Prevalence of antibiotic resistance genes in drinking and environmental water sources of the Kathmandu Valley, Nepal.

Antibiotic-resistant bacteria-associated infections are responsible for more than 1.2 million annual deaths worldwide. In low- and middle-income countries (LMICs), the consumption of antibiotics for human and veterinary uses is not regulated effectively. Overused and misused antibiotics can end up in aquatic environments, which may act as a conduit for antibiotic resistance dissemination. However, data on the prevalence of antibiotic resistance determinants in aquatic environments are still limited for LMICs. In this study, we evaluated the prevalence and concentration of antibiotic resistance genes (ARGs) in different drinking and environmental water sources collected from the Kathmandu Valley, Nepal, using droplet digital polymerase chain reaction to understand the current situation of ARG contamination. River water and shallow dug well water sources were the most contaminated with ARGs. Almost all samples contained sul1 (94%), and intI1 and tet(A) were detected in 83 and 60% of the samples, respectively. Maximum ARG concentration varied between 4.2 log10 copies/100 ml for mecA and 9.3 log10 copies/100 ml for sul1. Significant positive correlations were found between ARGs (r > 0.5, p < 0.01), except for mecA, qnrS, and vanA. As sul1 and intI1 were detected in almost all samples, the presence of these genes in a given sample may need to be considered as background antibiotic resistance in LMICs. Therefore, monitoring of ARGs, such as ß-lactam ARGs, quinolone resistance genes, and vancomycin resistance genes, may provide a better picture of the antibiotic resistance determinants in aquatic environments of LMICs.

N-Methyl-N-Nitrosourea-Induced Photoreceptor Degeneration Is Inhibited by Nicotinamide via the Blockade of Upstream Events before the Phosphorylation of Signalling Proteins.

N-methyl-N-nitrosourea (MNU), a known carcinogen, is generally used in animal models to chemically induce photoreceptor degeneration. It has been reported that nicotinamide (NAM) exerts a protective effect on MNU-induced photoreceptor degeneration. We investigated the molecular mechanisms on MNU-induced photoreceptor degeneration. Intraperitoneal MNU injection (75 mg/kg) in rats induced selective photoreceptor degeneration in 7 days. NAM administration completely inhibited photoreceptor degeneration. Photoreceptor layer abnormality was observed within 6 hours after MNU injection, whereas it was restored in the NAM-treated retina, as detected by optical coherence tomography. One day following MNU administration, phosphorylation of the cell death-associated signalling proteins c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38) increased, while the apoptosis-related proteins, full-length poly(ADP-ribose) polymerase (PARP) and apoptosis-inducing factor (AIF), were depleted. These changes were not observed in the NAM-treated retinas. Cell survival signalling, such as extracellular signal-regulated kinase (ERK), Akt, and cAMP response element binding protein (CREB) phosphorylation, increased in the MNU- but not in the NAM-treated rat retinas. Increased phosphorylated ERK (p-ERK) levels were observed within 6 hours after MNU administration, suggestive of cell survival signalling activation. This did not occur in NAM-treated retinas. These results indicate that NAM regulates upstream cellular events prior to the activation of cell death-related signalling events, such as JNK and p38 phosphorylation.