Gram positive bacteria

Interpretation of Key Phrases

• “Gram positive cocci in clusters” may suggest Staphylococcus 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

Cocci

Clusters (Staph Species)

• Coagulase Positive: Staph aureus
  • Always consider as true bacteremia (and not a contaminant) due to the danger of delaying treatment
• Coagulase Negative:
  • Staph epidermidis
    • Most common cause of catheter-related bacteremia
    • Most common skin contaminant found in blood cultures
  • Staph saprophyticus
    • UTIs in women
  • Staph lugdunensis
    • Rare cause of endocarditis, meningitis, and Skin and Soft Tissue Infections
    • Staphylococus lugdunensis should raise concerns for endocarditis with a single positive blood culture
  • Staph haemolyticus
    • Rare cause of endocarditis, meningitis

Chains or Pairs (Strep Species and Related)

• Enterococcus (e.g. Enterococcus faecalis, Enterococcus faecium)
  • May cause bacteremia in the proper clinical setting (UTI, intra-abdominal infections, infected vascular catheters, and endocarditis)
• Strep viridans
  • In general are low virulence pathogens and likely contaminants (21-50% of positive blood cultures are clinically significant)
  • 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
• Streptococcus pneumoniae (Pairs)
  • Asociated with pneumonia, meningitis, peritonitis and other severe infections
  • Isolation of this organism is always significant and should be treated
• Other Strep Species
  • 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

Antibiogram

Category

Organism

Strep. Group A, B, C, G

Strep. Pneumoniae

Viridans strep

Strep. anginosus gp

Enterococcus faecalis

Enterococcus faecium

MSSA

MRSA

CA-MRSA

Staph. Epidermidis

C. jeikeium

L. monocytogenes

Penicillins

Penicillin G

S

S

I

S

S

I

R

R

R

R

R

S

Penicillin V

S

S

I

S

S

I

R

R

R

R

R

R

Anti-Staphylocccal Penicillins

Methicillin

S

S

I

S

R

R

S

R

R

S

R

R

Nafcillin/Oxacillin

S

S

I

S

R

R

S

R

R

S

R

R

Cloxacillin/Diclox.

