Bacterial Diseases Part 1

Staphylococcal Infections

• S. aureus invades hair follicle → causes folliculitis (pimples)

• stye: infected follicle of an eyelash

• symptoms

  • boil (furuncle): localized region of pus surrounded by infected tissue

  • carbuncle: further infection; hard round deep inflammation of tissue under skin

• produces coagulase → clots fibrin in blood

• kills phagocytes with leucocidin

• peptidoglycan layer resists digestion by lysozymes

• repeated infection due to immune evasion

• toxins act as superantigens sometimes

• some can be asymptomatic carriers (30%-50%)

• MRSA acquired resistance to multiple antibiotics

Impetigo

highly contagious superficial skin infection caused by S. aureus and S. pyogenes → sometimes both as a mixed infection

Scaled Skin Syndrome

• toxin-mediated disease caused by certain strains of S. aureus

• produce exfoliative toxins → ETA and ETB

• cause bullous impetigo

• if enter bloodstream and circulate body → causes skin redness and peeling damage-separation of skin layers (exfoliation)

Toxic Shock Syndrome

• rare but life-threatening acute condition

• high fever, sunburn-like rash, shock, multiorgan failure

• TSST-1: superantigen produced by strains of S. aureus at a localized site of infection where the bacteria is growing

  • enters circulation → causes cytokine storm (large inflammatory response) → leads to shock and multi-organ failure

Streptococcal Infections

• Streptococcus pyogenes → aka Group A Streptococci (GAS) causes:

  • impetigo

  • erysipelas

  • cellulitis

  • necrotizing fasciitis

    • associated with Streptococcal Toxic Shock Syndrome (STSS) → rare life threatening condition caused by streptococcal superantigen toxin

  • strep throat → complication is scarlet fever

    • sandpaper-like rash caused by erythrogenic toxin encoded by a prophage

• S. pyogenes virulence factors → hemolysins, streptolysin, M protein, capsule, streptokinase, hyaluronidase, deoxyribonucleases

• ex: Acute Rheumatic Fever and Post-Streptococcal Glomerulonephritis

Acne

• skin condition associated with Cutibacterium acnes → part of the normal skin microflora

• sebaceous glands secrete excessive oil → C. acnes multiply using the sebum as a source

• overgrowth and byproducts trigger inflammation of clogged hair follicles → severe cases cause scarring

Pseudomonas dermatitis

• skin infection caused by Pseudomonas aeruginosa

  • opportunistic gram-negative pathogen

  • resistant to broad range of antibiotics and disinfectants

  • produces several exotoxins and possesses an endotoxin

  • grows in a biofilm

• “hot-tub rash” from contaminated water

• severe wound and burn infections in compromised patients

Pink Eye

• conjunctivitis caused by bacteria and some viruses

• caused by Staphylococcus, Streptococcus, Neisseria, Haemophilus influenzae, and Pseudomonas aeruginosa

• redness, irritation, and purulent discharge

• treated with antibiotic eye drops or ointments

Ophthalmia neonatorum

• conjunctivitis that affects newborns

• Neisseria gonorrhoeae or Chlamydia trachomatis in birth canal infects eyes of newborn during delivery

• before silver nitrate was the treatment, now its antibiotics

Trachoma

• chronic conjunctival infection caused by certain serovars of Chlamydia trachomatis

  • obligate intracellular bacterium

  • different than those that cause genital infections

• contagious

• prevalent in regions with poor sanitation and limited access to healthcare

• trichiasis: eyelashes turn inward → scars the cornea and potentially leads to blindness

• secondary bacterial infections are common

Urinary Tract Infections (UTI)

• occurs when pathogens ascend from the urethra into the bladder

• more common in women → shorter urethra

• E. coli causes 80% of UTIs but other fecal enter organisms can do so too (Proteus and Klebsiella)

