Differentiation of Bacterial Cultures based on Morphological and Physiological Characteristics
Group 1: Aerobic and Anaerobic Cocci
| Table 1. Aerobic cocci. | ||
| Gram stain | Arrangement | |
| Micrococcus spp. | + | tetrads |
| Neisseria gonorrhoeae | – | diplococci |
| Table 2. Anaerobic cocci. | ||||
| Catalase | Oxidase | Arrangement | Oxygen | |
| Staphylococcus spp (see Table 1) | + | – | clusters | Facultative anaerobe |
| Streptococcus spp.
(see Table 4) |
– | – | chains | Aerotolerant anaerobe |
| Enterococcus spp.
(see Table 4) |
– | – | chains | Aerotolerant anaerobe |
| Table 3. Differentiation of Staphylococcus spp. | |||
| Staphylococcus aureus | Staphylococcus epidermidis | Staphylococcus saprophyticus | |
| Coagulase | 4+ | – | 1–2+ |
| Mannitol Salt Agar | + | – | + |
| Urease | – or wk+ | + | + |
| Hemolysis | Beta (β) | – or wk + | – |
| Novobiocin resistance | Susc. (-) | Susc. (-) | Res. (+) |
| Table 4. Differentiation of Streptococcus and Enterococcus spp. | ||
| Streptococcus pyogenes | Enterococcus faecalis | |
| Hemolysis on BAP | Beta (β) | Gamma (γ) |
| Bile Esculin | No growth (-) | Growth/black (+) |
Group 2: Aerobic and Facultatively Anaerobic Bacilli
Gram positive bacilli
Endospore forming: Bacillus spp. (see Table 5)
Non-endospore forming: Corynebacterium xerosis
| Table 5. Differentiation of Bacillus spp. | |
| Endospore shape, location, sporangium | |
| B. cereus | Oval, central, sporangium not swollen |
| B. lentus | Oval, terminal, sporangium swollen |
Gram negative bacilli
Strictly aerobic: Pseudomonas aeruginosa
Facultatively anaerobic: Enterobacteriaceae (see Table 6)
| Table 6. Differentiation of Enterobacteriaceae | |||||
| TSI | Sulfide/Indole/Motility | Methyl Red | VP | Citrate | |
| Escherichia coli | A/A | – /+/+ | + | – | – |
| Enterobacter aerogenes | A/A | -/-/+ | – | + | + |
| Citrobacter freundii | A/A | -/-/+ | + | – | + |
| Klebsiella pneumoniae | A/A | -/-/- | – | + | + |
| Salmonella enteritidis | K/A | +/-/+ | + | – | + |
