Week Eleven: Bacterial Infections of Humans (Part I)

Bacterial adherence

The process by which bacteria attach to host cells or other surfaces.

Bacterial growth

The process by which bacteria multiply.

Colonization

The presence and persistence of bacteria without causing disease.

Infection

Bacterial invasion and/or harmful effects that produce disease and clinical findings.

Biofilm

A sticky matrix produced by bacteria that holds them together and helps them persist.

Bacterial invasion

The entry of bacteria into tissues or cells, potentially causing local or spreading infection.

Fimbriae / adhesive pili

Structures that allow bacteria to attach to host cells or other surfaces.

Bacterial capsule

An outer structure that helps bacteria resist engulfment by immune cells.

Flagella

Structures that enable bacterial movement toward suitable environments.

Peptidoglycan

The material that makes up bacterial cell walls and is targeted by beta-lactam antibiotics.

Outer membrane

A structure found in Gram-negative bacteria that contains LPS or LOS.

LPS

Lipopolysaccharide found in the outer membrane of Gram-negative bacteria; activates inflammation.

LOS

Lipooligosaccharide found in certain Gram-negative bacteria; can contribute to inflammation and sepsis.

Lipid A

The component of LPS/LOS responsible for triggering host inflammation.

Plasmid

An extra-chromosomal DNA element that can carry bacterial resistance genes.

Sex pilus

A bacterial structure that facilitates DNA transfer between bacteria.

Endospore

A bacterial survival form that resists harsh conditions and can persist after release.

Beta-lactam antibiotics

Antibiotics that target bacterial cell-wall synthesis.

Mycoplasma pneumoniae

A bacterium without a cell wall, making beta-lactam antibiotics ineffective.

Exotoxins

Proteins produced by certain bacteria that disrupt cell function or activate immune responses.

Endotoxin

Lipopolysaccharide in the outer membrane of Gram-negative bacteria that activates inflammation.

Host response

The body's immune and inflammatory reaction to bacteria, bacterial components, or toxins.

Inflammation

A protective response that can cause warmth, swelling, pain, and fever but may also injure tissue.

Sepsis

Life-threatening organ dysfunction caused by a dysregulated response to infection.

Bacteremia

The presence of bacteria in the bloodstream.

Gram-positive bacteria

Bacteria that stain purple and have thick peptidoglycan without an outer membrane.

Gram-negative bacteria

Bacteria that stain pink/red and have thin peptidoglycan plus an outer membrane.

Gram staining

An early laboratory method that provides clues about bacterial classification and structure.

Bacterial culture

A test used to grow and identify bacteria from a collected specimen.

Susceptibility testing

Testing that determines which antibiotics are likely to be effective against an identified bacterium.

NAAT

Nucleic acid amplification testing used to detect bacterial genetic material.

MRSA

Methicillin-resistant Staphylococcus aureus, which can colonize the nose or cause infection.

Asymptomatic MRSA colonization

The presence of MRSA, such as in the nose, without signs or symptoms of infection.

Catheter-associated biofilm

Bacterial growth within a sticky matrix on a catheter that can allow bacteria to persist.

Asymptomatic bacteriuria

Bacteria detected in urine without symptoms establishing a symptomatic urinary tract infection.

Cellulitis

An infection of the dermis and subcutaneous tissue, commonly producing warmth, swelling, and tenderness.

Impetigo

A superficial bacterial infection of the epidermis that produces sores, pustules, crusts, or blisters.

Nonbullous impetigo

Impetigo caused by S. aureus, S. pyogenes, or both, producing sores that rupture into honey-colored crusts.

Bullous impetigo

Impetigo caused by toxin-producing S. aureus, producing fragile fluid-filled blisters.

Exfoliative toxin

A toxin produced by certain S. aureus strains that disrupts connections between superficial skin cells.

Honey-colored crusts

The characteristic dried fluid crusts associated with nonbullous impetigo.

Poststreptococcal glomerulonephritis (PSGN)

Kidney inflammation that can develop weeks after group A streptococcal infection.

Necrotizing soft tissue infection (NSTI)

A rapidly progressive infection that causes soft tissue destruction and tissue death.

Necrotizing fasciitis

A severe necrotizing infection involving fascia, the connective tissue beneath the skin.

Crepitus

A crackling sensation under the skin that can be an advanced finding of necrotizing soft tissue infection.

Pain out of proportion

Severe pain greater than expected from visible skin changes; an early warning sign of NSTI.

Nonpurulent cellulitis

Cellulitis without pus, usually caused by streptococci, including S. pyogenes.

Purulent infection

An infection associated with pus or purulent drainage.

Bacterial conjunctivitis

An infection of the conjunctiva causing eye redness, irritation, and often thick or purulent discharge.

Conjunctiva

The membrane lining the eyelids and covering the white portion of the eye.

