcus aureus and Streptococcus pyogenes. It commonly affects infants and young children but can occur in individuals of any age.

Staphylococcus aureus: A Gram-positive bacterium that often causes skin infections including impetigo.

Streptococcus pyogenes: A Gram-positive bacterium known for causing various infections, including strep throat and impetigo.

Cellulitis: A bacterial skin infection that involves deeper layers of the skin compared to impetigo.

Folliculitis is an inflammation of the hair follicles commonly caused by bacterial infection, particularly Staphylococcus aureus. It often manifests as red, swollen, and pus-filled bumps on the skin.

Impetigo: A superficial skin infection caused mainly by Staphylococcus aureus or Streptococcus pyogenes.

Cellulitis: A deeper bacterial skin infection causing redness, swelling, and warmth.

Carbuncle: A cluster of connected boils often caused by a bacterial infection that extends deeper into the tissue.

Cellulitis is a bacterial infection of the skin and subcutaneous tissues characterized by redness, swelling, warmth, and pain. It commonly affects the lower legs but can occur anywhere on the body.

Impetigo: A contagious superficial bacterial skin infection often caused by Streptococcus pyogenes or Staphylococcus aureus.

Erysipelas: An acute infection involving the upper dermis and superficial lymphatics, usually caused by Streptococcus pyogenes.

Necrotizing Fasciitis: A severe bacterial infection causing rapid tissue death often involving deeper layers of skin and subcutaneous tissues.

Conjunctivitis, commonly known as pink eye, is an inflammation or infection of the conjunctiva, the transparent membrane that lines your eyelid and covers the white part of your eyeball. It can be caused by bacteria, viruses, allergens, or irritants.

Staphylococcus aureus: A common bacterium found on the skin and in the respiratory tract; it causes various infections including bacterial conjunctivitis.

Adenovirus: A group of viruses that can cause respiratory illnesses and are a common cause of viral conjunctivitis.

Antibiotic resistance: The ability of bacteria to resist the effects of drugs that once killed them; an important consideration when treating bacterial infections like bacterial conjunctivitis.

Keratitis is an inflammation of the cornea, the transparent, dome-shaped structure at the front of the eye. It can be caused by various factors, including bacterial infections, viral infections, fungal infections, trauma, or underlying medical conditions, and can lead to vision problems if left untreated.

Cornea: The transparent, dome-shaped structure at the front of the eye that helps focus light and protect the eye from damage.

Conjunctivitis: Inflammation of the conjunctiva, the thin, transparent membrane that covers the white part of the eye and the inner surface of the eyelids.

Blepharitis: Inflammation of the eyelids, often caused by a bacterial or seborrheic skin condition.

S. epidermidis is a type of Gram-positive bacterium that commonly resides on the human skin and mucous membranes. It is a member of the Staphylococcus genus and is considered part of the normal human microbiome, playing a role in maintaining skin health and preventing the colonization of more harmful pathogens.

Staphylococcus: A genus of Gram-positive, spherical-shaped bacteria that often occur in grape-like clusters. Staphylococcus species are a common cause of skin and soft tissue infections.

Microbiome: The community of microorganisms, including bacteria, archaea, fungi, and viruses, that naturally inhabit the human body and play important roles in health and disease.

Opportunistic Pathogen: A microorganism that is normally harmless but can cause disease in individuals with weakened immune systems or other predisposing factors.

S. pyogenes, also known as Streptococcus pyogenes, is a Gram-positive bacterium that is a common cause of skin and soft tissue infections, as well as more serious invasive diseases. It is a significant pathogen that can lead to a range of clinical manifestations, from mild skin infections to life-threatening conditions.

Gram-positive Bacteria: Gram-positive bacteria are a group of bacteria that have a thick, rigid cell wall made of peptidoglycan, which stains purple with the Gram staining technique.

Streptococcus: Streptococcus is a genus of Gram-positive, spherical bacteria that often form chains and are known to cause a variety of human diseases.

Skin and Soft Tissue Infections: Skin and soft tissue infections are a broad range of infections that can affect the skin, underlying soft tissues, or both, and can range in severity from mild to life-threatening.

Impetigo is a highly contagious bacterial skin infection characterized by red sores and blisters, primarily caused by Staphylococcus aureus and Streptococcus pyogenes. It commonly affects infants and young children but can occur in individuals of any age.

Staphylococcus aureus: A Gram-positive bacterium that often causes skin infections including impetigo.

