Are Proteus and Enterobacter Gram-Negative Bacteria?
Yes, both Proteus and Enterobacter are gram-negative bacteria belonging to the family Enterobacteriaceae.
Classification and Characteristics
Both organisms are classified as gram-negative enteric bacteria:
Proteus species (including P. mirabilis, P. vulgaris, and P. penneri) belong to the tribe Proteae within the Enterobacteriaceae family and are distinguished by their ability to deaminate phenylalanine and tryptophan, hydrolyze urea, and characteristic swarming motility 1.
Enterobacter species (including E. cloacae) are gram-negative bacilli within the Enterobacteriaceae family, commonly grouped with Klebsiella and Serratia in clinical microbiology 2.
Clinical Significance
Common Infection Sites
Both organisms cause various healthcare-associated and community-acquired infections:
Nosocomial sinusitis: Proteus mirabilis and Enterobacter species are among the usual gram-negative enteric pathogens, along with P. aeruginosa, Klebsiella pneumoniae, and Serratia marcescens 3.
Complicated skin and soft tissue infections: Enterobacter spp. (5.6%) and Proteus spp. (3.7%) are frequently isolated, with North American prevalence rates of 5.8% and 3.2% respectively 3.
Intra-abdominal infections: Both are part of the polymicrobial gram-negative flora causing complicated IAIs, particularly in healthcare-associated settings 3.
Urinary tract infections: Proteus species are commonly involved in UTIs and are recognized as urease-positive organisms that can cause catheter encrustation 4, 5.
Antimicrobial Resistance Patterns
Both organisms demonstrate concerning resistance profiles:
Proteus mirabilis shows natural resistance to colistin and reduced susceptibility to imipenem, with increasing reports of ESBL and carbapenemase production 6.
Enterobacter species are among the gram-negative bacteria with increasing multidrug resistance, particularly in healthcare settings 3, 7.
Both organisms are included in carbapenem-susceptible formulations (meropenem and imipenem) for treating serious gram-negative infections 8, 9.