Aims:  To compare bacterial populations and antimicrobial resistance patterns between clinical and sewage isolates from a regional hospital in northern Taiwan. The dissemination of antibiotic‐resistant bacteria from hospital compartments to the hospital sewage treatment plant was examined. Methods and Results:  A total of 1020 clinical isolates and 435 sewage isolates were collected between July and September 2005. The percentages of Gram‐negative bacteria from the clinical and sewage isolates were 87·2% and 91·0%, respectively (P = 0·033). Escherichia coli were the leading bacterial isolates in both groups. Antimicrobial susceptibility testing showed a significant difference (P < 0·001) in resistance to ampicillin (85·6%vs 94·1%), ampicillin/sulbactam (31·7%vs 55·4%), cefazolin (29·2%vs 71·5%) and cefuroxime (20·7%vs 61·9%) between clinical and sewage coliform isolates, respectively. Conclusions:  The sewage isolates had higher antimicrobial resistance rates than the clinical isolates from the same hospital. Significance and Impact of the Study:  The low efficacy of the hospital sewage treatment may contribute to the dissemination of multidrug resistant bacteria from this hospital compartments to the environment. Practices which limit the disposal of antimicrobial agents into the wastewater system may be the possible measure to prevent the selection of multidrug‐resistant bacteria from sewage treatment plants.

Sixty-six clinical P. aeruginosa isolates, 17 obtained from canine otitis specimens and 49 received from human patients with bloodstream infections, were collected between February 2007 and January 2008. The minimal inhibitory concentrations (MICs) of the antimicrobial agents of these isolates were determined. Multidrug resistance was common, with 23 (34.8%) isolates found to be ceftazidime resistant. To explore the mechanisms of ceftazidime resistance, PCR analyses were performed to detect drug-resistance genes. The prevalence rate of Ambler class A, B, and D β-lactamase genes were obtained, with bla TEM-1 100%, bla PSE-1 100%, bla OXA-2 96.2%, bla SHV-18 91.3%, bla OXA-17 78.3%, bla VIM-3 26.1%, bla OXA-10 21.7% and bla SHV-1 8.7%. An efflux inhibition assay with the PAβN compound was conducted. The ceftazidime resistance isolates were also tested by RT-qPCR to determine the mRNA expression levels of the oprM and ampC genes. Five (21.7%) of the ceftazidime resistance isolates appeared to overactivate the OprM efflux system. The ampD, ampE, and ampR genes and the ampC-ampR intergenic region were subsequently amplified and sequenced. Five (21.7%) of the ceftazidime resistance isolates from humans and canines had a point mutation in AmpR (Asp135-Asn, n = 3; Als194-Ser, n = 2), which induces AmpC overproduction from 10-to 80-fold. This study first reported ceftazidime resistance in P. aeruginosa from canine otitis specimens, which are closely related to ESBLs (50%), including the overproduction of AmpC (25%) and the OprM efflux system (25%). The ESBLs (100%) played an important role in all ceftazidime resistance isolates from humans, and either AmpC (21.1%) or OprM (21.1%) might be overexpressed within the same isolate. A human patient isolate (H307B) showed simultaneous expression of ESBLs, the OprM efflux system, and AmpC overproduction.