Types of Microorganisms [from smallest up]
** Viruses — Need electron microscope to visualize
** Small Bacteria — Need electron microscope to visualize- Mycoplasma, Chlamydia, Rickettsia
- Many identified by Gram stain
- Some need special techniques: e.g. TB (acid-fast stain), Spirochetes (darkfield microscopy)
- Some too few to see, cause disease by toxins (e.g. tetanus, pertussis)
** Protozoa — Seen by Light microscopy
** Fungi — Seen by Light Microscopy (KOH prep clears other debris)
** Helminths (worms)- Ova & Trophozites seen by Light Microscopy
- Some adults can be seen grossly (in all senses of the word)
Bacteria (the focus of “Bugs & Drugs”)
Defined by morphology (shape)- Cocci = round balls [singular: Coccus]
- Bacilli = rods [singular: Bacillus]
- Streptococci = cocci in chains (Greek strepso = “easily twisted”)
- Staphylococci = cocci in grapelike clusters (Greek staphylo = “grape”)
- Diplococcus = joined pair of cocci [coffee-bean shaped]
- Gram Positive = stains Blue
- Gram Negative = stains Red
Streptococci (Gram-Positive Cocci in Chains)
** Streptococcus pyogenes- Skin & Soft Tissue Pathogen
- Also causes Strep Throat, Scarlet Fever, Rheumatic Fever
- Group A beta-Hemolytic Strep (GABHS) (Lancefield grouping)
- a.k.a. “Pneumococcus”
- Causes the classic lobar pneumonia
- Most common upper respiratory pathogen (otitis, sinusitis)
- Does NOT affect skin / soft tissue
- Normal skin flora, non-pathogenic, contaminant
- Maybe a pathogen in cases of endocarditis
** Group A alpha-Hemolytic Strep — Not a pathogen
** Group B Strep- a.k.a. Streptococcus agalactiae
- Normal vaginal flora
- Causes neonatal sepsis, endometritis
- Cause sore throat like GABHS
- Do Not cause Rheumatic Fever
- a.k.a. Enterococcus faecalis (“Enterococcus”)
- Causes varied diseases in compromised hosts
Staphylococci (Gram-Positive Cocci in Grapelike Clusters)
** Staphyloccus aureus- Main Skin & Soft Tissue Pathogen (also colonizes nose)
- This is what’s meant when you hear “Staph”
- S. epidermidis, S. saprophyticus, etc.
- Non-pathogenic skin flora; Usually contaminants
- May cause IV-catheter-related infection, endocarditis
- S. saprophyticus may cause UTI
MORE on Micro when we discuss other organ systems