LECTURE 2 GRAM-NEGATIVE

Characteristics of Neisseria meningitidis

Aerobic diplococcus

Kidney/coffee-bean shaped

Only found in humans, within the nasopharynx

Transmits via respiratory droplets/close contact and can enter bloodstream to meninges

Virulence factors of Neisseria meningitidis

Polysaccharide capsule is antiphagocytic

Endotoxin (LOS) causes inflammation, fever, shock, DIC

IgA protease helps colonize mucosal surfaces

Clinical syndromes of Neisseria meningitidis

Meningitis: PMN neutrophils in the CSF

Meningococcemia: sepsis with petechial/purpuric rash and septic shock

Waterhouse-Friderichsen syndrome: adrenal hemorrhage and failure, DIC, shock

Prevention of Neisseria meningitidis

Vaccination

Chemoprophylaxis (rifampin/ciprofloxacin)

Characteristics of Neisseria gonorrhoeae

Aerobic diplococcus

No capsule

Human-only

Sexual contact or mother→ newborn transmission

Virulence factors of Neisseria gonorrhoeae

Pili: antigenic variations attach to mucosal cells

LOS endotoxin causes inflammation

IgA protease helps colonize mucosal surfaces

Clinical manifestations of Neisseria gonorrhoeae

Purulent discharge in men may lead to epididymitis, may lead to pelvic inflammatory disease in women

Ophthalmia neonatorum in newborns

Characteristics of Klebsiella pneumoniae

Facultative anaerobic rod

Prominent polysaccharide capsule (antiphagocytic)

Part of GI and upper RT flora

Transmission/Infection/Disease of Klebsiella pneumoniae

Pneumonia from aspiration of colonized secretions, especially in hospitalized (and alcoholic) people

UTI from intestinal flora

Can produce thick, bloody “currant-jelly” sputum

Characteristics of Salmonella typhi

Facultative anerobic rod

Motile → flagella

Human-only pathogen

Transmits through contaminated food or water via fecal-oral route

Chronic carriers may harbor bacteria in gallbladder

Virulence/Pathogenesis of Salmonella typhi

Vi capsule helps evade host defenses

Can surive and multiply in macrophages

Asplenic patients at higher risk

Can cause typhoid fever (rose spots on trunk)

Characteristics of Shigella sonnei and shigella dysenteriae

Nonmotile rods

Fecal-oral transmission via person-person

Very low ID50

Common in crowded environments

Clinical features of Shigella sonnei and shigella dysenteriae

Watery diarrhea (can progress to bloody)

Abdominal cramps

Fever

Differences between Shigella sonnei and shigella dysenteriae

S. sonnei causes milder shigellosis

S. dysenteriae produces Shiga toxin that can cause Hemolytic Uremic syndrome

Characteristics of Escherichia coli

Facultative anaerobe

Lactose fermenter (for lab identification)

Part of normal intestinal flora

Some strains are pathogenic (intestinal or extraintestinal)

Virulence factors of Escherichia coli

Pili/fimbriae (attaches to host cells)

Exotoxins

Capsules (antiphagocytic)

Flagella (motility)

Reservoir and Transmission of Escherichia coli

Cattle can contain Enterotoxigenic and Enterohemorrhagic strains

Contaminated food/water, produce, undercooked meat and unpasteurized products

Diarrheagenic strains are fecal-orally transmitted

Clinical Manifestations of Escherichia coli

Intestinal: ETEC (watery traveler’s tiarrhea), EHEC/STEC (bloody diarrhea, can cause HUS)

Extraintestinal: UTI, Neonatal meningitis, Sepsis

Characteristics of Pseudomonas aeruginosa

Aerobic, motile rod (flagella)

Produces LPS endotoxin

Exotoxin A inhibits protein synthesis causing tissue damage

Pyocyanin damages tissues and impairs ciliary function (blue-green pigment)

Fruity/grape like odor

Forms biofilms (antibiotic resistant)

Reservoir and risk groups of Pseudomonas aeruginosa

Water, soil, moist environments

Can colonize especially hospitalized patients

Immunocompromised/burn/cystic fibrosis/catheters/mechanical ventilation patients at rish

Common infections of Pseudomonas aeruginosa

Pneumonia (esp. CF/ventilated)

Sepsis

Ecthyma gangrenosum (skin infec.)