• dysuria, urinary urgency, frequent urination, and hematuria

• nosocomial infection: acquired from hospitals through catheters

Bacterial Vaginitis

• polymicrobial condition resulting from disruption of normal vaginal microbiota

• vaginal pH increases → normal flora organisms Gardnerella vaginalis overgrows and interact with anaerobic bacteria = infection

• symptom: thin, white discharge with odor

• diagnosis aided by presence of “clue cells” → vaginal epithelial cells coated with bacteria seen under microscope

Gonorrhea

• STI caused by Neisseria gonorrhoeae

  • fragile outside the human body

• virulence factors: attachment pili, endotoxin, Opa proteins that suppress T cell activation, and IgA protease

• survive inside polymorphonuclear leukocytes

• humans are the natural host

• transmission can occur from asymptomatic carrier

• untreated infection = pelvic inflammatory disease (PID)

• can disseminate → spread to other parts of the body by entering the bloodstream

• newborns: causes eye infections

Syphilis

• STI caused by Treponema pallidum

  • spirochete that can’t be cultured

  • enters bloodstream after infection

• stage 1: incubation

• stage 2: primary → painless chancre (sore)

• stage 3: secondary: organism spreads in circulation, causes systemic symptoms, skin rashes on palms and soles, and mucous patches in mouth

  • patient is highly contagious

• stage 4: latent → no symptoms

• stage 5: tertiary: occurs years later and all organs can be damaged

  • infected tissue becomes “walled off” from circulation due to inflammatory response (gumma)

• transmission is during sex or direct contact via infectious lesions

• congenital syphilis: bacterium crosses placenta → fetal death or neurological damage

Nongonococcal Urethritis (NGU)

• clinical term for urethritis not caused by Neisseria gonorrhoeae

• can have multiple etiologies (more than one type can cause the infection

• common STI in US → both men and women

• Chlamydia trachomatis most commonly causes NGU

• women → infection is asymptomatic but can progress to PID if untreated

• other common causes: Mycoplasma genitalium (can lead to PID) and Ureaplasma urealyticum

Streptococcal Pharyngitis (“Strep Throat”)

• infection of the throat caused by Streptococcus pyogenes (GAS)

• sore throat, fever, and inflammation of tonsils and pharynx

• can result in post-infectious complications (rheumatic fever or glomerulonephritis) if untreated

• transmitted person-to-person via respiratory droplets

Diphtheria

• caused by Corynebacterium diphtheriae

• organism makes a Diphtheria toxin (exotoxin) carried on a prophage that inhibits protein synthesis

• causes a pseudomembrane to be formed in the airway → causes suffocation if left untreated

• attempts to scrape it off causes bleeding

• exotoxin can enter circulation and damage organs of body

• humans are the only natural reservoir

• transmitted via respiratory droplets

• prevention: diphtheria toxoid in the DTaP vaccine

  • no longer toxic but can stimulate the body to produce antitoxins

  • D in DTaP

Whooping Cough (Pertusis)

• highly contagious respiratory infection

• caused by gram-negative bacterium Bordetella pertussis

• only infects humans

• makes tracheal cytotoxin, pertussis toxin, and possesses and endotoxin (LPS)

• toxins causes death of the epithelial cells of the trachea

• stage 1: catarrhal stage (common cold symptoms)

• stage 2: paroxysmal (violent coughing with potential complication of cyanosis from mucus build-up)

• stage 3: convalescent stage (gradual recovery with the change for secondary infections)

• DTaP vaccine uses purified components from B. pertussis

  • “aP” = acellular Pertussis → takes parts that can’t cause disease and can trigger immune system safely

Bacterial Pneumonia

• infection of lungs

• inflammation and fluid accumulation in the alveoli

• caused by Streptococcus pneumoniae leading to Pneumococcal Pneumonia

  • but Haemophilus influenzae and S. aureus can cause it

• virulence factor for S. pneumoniae: polysaccharide capsule

• vaccine composed of many serotypes for S. pneumoniae → recommended for children and older adults

Mycoplasmal Pneumonia

• caused by Mycoplasma pneumoniae → lacks a cell wall

• called primary atypical pneumonia or “walking pneumonia”

