S100As are calcium-binding proteins with two EF-hand calcium-binding motifs. In several studies, S100A proteins are described to play important roles in pro-inflammatory responses including damage-associated molecular pattern (DAMP) signaling and in the establishment of pregnancy. However, the role of S100As have not been determined in the uterine endometrium during the estrous cycle in pigs. Thus, this study was performed to investigate expression and regulation of S100A8, S100A9, and S100A12 in the uterine endometrial tissues during the estrous cycle in pigs. Real-time RT-PCR analysis showed that S100A8, S100A9, and S100A12 mRNAs were expressed in the uterine endometrium during the estrous cycle with higher levels on days 15 and 18 of the estrous cycle than other days of cycle. To investigate the effects of steroid hormones, estradiol (E2) and progesterone (P4), on expression of S100A8, S100A9, and S100A12 mRNAs, endometrial tissue explants from immature pigs were treated with steroid hormones. Levels of S100A8, S100A9, and S100A12 were increased by the treatment of P4, and the increased levels of S100A8, S100A9, and S100A12 by P4 were not inhibited by the treatment of progesterone receptor antagonist, RU486. However, levels of S100A8, S100A9, and S100A12 were decreased by treatment of MEK inhibitor, U0126. These results exhibited that S100As were expressed in the uterine endometrium during the estrous cycle in a cyclic stage-specific manner, and their expression was affected by P4. These suggest that S100As may play an important role in endometrial function during the proestrous period of the estrous cycle in pigs. [Supported by the Next Generation Biogreen 21 program (#PJ01119103), Rural Development Administration, and by Korea Research Foundation (#2015R1D1A1A01058356)]

Progesterone regulates endometrial functions to support implantation, placentation, and fetal/placental development in the uterus. It is known that actions of progesterone are mediated by nuclear progesterone receptor (PGR), using the signaling pathway referred to the genomic pathway. However, all physiological progesterone actions cannot be explained by the genomic pathway via PGR, and it is understood that there are non-genomic actions of progesterone though membrane progesterone receptors, progesterone receptor membrane components (PGRMCs) and progestin and adipoQ receptors (PAQRs). The expression and localization of PGRMCs and PAQRs has been reported in female reproductive tissues of several species such as human, mouse and cattle. Previously, we have shown that PGRMCs and PAQRs are expressed in the porcine uterine endometrium during the estrous cycle and pregnancy. However, the regulatory mechanism for expression of PGRMCs and PAQRs in the uterine endometrium has not been studied in pigs. Thus, to understand the regulatory mechanism of PGRMC1, PGRMC2, PAQR5, PAQR6, PAQR7, PAQR8, and PAQR9 expression in the uterine endometrium during the estrous cycle and pregnancy in pigs, we determined the effect of steroid hormones estrogen and progesterone on expression of PGRMCs and PAQRs using the endometrial tissue explants for immature pigs. Levels of PGRMC1, PGRMC2, PAQR5, PAQR6, PAQR7, PAQR8, and PAQR9 mRNAs were increased by increasing doses of progesterone, but not by estradiol in the uterine endometrium. Blocking PGR by treatment of RU486, a progesterone receptor antagonist, increased levels of endometrial PGRMCs and PAQRs mRNA. These data showed that membrane progesterone receptors were induced by progesterone in the uterine endometrium, suggesting that these membrane progesterone receptors may play an important role in mediating progesterone actions in the uterine endometrium for regulation of the estrous cyclicity and pregnancy. [Supported by the Next Generation Biogreen 21 Program (# PJ01119103), Rural Development Administration, Republic of Korea]

The objective of this study was to determine the effect of nitrification inhibitor dicyandiamide (DCD) and urease inhibitor hydroquinone (HQ) on ammonia (NH3) and nitrous oxide (N2O) emission from pig slurry applied to Timothy (Phleum pretense L.) sward. The daily emission of ammonia (NH3) and nitrous oxide (N2O) was monitored for 9 days in three different treatments; 1) control (only pig slurry application), 2) DCD treatment (pig slurry + DCD), and 3) HQ treatment (pig slurry + HQ). Most NH3 emission occurred after 4~5 days in three treatments. Total NH3 emission, expressed as a cumulative amount throughout the measurement time, was 1.33 kg N ha 1 in the control. The DCD and HQ treatment decreased total NH3 emission by 16.3% and 25.1%, respectively, compared to the control. Total N2O emission in the control was 47.1 g N ha 1. The DCD and HQ treatment resulted in a reduction of 67.9% and 41.8% in total N2O emission, respectively, compared to the control. The present study clearly indicated that nitrification and urease inhibitor exhibited positive roles in reducing N losses through NH3 and N2O emission.

