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Antimicrobial Agents and Chemotherapy, May 2005, p. 1957-1964, Vol. 49, No. 5
0066-4804/05/$08.00+0     doi:10.1128/AAC.49.5.1957-1964.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Cloning and Characterization of a Chromosomal Class C ß-Lactamase and Its Regulatory Gene in Laribacter hongkongensis

Susanna K. P. Lau,1 Pak-leung Ho,1 Maria W. S. Li,1 Hoi-wah Tsoi,1 Raymond W. H. Yung,2 Patrick C. Y. Woo,1 and Kwok-yung Yuen1*

Department of Microbiology, The University of Hong Kong, Hong Kong,1 Department of Microbiology, Pamela Youde Nethersole Eastern Hospital, Hong Kong2

Received 14 July 2004/ Returned for modification 3 October 2004/ Accepted 6 January 2005

Laribacter hongkongensis, a newly discovered bacterium recently shown to be associated with community-acquired gastroenteritis, is generally resistant to most ß-lactams except the carbapenems. We describe the cloning and characterization of a novel chromosomal class C ß-lactamase and its regulatory gene in L. hongkongensis. Two genes, ampC and ampR, were cloned by inserting restriction fragments of genomic DNA from L. hongkongensis strain HLHK5 into pBK-CMV to give the recombinant plasmid pBK-LHK-5. The ampR and ampC genes and their promoters were divergently oriented, with the ampR gene immediately upstream of the ampC gene and an intercistronic Lys-R motif, typical of inducible ampC-ampR regulatory systems. The deduced amino acid sequence of the cloned AmpC ß-lactamase (pI 8.1) contained consensus motifs characteristic of class C ß-lactamases but had identities no greater than 46% to known class C ß-lactamases. The kinetic properties of this AmpC were also compatible with those of a class C ß-lactamase. PCR of 20 clinical isolates of L. hongkongensis, including HLHK5, showed the presence of both ampC and ampR genes in all isolates. Southern hybridization suggested that the ampC gene of HLHK5 was chromosomally encoded. Subcloning experiments showed that the expression of the ampC gene of HLHK5 was regulated by its ampR gene, which acts as a repressor. The ß-lactamase characterized from strain HLHK5 was named LHK-5 (gene, blaLHK-5) and represents the first example of AmpC ß-lactamase in the ß subdivision of proteobacteria.

* Corresponding author. Mailing address: Department of Microbiology, The University of Hong Kong, University Pathology Building, Queen Mary Hospital, Hong Kong. Phone: (852) 28554892. Fax: (852) 28551241. E-mail: hkumicro{at}hkucc.hku.hk.

Antimicrobial Agents and Chemotherapy, May 2005, p. 1957-1964, Vol. 49, No. 5
0066-4804/05/$08.00+0     doi:10.1128/AAC.49.5.1957-1964.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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