305 week 9 bacterial infection

How many bacterial species are pathogenic?

Less than 1% of bacterial species are pathogenic.

What are common bacterial infections?

Pneumonia, urinary tract infections, wound infections, sepsis, food poisoning, sexually transmitted infections, tuberculosis, meningitis, sinus infections, and skin infections.

Why do antibiotics work against bacteria but not viruses?

Antibiotics target bacterial structures or processes, such as the cell wall, organelles, or DNA, that viruses do not possess in the same way.

Why are antibiotics ineffective against colds and influenza?

Colds and influenza are viral infections, and antibiotics act against bacteria rather than viruses.

What is normal flora?

Microorganisms that normally live on or in the body without causing disease under usual conditions.

What are the benefits of normal flora?

They synthesize vitamins such as B12 and K, aid digestion, compete with pathogens for space, and produce substances that inhibit other bacteria.

How can normal flora cause disease?

They may cause infection if they enter normally sterile or unusual body sites or if host defences are compromised.

Staphylococcus aureus as normal flora

Can colonize the nose but also cause disease when transferred to a susceptible host.

Streptococcus mutans

Normal mouth flora associated with dental caries.

Streptococcus pneumoniae

May colonize the upper respiratory tract but can cause pneumonia when it reaches the lower respiratory tract; it can also cause otitis media and meningitis.

Neisseria meningitidis

A cause of bacterial meningitis.

Escherichia coli (E. coli)

Normal flora of the large intestine that can cause UTIs when present in the urinary tract; some strains cause foodborne illness.

What are the main ways bacteria cause disease?

Toxin production, tissue damage, inflammation, tissue invasion, and intracellular or extracellular infection.

What are common manifestations of bacterial infection?

Pain, diarrhea, vomiting, redness, swelling, fever, chills, and fatigue.

Pseudomonas

An opportunistic, healthcare-associated pathogen that can cause pneumonia, UTIs, and wound infections, particularly in immunocompromised patients.

Vibrio cholerae

A Gram-negative rod transmitted through contaminated water that causes cholera by affecting the intestinal tract through toxin production.

Cholera incubation period

Approximately 1–4 days.

What is characteristic of cholera stool?

Rice-water stool containing mucus, epithelial cells, and large numbers of vibrios.

What proportion of cholera infections may be asymptomatic in endemic areas?

Approximately 60–70%.

What is the major danger of untreated cholera?

Severe illness and dehydration; the slides report a mortality rate of 25–50% without treatment.

Enteric bacteria

Gram-negative rods that can live anaerobically; examples include E. coli.

What diseases can enteric bacteria cause?

UTIs, foodborne illness, gastroenteritis, dysentery, and typhoid fever, depending on the organism.

Shigella species

Cause bacillary dysentery and severe diarrhea.

Salmonella enteritidis

Causes gastroenteritis and foodborne illness.

Salmonella Typhi

Causes typhoid fever, a systemic infection.

Typhoid fever: cause

Salmonella Typhi; Salmonella Paratyphi can cause a generally less severe illness.

Typhoid fever: transmission

Fecal–oral transmission through contaminated food or water, including transmission from asymptomatic carriers.

Why is typhoid fever associated with poor sanitation?

Contaminated food and water can transmit the bacteria through the fecal–oral route.

Typhoid fever: incubation period

Approximately 10–14 days.

Early symptoms of typhoid fever

Slowly rising fever, abdominal pain, muscle aches, abdominal distension, malaise, fatigue, headache, and early constipation followed by possible diarrhea.

Other signs of typhoid fever

Rose spots may appear; later disease may involve significant weight loss, apathy, confusion, or psychosis.

Serious complications of typhoid fever

Intestinal hemorrhage and perforation, which can be fatal.

Typhoid fever: treatment

Antibiotics, hydration, supportive care, and fever management.

Typhoid fever: chronic carriers

Approximately 3–5% of affected individuals may become chronic carriers.

Why is antibiotic resistance important in typhoid fever?

Multidrug-resistant bacterial strains are emerging, complicating treatment.

Food poisoning: common bacterial causes

E. coli, Salmonella, and Staphylococcus aureus.

Food poisoning: common symptoms

Nausea, vomiting, diarrhea, abdominal cramps, weakness, fatigue, loss of appetite, fever, and dehydration; blood may occur in stool depending on the pathogen.

How does Salmonella cause diarrhea?

It enters through contaminated food, invades intestinal epithelial cells, causes intestinal inflammation, and impairs water absorption.

Salmonella infection: common symptoms

Diarrhea, fever, nausea, vomiting, and headache.

Dysentery

Acute inflammation of the colon causing frequent diarrhea, blood or mucus in stool, severe abdominal cramps, fever, and risk of dehydration.

How does bacterial tooth decay develop?

Bacterial biofilms (plaque) form on teeth; bacterial acids dissolve enamel and then dentin. Untreated lesions can reach the pulp and cause an abscess.

Gingivitis

Inflammation of the gums.

Pyogenic cocci

Gram-positive spherical bacteria, including Staphylococcus and Streptococcus species, that commonly cause skin and soft-tissue infections and often produce pus.

Staphylococcus epidermidis

Normal skin flora that can cause opportunistic infections associated with medical devices.

Staphylococcus aureus

Can colonize the nose and cause opportunistic infections.

Streptococcus pyogenes

Causes strep throat, tonsillitis, wound and skin infections, and post-infectious complications such as rheumatic fever; its toxins can cause scarlet fever and toxic shock.

Streptococcus pneumoniae: common diseases

Pneumonia, otitis media, and meningitis.