Cluster-of-differentiation antigen 9 (CD9) gene expressed in the male germ line stem cells is crucial for sperm–egg fusion, and was therefore selected as a candidate gene to investigate Duroc boar semen motility and kinematic characteristics. This study was performed to investigatetheir association with semen motility and kinematic characteristics. DNA samples from 96 Duroc pigs with records of sperm motility and kinematic characteristics [Total motile spermatozoa (MOT, 82.27±5.58), Curvilinear velocity(VCL, 68.37±14.58), Straight-line velocity(VSL, 29.06±6.58), the ratio between VSL and VCL(LIN, 47.36±8.42), Amplitude of Lateral Head displacement(ALH, 2.88±0.70)] were used in present study. A single nucleotide polymorphism (g.358A>T) in intron 6 was associated with MOT, VCL, VAP and ALH in Duroc population (p<0.05). Therefore, we suggest that the porcine CD9 may be used as a molecular marker for Duroc boar semen quality, although its functional effect was not clear yet. These results will improve the understanding of the functions of the CD9 in spermatogenesis within the reproductive tracts, and will shed light on CD9 as a candidate gene in the selection of good sperm quality boars.

Carcasses of pigs were trench buried using either general soil or mature compost as a cover material and the malodorous substances discharged were observed about a year. With the soil burial method, the speed of decay was shown to be dominantly affected by the ambient air temperature. However the compost burial method’s decaying process took place quickly, even ambient air temperature was dropped; it holds the temperature of 40oC or higher. With the compost burial method, there was a period where, the temperature inside the pig carcasses and the temperature of cover-material layer were strongly reversed. From this discovery, level of decay process could be speculated. With the soil burial method there was a trend when malodorous substances concentration was high, the level of concentration in the cover soil was also tends to be high. However, the compost burial method had different result. When malodorous substances concentration was high the level of concentration in the compost cover layer was observed to be lower. This indicates compost burial method shown to intercept and absorb malodorous substances. Furthermore, the compost burial method appears to be able to contribute to deactivate the pathogens by quickly decompose the carcasses at a high temperature.

Odor in pig manure affects the distribution of the manure over grass and crop fields as fertilizer. The objective of this study was to investigate the effect of different types of microbes (Saccharomyces cerevisiae, Bacillus subtilis and Rodobacter capsulata) and incubation temperatures (20℃ and 35℃) on the levels of odorous compounds in pig manure. Pig manure was incubated with 0.03% microbes (v/v) at temperatures of 20℃ or 35℃. At incubation temperature of 20℃, the addition of Rodobacter capsulata significantly (p<0.05) decreased the levels of indoles and volatile fatty acid (VFA). At incubation temperature of 35℃, the addition of any microbes of the three used in this study did not significantly (p>0.05) affect the levels of odorous compounds. When incubation temperature was increased from 20℃ to 35℃, levels of odorous compounds were significantly (p<0.05) increased. Taken together, these results suggest that Rodobacter capsulata could be utilized to reduce odor from pig manure in the spring and fall when the average temperature is around 20℃. However, alternative odor-reducing technology is needed to be developed to apply onto pig manure during the hot summer season (35℃).

