MOST V - Bacteria Identification Fall 2025

MOST V - Bacteria Identification Fall 2025 Handout

Staphylococcus aureus, Staphylococcus epidermidis

Gram+ cocci, clusters, aerobic

Streptococcus pneumoniae, Viridans Streptococci

Gram+ cocci, pairs/chains, α-hemolytic, aerobic

Streptococcus pyogenes (Group A), Streptococcus agalactiae (Group B)

Gram+ cocci, pairs/chains, β-hemolytic, aerobic

Enterococcus faecium, Enterococcus faecalis

Gram+ cocci, pairs/chains, nonhemolytic, aerobic

Listeria monocytogenes

Gram+ bacilli, aerobic

Actinomyces

Gram+ bacilli, anaerobic

Clostridia spp., Clostridioides difficile

Gram+ bacilli, anaerobic

Peptostreptococcus

Gram+ cocci, anaerobic

Neisseria spp., Moraxella catarrhalis

Gram- diplococci, aerobic

Haemophilus influenzae

Gram- coccobacilli, aerobic

Enterobacter spp., Citrobacter spp., Escherichia coli, Klebsiella pneumoniae, Serratia spp.

Gram- bacilli, lactose fermenting, oxidase-, aerobic

Pseudomonas aeruginosa

Gram- bacilli, non-lactose fermenting, oxidase+, aerobic

Proteus spp., Morganella spp., Salmonella spp., Shigella spp., Stenotrophomonas maltophilia

Gram- bacilli, non-lactose fermenting, oxidase-, aerobic

Legionella spp.

Gram- bacilli, non-enteric, aerobic

Bacteroides, Fusobacterium, Prevotella spp.

Gram- bacilli, anaerobic

Mycoplasma spp., Chlamydia spp.

Atypical, aerobic

Gram Positive Bacteria

Bacteria retaining crystal violet stain; thick wall

Gram Negative Bacteria

Bacteria not retaining crystal violet; thin wall

Cocci

Spherical-shaped bacteria

Bacilli

Rod-shaped bacteria

Clusters

Arrangement pattern of cocci like grape clusters

Pairs/Chains

Arrangement pattern of cocci in twos or chains

Coagulase Positive

Bacteria producing enzyme to clot plasma

Coagulase Negative

Bacteria not producing plasma-clotting enzyme

α-Hemolytic

Partial RBC lysis (greenish zone) on blood agar

β-Hemolytic

Complete RBC lysis (clear zone) on blood agar

Nonhemolytic

No RBC lysis on blood agar

Aerobic Bacteria

Require oxygen to grow

Anaerobic Bacteria

Grow without oxygen

Lactose Fermenting

Ferment lactose to acid; pink on MacConkey agar

Non-Lactose Fermenting

Do not ferment lactose; colorless on MacConkey

Oxidase Positive

Contain cytochrome c oxidase enzyme

Oxidase Negative

Lack cytochrome c oxidase enzyme

Non-Enteric Bacilli

Gram- rods not typically found in GI tract

Atypical Bacteria

Bacteria lacking typical cell wall or Gram stain