Contribution of Phe-7 to Tat-dependent export of β-lactamase in Xanthomonas campestris.

Strains of Xanthomonas campestris pv. campestris isolated in Taiwan are commonly resistant to ampicillin owing to the constitutive expression of a chromosomally encoded β-lactamase that is secreted into the periplasm. In this study, we found that levels of β-lactamase vary among X.