본 연구에서는 UTC 시스템을 대표적인 농업시설인 돈사에 적용하기에 앞서, UTC 제어 시스템 및 프 로그램 개발에 따른 돈사 내 적정 사육 환경 유지 및 난방에너지 저감을 위한 기초자료로 활용하고자, 2 동의 실험돈사를 제작, UTC 제어 시스템 적용에 따른 실험돈사 내부 온도 변화 및 에너지를 비교, 분석 하였다. 제어 시스템은 T1∼T4, 총 4점의 온도를 측정 후 프로그램 내 알고리즘에 의해 O1∼O5, 총 5개 의 출력 신호를 ON/OFF 방식으로 각각 제어하도록 구성하였다. 온도 설정은 실험돈사 내부 온도 28. 0℃, UTC 내부 온도 34.0℃로 설정하였고, 측정된 온도와 비교를 통해 출력 신호를 제어하였다. 3일 간, 제어 시스템을 가동한 돈사의 경우 최고 온도는 평균 31.8℃로 측정되었다. 같은 시간, 비교돈사의 최고 온도는 평균 36.6℃로 제어 시스템을 가동한 돈사의 내부 온도가 약 4.8℃ 낮은 것으로 나타났다. 또한 제어 프로그램의 가동에 따라 UTC 플레넘 최고 온도는 평균 50.5℃까지 상승한 것으로 나타났다.

We developed a polymerase chain reaction (PCR)-based molecular method for sexing and identification using sexual dimorphism between the Zinc Finger-X and -Y (ZFX-ZFY) gene and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) for mitochondrial DNA (mtDNA) cytochrome B (CYTB) gene in meat pieces and commercial sausages from animals of different origins. Sexual dimorphism based on the presence or absence of SINE-like sequence between ZFX and ZFY genes showed distinguishable band patterns between male and female DNA samples and were easily detected by PCR analyses. Male DNA had two PCR products appearing as distinct two bands (ZFX and ZFY), and female DNA had a single band (ZFX). Molecular identification was carried out using PCR-RFLP of CYTB gene, and showed clear species classification results. The results yielded identical information on the sexes and the species of the meat samples collected from providers without any records. The analyses for DNA isolated from commercial sausage showed that pig was the major source but several sausages originated from chicken and Atlantic cod. Applying this PCR-based molecular method was useful and yielded clear sex information and identified the species of various tissue samples originating from livestock.

In this study, to improve the in vitro development of various cells including cloned embryos, the effects that isoproterenol and melatonin have on in vitro development of porcine parthenogenetic oocytes were investigated. Parthenogenetic activation was induced with electrical stimulation, BSA and 6-DMAP treatment. 10-7 M of melatonin and isoproterenol (10-10, 10-12 and 10-14 M) were supplemented for in vitro maturation (IVM) and in vitro culture (IVC) medium, with different concentrations. When isoproterenol and melatonin were supplemented in IVM medium with different concentrations, there was no significant (P<0.05) difference of maturation rate in the treatment groups as well as in that of only melatonin. As isoproterenol and melatonin were supplemented in IVM medium with different concentrations, blastocyst rates of isoproterenol 10-12 M treatment group (37.1%) were significantly (P<0.05) higher than control group (26.0%). Isoproterenol and melatonin were supplemented in IVC medium with different concentrations, then the cleavage rate of 10-12 M isoproterenol treatment group (82.2%) was significantly (P<0.05) higher than the group that melatonin was only supplemented (70.9%). There was no difference of blastocyst rate between the treatment groups. When isoproterenol and melatonin were supplemented for IVM+IVC medium with different concentrations, the cleavage rate of 10-12 M isoproterenol treatment group (92.5%) was significantly (P<0.05) higher than the control group (82.8%) and the group that melatonin was only treated (81.6%). The blastocyst rate of 10-12 M as 45.6% was significantly (P<0.05) higher than control group (25.2%) and melatonin treatment group (31.2%). The cell number of blastocyst in 10-12 M isoproterenol treatment group 35.5±3.4 was significantly (P<0.05) highest. The results of this study showed that the development rate of IVC when both isoproterenol and melatonin were supplemented was higher than when melatonin was only supplemented. Therefore, it is concluded that isoproterenol is rather effective in the activation of melatonin. 10-7 M melatonin and 10-12 M isoproterenol were considered suitable concentration.

