Conjugation-Mediated Transfer of Antibiotic-Resistance Plasmids Between Enterobacteriaceae in the Digestive Tract of Blaberus craniifer (Blattodea: Blaberidae).

Cockroaches, insects of the order Blattodea, seem to play a crucial role in the possible conjugation-mediated genetic exchanges that occur among bacteria that harbor in the cockroach intestinal tract. The gut of these insects can be thought of as an effective in vivo model for the natural transfer of antimicrobial resistance plasmids among bacteria. In our study, we evaluated the conjugation-mediated horizontal transfer of resistance genes between Escherichia coli and other microorganisms of the same Enterobacteriaceae family within the intestinal tract of Blaberus craniifer Burmeister, 1838 (Blattodea: Blaberidae). Different in vivo mating experiments were performed using E. coli RP4 harboring the RP4 plasmid carrying ampicillin, kanamycin, and tetracycline resistance genes as the donor and E. coli K12 resistant to nalidixic acid or Salmonella enterica serovar Enteritidis IMM39 resistant to streptomycin as the recipients. The RP4 plasmid was successfully transferred to both recipients, producing E. coli K12-RP4 and S. Enteritidis IMM39-RP4 transconjugants. Conjugation frequencies in vivo were similar to those previously observed in vitro. The transfer of the RP4 plasmid in all transconjugants was confirmed by small-scale plasmid isolation and agar gel electrophoresis, suggesting that the intestinal tract of cockroaches is an effective in vivo model for natural gene transfer. Our results confirm that cockroaches allow for the exchange of antimicrobial resistance plasmids among bacteria and may represent a potential reservoir for the dissemination of antibiotic-resistant bacteria in different environments. These findings are particularly significant to human health in the context of health care settings such as hospitals.

Insulin resistance and hyperinsulinemia in homozygous beta-thalassemia.

Insulin resistance and hyperinsulinemia have been reported in homozygous beta-thalassemia before the development of diabetes. However, insulin sensitivity (SI) has never been studied in normoinsulinemic patients. Furthermore, whether hyperinsulinemia is due to increased beta-cell secretion or to decreased hepatic insulin extraction is poorly understood. We estimated SI, beta-cell secretion, and hepatic insulin extraction using the minimal model analysis of a frequently sampled intravenous glucose tolerance test (2.8 g/m2) in two groups of nondiabetic pubertal patients with homozygous beta-thalassemia (seven hyperinsulinemic and seven normoinsulinemic patients) and seven control subjects matched for age, body mass index, and pubertal stage. In both thalassemic groups, SI was reduced by approximately 40% (3.52 +/- 0.57 and 3.74 +/- 0.66 v 6.89 +/- 1.02 10(-4).min-1 [microU/mL], P = .011) and was inversely correlated with iron overload (r = -.707, P = .006). All parameters of beta-cell secretion were not significantly different in patients and controls. On the other hand, basal posthepatic insulin delivery (BDR) was more than doubled in hyperinsulinemic patients with respect to normoinsulinemic patients or controls (15.1 +/- 2.4 v 6.1 +/- 1.1 and 7.5 +/- 2.3 pmol/L.min-1, P = .012), and the same was true for total posthepatic insulin delivery ([TID] 6.3 +/- 1.0 v 2.9 +/- 0.5 and 2.9 +/- 0.7 pmol/L.240 min-1, P = .015). Hepatic insulin extraction was significantly lower in hyperinsulinemic patients than in normoinsulinemic patients or controls (49.3% +/- 9.4% v 73.0% +/- 3.7% and 77.4% +/- 3.9%, P = .011), and in patients it was inversely correlated with iron overload (r = -.829, P = .0001). In conclusion, insulin resistance is present even in normoinsulinemic patients, beta-cell responsiveness to glucose is normal, and hyperinsulinemia is mainly due to decreased hepatic insulin extraction. In nondiabetic thalassemic patients, these defects are possibly related to iron overload.