The secondary growth model for Salmonella was developed based on the artificial neural network (ANN) with data collected from ComBase and FoodData Central. In addition to the existing secondary model variables (temperature, pH, Na+, and water contents), more input variables (sugar, carbohydrate, lipid, and protein contents) were considered. The output variables were microbial growth parameters (lag phase duration [l] and maximum growth rate [mmax]). A commercial ANN program (NeuralWorks Predict) was utilized with training at 80%, validation at 10%, and test data at 10%. ANN models were created using all data and cleansed data. Using the cleansed data, the training/testing root mean square error (RMSE) for mmax improved from 0.14/0.16 to 0.11/0.14, whereas the RMSE for l was still not acceptable, from 11.94/33.03 to 7.09/4.18. The l data were divided into two ranges with high and low goodness of fit, whereas the ANN model for each field was built, resulting in an optimally low RMSE.

본 연구에서는 대표적인 신선 잎채소류인 상추의 세척 단계에서 초음파 (37 kHz)와 염소 (100~300 ppm)의 병용 처리 후 냉장 ~ 실온저장 (10~25C)에 따른 이 식품 중의 Salmonella Typhimurium 의 성장예측모델을 개발하였다. 1차 모델 개발을 위해 Gompertz 방정식을 활용하여 각기 다른 실험 조건에서의 S. Typhimurium의 생육도 (SGR과 LT)를 조사했다 . 본 방정식에 의한 1차 모델 개발시 R2가 0.92 이상으로 우수하게 나타났으며 저장온도가 낮을수록 초음파에 사용된 염소의 농도가 높을수록 SGR 값은 감소하였고 LT 값은 증가하였다 . 이를 바탕으로 2 차 polynomial 모델을 개발하여 다양한 통계적 지표 (R2, MSE, Af 및 Bf)를 통해 분석한 결과 개발된 모델의 적합성을 확인할 수 있었다 . 따라서 개발된 모델이 초음파와 염소의 병용 세척에 따른 저장 중 상추에 대한 S. Typhimurium의 성장예측모델로 사용 가능하다고 판단되어지며 , 신선 잎채소류에서의 식중독을 예방하고 미생물학적 위생관리기준을 설정하는데 기초자료로 활용될 수 있을 것으로 사료된다 .

In order to investigate phenotype and genotype of Salmonella enterica subsp. enterica serovar Enteritidis, Forty-eight S. Enteritidis isolates from diarrhea patients were analysed using antimicrobial resistance typing, Phage typing, and Pulsed field gel electrophoresis in Seoul from 2004 to 2005. All of S. Enteritidis were resistant to streptomycin(SM, 37.5%), ampicillin(AM, 43.8%), t icarcillin(TIC, 43.8%), chloramphenicol(CM, 29.2%), t etracycline(TE, 10 .4%) and nalidixic acid(NA, 18.8%) among 16 antimicrobial drugs. Of 48 S. Enteritidis, 8 isolates(16.7%) were resistant to 1 drug, 3 isolates( 6.3%) to 2 drugs, 1 isolate (2.1%) to 3 drugs and 17 isolates(35.7%) to 4 drugs. The basic pattern of 4 drugs resistance was SM, TIC, TE, and CM but 1 drug resistant isolates represent all nalidixic acid resistance. Among 30 antibiotic r esistant S . Enteritidis, 2 1 isolates(70 %) were phage type 2 1, 8 i solates(26.7%) were phage t ype 2 3 and 1 isolate( 3.3%) was RDNC, respectively. Of the phage types observed, all of phage type 23(8 isolates) were nalidixic acid resistant and phage type 21 were AM-TIC-SM-CM multi-resistance(13 isolates; 43.3%), AM-TIC-SM-TE(4 isolates; 13.3%), AM-TIC-SM(1 isolate; 3.3%), AM-TIC-CM(1 isolate; 3.3%), and AM-TIC(2 isolates; 6.7%) resistance and 1 isolate of RDNC was NA-TE resistance. PFGE divided the isolates into two major clusters, A(n=14) and B(n=14). There were four different resistance profiles with resistance to AM, TIC, SM, TE, NA within PFGE A. Also resistance to AM, TIC, SM, CM was common within PFGE B. The PFGE A strains typed as PT21(n=5), PT23(n=8), and RDNC(n=1), While all the PFGE B strains typed as PT21(n=14). In consequence, there was the highly significant concurrence between resistance typing, phage typing and PFGE.