S

S

I

S

R

R

S

R

R

S

R

R

Amino-Penicillins

AMP/Amox

S

S

I

S

S

I

R

R

R

R

R

S

Amox-Clav

S

S

I

S

S

S

S

R

R

R

R

X2

AMP-Sulb

S

S

I

S

S

S

S

R

R

R

R

S

Anti-Pseudomonal Penicillins

Ticarcillin

S

S

I

S

I

I

R

R

R

I

R

S

Ticar-Clav

S

S

I

S

I

I

S

R

R

I

R

X2

Pip-Tazo

S

S

I

S

S

I

S

R

R

S

X1

X2

Piperacillin

S

S

I

S

S

I

R

R

R

R

R

S

Carbapenems

Doripenem

S

S

S

S

I

R

S

R

R

S

X1

S

Ertapenem

S

S

S

S

R

R

S

R

R

S

R

I

Imipenem

S

S

S

S

S

I

S

R

R

S

R

S

Meropenem

S

S

S

S

I

R

S

R

R

S

X1

S

Aztreonam

R

R

R

R

R

R

R

R

R

R

R

R

Fluroquinolones

Ciprofloxacin

I

I

R

R

U

R

S

R

I

S

R

S

Ofloxacin

I

I

R

R

U

R

S

R

X1

S

R

R

Pefloxacin

R

R

X1

X1

R

R

S

R

X1

S

X1

R

Levofloxacin

S

S

S

S

S

R

S

R

I

S

X1

S

Moxifloxacin

S

S

S

S

S

I

S

I

I

S

X1

S

Gemifloxacin

S

S

S

S

S

I

S

I

I

S

X1

S

Gatifloxacin

S

S

S

S

S

I

S

I

I

S

X1

S

1st G Cephalo

Cefazolin

S

S

S

X1

R

X1

S

R

R

I

R

R

2nd G. Cephalo

Cefotetan

S

S

S

X1

R

X1

S

R

R

I

R

R

Cefoxitin

S

S

S

X1

R

X1

S

R

R

I

R

R

Cefuroxime

S

S

S

X1

R

X1

S

R

R

I

R

R

3rd/4th G. Cephalo

Cefotaxime

S

S

S

X1

R

X1

S

R

R

I

R

R

Cefizoxime

S

S

S

X1

R

X1

S

R

R

I

R

R

CefTRIAXone

S

S

S

X1

R

X1

S

R

R

I

R

R

Ceftaroline

S

S

S

X1

S

X1

S

S

S

S

X1

X1

CefTAZidime

S

S

I

X1

R

X1

I

R

R

I

R

R

Cefepime

S

S

S

X1

R

X1

S

R

R

I

X1

R

Oral 1st G. Cephalo

Cefadroxil

S

S

S

X1

R

X1

S

R

R

I

R

R

Cephalexin

S

S

S

X1

R

X1

S

R

R

I

R

R

Oral 2nd G. Cephalo

Cefaclor/Loracarbef

S

S

S

X1

R

X1

S

R

R

I

R

R

Cefproxil

S

S

R

X1

R

X1

S

R

R

I

R

R

Cefuroxime axetil

S

S

S

X1

R

X1

S

R

R

I

R

R

Oral 3rd G. Cephalo

Cefixime

S

S

S

X1

R

X1

R

R

R

R

R

R

Ceftibuten

S

I

R

X1

R

X1

R

R

R

R

R

R

Cefpodox/Cefdinir/Cefditoren

S

S

S

X1

R

X1

S

R

R

I

X1

R

Aminoglycosides

Gentamicin

R

R

X1

X1

S

S

S

R

X1

I

R

S

Tobramycin

R

R

X1

X1

S

R

S

R

X1

I

R

S

Amikacin

R

R

X1

X1

S

R

S

R

X1

I

R

S

Chloramphenicol

S

S

X1

X1

I

I

I

R

X1

R

R

S

Clindamycin

S

S

X1

X1

R

R

S

R

I

R

R

X1

Macrolides

Erythromycin

I

I

X1

X1

R

R

I

R

I

I

R

S

Azithromycin

I

I

X1

X1

R

R

S

R

I

R

R

S

Clarithromycin

I

I

X1

X1

R

R

S

R

I

R

R

S

Ketolide

Telithromycin

S

S

X1

X1

I

R

S

R

I

R

R

S

Tetracyclines

Doxycycline

I

S

X1

X1

R

R

I

I

S

R

R

S

Minocycline

S

S

X1

X1

R

R

S

I

S

R

R

S

Glycylcycline

Tigecycline

S

S

X1

X1

S

S

S

S

S

S

S

S

Daptomycin

S

X23

X1

X1

S

S

S

S

S

S

S

I

Glyco/Lipoclycopeptides

Vancomycin

S

S

X1

X1

S

I

S

S

S

S

S

S

Teicoplanin

S

S

X1

X1

S

I

S

S

S

I

S

S

Telavancin

S

S

X1

X1

S

S

S

S

S

S

S

S

Fusidic Acid

I

I

X1

X1

S

X1

S

S

S

S

S

X1

Trimethoprim

S

I

X1

X1

S

R

I

I

S

S

R

S

TMP-SMX

X22

S

X1

X1

X22

R

S

S

S

I

R

S

Urinary Agents

Nitrofurantoin

S

S

X1

X1

S

S

S

S

S

X1

R

X1

Fosfomycin

X1

S

X1

X1

S

I

S

S

S

X1

X1

R

Other

Rifampin

S

S

X1

X1

I

R

S

S

S

S

S

S

Metronidazole

R

R

X1

X1

R

R

R

R

R

R

R

R

Quinupristin dalfoppristin

S

S

X1

X1

R

S

S

S

S

S

S

S

Linezolid

S

S

X1

X1

S

S

S

S

S

S

S

S

Colistimethate

R

R

X1

X1

R

R

R

R

R

R

R

R

Clinical Identification Chart

See Also

• Microbiology (Main)
• Bacteremia Versus Contaminated Blood Cultures‎