  • symptoms are usually mild

Legionnaires Disease

• form of pneumonia caused by Legionella pneumophila → gram negative rod

• survives and replicates inside macrophages

• transmitted via aerosolized water droplets from air conditioners, humidifiers, etc

• humans cannot be a reservoir → transmission between humans is rare

• affects the immunocompromised and the elderly

Tuberculosis

• caused by Mycobacterium tuberculosis

• grows slow and survives in macrophages

• survives in sputum (phlegm coughed up) for days to weeks

• primarily affects the lungs 

• since they can’t be destroyed inside macrophages → granulomas (tubercles) form

  • clusters of immune cells that surround infection to contain it

• spread via bloodstream to organs like bones or kidneys

• widespread dissemination called military TB

• can remain dormant in the body → reactivated if patient becomes immunocompromised

  • leading to death in AIDs patients

• skin test for diagnosis

• treatment: combination of isoniazid, rifampin, pyrazinamide, and ethambutol for 6 months

• no effective vaccine

• M. bovis can infect humans through unpasteurized milk

Food Poisoning

general term that describes any illness or condition that results from consuming contaminated food

Food Intoxication

• more specific term that refers to foodborne illnesses caused by the ingestion of preformed toxins in contaminated food

• Staphylococcus aureus enterotoxins

• Clostridium botulinum neurotoxin

• Bacillus cereus emetic toxin

S. aureus food intoxication

• makes enterotoxins that are heat stable

• ingested → preformed toxins irritate the intestinal lining and act directly on the gastrointestinal lining

  • stimulate nerve endings → trigger vomiting center int he brain

• symptoms develop within a few hours

  • nausea, vomiting, abdominal cramps, and sometimes diarrhea

B. cereus food poisonning

• can cause emetic or diarrheal illness

• forms endospores that survive cooking → these can germinate if food is improperly stored

• emetic toxin stored in food → causes rapid-onset vomiting

• diarrheal toxin produced in the intestine after ingestion → causes abdominal cramps and diarrhea 8-16 hours later

Clostridium perfringens food poisioning

• commonly found in soil and intestines of animals and humans

• forms endospores → survives cooking and persists in improperly stored food

• conditions allow → spores germinate and produces an enterotoxin

  • damages intestinal cells

  • causes diarrhea

• organism also causes “gas gangrene”

Salmonella Gastroenteritis (aka Non-Typhoidal Salmonellosis)

• Salmonella enterica is the dominant organism causing this

• many other serovars exist

• transmitted via the fecal-oral route → contaminated meat, eggs, dairy, water, and produce

• contact with infected animals (esp reptiles) also causes it

• infection: bacteria invade intestinal epithelial cells → produces enterotoxin

  • causes diarrhea, abdominal cramps, and moderate fever

• self-limiting illness → localized to the intestinal tract

  • resolves itself on its own

Typhoid Fever

• caused by Salmonella enterica serovar Typhi (S. Typhi) → only infects humans

• travels from intestines to lymphoid tissue → multiplies in macrophages

  • then organism can spread to multiple internal organs

• LPS endotoxin → causes systemic inflammation

  • septicemia (blood poisoning) → multiplies in blood and then spreads throughout body

  • sustained high fever

• requires antibiotic treatment

• survives in gallbladder → so a person can become a chronic carrier

• attenuated vaccine available

Shigellosis (Bacillary Dysentery)

• intestinal infection caused by Shigella species

  • gram-negative → has LPS endotoxin

• humans and primates are the only hosts

• infectious dose is very low

• transmission via fecal-oral route → contaminated food, water from unclean environments, or direct contact

• involves invasion/inflammation of colon mucosa → results in blood mucoid diarrhea (dysentery), dehydration, and electrolyte imbalance

• S. sonnei is the most common species

• S. dysenteriae makes exotoxin called Shiga toxin that leads to complicaiton

  • Hemolytic Uremic Syndrome

  • may exhibit neurotoxic effects