Anibiotic-resistance patterns and relative concentrations of bacteria (gram-negative rods) from ash deposits of various ages on the Krakatau Islands

The Krakatau islands Rakata, Sertung and Panjang, have been colonized by plants, animals and microorganisms over about a century, since the area was probably sterilized by the eruptions of August 1883. In 1930 the island of Anak Krakatau appeared and has since grown subaerially by periodic volcanic eruptions. Parts of this island may have been sterilized by ash eruptions in 1952 and 1953, and since 1962 lava flows have added new land surfaces to the island, the most recent being in 1980. At the northern end of Sertung Island, a long, narrow, sand spit built of eroded volcanic debris provides a land surface that is only a few decades old. These very new land habitats on Anak Krakatau and the Sertung spit, when examined for antibiotic-resistance patterns (resistotypes) of soil bacteria (Gramnegative rods, GNR), were shown to contain GNR much less antibiotic-resistant than those from the older habitats of Sertung on which over 100 years of post-eruptive colonization and succession has been possible. The concentration of soil microorganisms was also considerably less in these very young land habitats; only where vegetation had become established were soil GNR significantly resistant to antibiotics and soil microbial concentrations similar to those in the older habitats of the archipelago.