Streptococcus pyogenes: A Gram-positive bacterium known for causing various infections, including strep throat and impetigo.

Cellulitis: A bacterial skin infection that involves deeper layers of the skin compared to impetigo.

Erysipelas is a bacterial skin infection caused primarily by Streptococcus pyogenes, characterized by raised, red, and swollen patches on the skin. It often affects the face and legs and can be accompanied by fever and chills.

Cellulitis: A common bacterial skin infection that affects deeper layers than erysipelas.

Impetigo: A highly contagious skin infection causing red sores that can burst and develop honey-colored crusts.

Necrotizing Fasciitis: A severe bacterial infection causing tissue death; often called flesh-eating disease.

Cellulitis is a bacterial infection of the skin and subcutaneous tissues characterized by redness, swelling, warmth, and pain. It commonly affects the lower legs but can occur anywhere on the body.

Impetigo: A contagious superficial bacterial skin infection often caused by Streptococcus pyogenes or Staphylococcus aureus.

Erysipelas: An acute infection involving the upper dermis and superficial lymphatics, usually caused by Streptococcus pyogenes.

Necrotizing Fasciitis: A severe bacterial infection causing rapid tissue death often involving deeper layers of skin and subcutaneous tissues.

S. pneumoniae, also known as Streptococcus pneumoniae, is a Gram-positive bacterium that is a leading cause of serious infections, particularly in the skin and eyes. It is a common colonizer of the upper respiratory tract and can cause a wide range of diseases, from mild skin infections to life-threatening pneumonia and meningitis.

Pneumococcal Disease: Infections caused by S. pneumoniae, which can range from mild skin and eye infections to severe, invasive diseases like pneumonia, meningitis, and sepsis.

Capsule: A protective outer layer surrounding the S. pneumoniae cell that helps it evade the host's immune system and contributes to its virulence.

Pneumolysin: A toxin produced by S. pneumoniae that can damage host cells, particularly those in the lungs, and contribute to the development of pneumonia.

Conjunctivitis, commonly known as pink eye, is an inflammation or infection of the conjunctiva, the transparent membrane that lines your eyelid and covers the white part of your eyeball. It can be caused by bacteria, viruses, allergens, or irritants.

Staphylococcus aureus: A common bacterium found on the skin and in the respiratory tract; it causes various infections including bacterial conjunctivitis.

Adenovirus: A group of viruses that can cause respiratory illnesses and are a common cause of viral conjunctivitis.

Antibiotic resistance: The ability of bacteria to resist the effects of drugs that once killed them; an important consideration when treating bacterial infections like bacterial conjunctivitis.

Pseudomonas aeruginosa is a Gram-negative, opportunistic pathogen that can cause serious infections in humans. It is known for its resistance to antibiotics and ability to thrive in various environments.

Biofilm: A structured community of microbial cells enclosed in a self-produced polymeric matrix adherent to an inert or living surface.

Efflux Pump: A protein that bacteria use to expel toxic substances and antibiotics out of their cells.

Pyocyanin: A blue-green pigment produced by Pseudomonas aeruginosa that has antimicrobial properties and contributes to tissue damage during infection.

Propionibacterium acnes is an anaerobic, gram-positive bacterium that is a common inhabitant of the human skin and is associated with the development of acne. It plays a significant role in the normal microbiota of the skin and eyes, as well as in bacterial infections affecting these areas.

Anaerobic: Organisms that can survive and grow in the absence of oxygen.

Gram-positive: Bacteria that retain the crystal violet dye during the Gram staining procedure, indicating a thick peptidoglycan cell wall.

Microbiota: The community of microorganisms, including bacteria, fungi, and viruses, that naturally inhabit a particular environment, such as the human body.

Acne vulgaris is a common skin condition characterized by the development of pimples, blackheads, and other blemishes on the face, chest, and back. It is caused by a combination of factors, including overproduction of oil, clogged pores, and bacterial infection.

Sebum: The oily substance produced by the sebaceous glands in the skin, which can contribute to the development of acne.

Propionibacterium acnes: A type of bacteria that lives on the skin and can contribute to the development of acne by causing inflammation.

Comedones: Clogged pores in the skin, which can lead to the formation of blackheads and whiteheads, two common types of acne lesions.

Hair follicles are tubular structures in the skin from which hair grows. They play a crucial role in housing and protecting various microorganisms that form part of the skin's normal microbiota.

Sebaceous Glands: Glands associated with hair follicles that secrete sebum.

