• International Journal of Oral Biology
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• 제43권4호
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• pp.171-175
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• 2018

Quorum sensing (QS) is a cell density-dependent communication mechanism between bacteria through small signaling molecules. When the number of QS signaling molecules reaches a threshold, they are transported back into the cells or recognized by membrane-bound receptors, triggering gene expression which affects various phenotypes including bioluminescence, virulence, adhesion, and biofilm formation. These phenotypes are beneficial for bacterial survival in harsh environments. This review summarizes the application of QS inhibitors for control of biofilm formation and virulence expression of periodontal pathogens.

• 한국응용곤충학회지
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• 제18권2호
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• pp.77-84
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• 1979

벼 흰빛잎마름병균의 10균주(I군 3균주, II군 4균주, III군 3균주)를 저항성이 서로 다른 벼품종 '밀양 23호'(김남풍군), '유신'(황옥군), '통일'(Rantaiemas군)의 유묘기와 분얼초기, 최고분얼기, 지엽기에 각각 접종하였다. 그 결과 1) 병원성 발현의 양상이 균주 간 매우 다양하였다. 2) 특히 II군의 균주들은 같은 군균내에서도 변이가 매우 큰 것으로 나타났다. II군은 더 많은 균형으로 세분될 수 있었다. 3) 생육시기 별로 병원성 발현 양상이 달랐으며, 대체로 지엽기 이후 높은 발병을 나타내었다. II군중 G 7716균주는 출수이후에야 비로소 '유신'품종에 발병을 일으킬 수 있었다. 4) 통계분산분석(ANOVA) 결과, 각각 다른 균형의 균주, 품종, 생육시기가 발병정도의 분산에 주요인으로 작용하였고, 균주와 품종간의 상호작용(interaction)에 유의성이 있었으나 다른 요인간에는 없었다.

• 한국환경농학회지
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• 제13권3호
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• pp.288-300
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• 1994

재배지에서 경작된 아스파라거스의 이병조직으로 부터 Fusarium oxysporum이 가장 많이 분리되었고 F. moniliforme와 F. solani가 그다음 순으로 분리되었다. 유묘와 조직배양을 통해 얻은 개체를 이용한 병원성 검정 결과, F. oxysporum과 F. moniliforme는 병원성이 강한 것으로 밝혀졌고, F. solani와 잠두의 배축으로 부터 분리한 비 병원성 F. oxysporum (AVFO)은 병원성이 약하거나 없는 것으로 밝혀졌다. 또한, F. moniliforme가 F. oxysporum 보다 병원성이 더 강한 것으로 밝혀졌고, F. moniliforme가 F. oxysporum보다 더욱 일관된 병원성을 지니고 있음이 밝혀졌다. 비병원성 Fusarium균을 이용한 생물적 방제 실험 결과, 병원성 균주를 접종하기 5-7일전에 비병원성 균주들을 접종하여 방제효과를 거둘 수 있었다. 비병원성 F. oxysporum (AVFO)은 F. oxysporum에 대해서 보다 F. moniliforme에 대해 더욱 효과적인 방제효과를 나타냈고, F. solani는 F. moniliforme에 대해서 보다 F. oxysporum의 방제에 더욱 효과적이었다.

• 한국식물병리학회지
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• 제2권3호
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• pp.150-157
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• 1986

벼흰빛잎마름병균의 균주를 효과적으로 보관하기 위하여 동결건조, 동결, 액체파라핀, 살균수, 계대배양등의 방법을 사용하여 생존율과 병원성유지 정도를 4개월에 걸쳐 조사하였다. 실험결과 $10\%$ sucrose와 $1\%$ gelatin을 함유한 현탁액에서 가장 높은 생존율을 나타냈으며 병원성은 $2\%$ dextrin, $0.5\%$ ascorbic acid, $0.5\%$ ammonium chloride, $0.5\%$ tguiyrea, $0.85\%$ NaCl 등을 함유한 현탁액에서 가장 잘 유지되었다. 계대배양한 균주는 병원성이 약화되었다. 거친집락형은 동결건조 또는 동결과정에서 모두 나타났으며 이는 정상집락에 반해 주름진 집락모습과 사상형이었다. 거친집락형은 병원성이 매우 약하였으며, 탄소원 요구도가 다양하였으므로 동결건조 과정에서 대사작용의 저해가 일어난 것으로 추측되었다.

