Bacterial Strains

As the first step to identification of the antibiotic resistance determinants of ancient bacteria, we tested permafrost strains from our collection for the presence of known genes encoding for streptomycin resistance. Seven strains resistant to different antibiotics (Table 2) isolated from different locations of Siberian and Antarctic permafrost were chosen for comparative analysis of antibiotic resistance determinants (Table 7). Four of these strains contained plasmids and (or) transposons (Table 3 and data not shown).

These strains were screened for the presence of streptomycin, sulphathiazole and tetracycline resistance genes, which are prevalent among present-day clinically important bacteria and which are usually associated with mobile elements such as plasmids, transposons and integrons.

PCR, Southern blot analysis and partial sequencing revealed that the antibiotic resistant bacteria studied contained genes highly homologous to the known present-day antibiotic resistance genes. Thus, streptomycin-resistant permafrost strains contained streptomycin-resistance determinants of the two known types. In six of these strains streptomycin-resistance was encoded by the linked strA-strB genes, which encode aminoglycoside phosphotransferases and are distributed among present-day bacterial isolates from human, animals, and plants [Sundin, 2002]. In particular, we for the first time identified the strA-strB-like genes in ancient Gram-negative bacterial strains belonging to Psychrobacter and Brevundimonas genera and also in a strain VSH72 of a Gram-positive bacterium Paenibacillus amyloliticus. Other streptomycin-resistant strains of Gram-negative bacteria from permafrost contained adenylyltransferase genes related to the aadA -genes of present-day bacteria [Hall & Collis, 1998; Clark et al., 1999]. Intriguingly, two of the streptomycin resistance strains (Tik3 and VSH72) contained both the strA-strB and aadA genes. While the reasons for having two types of streptomycin resistance in the same cell remain unknown, similar strains harbouring both the strA-strB and aadA genes were recently detected among streptomycin resistant Escherichia coli of domestic animals in Norway [Sunde & Norström, 2005].

Table 7. Genes of antibiotic resistance revealed in permafrost strains

Strain designation

Region and age of permafrost

Taxonomic position

Revealed genes of resistance

ED23-35

Bank of river Homus-Yuryiah, 15-40 K

Acinetobacter sp.

strA-strB

MR29-12

Coast of East-Siberian Sea, 15-35K

Psychrobacter psychrophilus

strA-strB, tetR-tet(H)

Tiki

Coast of Laptev Sea, 200-600K

Pseudomonas putida

strA-strB

Tik3

Coast of Laptev Sea, 200-600K

Pseudomonas sp.

strA-strB, aadA, sull

EK41

Antarctida, 50-300K

Brevundimonas vesicularis

strA-strB

VSH72

Kolyma lowland 200-600K

Paenibacillus amyloliticus

strA-strB, aadA

VSH76

Kolyma lowland 200-600K

Paenibacillus amyloliticus

aadA

A single strain that was resistant to both streptomycin and tetracycline (Psychrobacter psychrophilus MR29-12) carried tetR-tet(H) genes in addition to the strA-strB streptomycin resistance determinants. Previously, the tetR-tet(H) genes were found in clinical bacterial strains belonging to Pasteurella, Mannheimia, Acinetobacter, Moraxella, and Actinobacillus genera [Kehrenberg et al., 2001; Blanco et al., 2006].

Was this article helpful?

0 0

Post a comment