Triclosan is an antiseptic frequently added to items as diverse as soaps, lotions, toothpaste, and many commonly used household fabrics and plastics. Although wild-type Pseudomonas aeruginosa expresses the triclosan target enoyl-acyl carrier protein reductase, it is triclosan resistant due to expression of the MexABOprM efflux system. Exposure of a susceptible ⌬(mexAB-oprM) strain to triclosan selected multidrug-resistant bacteria at high frequencies. These bacteria hyperexpressed the MexCD-OprJ efflux system due to mutations in its regulatory gene, nfxB. The MICs of several drugs for these mutants were increased up to 500-fold, including the MIC of ciprofloxacin, which was increased 94-fold. Whereas the MexEF-OprN efflux system also participated in triclosan efflux, this antimicrobial was not a substrate for MexXY-OprM.Pseudomonas aeruginosa is a clinically significant pathogen, particularly in immunocompromised hosts (36). Infections caused by this bacterium are difficult to treat due to its many intrinsic and acquired antibiotic resistances. Intrinsic resistance is mostly attributable to the expression of several multidrug resistance (MDR) efflux systems. The P. aeruginosa genome (35) contains structural genes for at least 12 resistance nodulation type efflux systems, of which only 4, i.e., MexABOprM (27), MexCD-OprJ (26), MexEF-OprN (13), and MexXY (1, 21, 38), have been characterized. Exposure to selected substrates can select for their upregulated or constitutive expression (13,14,26,38).2-Hydroxyphenylethers are a class of compounds that exhibit broad-spectrum antimicrobial activity. Triclosan is the most potent and widely used member of this class (2, 5) and is used in hand soaps, lotions, toothpastes, and oral rinses, as well as in fabrics and plastics. It was long thought to act as a nonspecific "biocide" (29), but recent biochemical and genetic studies have shown that triclosan acts on a defined bacterial target in the fatty acid biosynthetic pathway, enoyl-acyl carrier protein (ACP) reductase (FabI) (7,9,10,12,18,20) or its homolog InhA in mycobacteria (18). Some bacteria possess triclosan-resistant enoyl-ACP reductase homologs (FabK), and to date P. aeruginosa is unique among gram-negative bacteria in that it possesses both triclosan-sensitive and -resistant enzymes (8). Alterations in FabI active-site residues confer resistance to triclosan (9,10,20). Of particular concern is that such amino acid changes selected by exposure to triclosan lead to cross-resistance with other antimicrobial agents (9), including clinically used front-line drugs, since some mutations leading to triclosan resistance in Mycobacterium smegmatis also caused resistance to isoniazid (18). Moreover, triclosan is a substrate of a multidrug efflux pump in clinical and laboratory Escherichia coli strains (19). We have recently shown that P. aeruginosa strain PAO1 is intrinsically resistant to triclosan by virtue of expression of the MexAB-OprM efflux pump (32), and the same is true for all strains of this species tested to date (...

Using the biocide triclosan as a selective agent, several triclosan-resistant mutants of a susceptible Pseudomonas aeruginosa strain were isolated. Cloning and characterization of a DNA fragment conferring triclosan resistance from one of these mutants revealed a hitherto uncharacterized efflux system of the resistance nodulation cell division (RND) family, which was named MexJK and which is encoded by the mexJK operon. Expression of this operon is negatively regulated by the product of mexL, a gene located upstream of and transcribed divergently from mexJK. The triclosan-resistant mutant contained a single nucleotide change in mexL, which caused an amino acid change in the putative helix-turn-helix domain of MexL. The MexL protein belongs to the TetR family of repressor proteins. The MexJK system effluxed tetracycline and erythromycin but only in the presence of the outer membrane protein channel OprM; OprJ and OprN did not function with MexJK. Triclosan efflux required neither of the outer membrane protein channels tested but necessitated the MexJ membrane fusion protein and the MexK inner membrane RND transporter. The results presented in this study suggest that MexJK may function as a two-component RND pump for triclosan efflux but must associate with OprM to form a tripartite antibiotic efflux system. Furthermore, the results confirm that triclosan is an excellent tool for the study of RND multidrug efflux systems and that this popular biocide therefore readily selects mutants which are cross-resistant with antibiotics.

