From the Guidelines
Bactrim (trimethoprim-sulfamethoxazole) does cover many gram-negative bacilli, including some fermentative species, but its effectiveness can vary depending on the specific organism and local resistance patterns, as noted in a 2021 study 1. It is effective against common gram-negative pathogens such as Escherichia coli, Klebsiella pneumoniae, Enterobacter species, and Proteus mirabilis, which are fermentative gram-negative bacilli. However, Bactrim's coverage is not universal for all gram-negative bacilli. It has limited activity against Pseudomonas aeruginosa and may not be effective against certain other non-fermenters. Additionally, resistance to Bactrim has increased among some gram-negative organisms over time, as highlighted in a 2017 study 1 and a 2023 guideline 1. The medication works by inhibiting two sequential steps in bacterial folate synthesis, with sulfamethoxazole blocking dihydropteroate synthase and trimethoprim inhibiting dihydrofolate reductase. This dual mechanism provides a synergistic antibacterial effect that is particularly effective against many urinary tract pathogens, gastrointestinal pathogens, and respiratory pathogens. When treating suspected gram-negative infections, it's essential to consider local resistance patterns and, when possible, obtain culture and sensitivity testing to confirm susceptibility, as recommended in the 2021 study 1 and the 2023 guideline 1. Some key points to consider when using Bactrim include:
- Its effectiveness against specific gram-negative organisms
- Local resistance patterns
- The need for culture and sensitivity testing
- The potential for resistance to develop over time
- The importance of considering alternative treatment options when necessary, as discussed in the 2017 study 1 and the 2023 guideline 1.
From the FDA Drug Label
Sulfamethoxazole and trimethoprim has been shown to be active against most isolates of the following microorganisms, both in vitro and in clinical infections as described in the INDICATIONS AND USAGE section Aerobic gram-positive bacteria Aerobic gram-negative bacteria Escherichia coli (including susceptible enterotoxigenic strains implicated in traveler’s diarrhea) Klebsiella species Enterobacter species Haemophilus influenzae Morganella morganii Proteus mirabilis Proteus vulgaris Shigella flexneri Shigella sonnei
Bactrim (sulfamethoxazole and trimethoprim) covers some gram-negative bacteria, including:
- Escherichia coli
- Klebsiella species
- Enterobacter species
- Haemophilus influenzae
- Morganella morganii
- Proteus mirabilis
- Proteus vulgaris
- Shigella flexneri
- Shigella sonnei However, it does not explicitly state that it covers Bacillus fermentative, which is likely referring to a type of gram-negative bacillus. Therefore, based on the provided information, no conclusion can be drawn about the coverage of Bacillus fermentative by Bactrim 2.
From the Research
Bactrim Coverage
- Bactrim, a combination of trimethoprim and sulfamethoxazole, has antimicrobial activity against various gram-positive and gram-negative bacteria 3, 4, 5.
- It is effective against some gram-negative aerobic bacilli, including E. coli 3, 6.
- However, its effectiveness against gram-negative bacilli can vary depending on the specific organism and the presence of resistance mechanisms 6.
Resistance Mechanisms
- Resistance to trimethoprim can be intrinsic or acquired, with acquired resistance often resulting from chromosomal mutations or the presence of resistance genes 3, 6.
- Class 1 integron and insertion sequence common regions (ISCRs) can also contribute to trimethoprim-sulfamethoxazole resistance in gram-negative bacilli 6.
Specific Organisms
- Bactrim is effective against E. coli, but its effectiveness against other gram-negative bacilli, such as Pseudomonas aeruginosa and Acinetobacter spp., may be limited due to resistance mechanisms 6, 7.
- There is no specific information available on the effectiveness of Bactrim against Bacillus fermentative, a type of gram-negative bacillus.
Treatment Options
- For infections caused by nonfermenting gram-negative bacilli, including those resistant to Bactrim, several new agents are under development, such as durlobactam-sulbactam, cefepime-taniborbactam, and cefepime-zidebactam 7.