UTIs

Malignant otitis externa (esp. diabetes)

Osteomyelitis

Characteristics of Helicobacter pylori

Curved/spiral rod

Flagella (cockscrew motility)

Adhesions

Virulence/pathogenesis of Helicobacter pylori

Urease converts urea to NH3 to help neutralize local acidity allowing survival

Causes chronic gastric inflammation and mucosal damage

Two virulence factors promote inflammation and damage gastric epithelial cells: CagA (virulence protein) and VacA (exotoxin)

Clinical Manifestations of Helicobacter pylori

Chronic gastritis

Peptic ulcer disease

Gastric adenocarcinoma

Gastric MALT lymphoma

Characteristics of Vibro cholera

Curved/comma-shaped rod

Transmits through contaminated food and water

Virulence/Pathogenesis and clinical effects of Vibro cholera

Produces cholera toxin (exotoxin)

Increase in cAMP within intestinal epithelial cells leads to water/electrolyte loss

“rice-water” diarrhea

Hypokalemia (loss of K+) and Metabolic acidosis (Loss of HCO3-)

Can lead to hypovolemic shock

Characteristics of Bordetella pertussis

Small coccobacillus

Strict aerobe

Human-only

Highly contagious respiratory droplets

Pathogenesis/Virulence of Bordetella pertussis

Adhesins attach bacteria to ciliated respiratory epithelial cells

Pertussis exotoxin increases cAMP impairing phagocyte function reducing bacterial clearance

Other toxins damage ciliated cells

Impairs mucus clearance leading to severe paroxysmal coughing

Generally localized to respiratory tract

3 phases: Catarrhal phase, Paroxysmal phase (whooping cough), convalescent phase

Characteristics of Legionella pneumophilia

Thin, pleomorphic rod

Facultative intracellular pathogen

Survives within macrophages

Transmits through inhalation of aerosolized contaminated water

Person-to-person unusual

Clinical effects of Legionella pneumophilia

Atypical pneumonia

Dry of mildly productive couth

Chest/pleuritic pain

Characteristics of Hemophilus influenzae

Pleomorphic coccobacillus

Type b (Hib) is encapsulated (major virulence factor)

Transmits through respiratory droplets (found in humans only)

Clinical features of Hemophilus influenzae

Hib (invasive) causes meningitis, epiglottitis, esp. in young unvaccinated children

Characteristics of Borrelia burgdorferi

Spirochete (cockscrew-shaped)

Lacks LPS

Vector: Ixodes tick

Found in white-footed mice and other small mammals

Deer are hosts for tick reproduction

Stages of Borrelia burgdorferi

Early localized stage: Expanding red rash (sometimes bulls-eye)

Early dissimated stage: multiple EM lesions, migratory arthralgia/myalgia, Neuralgic symptoms, cardiac symptoms (AV conduction block)

Late disease: Lyme arthritis (intermittent swelling of joints, especially knee)

Characteristics of Treponema pallidum

Slender, spiral-shaped spirochete

Found in humans only, primarily through sexual contact (can also cross placenta)S

Syphilis caused by Treponema pallidum

Primary: painless, firm chancre at site of infections; lesion contains many highly-infectious spirochetes

Secondary: systemic dissemination, maculopapular rash involving palms and soles, Condylomata lata (moist, highly infectious lesions around genital/perianal region)

Latent: positive serologic test, no symptoms

Tertiary: occurs years later due to immune-mediated damage (Gummas, neurologic, cardiovascular damage)

Basic Characteristics of Chlamydia trachomatis

Stains poorly

Obligate intracellular pathogen (replicates inside)

Small, nonmotile, coccoid

Infections caused by Chlamydia trachomatis

Often asymptomatic but highly transmissible

Men: Nongonococcal urethritis → Dysuria, usually clear/mucoid discharge (may cause epididymitis and proctitis)

Women: cervicitis, urethritis (may progress to PID, causing infertility and ectopic pregnancy)

Neonatal: Conjunctivitis, Pneumonia, acquired through infected birth canal

Trachoma: conjunctival scarring → corneal damage → blindness