• The Plant Pathology Journal
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• 제36권5호
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• pp.450-458
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• 2020

Pepper and tomato plants infected with two Clavibacter species, C. capsici and C. michiganensis have shown different patterns of disease development depending on their virulence. Here, we investigated how pepper and tomato plants respond to infection by the high-virulent or low-virulent Clavibacter strains. For this, we chose two strains of each Clavibacter species to show different virulence level in the host plants. Although low-virulent strains showed less disease symptoms, they grew almost the same level as the high-virulent strains in both plants. To further examine the response of host plants to Clavibacter infection, we analyzed the expression patterns of plant defense-related genes in the leaves inoculated with different strains of C. capsici and C. michiganensis. Pepper plants infected with high-virulent C. capsici strain highly induced the expression of CaPR1, CaDEF, CaPR4b, CaPR10, and CaLOX1 at 5 days after inoculation (dai), but their expression was much less in low-virulent Clavibacter infection. Expression of CaSAR8.2 was induced at 2 dai, regardless of virulence level. Expression of GluA, Pin2, and PR2 in tomato plants infected with high-virulent C. michiganensis were much higher at 5 dai, compared with mock or low-virulent strain. Expression of PR1a, Osmotin-like, Chitinase, and Chitinase class 2 was increased, regardless of virulence level. Expression of LoxA gene was not affected by Clavibacter inoculation. These results suggested that Clavibacter infection promotes induction of certain defense-related genes in host plants and that differential expression of those genes by low-virulent Clavibacter infection might be affected by their endophytic lifestyle in plants.

• Journal of Microbiology and Biotechnology
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• 제19권8호
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• pp.765-773
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• 2009

Edwardsiella tarda is a pathogen with a broad host range that includes human and animals. The E. tarda hemolysin (Eth) system, which comprises EthA and EthB, is a noted virulence element that is widely distributed in pathogenic isolates of E. tarda. Previous study has shown that the expression of ethB is regulated by iron, which suggests the possibility that the ferric uptake regulator (Fur) is involved in the regulation of ethB. The work presented in this report supports the previous findings and demonstrates that ethB expression was decreased under conditions when the E. tarda Fur ($Fur_{Et}$) was overproduced, and enhanced when $Fur_{Et}$ was inactivated. We also identified a second ethB regulator, EthR, which is a transcription regulator of the GntR family. EthR represses ethB expression by direct interaction with the ethB promoter region. In addition to ethB, EthR also modulates, but positively, luxS expression and AI-2 production by binding to the luxS promoter region. The expression of ethR itself is subject to negative autoregulation; interference with this regulation by overexpressing ethR during the process of infection caused (i) drastic changes in ethB and luxS expressions, (ii) vitiation in the tissue dissemination and survival ability of the bacterium, and (iii) significant attenuation of the overall bacterial virulence. These results not only provide new insights into the regulation mechanisms of the Eth hemolysin and LuxS/AI-2 quorum sensing systems but also highlight the importance of these systems in bacterial virulence.

• Journal of Microbiology and Biotechnology
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• 제13권1호
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• pp.149-154
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• 2003

Numerous virulence factors such as O antigen have been proposed to account for the fulminating and destructive nature of V. vulnificus infections. To better characterize the role of O antigen, a pmm gene encoding a phosphomannomutase was identified and cloned from V. vulnificus. The deduced amino acid sequence of the pmm was 42 to 71% similar to that reported from other Enterobacteriaceae. Functions of the pmm gene in virulence were assessed by the construction of an isogenic mutant, whose pmm gene was inactivated by allelic exchanges, and by evaluating its phenotype changes in vitro and in mice. The disruption of pmm resulted in a loss of more than 90% of phosphomannomutase, and reintroduction of recombinant pmm could complement the decrease of phosphomannomutase activity, indicating that the pmm gene encodes the phosphomannomutase of V. vulnificus. There was no difference in the $LD_50S$ of the wild-type and the pmm mutant in mice, but the $LD_50S$ observed by the mutant complemented with recombinant pmm were lower. Therefore, it appears that PMM is less important in the pathogenesis of V. vulnificus than would have been predicted by examining the effects of injecting purified LPS into animals, but it is not completely dispensable for virulence in mice.

