Bactrim is NOT a Narrow Spectrum Antibiotic for Enterobacter cloacae
Trimethoprim-sulfamethoxazole (Bactrim) is a broad-spectrum antibiotic that has activity against Enterobacter cloacae, but it is not considered a narrow-spectrum agent for this organism.
Spectrum of Activity of Trimethoprim-Sulfamethoxazole
Trimethoprim-sulfamethoxazole (TMP-SMX) has a broad spectrum of activity against many pathogens:
According to the FDA drug label, TMP-SMX is active against numerous organisms including Escherichia coli, Klebsiella species, Enterobacter species, Morganella morganii, Proteus mirabilis, and Proteus vulgaris 1.
TMP-SMX works by inhibiting two consecutive steps in bacterial folate synthesis: sulfamethoxazole inhibits dihydrofolic acid synthesis by competing with para-aminobenzoic acid, while trimethoprim blocks the production of tetrahydrofolic acid by inhibiting dihydrofolate reductase 1.
Enterobacter cloacae and Antibiotic Selection
When treating Enterobacter cloacae infections specifically:
First and second-generation cephalosporins are generally not effective against Enterobacter infections. Even third-generation cephalosporins are not recommended due to increased likelihood of resistance, particularly for Enterobacter cloacae 2.
Fourth-generation cephalosporins could be used if Extended-Spectrum beta-lactamase (ESBL) is absent, but carbapenems represent a more valid therapeutic option for multidrug-resistant Enterobacter infections 2.
While TMP-SMX has activity against Enterobacter species, resistance can be a concern. In one study of carbapenem-resistant Enterobacteriaceae, only 29% of tested isolates were susceptible to TMP-SMX 3.
Clinical Applications for Enterobacter Infections
For Enterobacter cloacae infections specifically:
For serious infections like meningitis, TMP-SMX has shown benefit in treating gram-negative bacillary meningitis caused by organisms only moderately susceptible to third-generation cephalosporins, including Enterobacter cloacae 4.
For intra-abdominal infections where Enterobacter cloacae may be present (it accounts for approximately 7.2% of isolates in complicated intra-abdominal infections), broader-spectrum agents are typically recommended 2.
For healthcare-associated infections, where Enterobacter species may be present, antibiotic regimens with broader spectra of activity are preferred over narrow-spectrum agents 2.
Important Considerations When Using TMP-SMX
TMP-SMX should not be used in pregnant women in the third trimester, nursing mothers, or infants aged <2 months due to the potential risk for kernicterus 2.
Rare severe allergic reactions (Stevens-Johnson syndrome) can occur with TMP-SMX, making it potentially undesirable if alternative treatments exist 2.
For patients with MRSA skin and soft tissue infections, TMP-SMX is considered an appropriate treatment option, further demonstrating its broad rather than narrow spectrum 2.
Conclusion
TMP-SMX (Bactrim) should be considered a broad-spectrum antibiotic with activity against multiple gram-positive and gram-negative organisms, including Enterobacter cloacae. When treating serious Enterobacter cloacae infections, particularly in healthcare-associated settings, carbapenems are generally preferred due to increasing resistance patterns among Enterobacteriaceae to other antibiotics, including TMP-SMX.