Folliculitis: An infection of hair follicles characterized by inflammation and pus formation.

Infundibulum: The upper part of the hair follicle where it opens to the skin surface.

Chlamydia trachomatis is a species of obligate intracellular bacteria that is the causative agent of several human diseases, including trachoma, lymphogranuloma venereum, and various sexually transmitted infections. It is a significant public health concern due to its ability to infect and impact multiple body systems.

Trachoma: A chronic eye infection caused by Chlamydia trachomatis that can lead to blindness if left untreated.

Lymphogranuloma Venereum (LGV): A sexually transmitted infection caused by specific serovars of Chlamydia trachomatis that can lead to genital ulcers and lymphadenopathy.

Sexually Transmitted Infection (STI): An infection that is primarily transmitted through sexual contact, including Chlamydia trachomatis, which is one of the most common STIs worldwide.

Trachoma is a bacterial infection of the eye caused by Chlamydia trachomatis, leading to inflammation and possible blindness if untreated. It is a significant cause of preventable blindness worldwide.

Chlamydia trachomatis: A gram-negative bacterium that causes various infections including trachoma.

Trichiasis: A condition where eyelashes grow inward towards the eye, often resulting from repeated trachoma infections.

PCR (Polymerase Chain Reaction): A laboratory technique used to amplify DNA sequences, useful in diagnosing bacterial infections like trachoma.

Moraxella is a genus of Gram-negative, aerobic bacteria that are known to cause various infections, particularly in the skin and eyes. These opportunistic pathogens are commonly found in the upper respiratory tract and can lead to conditions like conjunctivitis, keratitis, and skin infections.

Conjunctivitis: Inflammation of the conjunctiva, the thin, transparent membrane that covers the front of the eye and lines the inner eyelid, often caused by Moraxella bacteria.

Keratitis: Inflammation of the cornea, the transparent front part of the eye, which can be caused by Moraxella infections.

Opportunistic Pathogen: A microorganism that typically does not cause disease in healthy individuals but can take advantage of a weakened immune system or compromised host to cause infection.

Haemophilus is a genus of Gram-negative, coccobacillary bacteria that are known to cause various infections, including those affecting the skin and eyes. These bacteria are obligate aerobes and require specific growth factors, such as hemin and nicotinamide adenine dinucleotide (NAD), for their survival and proliferation.

Haemophilus influenzae: A species of Haemophilus that is a common cause of respiratory tract infections, meningitis, and other invasive diseases, particularly in children.

Haemophilus ducreyi: The causative agent of the sexually transmitted infection chancroid, which manifests as painful genital ulcers.

Hemin: An iron-containing compound that is an essential growth factor for Haemophilus species, as they are unable to synthesize it themselves.

Mupirocin is a topical antibiotic medication primarily used to treat bacterial skin infections. It is effective against a wide range of gram-positive bacteria, including Staphylococcus aureus, and is commonly used to prevent and treat conditions like impetigo, folliculitis, and other skin infections.

Topical Antibiotic: A medication that is applied directly to the skin or other affected area, rather than being taken orally or administered systemically.

Gram-Positive Bacteria: Bacteria that retain the crystal violet stain during the Gram staining process, indicating a thick peptidoglycan cell wall.

Impetigo: A highly contagious bacterial skin infection that commonly affects children, characterized by red sores and blisters.

Cephalexin is a first-generation cephalosporin antibiotic used to treat a variety of bacterial infections, particularly those affecting the skin and eyes. As a broad-spectrum antibiotic, it is effective against both Gram-positive and Gram-negative bacteria, making it a common choice for treating common skin and eye infections.

Cephalosporins: A class of antibiotics derived from the Cephalosporium fungus, which are structurally similar to penicillins and used to treat a wide range of bacterial infections.

Gram-positive Bacteria: Bacteria that stain purple with the Gram stain technique, indicating a thick peptidoglycan cell wall, and are generally more susceptible to certain antibiotics.

Gram-negative Bacteria: Bacteria that stain pink with the Gram stain technique, indicating a thin peptidoglycan cell wall and an outer lipopolysaccharide membrane, making them generally more resistant to certain antibiotics.

Dicloxacillin is a semi-synthetic penicillin antibiotic used to treat bacterial infections, particularly those caused by Staphylococcus aureus. It is commonly prescribed for skin and eye infections due to its effectiveness against gram-positive bacteria.

