Ertapenem has been shown to be active against most strains of the following microorganisms in vitro and in clinical infections (SEE INDICATIONS AND USAGE)

Aerobic gram-positive microorganisms:
Staphylococcus aureus (methicillin susceptible strains only)
Streptococcus agalactiae
Streptococcus pneumoniae (penicillin susceptible strains only)
Streptococcus pyogenes
Note: methicillin-resistant staphylococci and enteroccocus spp. are resistant to ertapenem.

Aerobic gram-negative microorganisms:
Escherichia coli
Haemophilus influenzae (Beta lactamase negative strains only)
Klebsiella pneumoniae
Moraxella catarrhalis

 Anaerobic microorganisms:
Bacteroides fragilis
Bacteroides distasonis
Bacteroides ovatus
Bacteroides thetaiotaomicron
Bacteroides uniformis
Clostridium clostridioforme
Eubacterium lentum
Peptostreptococcus species
Porphyromonus asaccharolytica
Prevotella bivia

The following in vitro data are available, but their clinical significance is unknown:At least 90% of the following microorganisms exhibit an in vitro minimum inhibitory concentration (MIC) less than or equal to the susceptible breakpoint of ertapenem; however the safety and effectiveness of ertapenem in treating clinical infections due to these microorganisms have not been established in adequate and well controlled clinical studies:

Aerobic gram-positive microorganisms:
Streptococcus pneumoniae (penicillin intermediate strains only)

Aerobic gram-negative microorganisms:
Citrobacter freundii
Citrobacter koseri
Enterobacter aerogenes
Enterobacter cloacae
Haemophilus influenzae (Beta lactamase positive strains)
Haemophilus parainfluenzae
Klebsiella oxytoca (excluding ESBL producing strains)
Morganella morganii
Proteus mirabilis
Proteus vulgaris
Serratia marcescens

Anaerobic microorganisms:
Clostridium perfringens
Fusobacterium spp.