In order to investigate the resistance patterns and molecular characteristics of resistance gene of 9 NA-resistant Salmonella enterica subsp. enterica serovar Enteritidis, Total of 101 isolates were isolated from stool sampes from 2005 to 2006. Among them, 48 isolates(47.5%) were identified S. Enteritidis, 24 isolates(23.8%) S. Typhi, 8 isolates(42.5%) S. Typhimurium, 7 isolates(6.9%) S. Paratyphi A and 14 isolates (13.9%) others Salmonellas. All of S. Enteritidis were resistant to ampicillin(43.8%), ticarcillin(43.8%), streptomycin(37.5%), chloramphenicol(29.2%), tetracycline(10.4%) and nalidixic acid(18.8%), respectively. All nalidixic acid-resistance isolates represented one point mutation in the quinolone resistance determining region(QRDR) of gyrA gene. Among them, 8(89%) isolates were substituted Tyr for Ser at position amino acid 83th or 1(11%) isolate was substituted Asn for Asp at position amino acid 87th. In consequence, Continued surveillance of NA-resistance among non-Typhi S. entetica isolates is needed to mitigate the increasing prevalence of nalidixic acid resistance.

Biological organisms require iron for optimal metabolism. Intracellular pathogens also must secure iron especially during infection of animal hosts expressing NRAMP(natural resistance-associated macrophage protein), a transporter protein sequestering metal ions from pathogens. This study shows that extracytoplasmic function sigma factor σE is required for Salmonella virulence in NRAMP1-expressing mice, and further shows that iron deprivation turns on σE expression of Salmonella. The virulence of σE -deficient Salmonella is completely attenuated in C3H/HeN mice while wild type Salmonella kills all mice. Addition of an iron-chelator DTPA(Diethylene triamine pentaacetic acid) to culture media induces σE expression of Salmonella, but iron supplementation abrogates this induction. These findings suggest that iron limitation in host macrophages can trigger σE -dependent virulence system of Salmonella that may include bacterial iron homeostasis.

To investigate antimicrobial susceptibility and relationships of the multidrug resistance and phage types of 49 Salmonella enterica serovar Typhimurium isolated from diarrhea patients in Seoul between 1999 and 2002, we analyed stranis by serotyping, antimicrobial susceptibility test and phage typing. Out of 2,705 samples examined for the causative agent from diarrhea patients, total of 512 isolates were confirmed to be genus Salmonella. Out of 512 isolates, 49 isolates(9.6%) were identified as S. Typhimurium. All of the S. Typhimurium strains represented 100% susceptibility to ceftriaxone, cefoxitin, amikacin and ciprofloxacin and were over 90% susceptibility to gentamicin, cephalothin and kanamycin, but were resistant to tetracycline(75.5%), streptomycin(59.2%), sulfonamides(55.1%), ticarcillin(36.7%), ampicillin( 28.6%), and chloramphenicol(20.4%). Out of 49 S. Typhimurium, only 3 isolates(20.4%) were resistant to one drug, 6 isolates(12.2%) to two drugs and 12 isolates(24.5%) to 3 drugs, 1 isolate(2.0%) to 4 drugs, 2 isolates (4.1%) to 5 drugs, and 6 isolates(12.2%) to 6 drugs and 5 isolates (10.2%) to 7 drugs. Out of 49 S. Typhimurium, 10 isolates(20.4%) were DT195, 5 isolates(10.2%) were DT193 and DT206, 4 isolates(8.2%) were DT104L, DT146, DT203 and RDNC, respectively. Phage types observed the resistant patterns of more than 6 drugs were DT104L, DT193, DT194, DT195 and DT67, but those of 3 drugs representing S-S3-TE type was DT195.