Response to: Buehlmann etal. 'Effectiveness of a new decolonisation regimen for eradication of extended-spectrum β-lactamase-producing Enterobacteriaceae'

Madam,

We read with great interest the paper of Buehlmann et al., who studied the effectiveness of a new decolonisation regimen for eradication of extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae. ESBL-producing Enterobacteriaceae have emerged worldwide as pathogens of both hospital- and community-acquired infections, even in countries with low antibiotic consumption among humans such as The Netherlands.

Search-and-destroy policies, which have been shown to be effective for meticillin-resistant Staphylococcus aureus (MRSA), do not yet exist for antimicrobial-resistant Gram-negative micro-organisms. The human intestinal tract provides an important reservoir for ESBL-producing bacteria and colonised people are at risk for subsequent infection by these micro-organisms. Therefore, the study by Buehlmann et al. is encouraging and provides a tool to handle carriage. However, we have some comments on the methods of the study.

Firstly, the method used for detection of ESBL-producing Enterobacteriaceae in follow-up cultures is not described. It is of utmost importance to use an enrichment broth in combination with a selective method, to achieve the highest sensitivity, especially when ESBL producers are present in low numbers in the intestines, as can be expected after an attempt of decolonisation. Secondly, successful ESBL elimination was defined as at least one set of negative screening samples including throat, rectal area, urine, and any other previously ESBL-positive site without any further positive screenings. Follow-up screening was not strictly standardised. The decolonised patients remained free of ESBL producers with a mean of 3.5 negative screening samples. For MRSA, it has recently been shown that at least five follow-up culture sets should be taken to ascertain the success rate of the eradication treatment. Thirdly, household contacts were not screened. High rates of intestinal colonisation with ESBL-producing organisms have been observed in household contacts of patients with community-acquired infections due to ESBL producers. Whether this was due to a common source, or caused by person-to-person transmission in the household, remains unknown. In the case of MRSA, it is known that successful eradication requires screening and simultaneous treatment of household contacts. Finally, the question remains how many strains were susceptible to paromomycin? It was reported that 5% of the strains showed reduced susceptibility or resistance to aminoglycosides, but it was not stated which aminoglycoside was tested. Due to different aminoglycoside-modifying enzymes, susceptibility results cannot be inferred from known results of other aminoglycosides as they often exhibit markedly different substrate specificities. Also, little is known about paromomycin resistance mechanisms.

Despite our comments, we believe that decolonisation could be beneficial for selected patients. Further studies are needed to corroborate the findings of Buehlmann et al., to determine indications for treatment, to rule out possible long term side-effects, and to design strict protocols for culture methods, treatment regimens and follow-up schemes.