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The objective of the study was to improve the understanding of antibiotic resistance (AR) ecology through characterization of antibiotic-resistant commensal isolates associated with an aquaculture production system. A total of 4767 isolates non-susceptible to sulfamethoxazole/trimethoprim (Sul/Tri), tetracycline (Tet), erythromycin (Erm), or cefotaxime (Ctx), originated from fish, feed, and environmental samples of an aquaculture farm with no known history of antibiotic applications were examined. Close to 80% of the isolates exhibited multi-drug resistance in media containing the corresponding antibiotics, and representative AR genes were detected in various isolates by PCR, with feed isolates had the highest positive rate detected. Identified AR gene carriers involved 18 bacterial genera. Selected AR genes led to acquired resistance in other bacteria by transformation. The AR traits in many isolates were stable in the absence of selective pressure. AR-rich feed and possibly environmental factors may contribute to AR in the aquaculture ecosystem. For minimum inhibitory concentration test, brain heart infusion medium was found more suitable for majority of the bacteria examined than cation-adjusted Mueller Hinton broth, with latter being the recommended medium for clinical isolates by standard protocol. The data indicated a need to update the methodology due to genetic diversity of microbiota for better understanding of the AR ecology. [ABSTRACT FROM AUTHOR]

The formation of Listeria monocytogenes biofilms contributes to persistent contamination in food processing facilities. A microarray comparison of L. monocytogenes between the transcriptome of the strong biofilm forming strain (Bfms) Scott A and the weak biofilm forming (Bfmw) strain F2365 was conducted to identify genes potentially involved in biofilm formation. Among 951 genes with significant difference in expression between the two strains, a GntR-family response regulator encoding gene (LMOf2365_0414), designated lbrA, was found to be highly expressed in Scott A relative to F2365. A Scott A lbrA-deletion mutant, designated AW3, formed biofilm to a much lesser extent as compared to the parent strain by a rapid attachment assay and scanning electron microscopy. Complementation with lbrA from Scott A restored the Bfms phenotype in the AW3 derivative. A second microarray assessment using the lbrA deletion mutant AW3 and the wild type Scott A revealed a total of 304 genes with expression significantly different between the two strains, indicating the potential regulatory role of LbrA in L. monocytogenes. A cloned copy of Scott A lbrA was unable to confer enhanced biofilm forming potential in F2365, suggesting that additional factors contributed to weak biofilm formation by F2365. [ABSTRACT FROM AUTHOR]

This study examined the prevalence of antibiotic-resistant (ART) bacteria and representative antibiotic resistance (AR)-encoding genes associated with several aquaculture products from retail markets in Guangzhou, China. ART commensal bacteria were found in 100% of the products examined. Among 505 multidrug-resistant isolates examined, close to one-fourth contained intl and sul1 genes: 15% contained sul2 and 5% contained tet(E). Incidences of β-lactamase-encoding genes blaTEM, blaCMY and erythromycin resistance determinants germ and germ were 4.5, 1.7, 1.3, and 0.3%, respectively. Most of the ART isolates identified from the rinse water were Aeromonas spp.; those from intestines belonged to the Enterobacteriaceae. Plasmid-associated intl and AR-encoding genes were identified in several ART isolates by Southern hybridization. Three multidrug resistance-encoding plasmids were transferred into Escherichia colt DH5α by chemical transformation and led to acquired AR in the transformants. In addition, the AR traits in many isolates were quite stable, even in the absence of selective pressure. Further studies are needed to reveal risk factors associated with the aquaculture production chain for targeted AR mitigation. [ABSTRACT FROM AUTHOR]

Proper knowledge of antibiotic resistance (AR) dissemination is essential for effective mitigation. This study examined the profiles of tetracycline-resistant (Tetr) commensal bacteria from representative ready-to-consume food samples from salad bars at local grocery stores and restaurants. Out of 900 Tetr isolates examined, 158 (17.6%) carried one or more of tetM, tetL, tetS, and tetK genes by conventional PCR, 28 harbored more than one Tetr determinants. The most prevalent genotype was tetM, which was detected in 70.9% of the AR gene carriers, followed by tetL (31.6%), tetS (13.9%), and tetK (2.5%). Identified AR gene carriers included Enterococcus, Lactococcus. Staphylococcus, Brochothrix, Carnobacterium, Stenotrophomonas, Pseudomonas. and Sphingobacterium, by 16S rRNA gene sequence analysis. AR determinants were successfully transmitted, and led to resistance in Streptococcus mutans via natural gene transformation and Enterococcus faecalis via electroporation, suggesting the functionality and mobility of the AR genes from the food commensal bacteria. In addition, the AR traits in many isolates are quite stable, even in the absence of the selective pressure. The identification of new commensal carriers for representative AR genes revealed the involvement of a broad spectrum of bacteria in the horizontal transmission of AR genes. Meanwhile, the spectrum of the antibiotic-resistant bacteria differed from the spectrum of the total bacteria (by denaturing gradient gel electrophoresis) associated with the food items. Our data revealed a common avenue in AR exposure and will assist in proper risk assessment and the development of comprehensive mitigation strategies to effectively combat AR. [ABSTRACT FROM AUTHOR]

