Submitted to: National Foundation for Infectious Disease
Publication Type: Abstract Only
Publication Acceptance Date: 5/7/2004
Publication Date: 6/28/2004
Citation: Poole, T.L., Bischoff, K.M., Callaway, T.R., Genovese, K.J., Nisbet, D.J. 2004. Macrolide inactivation gene cluster mpha-mrx-mphr present in aeromonas hydrophila isolated from a diarrheic pig in Oklahoma [abstract]. National Foundation for Infectious Disease. Interpretive Summary:
Technical Abstract: Aeromonas hydrophila is a Gram-negative, beta-hemolytic fish pathogen and an opportunistic human pathogen. Aeromonas spp are cold tolerant, psychrotrophic food pathogens of fish and other meats. The gene cluster (mphA-mrx-mphR) that encodes high level resistance to macrolide antibiotics was found adjacent to a class I integron in A. hydrophila, strain CVM861, isolated from a diarrheic pig in Oklahoma. PCR and sequence analysis of CVM861 genomic DNA mapped the mphA-mrx-mphR gene cluster immediately downstream of the class I integron sulI gene. The mphA-mrx-mphR gene cluster is in the reverse orientation in relation to the integron gene cassette. The gene order determined by sequencing was: intI1-aadA2-dhfrII-qacdeltaE-sulI-mphR-mrx-mphA (Genbank Accession # AY522923). Because the mphA-mrx-mphR gene cluster in not present within the integron gene cassette region it is not subject to excision by the intI1 integrase. However, linkage to a class I integron suggests the gene cluster is present on a mobile genetic element. Mobility was assessed in bacterial conjugation experiments. Horizontal transmission of high level macrolide resistance from CVM861 to E. coli JM109 was demonstrated at a conjugation frequency of 3.5 × 10**-3. This is the first report of the mphA-mrx-mphR gene cluster on a mobile DNA element in A. hydrophila. Both mobility and linkage to other resistance genes are contributing factors to environmental persistence of resistance genes in the absence of selection. Long term persistence of the mphA-mrx-mphR gene cluster in a gastrointestinal environment may facilitate transfer to Gram positive bacteria.