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author:("Cui, shengmui")
1.  Differential Gene Expression by RamA in Ciprofloxacin-Resistant Salmonella Typhimurium 
PLoS ONE  2011;6(7):e22161.
Overexpression of ramA has been implicated in resistance to multiple drugs in several enterobacterial pathogens. In the present study, Salmonella Typhimurium strain LTL with constitutive expression of ramA was compared to its ramA-deletion mutant by employing both DNA microarrays and phenotype microarrays (PM). The mutant strain with the disruption of ramA showed differential expression of at least 33 genes involved in 11 functional groups. The study confirmed at the transcriptional level that the constitutive expression of ramA was directly associated with increased expression of multidrug efflux pump AcrAB-TolC and decreased expression of porin protein OmpF, thereby conferring multiple drug resistance phenotype. Compared to the parent strain constitutively expressing ramA, the ramA mutant had increased susceptibility to over 70 antimicrobials and toxic compounds. The PM analysis also uncovered that the ramA mutant was better in utilization of 10 carbon sources and 5 phosphorus sources. This study suggested that the constitutive expression of ramA locus regulate not only multidrug efflux pump and accessory genes but also genes involved in carbon metabolic pathways.
doi:10.1371/journal.pone.0022161
PMCID: PMC3139621  PMID: 21811569
2.  Identification and Characterization of Shiga Toxin Type 2 Variants in Escherichia coli Isolates from Animals, Food, and Humans▿  
Applied and Environmental Microbiology  2008;74(18):5645-5652.
There is considerable heterogeneity among the Shiga toxin type 2 (Stx2) toxins elaborated by Shiga toxin-producing Escherichia coli (STEC). One such Stx2 variant, the Stx2d mucus-activatable toxin (Stx2dact), is rendered more toxic by the action of elastase present in intestinal mucus, which cleaves the last two amino acids of the A2 portion of the toxin A subunit. We screened 153 STEC isolates from food, animals, and humans for the gene encoding Stx2dact by using a novel one-step PCR procedure. This method targeted the region of stx2dact that encodes the elastase recognition site. The presence of stx2dact was confirmed by DNA sequencing of the complete toxin genes. Seven STEC isolates from cows (four isolates), meat (two isolates), and a human (one isolate) that carried the putative stx2dact gene were identified; all were eae negative, and none was the O157:H7 serotype. Three of the isolates (CVM9322, CVM9557, and CVM9584) also carried stx1, two (P1332 and P1334) carried stx1 and stx2c, and one (CL-15) carried stx2c. One isolate, P1130, harbored only stx2dact. The Vero cell cytotoxicities of supernatants from P1130 and stx1 deletion mutants of CVM9322, CVM9557, and CVM9584 were increased 13- to 30-fold after treatment with porcine elastase. Thus, Stx2dact-producing strains, as detected by our one-step PCR method, can be isolated not only from humans, as previously documented, but also from food and animals. The latter finding has important public health implications based on a recent report from Europe of a link between disease severity and infection with STEC isolates that produce Stx2dact.
doi:10.1128/AEM.00503-08
PMCID: PMC2547040  PMID: 18658282
3.  Prevalence and Antimicrobial Resistance of Campylobacter spp. and Salmonella Serovars in Organic Chickens from Maryland Retail Stores 
Retail organic (n = 198) and conventional (n = 61) chickens were analyzed. Most organic (76%) and conventional (74%) chickens were contaminated with campylobacters. Salmonellae were recovered from 61% of organic and 44% of conventional chickens. All Salmonella enterica serovar Typhimurium isolates from conventional chickens were resistant to five or more antimicrobials, whereas most S. enterica serovar Typhimurium isolates (79%) from organic chickens were susceptible to 17 antimicrobials tested.
doi:10.1128/AEM.71.7.4108-4111.2005
PMCID: PMC1169031  PMID: 16000828

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