How can Streptococcus pneumoniae reach the lungs or middle ear?

It may colonize the nasopharynx and gain access to the lungs or the Eustachian tube.

Conjunctivitis (pink eye)

Inflammation of the conjunctiva that can be caused by bacteria or viruses.

Common bacterial causes of conjunctivitis

Staphylococcus aureus, Streptococcus pneumoniae, and Haemophilus influenzae.

Conjunctivitis: common symptoms

Eye redness, swelling, and pus-like discharge.

Acne

Inflammation of hair follicles associated with bacterial growth and blocked follicles; may produce pustules and other lesions.

Boils (furuncles)

Localized infections, usually caused by Staphylococcus species, characterized by redness, swelling, pain, warmth, and pus.

Anthrax: cause

Bacillus anthracis.

Anthrax: routes of infection

Contact through the skin, inhalation, or intestinal absorption.

Anthrax: forms

Cutaneous anthrax affects the skin; inhalation anthrax affects the respiratory system; gastrointestinal anthrax affects the digestive tract.

Anthrax: treatment

Antibiotics and antitoxin.

Necrotizing fasciitis

A rapidly spreading bacterial infection affecting fascia and surrounding tissues that causes severe pain, swelling, and tissue necrosis and can progress to sepsis and shock.

Necrotizing fasciitis: portals of entry

Cuts, scrapes, puncture wounds, surgical wounds, and insect bites.

Monomicrobial necrotizing fasciitis

Infection caused by one organism, often Streptococcus pyogenes or Staphylococcus aureus.

Polymicrobial necrotizing fasciitis

Infection caused by multiple organisms, often a mixture of aerobic and anaerobic bacteria, making treatment more complex.

Leprosy (Hansen's disease): cause

Mycobacterium leprae.

Leprosy: progression and effects

A slowly progressing infection that damages the skin and peripheral nerves; incubation can last months to years.

Early symptoms of leprosy

Pale or reddish skin lesions and numbness or loss of sensation.

How does leprosy-related nerve damage cause complications?

Loss of sensation and temperature perception can lead to unnoticed injuries, chronic wounds, muscle weakness, tissue damage, and deformities.

Leprosy: treatment

Long-term antibiotic therapy; early diagnosis helps prevent complications.

Strep throat: cause

Streptococcus pyogenes.

Strep throat: symptoms

Sore throat, difficulty swallowing, fever, fatigue, and swollen lymph nodes.

Strep throat: treatment

Antibiotics when indicated and supportive care.

Why can lower respiratory infections be especially serious?

They can impair breathing and oxygen exchange and may be more severe in older adults, immunocompromised people, or after viral illness.

Pertussis (whooping cough): cause

Bordetella pertussis, a Gram-negative bacterium for which humans are the primary host.

Pertussis: transmission

Respiratory droplets; it is highly contagious.

Pertussis: characteristic symptoms

Severe coughing fits, an inspiratory whoop, vomiting after coughing, and usually minimal or absent fever.

Pertussis: early clinical course

Initially resembles a common cold before severe coughing fits develop.

Pertussis: infant complications

Apnea, pneumonia, seizures, encephalopathy, and death.

Pertussis: prevention

Vaccination with DTaP or Tdap.

Pneumonia

An infection and inflammation of the lungs that may be bacterial, viral, or fungal.

Pneumonia: common symptoms

Fever, chills, sputum production, chest pain, and cough; symptoms depend on the infection site.

Tuberculosis (TB): cause

Mycobacterium tuberculosis.

TB: transmission

Airborne droplets; infection usually requires prolonged exposure.

Latent TB

Bacteria remain contained within granulomas; the person has no symptoms and is not contagious.

Active TB

Granulomas break down, bacteria multiply and spread, symptoms develop, and the disease may be contagious.

What proportion of TB infections develop into active disease according to the slides?

Approximately 10%.

How does pulmonary TB damage the lungs?

It causes chronic infection, granuloma formation with caseous lesions, and progressive tissue destruction.

Pulmonary TB: common symptoms

Persistent cough, coughing blood (hemoptysis), chest pain, fatigue, weight loss, night sweats, and loss of appetite.

Extrapulmonary TB

TB affecting sites outside the lungs, including lymph nodes, bones, kidneys, or meninges.

Miliary TB

Disseminated TB that spreads through the bloodstream and affects multiple organs.

TB: treatment

Multiple antibiotics over several months; drug-resistant strains are increasing.

UTIs: most common bacterial cause

Escherichia coli (E. coli).

Why are UTIs more common in females?

The urethra is shorter and closer to the anus.

UTI risk factors

Sexual activity, pregnancy, and urinary retention.

Progression of an ascending urinary infection

Urethritis → cystitis → pyelonephritis.

Cystitis

Inflammation or infection of the bladder.

Cystitis: common symptoms

Dysuria, urinary frequency, urgency, suprapubic discomfort, cloudy or foul-smelling urine, and possible blood in the urine.

Cystitis: treatment

Antibiotics, increased fluid intake, and symptom management.

Urethritis

Inflammation of the urethra.

Urethritis: common symptoms

Burning during urination, urinary frequency, urethral irritation or swelling, and urethral discharge.

Possible bacterial causes of urethritis

E. coli, Neisseria gonorrhoeae, and Chlamydia.

Acute glomerulonephritis

Inflammation of the glomeruli that may occur 1–4 weeks after a streptococcal infection.

Acute glomerulonephritis: symptoms

Flank pain, fever, malaise, loss of appetite, swelling around the eyes and ankles, reduced urine output, blood in urine, and casts in urine.