• Journal of Microbiology and Biotechnology
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• 제25권9호
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• pp.1460-1466
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• 2015

In this study, the prevalence of Shiga toxin-producing Escherichia coli (STEC) was investigated among raw meat or meat products from slaughterhouses and retail markets in South Korea, and their potential for antibiotic resistance and virulence was further analyzed. A total of 912 raw meats, including beef, pork, and chicken, were collected from 2008 to 2009. E. coli strains were frequently isolated in chicken meats (176/233, 75.9%), beef (102/217, 42.3%), and pork (109/235, 39.2%). Putative STEC isolates were further categorized, based on the presence or absence of the Shiga toxin (stx) genes, followed by standard O-serotyping. Polymerase chain reaction assays were used to detect the previously defined virulence genes in STEC, including Shiga toxins 1 and Shiga toxin 2 (stx1 and 2), enterohemolysin (ehxA), intimin (eaeA), STEC autoagglutination adhesion (saa), and subtilase cytotoxin (subAB). All carried both stx1 and eae genes, but none of them had the stx2, saa, or subAB genes. Six (50.0%) STEC isolates possessed the ehxA gene, which is known to be encoded by the 60-megadalton virulence plasmid. Our antibiogram profiling demonstrated that some STEC strains, particularly pork and chicken isolates, displayed a multiple drug-resistance phenotype. RPLA analysis revealed that all the stx1-positive STEC isolates produced Stx1 only at the undetectable level. Altogether, these results imply that the locus of enterocyte and effacement (LEE)-positive strains STEC are predominant among raw meats or meat products from slaughterhouses or retail markets in Korea.

• Journal of Microbiology and Biotechnology
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• 제25권6호
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• pp.872-879
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• 2015

Many strains of Bacillus cereus cause gastrointestinal diseases, and the closely related insect pathogen Bacillus thuringiensis has also been involved in outbreaks of diarrhea. The diarrheal diseases are attributed to enterotoxins. Sixteen reference strains of B. cereus and nine commercial and 12 reference strains of B. thuringiensis were screened by PCR for the presence of 10 enterotoxigenic genes (hblA, hblC, hblD, nheA, nheB, nheC, cytK, bceT, entFM, and entS), one emetogenic gene (ces), seven hemolytic genes (hlyA, hlyII, hlyIII, plcA, cerA, cerB, and cerO), and a pleiotropic transcriptional activator gene (plcR). These genes encode various enterotoxins and other virulence factors thought to play a role in infections of mammals. Amplicons were successfully generated from the strains of B. cereus and B. thuringiensis for each of these sequences, except the ces gene. Intriguingly, the majority of these B. cereus enterotoxin genes and other virulence factor genes appeared to be widespread among B. thuringiensis strains as well as B. cereus strains.

• 한국수산과학회지
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• 제47권3호
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• pp.220-226
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• 2014

Sixty-seven Vibrio parahaemolyticus isolates from surface seawater from the Wando area, on the southern coast of Korea, were analyzed for their susceptibility to 15 different antimicrobials and the presence of virulence genes. According to the disk diffusion susceptibility test, all of the strains studied were resistant to ampicillin and oxacillin, while decreasing percentages were resistant to vancomycin (64.2%), streptomycin (56.7%), amikacin (31.3%), kanamycin (22.3%), cephalothin (20.9%), erythromycin (10.4%), ciprofloxacin (4.5%), and tetracycline (3.0%). All of the strains were susceptible to five antimicrobials: chloramphenicol, gentamycin, nalidixic acid, sulfamethoxazole/trimethoprim, and trimethoprim. Fifty-nine isolates (88.1%) were resistant to three or more classes of antimicrobial and defined as multidrug resistant, and two strains were resistant to seven antimicrobial agents. The minimum inhibitory concentration (MIC) of the 67 V. parahaemolyticus isolates to ampicillin and oxacillin ranged from 512-2,048 and $64-512{\mu}g/mL$, respectively. All 67 isolates were also examined for the presence of the tdh and trh virulence genes using the polymerase chain reaction (PCR). However, no isolates possessed either tdh or trh. The VPA0477 (${\beta}$-lactamase) gene, present in all of the tested strains, was validated as a new specific marker gene in PCR assays for the accurate detection and identification of V. parahaemolyticus.