The principal hygienic problem caused by livestock industry is the odor exposed to farm workers. This study was performed to assess air cleaner efficiency for reducing odor through on-site evaluation. The concentration of ammonia and hydrogen sulfide, which are major odorous compounds generated from livestock building, were monitored by realtime direct recorder. The odor mixture was measured by air dilution method applying human noses of five panels. Their reduction efficiencies were represented by difference between initial concentration exhausted by non-treatment and concentration measured after treatment of respective control mechanism (water, germicide and plasma ion) of air cleaner. Mean levels of ammonia and hydrogen sulfide were 1.84 (SD:0.22) ppm and 76.83 (SD:1.37) ppb for non-treatment, 1.23 (SD:0.09) ppm and 59.07 (SD:2.68) ppb for wet scrubber (water), 1.08 (SD:0.03) ppm and 58.55 (SD:1.62) ppb for wet scrubber (germicide), and 0.96 (SD:0.03) ppm and 53.66 (SD:1.37) ppb for plasma ion, respectively. Mean dilution factors of odor mixture were 100 for non-treatment, 66.9 for wet scrubber (water), 144.2 for wet scrubber (germicide), and 66.94 for plasma ion, respectively. Based on the results obtained from on-site evaluation, ammonia and hydrogen sulfide showed the mean reduction efficiency of 40% and 25.7% compared with non-treatment process of air cleaner, respectively. In the case of odor mixture, the highest dilution factor was observed at wet scrubber (germicide) compared with other control mechanism of air cleaner.

Xenotransplantation of pig islet regarded as a good alternative to allotransplantation. However, cellular death mediated by hypoxia-reoxygenation injury after transplantation disturb success of this technique. In the present study, we produce transgenic pig expressing human heme oxygenase 1 (HO1) genes to overcome cellular death for improving efficiency of islet xenotransplantation. Particularly, Korean miniature pig breed, Micro-Pig, was used in the present study. Somatic cell nuclear transfer (SCNT) technique was used to produce the HO1 transgenic pig. Six alive transgenic piglets were produced and all the transgenic pigs were founded to have transgene in their genomic DNA and the gene was expressed in all tested organs. Also, in vitro cultured fibroblasts derived from the HO1 transgenic pig showed low reactive oxygen species level, improved cell viability and reduced apoptosis level

본 연구는 교잡돈의 출하일령은 약 200일 이고, 175두의 돼지를 도축하여 3개의 그룹(59 ~ 95kg, 96 ~ 110kg, 111 ~ 148kg)으로 나누어, 등심, 상완세갈래근, 대퇴두갈래근, 반막모양근의 육질 특성을 조사하였다. 콜라겐과 지방함량은 반막모양근, 대퇴두갈래근이 111 ~ 148kg 그룹에서 다름 그룹에 비 해 낮은 함량을 나타내었으며(p<0.05), 단백질함량은 반막모양근, 대퇴두갈래근과 상완세갈래근이 111 ~ 148kg 그룹에서 다른 그룹에 비해 높은 함량을 나타내었다(p<0.05). 등심과 반막모양근의 명도는 111 ~ 148kg 그룹에서 높게 나타내었으며(p<0.05), 적색도와 황색도는 유의적인 차이가 나타나지 않았 다(p>0.05). pH는 등심에서 체중이 증가함에 따라 낮은 값을 나타냈었다(p<0.05). 가열감량은 등심, 반 막모양근, 대퇴두갈래근, 상완세갈래근이 111 ~ 148kg 그룹에서 보다 59 ~ 95kg 그룹에서 낮게 나타 났으며(p<0.05), 보수력은 반막모양근과 대퇴두갈래근에서 체중이 증가할수록 높게 나타났다(p<0.05). 전단력은 등심과 상완세갈래근에서 체중이 증가할수록 낮게 나타났다(p<0.05). 등심의 지방산 분석 결 과는 96 ~ 110kg 그룹에서 oleic acid, MUFA, MUFA/SFA가 높았고(p<0.05), 111 ~ 148kg 그룹에서 trans-vaccenic acid와 SFA가 높았지만(p<0.05), UFA는 낮았다(p<0.05).등심의 관능평가는 연도와 다 즙성이 96 ~ 110kg 그룹에서 높은 점수를 받았다(p<0.05).

