Distribution and in-vitro transfer of tetracycline resistance determinants in clinical and aquatic Acinetobacter strains

Abstract

Following characterisation by phenotypic tests and ampli®ed ribosomal DNA restriction analysis (ARDRA), 50 tetracycline-resistant (MIC > 16 mg=L) Acinetobacter strains from clinical (n 35) and aquatic (n 15) samples were analysed by PCR for tetracycline resistance (Tet) determinants of classes A±E. All the clinical strains were A. baumannii; most (33 of 35) had Tet A (n 16) or B (n 17) determinants, and only two did not yield amplicons with primers for any of the ®ve tetracycline resistance determinants. The aquatic strains belonged to genomic species other than A. baumannii, and most (12 of 15) did not contain determinants Tet A±E. Strains negative for Tet A±E were also negative for Tet G and M; further analysis of two aquatic strains with speci®c primers for Tet O and Tet Y and degenerate primers for Tet M-S-O-P(B)-Q also showed negative results. Transfer of tetracycline resistance was tested for 20 strains with three aquatic Acinetobacter strains and Escherichia coli K-12 as recipients. Transfer of resistance was demonstrated between aquatic strains from distinct ecological niches, but not from clinical to aquatic strains, nor from any Acinetobacter strain to E. coli K-12. Most transconjugants acquired multiple relatively small plasmids (< 36 kb). Transfer did not occur when DNA from the donor strains was added to the recipient cultures and was not affected by deoxyribonuclease I, suggesting a conjugative mechanism. It is concluded that Tet A and B are widespread among tetracycline-resistant A. baumannii strains of clinical origin, but unknown genetic determinants are responsible for most tetracycline resistance among aquatic Acinetobacter spp. These differences, together with the inability of clinical strains to transfer tetracycline resistance in vitro to aquatic strains, contra-indicate any important¯ow of tetracycline resistance genes between clinical and aquatic acinetobacter populations.

The involvement of tetA and tetE tetracycline resistance genes in plasmid and chromosomal resistance of Aeromonas in Brazilian strains

“…Acinetobacter sp. RUH 2158 H5, MIC value ≥ 16 mg ml -1 (Guardabassi et al 2000), and Escherichia coli strain D22-14, MIC value ≥ 10 mg ml -1 (Marshall et al 1986), were used as positive control in reactions using tetA and tetE primers. The Aeromonas strains A. caviae 32 and A. hydrophila (Ah) 21 (from our collection), both tetracycline-sensitive, were used as negative controls in both PCR reactions.…”

“…The purified plasmid and the recombinant plasmids obtained in the cloning experiments were also used as DNA templates for PCR. The PCR assay was carried out according to the method described by Guardabassi et al (2000). Acinetobacter sp.…”

“…strains were examined for the presence of resistance determinants by polymerase chain reaction (PCR), using specific primers for tetA (Guardabassi et al 2000) and tetE (Tovar et al 1988) genes. Crude lysates were obtained by centrifugating 1 ml of the bacterial growth at 10,000 g for 4 min.…”

Limited genetic diversity and extensive antimicrobial resistance in clinical isolates of Acinetobacter baumannii in north-east Iran

“…Resistance to tetracycline occurs in response to active efflux pump (tetA, tetB and tetH) and ribosomal protection (tetM) (Guardabassi et al, 2000). Aminoglycoside resistance genes confer resistance to this class of antibiotics by different modifying enzymes, including phosphotransferases (aphA1 and aphA6), nucleotidyltransferases (aadA1 and aadB) and acetyltransferase (aacC1) (Ramirez & Tolmasky, 2010).…”

A profile of drug resistance genes and integrons in E. coli causing surgical wound infections in the Faisalabad region of Pakistan

“…This may be due to some other resistance phenomenon not studied in this work such as efflux pumps. 20 Chloramphenicol is a broad-spectrum bacteriostatic, inhibitor of protein synthesis that has utility in human clinical practice. Surprisingly, it was relatively the most effective drug (with 41.4% sensitivity) besides amikacin in our study.…”