Apart from feral pigs on Panjang, rats ( Rattus rattus and Rattus tiomanicus ) and bats (various families, genera and species) are the only mammals resident on the Krakatau Islands. The two species of rat occur on separate islands, R. rattus on Rakata and R. tiomanicus on Panjang and Sertung. Both occur on Java. Of the two genera of bats examined, species of Cynopterus were found on Java and all the Krakatau islands, whereas Myotis muricola muricola was detected only on Java and Rakata. The main faecal bacteria of these mammals were shown to be Escherichia coli and species of Klebsiella , Enterobacter and Citrobacter , with other bacteria (e.g. Proteus sp., Pseudomonas sp., Aeromonas sp., Serratia sp., Proteus/ Providenca sp., Morganella sp. and Streptococcus faecalis ) being present in only a minority of individuals Significant differences were noted between the faecal floras of the two rat species. E. coli was always present in R. rattus , but was less frequent in R. tiomanicus (p < 0.05), whereas species of Klebsiella and Citrobacter were less frequent in R. rattus than in R. tiomanicus (p < 0.05). Differences between the faecal floras of the two bat genera were less significant, with the four main faecal bacteria being present in each genus. However, some individual M. muricola muricola yielded S. faeclis, Morganella sp. and Proteus/Providencia sp. whereas species of Cynopterus did not ( p < 0.05). S. faecalis was detected in rats and the bat M. muricola muricola on Java, but not in mammals on the Krakataus. This may be related to the absence of humans and their domesticated animals on the Krakatau islands. Only on Java did rats carry tetracycline-resistant E. coli or tetracycline-resistant species of Klebsiella . This may be related to the widespread use of tetracycline by humans on Java, where tetracycline is available without medical supervision. Isolates of E. coli from rats on Panjang were more resistant to chloramphenicol than were E. coli isolated from rats on the other islands of the Krakatau group, and isolates of Klebsiella from bats on Panjang were more resistant to sulphamethoxazole than were Klebsiella species isolated from bats on Rakata. The reason for faecal bacteria from Panjang mammals being more antibiotic resistant than those from mammals on other islands of the group is unclear, but may be related to differences in diet and vegetation, or the presence of feral pigs on Panjang only.
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.
A small survey of faecal bacteria from six species of reptile on West Java and the Krakatau Islands showed that species of Citrobacter were present in 17 out of 19 individual reptiles sampled. Species of Enterobacter, Klebsiella and Pseudomonas were also common but Escherichia coli was rare (present in only 2 out of 19 individual reptiles). Streptococcus faecalis was not detected in any reptile. Species of Pseudomonas were not detected in the faeces of any of the three gecko species sampled ( Gekko gecko, Gekko monarchus and Hemidactylus frenatus ), although they were detected in samples from the other three reptile species ( Mabuia multifasciata, Chrysopelea paradisi and Varanus salvtor ). Species of Citrobacter and Pseudomonas were more common and E. coli less common in reptiles than in mammals (rats and bats) living in the same area. The antibiotic-resistance patterns of the Citrobacter species were not significantly different between islands of the Krakatau group. Citrobacter species from reptiles were more resistant to chloramphenicol (43 % resistant) than those from mammals (8 % resistant). None of the isolates of Klebsiella and E. coli from reptiles was resistant to tetracycline.
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