Common Bacterial Pathogens Flashcards
Staphylococcus aureus
- Gram-positive cocci
- Cutaneous infection (often localized abscess)
- fibrinous capsule assoc. w/ coagulase
- main cytotoxic agent: alpha-toxin
- often assoc. w/ foreign object - Toxin-mediated diseases: toxic shock, food poisoning
- superantigen toxins > massive T cell activation
- toxic shock: fever, coma, organ failure - Pnemonia: common in pts who develop pneumonia in healthcare setting
- Foreign-body associated infections: joint, pacemaker, graft
- # 1 organism for: Bacteremia/endocarditis: heart valve infection
Staphylococcus epidermidis
- Gram-positive cocci
- SSNA (staph species, not aureus)
- CNS (coagulase negative staph)
- normal skin flora, relatively non-pathogenic
- localized infection, typically assoc. w/ foreign objects (to treat, often need removal of device)
- CNS= 1 of 3 most common organisms responsible for infective bacterial endocarditis
genus Streptococcus (and relatives)
- Gram-positive cocci often in chains or pairs
- Catalase negative (Staphylococci are catalase positive)
- Streptococcus pyogenes
- Streptococcus pneumoniae
- “Viridans” streptococci
- Enterococcus faecalis/Enterococcus faecium
Streptococcus pyogenes (“Group A Strep”, GAS)
*Gram-positive cocci
*Pharyngeal infection: strep throat
- virulence factor = M protein which inhibits phagocytosis and killing by neutrophils and enhances adherence to epithelial cells
* Skin and wound infections: typical lesion = spreading infection of the cutaneous and subcutaneous
tissues (cellulitis)
*Post-streptococcal diseases: glomerulonephritis, rheumatic fever (fever and inflammation of the heart, joints, and other tissues)
Streptococcus pneumoniae
- Gram-positive cocci
- Normal flora in UR tract of some ppl
- Pneumonia (one of most freq. causes of bact. pneumonia)
- Others: sinusitis, otitis media, bronchitis, meningitis, bacteremia/septicemia, pneumonia with septicemia
- Pathogenesis is most closely related to ability to grow and evade host defenses
- vaccine for adults and children
- Emerging pencillin resistance due to alterations of penicillin-binding proteins
“Viridans streptococci”
*Gram-positive cocci
*one of the important causes of infective (bacterial) endocarditis
*abundant in mouth
*produce dextrans, which are important for adherence to teeth and other oral tissues
* also allows them to serendipitously adhere to the fibrin
and platelet deposits on damaged heart valves
Enterococcus faecalis and Enterococcus faecium
- Gram-positive cocci
- normal flora in the intestines
- primary causes of enterococcal infections
- Common sites of infection: Urinary tract, surgical wounds, biliary tract, endocarditis
- Frequent cause of nosocomial infections
- Biggest problem: vancomycin-resistant enterococci
genus Clostridium
- G+ rods
- Strict anaerobes: growing cells are KILLED by molecular oxygen
- Endospore-formers: resilient, metabolically inactive developmental stage of these bacteria
Clostridium difficile
*G+ rod
*Normal flora of the GI tract in ~10% of healthy individuals
*Typically a hospital-acquired (nosocomial) infection, and the Clostridia that is most likely to be
encountered in the hospital
*Diarrhea and Colitis
*Relatively resistant to most common antibiotics
*Disease is believed to result from depletion of the intestinal flora by antibiotic treatment, and resulting overgrowth
Clostridium tetani
- G+ rod
- Common organism in soil and GI tract of animals
- Local infection (anaerobic) and toxin production
- Toxin blocks inhibitory interneurons in CNS resulting in “spastic paralysis”
- Vaccine: tetanus shot
Clostridium botulinum
- G+ rod
- Common organism in soil and GI tract of animals
- Bacteria grow in contaminated food under anaerobic conditions (canned foods)
- Toxin: botulinum
- acetylcholine transmission at neuro-muscular junctions, resulting in “flaccid paralysis”
Clostridium perfringens
*G+ rod
*Wound infections (esp. w/ compromised blood flow)
- alpha toxin kills
phagocytic cells and muscle tissue
*Food Poisoning: entertoxin
- disrupts tight junctions between endothelial cells in the ilium
resulting in a dysregulation of fluid transport
E. coli (Escherichia coli)
*G- rod (aerobic and facultative)
*Normal flora in large intestine
*GI disease: contaminated food and water
*Urinary tract infections: from GI tract
*Abdominal infections: release/escape of contents of colon to peritoneal cavity and adjacent tissues
- surgical/traumatic wounds, colon cancer
*One of the most common organisms to
acquire resistance thru acquisition of drug-resistant plasmids
Pseudomonas aeruginosa
*G- rod (aerobic and facultative)
*Common environmental bacterium
*Infections of traumatic injuries, surgical wounds, and especially BURNS
*Lung infection in cystic fibrosis pts: bacteria relatively protected from phagocytosis by the pt’s viscous lung secretions
*Hospital-acquired infections (UTIs, pneumonia)
*Intrinsic resistance of P. aeruginosa to
many antimicrobials
Neisseria gonorrhoeae (gonococcus)
*G- (diplo)cocci
*Causative agent of gonorrhea and of conjunctivitis leading to blindness in infants born to
infected mothers
*Growth on mucosal surface > robust inflammatory response > purulent discharge & local tissue invasion
*Pilus= key to infectivity: required for adherence and interferes with bacterial killing by neutrophils
*Pts may be repeatedly infected with strains that
have antigenically distinct pili
*Resistant to penicillin & fluoroquinolone, becoming less sensitive to cephalosporins
