Stenotrophomonas maltophilia is an opportunistic, multidrug-resistant Gram-negative bacillus. The agent of choice for treating infections caused by this organism is sulfamethoxazole/trimethoprim (TMP-SMX). This recommendation is based on its consistent in vitro activity and established clinical efficacy. S. maltophilia is characteristically and intrinsically resistant to carbapenems (e.g., meropenem) due to the production of two beta-lactamases. While other agents like fluoroquinolones may show some activity, resistance is common and can emerge during therapy, making TMP-SMX the most appropriate and reliable first-line treatment.

A. Meropenem: S. maltophilia is intrinsically resistant to carbapenems due to its production of metallo-β-lactamases (L1) and serine-β-lactamases (L2).

B. Vancomycin: This antibiotic is primarily active against Gram-positive bacteria and has no clinically significant activity against Gram-negative organisms like S. maltophilia.

C. Ciprofloxacin: Resistance rates to fluoroquinolones are high and can develop rapidly during treatment, making it a less reliable option than TMP-SMX.

E. Ampicillin: S. maltophilia is resistant to most penicillins due to the production of beta-lactamases that hydrolyze the antibiotic.

1. Brooke

J. S. (2012). Stenotrophomonas maltophilia: an emerging global opportunistic pathogen. Clinical Microbiology Reviews

25(1)

2–41. (See page 20

"Therapy

" which states

"Trimethoprim-sulfamethoxazole (SXT) is currently the antimicrobial agent of choice for the treatment of S. maltophilia infections."). DOI: https://doi.org/10.1128/CMR.00019-11

2. Looney

W. J.

Narita

M.

& Mühlemann

K. (2009). Stenotrophomonas maltophilia: an emerging opportunist human pathogen. The Lancet Infectious Diseases

9(5)

312–323. (See page 318

Table 2

which lists Trimethoprim-sulfamethoxazole as the "Drug of choice" and notes intrinsic resistance to carbapenems). DOI: https://doi.org/10.1016/S1473-3099(09)70083-0

3. DiPiro

J. T.

Yee

G. C.

Posey

L. M.

Haines

S. T.

Nolin

T. D.

& Ellingrod

V. L. (2020). Pharmacotherapy: A Pathophysiologic Approach (11th ed.). McGraw-Hill Education. In Chapter 95

"Nosocomial Pneumonia

" the section on Stenotrophomonas maltophilia identifies trimethoprim-sulfamethoxazole as the drug of choice.