Diabetes mellitus, the most common metabolic disorder, is divided into two types: type 1 and type 2. The essential treatment of type 1 diabetes, caused by immune-mediated destruction of β-cells, is transplantation of the pancreas; however, this treatment is limited by issues such as the lack of donors for islet transplantation and immune rejection. As an alternative approach, stem cell therapy has been used as a new tool. The present study revealed that bone marrowderived mesenchymal stromal cells (BM-MSCs) could be transdifferentiated into pancreatic cells by the insertion of a key gene for embryonic development of the pancreas, the pancreatic and duodenal homeobox factor 1 (PDX1). To avoid immune rejection associated with xenotransplantation and to develop a new cell-based treatment, BM-MSCs from α-1,3-galactosyltransferase knockout (GalT KO) pigs were used as the source of the cells. Transfection of the EGFP-hPDX1 gene into GalT KO pig-derived BM-MSCs was performed by electroporation. Cells were evaluated for hPDX1 expression by immunofluorescence and RT-PCR. Transdifferentiation into pancreatic cells was confirmed by morphological transformation, immunofluorescence, and endogenous pPDX1 gene expression. At 3∼4 weeks after transduction, cell morphology changed from spindle-like shape to round shape, similar to that observed in cuboidal epithelium expressing EGFP. Results of RT-PCR confirmed the expression of both exogenous hPDX1 and endogenous pPDX1. Therefore, GalT KO pig-derived BM-MSCs transdifferentiated into pancreatic cells by transfection of hPDX1. The present results are indicative of the therapeutic potential of PDX1-expressing GalT KO pig-derived BM-MSCs in β-cell replacement. This potential needs to be explored further by using in vivo studies to confirm these findings.

Deposits discharged through the cleaning mainly were cement mortar, bitumen paintings and rust pieces, and fragments of perforation, stones and gravels. Deposits were more removed through swabbing pig cleaning rather than air scouring cleaning on the whole. However, air scouring cleaning were not influenced by the constraint conditions such as a change in the diameter or the presence of the valve in water mains compare to swabbing pig cleaning. So, it was thought that air scouring cleaning might be more favorable to water distribution network cleaning in the future. After the cleaning, water quality including residual chlorine and turbidity also was improved because of the removal of a significant amount of the deposits. Therefore, if the cleaning is continuously and regularly implemented in water mains, it is expected that it will help to recover the reliability and to preserve the health of water quality.

동물의 장기를 인간에게 이식하게 되면 초급성거부반응(Hyperacute rejection, HAR)이 일어난다. 초급성거부반응은 면역계의 구성요소 중 보체(complement)에 의해 일어나는 거부반응으로 돼지의 혈관세포 표면에 있는 Galα(1,3)Gal 당분자에 인간의 항체가 즉각 반응하기 때문에 일어나며, α1,3-galactosyltransferase(α1,3-GT) 유전자는 돼지 혈관세포 표면의 Galα(1,3)Gal 당분자 생성에 관여한다. 따라서 인간에게 돼지의 장기를 이식하기 위해서는 α1,3-galactosyltransferase 유전자를 제거하는 것이 필요한 것으로 알려져 있다. 본 연구실의 이전 연구에서, 시카고 미니돼지 귀체세포에서 상동 재조합(Homologous recombination)을 통해 α1,3-galactosyltransferase 유전자가 제거된 체세포를 개발한 바 있으며, 이 체세포를 통하여 α1,3-GT 유전자가 제거된 돼지도 생산된 바 있다. 본 연구에서는, human serum 처리 시 돼지 세포를 보호해 준다고 보고되고 있는 human complement regulator인 human Decay-accelerating factor(hDAF)와 human α1,2-fucosyltransferase(hHT)유전자를 α1,3-GT 유전자 위치에 gene targeting하여 동시에 hDAF와 hHT가 발현하는 체세포를 개발하였다. Knock-in vector는 hDAF와 hHT 두 유전자가 발현할 수 있도록 IRES로 연결하였으며, α1,3-GT 유전자의 start codon을 이용하여 발현할 수 있도록 구축하였다. 구축한 vector는 electroporation을 통해 미니돼지 체세포에 도입하였으며, PCR 결과, α1,3-GT 유전자 위치에서 상동 재조합이 일어났음을 확인하였다. Positivenegative 선별 방법을 통해 얻은 gene targeting 된 체세포는 RT-PCR에 의해 hDAF와 hHT 유전자의 발현이 확인되었으며, 대조군(NIH minipig)에 비해 α1,3-GT 유전자의 발현이 감소하였다. 또한 이들 세포에 100% human complement serum을 처리하였을 때 knock-in 세포가 대조군에 비해 30% 정도 더 높은 생존율을 보였다. 따라서 개발된 체세포는 이종간 장기이식을 위한 돼지 생산과 함께 이를 이용한 이종간의 장기 이식 시 초급성 거부반응을 억제하는 데 사용될 수 있을 것으로 생각된다.

