Low prevalence of blaTEM genes in Arctic environments and agricultural soil and rhizosphere

The prevalence of blaTEM genes conferring ampicillin resistance (Ampr) in different soils was determined to clarify the environmental distribution of resistance determinants of major clinical importance. Samples were collected from 14 sites in New Zealand, mainland Norway, Svalbard, and 2 soil microcosms made of compost purchased in Italy. The Ampr bacteria represented 1.7–100% of the cultivable microflora with an average of 28%. Approximately 1200 Ampr isolates were further analyzed. Although >50% of the resistant isolates were capable of β-lactam-ring (nitrocefin) degradation, none carried a PCR-detectable blaTEM gene. The proportion of blaTEM genes in the culturable Ampr isolates was <0.07%. The overall blaTEM gene prevalence was determined by blaTEM-specific PCR of DNA extracted directly from the environmental sample. DNA hybridization was performed on selected samples with a detection limit of 11 blaTEM genes per PCR sample. Our analysis indicates that the prevalence of blaTEM carrying bacteria is <1 per 1000 to 100 000 bacteria in the samples analyzed. The study suggests that blaTEM genes are rare in soil environments, in contrast to their increasing prevalence in some clinical and commensal bacterial populations. The frequent observation of nitrocefin-degrading capacity among the sampled isolates suggests that other mechanisms conferring enzyme-mediated resistance to β-lactam antibiotics are widespread in Arctic and agricultural soil environments.