Keratitis

Corneal involvement that may be suspected with significant eye pain, light sensitivity, or reduced vision.

Acute bacterial otitis media

An infection and inflammation of the middle ear, commonly occurring in children.

Eustachian tube

The tube connecting the middle ear to the back of the throat.

Bulging tympanic membrane

A key examination finding associated with acute otitis media.

Mastoiditis

An uncommon complication of otitis media involving swelling or tenderness behind the ear.

Group A Streptococcus (GAS)

Streptococcus pyogenes, the bacterium responsible for group A streptococcal pharyngitis.

Bacterial pharyngitis

Infection and inflammation of the throat and tonsils caused by bacteria.

Rapid antigen detection test (RADT)

A rapid test used to detect group A streptococcal antigens in a throat specimen.

Throat culture

A test used to identify group A Streptococcus; used as backup after a negative RADT in children aged 3 years and older.

Acute rheumatic fever

A delayed immune complication of group A streptococcal infection that can injure the heart and joints.

Peritonsillar or neck abscess

A possible local complication suggested by one-sided swelling, muffled voice, or difficulty opening the mouth.

Pertussis

A highly contagious bacterial respiratory infection also called whooping cough.

Bordetella pertussis

A small Gram-negative rod that causes pertussis.

Pertussis toxin effects

Toxins impair airway cilia and cause inflammation, making mucus harder to clear.

Ciliated airway cells

Airway cells with cilia that help move mucus and particles out of the respiratory tract.

Apnea

The temporary cessation of breathing; infants with pertussis may experience apnea with little or no cough.

Posterior nasopharyngeal swab

A specimen collected from the back of the nose for pertussis PCR and/or culture.

Pertussis culture

Most useful during the first two weeks of cough.

Pertussis PCR

Most useful during the first three to four weeks of cough.

Bacterial pneumonia

An infection of the lower respiratory tract in which inflammation and fluid collect in the air sacs, impairing gas exchange.

Community-acquired pneumonia

Pneumonia associated with organisms such as S. pneumoniae, M. pneumoniae, H. influenzae, and Legionella.

Hospital-associated pneumonia

Pneumonia associated with organisms such as S. aureus, including MRSA, and P. aeruginosa.

Legionella pneumophila

A bacterium associated with pneumonia transmitted through inhalation of contaminated water mist.

Aspiration

The entry of bacteria from the mouth or throat into the lower respiratory tract.

Crackles

Abnormal lung sounds that may occur with pneumonia.

Hypoxemia

Low blood oxygen levels that may result when pneumonia impairs gas exchange.

Tuberculosis (TB)

A bacterial infection caused by Mycobacterium tuberculosis.

Mycobacterium tuberculosis

An acid-fast bacillus that causes tuberculosis.

Acid-fast bacillus

A bacterium with special cell-wall characteristics that allow it to retain an acid-fast stain.

Granuloma

A cluster of immune cells that can help contain tuberculosis bacteria.

Latent TB infection

TB bacteria remain in the body without causing symptoms or contagious active disease.

Active TB disease

A condition in which TB bacteria multiply and cause disease in the lungs or elsewhere.

IGRA

Interferon-gamma release assay; a blood test that detects TB infection but does not determine disease activity.

TB skin test

A test that detects TB infection but cannot independently distinguish latent infection from active disease.

AFB smear

A sputum test used to look for acid-fast bacilli.

TB NAAT

A molecular test used to detect TB genetic material.

TB culture

A laboratory test used to grow and identify Mycobacterium tuberculosis.

Airborne infection isolation room (AIIR)

A specialized room used for patients with suspected infectious airborne diseases such as pulmonary TB.

N95 respirator

A fit-tested respiratory protective device worn by healthcare staff caring for patients with suspected infectious TB.

Standard Precautions

Basic infection-prevention measures used for all patients.

Contact Precautions

Additional precautions used when infection can spread through direct or indirect contact.

Droplet Precautions

Additional precautions used for infections transmitted through respiratory droplets.

Airborne Precautions

Precautions used for infections transmitted through airborne particles.

What is the difference between adherence, growth, and colonization?

Adherence means bacteria attach; growth means they multiply; colonization means they remain without causing disease.

Does a positive bacterial test automatically mean the patient has an infection?

No. Interpret the result with symptoms, examination findings, and the suspected infection site.

A patient has a positive nasal MRSA screen but no symptoms. What does this indicate?

MRSA colonization or carriage, not necessarily an active infection.

Why can colonized patients still require infection-prevention measures?

They can spread bacteria to other people.

What bacterial structure helps E. coli attach to urinary tract cells?

Fimbriae or adhesive pili.

How does a bacterial capsule contribute to infection?

It helps bacteria resist engulfment by immune cells.

Which bacterial structure helps H. pylori move through gastric mucus?

Flagella.