Detection of erythromycin resistance by the polymerase chain reaction using primers in conserved regions of erm rRNA methylase genes

Rapid increase of resistance to erythromycin and clindamycin in Streptococcus pyogenes in Italy, 1993-1995. The Italian Surveillance Group for Antimicrobial Resistance

A survey of antibiotic resistance in Streptococcus pyogenes in Italy showed a sharp increase in erythromycin resistance. In 1993, the incidence of erythromycin-resistant strains was on average 5.1%, with marked variations by geographic area. Two years later, the incidence of these strains had registered a 1.5- to roughly 20-fold increase, with a mean value of 25.9%, exceeding 40% in three centers out of 13 and 30% in another four. For all the strains studied, normal levels of susceptibility to penicillin were reported.

Characterization of tetracycline and erythromycin resistance in Actinobacillus pleuropneumoniae

Minimum inhibitory concentrations to tetracycline and erythromycin were determined for nineteen isolates of Actinobacillus pleuropneumoniae of Norwegian origin. The isolates were screened for rRNA methylase determinants (Erm genes) and for the tetracycline resistance Tet B determinant, using oligonucleotide probes, polymerase chain reaction and hybridization. Ten isolates (53%) carried the Erm C determinant, two isolates (10%) carried the Erm A determinant, four isolates (21%) carried both the Erm A and the Erm C determinants, and three isolates (16%) carried none of the Erm determinants examined. Eight isolates (45%) carried the Tet B determinant. Selected isolates were shown to transfer the Erm C and Erm A determinants at a frequency of 10(-7)-10(-9) per recipient cell. This is the first description of A. pleuropneumoniae carrying either Erm A, Erm C or/and Tet B determinants.

Transferable erythromycin resistance in Listeria spp. isolated from food

An erythromycin-resistant (Emr) Listeria innocua and an Emr Listeria monocytogenes isolate both carried ermC genes, which code for rRNA methylases. The ermC genes were transferable by conjugation to recipient L. monocytogenes, Listeria ivanovii, and Enterococcus faecalis but did not appear to be associated with conjugative plasmids.

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

A gene encoding an acetyltransferase inactivating streptogramin A (SgA) and structurally similar compounds was isolated from a staphylococcal plasmid and sequenced. This gene, designated vatB, potentially encodes a 212-amino-acid protein, VatB, of 23,320 Da with 47.4 and 58.4% amino acid identities with two other enzymes with the same activity, Vat and SatA, respectively, which are encoded by a staphylococcal plasmid and an enterococcal plasmid, respectively. The C-terminal parts of these three enzymes share significant homology with the C-terminal parts of 10 other acetyltransferases modifying various substrates. A pair of degenerate primers representing the conserved motifs shared by VatB, Vat, and SatA was designed to detect the three genes encoding these SgA acetyltransferases. Five of 12 clinical SgAr Staphylococcus aureus isolates tested carried neither these genes nor the gene vga, which confers resistance to SgA by a different mechanism, suggesting that another gene(s) and possibly another mechanism of resistance to SgA in staphylococci remains to be characterized.

Detection of aac(6')-I genes in amikacin-resistant Acinetobacter spp. by PCR

The distribution of aac(6')-I genes in 62 strains of Acinetobacter spp. resistant to amikacin, netilmicin, and tobramycin and susceptible to gentamicin, a phenotype compatible with synthesis of an AAC(6')-I enzyme, was studied by PCR and by DNA hybridization. Both methods gave similar results. Among the 51 Acinetobacter baumannii strains, aac(6')-Ib was found in 19 isolates and aac(6')-Ih was found in the remaining strains. The aac(6')-Ig gene was present in all 10 A. haemolyticus strains studied and was detected only in this species. A pair of degenerate oligonucleotides complementary to conserved regions of aac(6')-Ic, -Id, -If, -Ig, and -Ih enabled detection of these genes and also of aac(6')-Ij, recently recognized in Acinetobacter sp. strain 13.

Characterization of antibiotic resistance in Streptococcus suis

Twenty one isolates of Streptococcus suis were screened for antibiotic resistance by growth on antibiotic-containing media, by measuring minimum inhibitory concentrations, by hybridization to specific DNA and oligonucleotide probes for antibiotic resistance genes, and by PCR. The isolates were from a slaughter house survey of respiratory pathogens in Norwegian pigs in 1986. Fifteen isolates were resistant to tetracycline, with MICs ranging from 4-128 micrograms/ml. Genes coding for the Tet O and Tet M determinants were detected in eight and five isolates, respectively. Genes coding for other Gram positive Tet determinants, Tet K, Tet L, and Tet P, were not detected. One isolate was constitutive resistant to erythromycin with MIC of 128 micrograms/ml. Five other isolates carried inducible erythromycin resistance. All these isolates, and five others, were positive in a PCR assay for erythromycin resistance, and hybridized with the Erm C and/or Erm B probes. No resistance against chloramphenicol (5 micrograms/ml) or rifampin (10 micrograms/ml) could be could be detected, but five isolates were resistant to streptomycin (250 micrograms/ml), four isolates were resistant to kanamycin (10 micrograms/ml), and one isolate was resistant to fusicic acid (10 micrograms/ml). In mating experiments with Enterococcus faecalis JH2-2 as recipient, tetracycline, erythromycin, and kanamycin genes were transferred separately to the recipient strain at a rate of 10(-7) transconjugants/recipient cell.

Macrolide-lincosamide resistance determinants in streptococcal species isolated from the bovine mammary gland

Seventy one streptococci isolated from dairy cows with clinical mastitis were tested for erythromycin and lincomycin susceptibility. Ten isolates (7.1%) were resistant to erythromycin and/or lincomycin and seven were constitutive and three were inducibly resistant. Nine of the isolates hybridized with one or more of the Erm probes tested and eight isolates gave PCR products with rRNA methylase primers. The Erm determinants were transferable at frequency of 10(-5) to 10(-6) per recipient.

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

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, catpC194, catpSCS7, 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 (catpC221, catpC194, and catpSCS7) were detected on the 10 enterococcal plasmids studied here that encode resistance to chloramphenicol.

New microbial diagnosis

Rapid methods for comprehensive nucleic acid analysis are essential for the progress in basic research. In microbial diagnosis nucleic acid analyses are useful for achieving quick, sensitive results with new dimensions of specificity. As to specificity, hybridisation tests are easily constructed for genus or species specific microbial typing or for the detection of genes accounting for pathogenic properties. Modern sequence analysis allows rapid detection of mutations eg., those conferring antiviral resistance. A new level of sensitivity comparable to that of the conventional enrichment culture is obtainable by enzymatic amplification (PCR) of microbial nucleic acids before detection. PCR-technology has proved particularly useful in the diagnosis of microbial infections when the organisms are impossible or tedious to cultivate. For reliable diagnostic use the performance of in vitro amplification requires extreme care to prevent false positive results owing to carry over problems. In conclusion, nucleic acid analyses are expanding the potential for diagnosing microbial infections and may well replace some conventional diagnostic methods.

Bacterial resistance to macrolide, lincosamide, and streptogramin antibiotics by target modification

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