Study of heterogeneity of chloramphenicol acetyltransferase (CAT) genes in streptococci and enterococci by polymerase chain reaction: characterization of a new CAT determinant

Abstract

An assay based on the utilization of degenerate primers that enable enzymatic amplification of an internal fragment of cat genes known to be present in gram-positive cocci was developed to identify the genes encoding chloramphenicol resistance in streptococci and enterococci. The functionality of this system was illustrated by the detection of cat genes belonging to four different hydridization classes represented by the staphylococcal genes catpC221, catpC1949 catpSCS79 and the clostridial gene catP, and by the characterization of a new streptococcal cat gene designated catS. A sequence related to the clostridial catQ gene, which was present in one streptococcal strain, was not detected by this assay. These results reveal that these six cat genes account for chromosomal-borne chloramphenicol resistance in 12 group A, B, and G streptococci tested. By contrast, only three of these six cat genes (catp'221, catj%94 and catpsCS7) were detected on the 10 enterococcal plasmids studied here that encode resistance to chloramphenicol.Chloramphenicol resistance (Cmr) in bacteria of clinical importance is generally due to the synthesis of the enzyme chloramphenicol acetyltransferase (CAT) which inactivates the antibiotic by converting it successively to 3-acetyl and 1,3-diacetyl derivatives (31). Comparison of the amino acid sequences of 17 CAT proteins from gram-negative and gram-positive bacteria has revealed a significant degree of homology between the various enzymes, and their phylogenetic relationship has been established (2, 18, 29). Nucleotide sequences are now available for 13 cat genes originating in gram-positive bacteria. These are the gene cat-86 from Bacillus pumilus (10); those carried by the staphylococcal plasmids pC194 (11), pC221 (32), pSCS1 (30), pSCS5 (28), pSCS6 (7), pSCS7 (29), and pUB112 (5) and by the streptococcal plasmid pIP501 (12,35) Utilization of degenerate primers in polymerase chain reaction (PCR) enables the detection of rRNA methylase genes that confer resistance to macrolide-lincosamide-streptogramin B-type (MLS) antibiotics in gram-positive bacteria (1). We have developed a similar assay in order to characterize the cat genes present in the remaining seven plasmidfree streptococci (23) and in the three Enterococcus faecalis plasmids (26) which did not detectably hybridize with catp.221 (or catpIP501) and cat C194* In addition, one E. faecalis and six Enterococcus [aecium plasmids coding for Cmr were included in this study. MATERIALS AND METHODSBacterial strains and culture conditions. The main characteristics of the strains and plasmids used in this study which carried unidentified cat genes are listed in Table 1

Molecular Basis of Resistance to Macrolides and Other Antibiotics in Commensal Viridans Group Streptococci and Gemella spp. and Transfer of Resistance Genes to Streptococcus pneumoniae

“…The tet(M) gene appears to be widespread in erythromycin-resistant VGS and Gemella spp., as is the case in pneumococci (39,50). The cat pC194 gene is believed to be the main gene responsible for chloramphenicol resistance in pneumococci, whereas other classes of cat genes are more prevalent in streptococci of groups A, B, and G (55,57). We detected the cat pC194 gene in all chloramphenicol-resistant VGS, but we found no significant association with the erm(B) gene, as reported in pneumococci by Seral et al (50).…”

Diversity among the gram-positive acetyltransferases inactivating streptogramin A and structurally related compounds and characterization of a new staphylococcal determinant, vatB

“…The deduced amino acid sequences of these three genes are related by 47.4 to 58.5% identity. The fact that plasmid or chromosomal antibiotic re- sistance genes carried by enterococci can be transferred by conjugation in vitro into S. aureus recipients (9,11,33,46), as well as the fact that closely related genes or transposons are present in enterococci and staphylococci (4,7,18,31,37,45,56,61,65), suggests that genetic exchange may occur between these two genera in vivo. The three SgA r genes described to date may be distant derivatives of a parental gene inherited long ago by a staphylococcal or an enterococcal isolate.…”

Tn 5253 Family Integrative and Conjugative Elements Carrying mef (I) and catQ Determinants in Streptococcus pneumoniae and Streptococcus pyogenes

“…The novelty of the gene combination was further enhanced by the fact that mef(I) was a newly detected mef subclass with an adjacent new msr(D) gene variant (2), and catQ had until then been described only in Clostridium perfringens (3,4), even if a catQ-like gene was previously reported in a single isolate of Streptococcus agalactiae (5). mef(I) and catQ were found in the so-called IQ element, a module-containing two identical tnp1 transposase genes at either end, which represented a moiety of a composite structure (5216IQ complex, ϳ30.5 kb); the other moiety was formed by fragments of transposons Tn5252 and Tn916, with Tn916 containing a silent tet(M) gene (1).…”