Microbiology Overview

Gram Positive — thick peptidoglycan layer (purple stain)

Cocci

  • Clusters — physically or genetically grouped together

    • Staphylococci

      • Coagulase positive — can produce coagulase which clots blood plasma (highly pathogenic — skin infections, pneumonia, septic arthritis)

        • Staphylococcus aureus

          • Methicillin-susceptible Staphylococcus aureus (MSSA)

          • Methicillin-resistant Staphylococcus aureus (MRSA)

      • Coagulase negative — lack the enzyme coagulase (opportunistic — medical devices)

        • Staph. epidermidis

        • Staph. saprophyticus

        • Staph. hominis

        • Staph. hemolyticus

        • Staph. warneri

  • Pairs — bacteria divide through binary fission but fail to fully separate (attached to each other)

    • Pneumococci

      • Streptococcus pneumoniae (pneumonia primary cause)

  • Chains — bacteria remains attached to each other after cell division

    • Streptococci

      • ß-hemolytic

        • Group A

          • Strep. pyogenes (strep throat, rheumatic fever)

        • Group B

          • Strep. agalactiae (cervical and vaginal cultures)

        • Group D

          • Streptococcus bovis (GI tract)

      • α-hemolytic

        • Viridans streptococci

        • streptococcus pneumoniae

    • Enterococcus (GI tract)

      • enterococcus faecalis, E. faecium

        • vancomycin resistant enterococci (VRE)


Bacilli

  • Small

    • listeria

    • Cutibacterium

    • Corynebacterm

    • Gardnerella

  • Large

    • spore forming

      • costridium

      • bacillus

    • Non-spore forming

      • lactobacillus

  • Branching or filamentous

    • nocardia

    • actinomyces

    • erysipelothrix


Anaerobic (mouth and upper GI tract)

  • peptostreptococcus

  • peptococcus

  • propionibacterium acnes

  • clostridium spp.

  • finegoldia magna

  • anaerococcus spp.



Gram Negative — thin peptidoglycan layer + outer membrane (pink/red stain)

Cocci

  • Neisseria meningitidis

  • Neisseria gonorrhoeae

  • Veillonella


Bacilli

  • Lactose fermenter

    • Oxidase-positive — bacteria produce enzyme cytochrome C oxidase (aerobic respiration)

      • aeromonas

      • pasteurella

      • vibrio

    • Oxidase negative — bacteria lacks cytochrome C oxidase enzyme

      • Escherichia coli

      • klebsiella spp.

      • enterobacter spp.

      • citrobacter spp.

  • Non lactose fermenter

    • Oxidase positive

      • pseudomonas spp.

      • flavobacterium spp.

      • alcaligenes spp.

      • achromobacter spp.

      • moraxella spp.

    • Oxidase negative

      • proteus spp.

      • proficendia spp.

      • serratia spp.

      • morganella spp.

      • salmonella spp.

      • shigella spp.

      • stenotrophomonas acinetobacter spp. (coccobacilli)

  • Gram negative coccobacilli

    • haemophilus influenzae

    • moraxella catarrhalis


Non-Gram’s Staining

  • Chlamydia spp.

  • Mycoplasma pneumoniae

  • Legionella spp.

  • Mycobacteria

  • Rickettsiae

  • Spirochetes

  • Viral Organisms

    • influenza A and B

    • Hepatitis viruses

    • Cytomegaloviruses