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This study aimed to examine the prevalence and antimicrobial resistance (AMR) of Salmonella isolates from broiler chickens, pigs and their associated meat products in the Thailand-Cambodia border provinces. A total of 941 samples were collected from pigs and broiler chickens at slaughter houses and from carcasses at local fresh markets in Sa Kaeo, Thailand (n = 554) and Banteay Meanchey, Cambodia (n = 387) in 2014 and 2015. From these samples, 345 Salmonella isolates were collected from Sa Keao (n = 145; 23%) and Banteay Meanchey (n = 200; 47%) and assayed for antimicrobial susceptibility, class 1 integrons and extended-spectrum β-lactamase (ESBL) genes. Serovars Typhimurium (29%) and Rissen (29%) were the most common serotypes found in Thai and Cambodian isolates, respectively. Multidrug resistance was detected in 34% and 52% of isolates from Sa Keao and Banteay Meanchey, respectively. The majority of the Thai isolates were resistant to ampicillin (72.4%), whereas most Cambodian isolates were resistant to sulfamethoxazole (71%). Eleven isolates from Sa Keao and 44 from Banteay Meanchey carried class 1 integrons comprising resistance gene cassettes. The most common gene cassette array was dfrA12-aadA2 (61.1%). Six isolates were ESBL producers. The β-lactamase genes found included bla , bla and bla . Some of these class 1 integrons and ESBL genes were located on conjugative plasmid. In conclusion, multidrug-resistant Salmonella are common in pigs, chickens and their products in the Thailand-Cambodia border provinces. Our findings indicate that class 1 integrons play a role in spread of AMR in the strains in this study.

This study aimed to examine occurrence and antimicrobial resistance characteristics of Salmonella from pigs, pork and humans in Thailand and Laos provinces. The samples were collected from pigs, carcasses and workers in slaughterhouses, retail pork and butchers in fresh markets and patients in hospitals in Thailand (n=729) and Laos (n=458). A total of 295 of 729 samples (34.6 %) collected in Thailand and 253 of 458 (47.4 %) samples collected in Laos were positive for Salmonella. A total of 548 Salmonella isolates from Thailand (n=295) and Laos (n=253) were further analysed. Serovar Typhimurium was the most common serotype in Thai (34 %) and Laos (20.6 %) samples. Approximately 2.4 % of Thai isolates produced extended-spectrum b-lactamase (ESBL). All the ESBL producers possessed bla CTX-M-14 , some of which were horizontally transferred. Class 1 integrons were common in Thai (31.9 %) and Laos (39.1 %) isolates, but none were associated with SGI1. The resistance cassette dfrA12-aadA2 was the most common, while the least common was aadA2-linG (n=1). The dfrA12-aadA2 gene cassette in five isolates and aadA2-linG were located on conjugative plasmid. Three pork isolates were fluoroquinolone resistant and carried an amino acid substitute, Ser-83-Tyr, in GyrA. The qnrS gene was found in 7.1 and 5.5 % of the Thai and Laos isolates, respectively, while qnrB was carried in another Laos isolate (1.9 %). All ESBL producers carried qnrS. In conclusion, multidrug-resistant Salmonella was common in pigs, pork and human samples in this region. The bacteria carried mobile genetic elements and resistance genes on conjugative plasmids that could be readily transferred to other bacterial species.

MexJK requires OprM for erythromycin efflux but not for triclosan efflux. Deletion of 15 OprM family outer membrane proteins (OMPs) revealed that only the TolC homolog OpmH functions with MexJK for triclosan efflux. This is the first report of natural utilization of multiple OMPs by a given resistance nodulation cell division transporter/membrane fusion protein pair.

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ABSTRACT. A total of 184 resistant Salmonella enterica isolated from poultry and swine were investigated for the distribution of and associations between various antimicrobial resistance genes. All the isolates were screened for the presence of class 2 and 3 integrase genes and 18 resistance genes corresponding to their resistance phenotypes. None of the isolates carried class 2 and 3 integrons. The investigated resistance genes were responsible for resistance in 78% of the isolates. All the strains harboring more than one resistance gene were resistant to three or more antimicrobials. The bla TEM , cmlA, tetA, dfrA12, sul3, aadA1 genes were detected in the majority of strains resistant to ampicillin (87%), chloramphenicol (63%), tetracycline (60%), trimethoprim (42%), sulphonamides (42%) and streptomycin/ spectinomycin (61%), respectively. Two ciprofloxacin-resistant isolates had a single point mutation leading to Ser-83-Phe in GyrA or Thr-57-Ser in ParC. Statistical analysis revealed good correlation between the presence of antimicrobial resistance genes and corresponding resistance phenotype (p<0.01). The results indicated that the resistance genes play a major role in conferring resistance among the Salmonella isolates investigated.