Dr. Alejandro Petroni
National Institute of Infectious Diseases

Epidemiology of bacterial infections: resistance to antibiotics

Bacterial infections contribute to morbidity and mortality of several diseases and it is also a significant contributing factor to infant mortality.

The clinical significance of Vibrio cholerae non-O1, non-139 strains is being increasingly recognized since several outbreaks of diarrhea occurred in the early 1990s. A high prevalence of V. cholerae non-O1, non-O139 ampicillin-resistant isolates from both clinical and environmental origins was reported. Our original studies showed that ampicillin-nonsusceptible (resistant plus intermediate categories) strains of V. cholerae non-O1, non-O139 isolated from aquatic environments and diarrhea stools and a waterway in the west region of Argentina produced beta-lactamses. Analysis of some of them permitted us to detect a new 288-amino acids protein, designated CARB-7, that shares 88.5% homology with the CARB-6 enzyme; an overall 83.2% homology with PSE-4, PSE-1, CARB-3, and the Proteus mirabilis N29 enzymes; and 79% homology with CARB-4. The gene for beta-lactamase could not be transferred to Escherichia coli by conjugation. The nucleotide sequence of the flanking regions of the blaCARB-7 gene showed the occurrence of three 123-bp V. cholerae repeated sequences, all of which were found outside the predicted open reading frame. The upstream fragment of the blaCARB-7 gene shared 93% identity with a locus situated inside V. cholerae’s chromosome 2. These result strongly suggest a chromosomal location of the blaCARB-7 gene, making this the first case of a beta-lactamase gene located on the VCR island of the V. cholerae genome. We have recently identified a new beta-lactamase gene, blaCARB-9, which was located in the V. cholerae super-integron, but in a different location relative to blaCARB-7. CARB-9 (pI 5.2) conferred beta-lactam MICs four to eight times lower than those conferred by CARB-7, differing at Ambler’s positions V97I, L124F, and T228K. Comparison of the genetic environments of all reported CARB genes indicated that the CARB enzymes constitute a family of cassette-encoded beta-lactamases.
This project will consist of the identification and characterization of new genes, determination of their location, and analysis of their transmissibility to other bacteria.