Penicillin: A class of antibiotics derived from the Penicillium fungus that interfere with bacterial cell wall synthesis, effectively killing or inhibiting the growth of bacteria.

Staphylococcus aureus: A gram-positive bacterium that is a common cause of skin and soft tissue infections, including impetigo, folliculitis, and cellulitis.

Gram-positive bacteria: Bacteria that have a thick peptidoglycan cell wall and stain purple with the Gram staining technique, in contrast to gram-negative bacteria.

Vancomycin is a glycopeptide antibiotic used to treat serious bacterial infections caused by Gram-positive bacteria. It inhibits cell wall synthesis by binding to the D-alanyl-D-alanine terminus of cell wall precursor units.

MRSA: Methicillin-resistant Staphylococcus aureus, a type of bacteria resistant to several antibiotics including methicillin.

VRE: Vancomycin-resistant Enterococci, a group of bacterial strains that have acquired resistance to vancomycin.

Nephrotoxicity: Kidney damage or impairment caused by exposure to toxic substances, such as certain drugs including vancomycin.

Erythromycin is a macrolide antibiotic that inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit. It is effective against a wide range of Gram-positive and some Gram-negative bacteria.

Macrolides: A class of antibiotics that includes erythromycin, characterized by their macrocyclic lactone rings.

Ribosome: The cellular machinery responsible for protein synthesis, targeted by many antibiotics.

Antibiotic Resistance: The ability of bacteria to withstand the effects of an antibiotic through various mechanisms.

Ciprofloxacin is a broad-spectrum antibiotic belonging to the fluoroquinolone class, effective against various bacterial infections. It operates by inhibiting DNA gyrase and topoisomerase IV, enzymes crucial for bacterial DNA replication.

Fluoroquinolone: A class of antibiotics that inhibit bacterial DNA synthesis.

DNA Gyrase: An enzyme targeted by fluoroquinolones involved in supercoiling of bacterial DNA.

Drug Resistance: The reduction in effectiveness of a medication such as an antimicrobial in curing a disease or condition.

Trachoma is a bacterial infection of the eye caused by Chlamydia trachomatis, leading to inflammation and possible blindness if untreated. It is a significant cause of preventable blindness worldwide.

Chlamydia trachomatis: A gram-negative bacterium that causes various infections including trachoma.

Trichiasis: A condition where eyelashes grow inward towards the eye, often resulting from repeated trachoma infections.

PCR (Polymerase Chain Reaction): A laboratory technique used to amplify DNA sequences, useful in diagnosing bacterial infections like trachoma.

Azithromycin is a broad-spectrum macrolide antibiotic effective against a variety of bacterial infections. It works by inhibiting bacterial protein synthesis.

Macrolide Antibiotics: A class of antibiotics that includes erythromycin, clarithromycin, and azithromycin, known for inhibiting bacterial protein synthesis.

Chlamydia trachomatis: A type of bacteria that can cause various infections including sexually transmitted diseases; often treated with azithromycin.

Mycoplasma pneumoniae: An atypical bacterium causing respiratory infections; commonly treated with azithromycin.

Tetracycline is a broad-spectrum antibiotic used to treat a wide variety of bacterial infections. It works by inhibiting protein synthesis in bacteria, preventing them from growing and multiplying.

Antibiotic: A substance that inhibits the growth of or kills microorganisms.

Gram-Positive Bacteria: Bacteria that have a thick peptidoglycan cell wall which retains the crystal violet stain used in Gram staining.

Protein Synthesis Inhibitor: A class of antibiotics that work by disrupting the process of protein synthesis in bacteria.

MRSA (Methicillin-resistant Staphylococcus aureus) is a type of Gram-positive bacterium that is resistant to several widely used antibiotics, making it difficult to treat. It commonly causes skin and soft tissue infections but can lead to more severe invasive diseases.

Staphylococcus aureus: A common bacterium found on the skin and in the respiratory tract that can cause a range of illnesses.

Gram-Positive Bacteria: Bacteria that have a thick peptidoglycan cell wall which retains the crystal violet stain used in Gram staining.

Vancomycin: An antibiotic used as a treatment for serious bacterial infections, especially those caused by Gram-positive bacteria like MRSA.

Nosocomial infections, also known as hospital-acquired infections, are infections that patients develop while receiving treatment in a healthcare facility. These infections are not present or incubating at the time of admission and can have significant implications for patient health and healthcare costs.

