When identifying a bacterium, the first step is Gram stain, which can tell us whether it has a Gram-positive or Gram-negative cell wall, and can give us information about the size and shape (bacilli or cocci, usually). Everyone needs to know how to interpret a Gram-stain report, since it is still one of the first pieces of information we get about a bacterial infection.
Gram-positive Bacteria
Cocci
Clusters or Groups
| Species
|
Clinical Syndromes
|
| Staphylococcus aureus
|
Purulent skin and soft tissue infections, abscesses, endocarditis, HAP/VAP, food poisoning
|
| Coagulase-negative Staphylococci
|
Line infections, UTIs (S. saprophyticus)
|
Pairs or Chains
| Species
|
Clinical Syndromes
|
| Streptococcus pyogenes/Group A Streptococcus
|
Cellulitis, necrotizing fasciitis, toxic shock syndrome
|
| Other Lancefield-group streptococci
|
Cellulitis, UTIs, endocarditis
|
| Streptococcus pneumoniae
|
Pneumonia, meningitis
|
| Enterococcus species
|
UTIs, line infections, endocarditis
|
Bacilli
| Species
|
Clinical Syndromes
|
| Clostridium difficile/tetani/botulinum/perfringens
|
Diarrhea/tetanus/botulism/nec. fasc.
|
| Bacillus cereus
|
Food poisoning; often contaminant
|
| Other Bacillus species
|
Often contaminant
|
| Listeria monocytogenes
|
Meningitis
|
Gram-negative Bacteria
Bacilli
Enterobacterales (Poop!)
| Species
|
Clinical Syndromes
|
| Yersinia/Shigella/Salmonella/E.coli O157:H7/Campylobacter
|
Infectious diarrhea/dysentery
|
| Escherichia coli
|
Intraabdominal infections, UTIs, HAP/VAP
|
| Klebsiella spp.
|
Intraabdominal infections, UTIs, HAP/VAP
|
| Proteus spp.
|
Intraabdominal infections, UTIs, HAP/VAP
|
| SPICE bugs
|
Very resistant, generally use carbapenems empirically
|
Others
| Species
|
Clinical Syndromes
|
| Pseudomonas aeruginosa
|
Otitis externa, hot-tub folliculitis, UTIs, pneumonias... very resistant to antibiotics
|
Cocci
| Species
|
Clinical Syndromes
|
| Neisseria meningitidis
|
Meningitis
|
| Neisseria gonorrhoeae
|
Urethritis, PID, disemminated gonococcal infection
|
Miscellaneous Bacteria
| Feature
|
Species
|
Clinical Syndromes
|
| Acid-fast bacilli
|
Mycobacterium tuberculosis
|
Pulmonary tuberculosis, extrapulmonary tuberculosis
|
| Spirochetes
|
Treponema pallidum
|
Syphilis (primary, secondary, tertiary)
|
| Borrelia burgdorferi
|
Lyme disease
|
| Intracellular bacteria
|
Chlamydia trachomatis
|
Urethritis, PID
|
| Chlamydia pneumophila
|
Atypical pneumonia
|
| Bacteria without a cell wall
|
Mycoplasma pneumoniae
|
Atypical pneumonia
|
