Virulence Factors & Features Important in Disease

Surface adherence & colonization ➲ Gram-positive teichoic acids ➲ M fimbriae of Streptococcus pyogenes ➲ Gram-negative pili ➲ IgA proteases: Streptococcus pneumoniae Neisseria spp. Haemophilus influenzae ➲ Biofilms Staphylococcus epidermidis biofilms adhere to artificial body parts & catheters Streptococcus mutans biofilms cause dental plaque

Antiphagocytic structures ➲ Capsules Streptococcus pyogenes]SOME Klebsiella pneumoniae&]KILLERS K1 strains of Escherichia coli Haemophilus influenzae]HAVE Pseudomonas aeruginosa]PRETTY Neisseria meningitidis]NICE Cryptococcus neoformans]CAPSULES ➲ Pili of Neisseria gonorrheae ➲ M protein of Streptococcus pyogenes ➲ A protein of Staphylococcus aureus

Toxins Toxin with ADP-ribosyl transferase activity ToxinADP-ribosylatesResult Cholera toxinGs alpha protein of small intestinal cells Stimulates Gs, increase in CAMP; Massive fluid loss (diarrhea) E. Coli heat-labile toxin (LT) Gs protein of small intestinal cells Stimulates Gs, increase in CAMP; Fluid loss (diarrhea) Pertussis toxinG1 (inhibits the negative regulator of adenylate cyclase) Inhibits G1 Increase cAMP, lymphocytosis, increased insulin secretion Diphtheria toxinEF-2Shuts down protein synthesis Pseudomonas aeruginosa exotoxin A EF-2Shuts down protein synthesis

Heat stability of bacterial toxins 1.Heat stable at boiling point of water Endotoxin 2.Heat stable at 60oC for 10 mins S. aureus enterotoxin Stable toxin (ST) of E. coli Yersinia enterocolitica toxin 3.Denatured by moderate heat All the rest of the bacterial toxins

Toxins that cause membrane damage Clostridium perfringens Alpha toxin (lecithinase) S. aureus Alpha toxin (pore-forming toxin)

Other virulence factors ➲ Coagulase Staphylococcus aureus Yersinia pestis ➲ Urease Cryptococcus neoformans Nocardia Helicobacter pylori Proteus] increase urine pH in UTI Ureaplasma urealyticum] causing kidney stones esp Proteus ➲ Hyaluronidase Group A streptococci S. aureus

IDENTIFIERS OF MICROORGANISMS

Stain Reactions Non-Gram staining or poorly seen on Gram stain No cell wall  Mycoplasmas, Ureaplasma Too small  Chlamydia, Rickettsia Too thin  spirochetes (Treponema, Borrelia, Leptospira) Gram-neg stain seen only if counterstain time is increased

Stain Reactions Acid-fast Mycobacterium Nocardia (partially) Legionella micdadei Cryptosporidium oocysts Isospora oocysts

Stain Reactions Silver staining Fungi Legionella Periodic acid-Schiff Fungi stain red Calcofluor white Fungi fluoresce blue-white on black India Ink wet mount Cryptococcus – colorless cells with halos on black Misses 50%

Special culture limitations Intracellular pathogens Obligate intracellular ALL viruses Chlamydia aLL Rickettsias except Bartonella (Rochalimea) Mycobacterium leprae Plasmodia Toxoplasma Facultative intracellular Listeria Mycobacteria Histoplasma Brucella

Special culture limitations Non-intracellular pathogens that can’t be cultured routinely T. pallidum Pneumocystis

Anaerobes – Actinomyces – Bacteroides – ClostridiumMicroaerophilic – Campylobacter grows at 42oC – Helicobacter = 37oC Obligate aerobes – Mycobacterium tuberculosis – Pseudomonas – Mycoplasma pneumoniae

Media or Growth Factors ➲ Charcoal yeast extract agar → Legionella ➲ Cholesterol → Mycoplasmas & Ureaplasma ➲ Salt tolerant ➲ Staphylococcus aureus ➲ Enterococcus faecalis ➲ Streptococcus bovis ➲ Vibrio parahaemolyticus ➲ V. vulnificus ➲ X & V factors (hematin & NADH) ➲ H. influenzae

Media or Growth Factors ➲ Chocolate agar ➲ Haemophilus & Neisseria ➲ Thayer Martin ➲ Neisseria ➲ Regan-Lowe ➲ Bordetella pertussis ➲ Lowenstein-Jensen ➲ Mycobacteria

Specific inhibitors Bacitracin – “A” disk inhibits Streptococcus pyogenes (Grp A) Optochin “P” disk inhibits (& bile lyses) Pneumococcus

DiseaseCausative AgentReservoirMode of Transmission All STDs T. pallidum N. gonorrheae Chlamydia HPV HSV-2,etc HUM ANs only Sexual. Birth, or other direct contact; T. pallidum crosses placenta Typhoid Salmonella typhi HUM ANs only Fecal-oral Leprosy M. leprae Humans (also armadillos, mangabey monkeys) Respiratory droplets & direct contact Tuberculosis M. tuberculosis Humans Respiratory droplets or droplet nuclei Bloody diarrheas Campylobacter E. Coli O157:H7 Domestic animals Cattle Undercooked chicken Undercooked hamburger Salmonellosis S. enteritidis Chicken, eggsUndercooked chicken

DiseaseCausative Agent ReservoirMode of Transmission Leptospirosis Leptospira interrogans Rats, cattleAnimal urine in floods, recreational waters, sewers Legionnaire’s disease Legionella sp.Water & amoebas Air conditioning Plague Yersinia pestis Rats, small wild animals Flea bite, or respiratory droplets Lyme disease Borrelia burgdorferi Deer, deer mice, Ixodes ticks Ixodes tick bite (nymph or adult)