Gram positive bacteria

Cocci

Clusters (Staph Species)

1. Coagulase Positive: Staph aureus
   1. Always consider as true bacteremia (and not a contaminant) due to the danger of delaying treatment
2. Coagulase Negative:
   1. Staph epidermidis
      1. Most common cause of catheter-related bacteremia
      2. Most common skin contaminant found in blood cultures
   2. Staph saprophyticus
      1. UTIs in women
   3. Staph lugdunensis
      1. Rare cause of endocarditis, meningitis, and Skin and Soft Tissue Infections
   4. Staph haemolyticus
      1. Rare cause of endocarditis, meningitis

Chains or Pairs (Strep Species and Related)

1. Enterococcus (e.g. Enterococcus faecalis, Enterococcus faecium)
   1. May cause bacteremia in the proper clinical setting (UTI, intra-abdominal infections, infected vascular catheters, and endocarditis)
2. Strep viridans
   1. 1. In general are low virulence pathogens and likely contaminants (21-50% of positive blood cultures are clinically significant)
      2. Risk factors for VGS bacteremia include: neutropenia, oral mucositis, irradiation to the oral cavity, antibiotic prophylaxis with trimethoprim-sulfamethoxazole and fluoroquinolones, intravenous hyperalimentation, high dose chemotherapy
3. Streptococcus pneumoniae (Pairs)
   1. Asociated with pneumonia, meningitis, peritonitis and other severe infections
   2. Isolation of this organism is always significant and should be treated
4. Other Strep Species
   1. 1. ß-hemolytic streptococcus (Group A Streptococcus, Group B Streptococcus, etc)

Rods (Bacilli)

Organism		Cult	Morphology
Listeria monocytogenes	Small	Aero	tumbling
Diphtheroids	Small	Anaero	pallisades
Actinomyces	Small	Anaero	Branching
Propionibac	Small	Anaero	clumps/pleo
Lactobacillus	Variable	Both	may chain
Clostridium	Large	Anaero	Spores
Bacillus	Large	Aero	Spores

Interpretation of Key Phrases

• “Gram positive cocci in clusters” may suggest Staphyloccocus species.
• "Gram positive cocci in pairs and chains" may suggest Streptococcus species or Enterococcus species
• “Branching Gram positive rods, modified acid fast stain positive” may suggest Nocardia or Streptomyces species

Clinical Identification Chart

See Also

• Microbiology (Main)
• Bacteremia Versus Contaminated Blood Cultures‎