Healthcare-Associated Infections (HAIs): A broader term that encompasses nosocomial infections and includes infections acquired in any healthcare setting, such as hospitals, long-term care facilities, outpatient clinics, and dialysis centers.

Antimicrobial Resistance: The ability of microorganisms to resist the effects of antimicrobial drugs, making nosocomial infections more difficult to treat and increasing the risk of complications and mortality.

Infection Control Measures: Protocols and procedures implemented in healthcare settings to prevent the transmission of nosocomial infections, such as hand hygiene, use of personal protective equipment, and environmental cleaning.

Biofilms are complex communities of microorganisms that adhere to surfaces and are embedded within a self-produced matrix of extracellular polymeric substances. They provide protection to the bacteria from environmental stresses and antimicrobial agents.

Extracellular Polymeric Substances (EPS): A complex mixture of polymers secreted by microorganisms in a biofilm, providing structural stability.

Planktonic Cells: Free-floating microbial cells that live independently rather than in a community like a biofilm.

Confocal Laser Scanning Microscopy: A powerful imaging technique used to obtain high-resolution images of thick specimens like biofilms.

Biofilms are complex communities of microorganisms that adhere to surfaces and are embedded within a self-produced matrix of extracellular polymeric substances. They provide protection to the bacteria from environmental stresses and antimicrobial agents.

Extracellular Polymeric Substances (EPS): A complex mixture of polymers secreted by microorganisms in a biofilm, providing structural stability.

Planktonic Cells: Free-floating microbial cells that live independently rather than in a community like a biofilm.

Confocal Laser Scanning Microscopy: A powerful imaging technique used to obtain high-resolution images of thick specimens like biofilms.

Quorum sensing is a communication mechanism used by bacteria to coordinate gene expression and behavior in response to changes in cell population density. It allows bacteria to sense and respond to the presence of other bacteria, enabling them to act in a coordinated manner as a community rather than as individual cells.

Autoinducer: Small signaling molecules produced by bacteria that are used in quorum sensing to detect cell population density.

Biofilm: A structured community of bacterial cells enclosed in a self-produced extracellular matrix and adherent to a surface.

Virulence Factors: Molecules or structures produced by pathogens that contribute to their ability to cause disease.

Debridement is the medical removal of dead, damaged, or infected tissue to improve the healing potential of the remaining healthy tissue. It is often used in treating severe skin and eye bacterial infections.

Necrosis: The death of cells or tissues through injury or disease.

Antibiotics: Medications used to treat bacterial infections.

Wound Care: The process of preventing infection and promoting healing in wounds.

Bacterial virulence factors are specific molecules or characteristics that enable pathogenic bacteria to infect, colonize, and cause harm to their host. These factors contribute to the ability of bacteria to evade the host's immune defenses, adhere to and invade host cells, and produce toxins or other damaging substances.

Adhesins: Bacterial surface proteins that allow the bacteria to attach to and colonize host cells or tissues.

Toxins: Harmful substances produced by bacteria that can damage or kill host cells.

Enzymes: Bacterial proteins that can break down or modify host tissues, helping the bacteria to invade and spread.

The host immune response refers to the complex system of biological mechanisms and processes by which the human body recognizes and defends itself against harmful pathogens, such as bacteria, viruses, fungi, and parasites. This response is crucial in maintaining health and preventing the development of infectious diseases.

Innate Immunity: The body's first line of defense against pathogens, consisting of physical barriers, chemical defenses, and immune cells that respond immediately to threats.

Adaptive Immunity: The second line of defense, involving specialized lymphocytes (B cells and T cells) that learn to recognize specific pathogens and mount a targeted response.

Inflammation: The body's response to injury or infection, characterized by redness, swelling, heat, and pain, which helps to eliminate the threat and initiate the healing process.

Antibiotic resistance mechanisms refer to the various ways in which bacteria can develop the ability to withstand and survive the effects of antibiotics, rendering these antimicrobial drugs ineffective. Understanding these mechanisms is crucial in the context of bacterial infections of the skin and eyes, as they can impact treatment strategies and patient outcomes.

Genetic Mutation: Genetic changes in bacterial DNA that can lead to the development of antibiotic resistance by altering the target site or mechanism of action of the antibiotic.

Efflux Pumps: Specialized transport systems in bacteria that actively pump out antibiotics, preventing them from reaching their intended targets and conferring resistance.

Enzymatic Inactivation: The production of enzymes by bacteria that can chemically modify and deactivate antibiotics, rendering them ineffective.