Extended spectrum beta-lactamase reactions in Stenotrophomonas maltophilia

Double-disk synergy test positivity inStenotrophomonas maltophilia clinical strains

The double-disk synergy test (DDST) using Mueller-Hinton agar and antibiotic disks with centrally positioned disks of amoxicillin-clavulanate, ampicillin-sulbactam, and piperacillin-tazobactam and, at a center-to-center distance of 25-30 mm, 2-4 disks with 10 various beta-lactam antibiotics per one plate was performed in 58 clinical isolates of Stenotrophomonas maltophilia to determine the effectivity of 3 beta-lactamase inhibitors. When tested with clavulanate as the central beta-lactamase inhibitor synergic action on tested strains was the most frequent with aztreonam (81.0% of strains), cefoperazone (63.8%), and cefepime (60.3%). With sulbactam the synergic action, i.e. DDST positivity, was high in the case of cefoperazone (15.5%), ampicillin, aztreonam and piperacillin (8.6% each); with tazobactam it was the most frequent with aztreonam (53.4%), cefoperazone (44.8%) and cefepime (37.9%). No synergy was demonstrated after application of meropenem regardless of the kind of beta-lactamase inhibitor used. In 58 strains of S. maltophilia, 55 different profiles of DDST positivity were found. The results confirm that clavulanate is the most effective inhibitor of S. maltophilia beta-lactamases. The utilization of DDST (performed in the recommended way) for the typization of strains Stenotrophomonas species and for the estimation of potential effectiveness combinations of beta-lactams with beta-lactamase inhibitors for the therapy of stenotrophomonade infections was suggested.

Severe cellulitis/myositis caused by Stenotrophomonas maltophilia

OBJECTIVE

To present a case of cellulitis/myositis due to Stenotrophomonas maltophilia in the absence of trauma and to discuss a potentially novel treatment option.

CASE SUMMARY

A 57-year-old white man, having undergone an allogeneic bone marrow transplant, developed myositis with S. maltophilia of the left soleus muscle; there had been no trauma. Risk factors for infection included neutropenia, prolonged hospitalization and intensive care unit stay, and broad-spectrum antibiotic exposure. The affected area of muscle was resected and the patient successfully treated with trimethoprim/sulfamethoxazole (TMP/SMX), ticarcillin/clavulanate, and aztreonam.

DISCUSSION

In severe myositis/cellulitis caused by S. maltophilia, TMP/SMX is considered the drug of choice. However, bacteriostatic agents such as TMP/SMX are less than ideal in neutropenic patients. The combination of ticarcillin/clavulanate plus aztreonam has been shown to improve activity in vitro against this organism compared with TMP/SMX. This is likely due to inhibition of the 2 beta-lactamases this organism produces by clavulanate and aztreonam. In our study of clinical isolates of S. maltophilia, this combination reduced the minimum inhibitory concentration at 90% by 128-fold and was synergistic against 10 of 12 isolates tested in time-kill analysis.

CONCLUSIONS

S. maltophilia is emerging as an important pathogen in patients with compromised immunity, leading to severe infections that are difficult to treat. Based on in vitro synergy studied, we recommend considering ticarcillin/clavulanate plus aztreonam as a potential treatment option in immunocompromised patients with S. maltophilia infection.