Background and Aims: Cigarette smoking affects colonic inflammation, but the exact mechanism by which it does so is unclear. The aim of this study was to investigate the underlying mechanism by examining the effect of cigarette smoking on 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced colitis in rats. Method: Experimental colitis was induced by administrating TNBS enema in Sprague-Dawley rats. The effect of cigarette smoking was assessed by measuring the colonic edema, mucosal lesion area, histopathological score, mucosal myeloperoxidase (MPO) activity and tumor necrosis factor-α (TNF-α). The expression of α7-nicotinic acetylcholine receptor (α7nAChR) was examined after cigarette smoking to identify whether the α7nAChR is involved in inflammation. Results: TNBS induced severe colitis as evidenced by increased colonic edema, mucosal lesion area, histopathological score, MPO activity, and TNF-α level. Inflammation was aggravated by cigarette smoke exposure. Colonic tissue expressed α7nAChR (0.41 ± 0.11), and TNBS up-regulated the receptor expression (0.46 ± 0.11), but the difference was not significant (p > 0.05). Cigarette smoking with 2 and 4% respectively significantly increased the expression of α7nAChR (0.55 ± 0.05 and 0.64 ± 0.08) (p < 0.05). Conclusions: The up-regulated expression of α7nAChR after exposure to cigarette smoking indicates that α7nAChR in colonic tissue may be involved in cigarette smoking damage in TNBS-induced colitis in rats. Copyright © 2007 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

BSTRACT: Rapid detection of pathogenic and spoilage microorganisms is essential for ensuring the safety and quality of food. Real-time polymerase chain reaction (PCR) technology has the potential to achieve rapid, sensitive, and specific detection of these microorganisms in food. In this review, we discuss real-time PCR technologies in use today, applications of real-time PCR in food systems, and some of the associated challenges and limitations. [ABSTRACT FROM AUTHOR]

The importance of conjugation as a mechanism to spread biofilm determinants among microbial populations was illustrated with the gram-positive bacterium Lactococcus lactis. Conjugation triggered the enhanced expression of the clumping protein CluA, which is a main biofilm attribute in lactococci. Clumping transconjugants further transmitted the biofilm-forming elements among the lactococcal population at a much higher frequency than the parental nonclumping donor. This cell-clumping-associated high-frequency conjugation system also appeared to serve as an internal enhancer facilitating the dissemination of the broad-host-range drug resistance gene-encoding plasmid pAMβ1 within L. lactis, at frequencies more than 10,000 times higher than those for the nonclumping parental donor strain. The implications of this finding for antibiotic resistance gene dissemination are discussed. [ABSTRACT FROM AUTHOR]

Controlling antibiotic-resistant (ART) bacteria in cheese fermentation is important for food safety and public health. A plant-maintained culture was found to be a potential source for ART bacterial contamination in cheese fermentation. Antibiotics had a detectable effect on the ART population from contamination in the finished product. The decrease in the prevalence of antibiotic resistance (AR) in retail cheese samples from 2010 compared to data from 2006 suggested the effectiveness of targeted AR mitigation in related products. [ABSTRACT FROM AUTHOR]

A tetracycline-resistant (Tetr) dairy Enterococcus faecium isolate designated M7M2 was found to carry both tet(M) and tet(L) genes on a 19.6-kb plasmid. After consecutive transfer in the absence of tetracycline, the resistance-encoding plasmid persisted in 99% of the progenies. DNA sequence analysis revealed that the 19.6-kb plasmid contained 28 open reading frames (ORFs), including a tet(M)-tet(L)-mob gene cluster, as well as a 10.6-kb backbone highly homologous (99.9%) to the reported plasmid pRE25, but without an identified toxin-antitoxin (TA) plasmid stabilization system. The derived backbone plasmid without the Tetr determinants exhibited a 100% retention rate in the presence of acridine orange, suggesting the presence of a TA-independent plasmid stabilization mechanism, with its impact on the persistence of a broad spectrum of resistance-encoding traits still to be elucidated. The tet(M)-tet(L) gene cluster from M7M2 was functional and transmissible and led to acquired resistance in Enterococcus faecalis OG1RF by electroporation and in Streptococcus mutans UA159 by natural transformation. Southern hybridization showed that both the tet(M) and tet(L) genes were integrated into the chromosome of S. mutans UA159, while the whole plasmid was transferred to and retained in E. faecalis OG1RF. Quantitative real-time reverse transcription-PCR (RT-PCR) indicated tetracycline-induced transcription of both the tet(M) and tet(L) genes of pM7M2. The results indicated that multiple mechanisms might have contributed to the persistence of antibiotic resistance-encoding genes and that the plasmids pM7M2, pIP816, and pRE25 are likely correlated evolutionarily. [ABSTRACT FROM AUTHOR]