Amphiregulin (AREG), a glycoprotein that is a member of the epidermal growth factor (EGF) family, is expressed by the porcine conceptus and endometrium. AREG genotypes were determined based on an SNP in the intron 3 of the gene. Contradictory effects of AREG genotypes on reproductive traits in different pig breeds were reported previously. G allele had undesirable effect on reproductive trait in Meishan breed, while it had favorable effects in Polish Landrace and Large White. We determined AREG genotypes of 179 pigs including the Duroc, Landrace, Yorkshire, Korean native pig (KNP), and Meishan breeds. Two new SNPs were identified near the previously reported SNP in the intron 3 of AREG. Frequencies of AREG alleles among the Duroc, Landrace, Yorkshire, and KNP sows were significantly different (p<0.001), indicating association between AREG genotypes and pig breeds. The first parity litter size was significantly affected by the breeds (p=0.014), but not by AREG genotypes (p=0.148). However, there were breed and AREG genotype associated trends in the first parity litter size. The first parity litter size appeared to be higher in Duroc and KNP sows with G allele, while it appeared to be lower in Landrace sows with G allele. Significant variability of AREG alleles among pig breeds, for the first time in Duroc and KNP sows, was identified. AREG genotypes may influence reproductive traits differentially for each breed and thus, AREG genotypes may need to be considered when sows are bred to increase litter size.

근래의 육종산업에 있어서 재래 혹은 토착품종 등 고유 가축유전자원의 효율적인 보존 및 관리는 중요한 관심사이다. 본 연구는 제주재래돼지와 외래돼지 품종들간의 유전적 다양성, 집단의 구성 및 근연관계를 구명하기 위하여 수행되었다. 제주재래돼지, Landrace, Yorkshire, Berkshire 등 4품종 총 200개체를 대상으로 30개 초위성체 마커를 대상으로 대립유전자를 분석한 결과, 전체 265개의 대립유전자가 관찰되었다. 대립유전자 수의 범위는 5개(SW168)에서 22개(S0005)였으며, 전체 좌위에 대한 평균 값은 8.83개로 산출되었다. 30개 마커에 대한 기대 및 관측 이형접합도의 평균치는 0.731 및 0.615, 다형정보지수의 평균값은 0.697로 확인되었다. 제주재래돼지의 유전적 다양성은 외래 품종에 비하여 낮게 나타났다. 계통유전학적 유연관계, 요인대응분석 및 집단구조 분석 결과, 제주재래돼지는 서양유래의 상용품종과 유전적으로 명확히 구분되었다. 따라서 본 연구 결과는 제주재래돼지의 유전적 고유성 및 유전자원으로써 가치판단을 위한 과학적 근거가 될 것으로 사료된다.

본 연구는 무창돈사에서 폐기되는 에너지를 재이용하기 위해 열회수형 환기장치의 효율 및 돈사 내부 환경에 미치는 영향을 분석하여, 실제돈사에 적용 가능성을 구명하고자 한다. 이를 위해 열회수형 환기장치의 적용에 따른 내부 온도, 상대습도, CO2 및 부유미생물을 측정, 분석하여 돈사 내 열회수형 환기장치 적용 시 연료비 절감 및 돼지 사육 환경의 최적 조건 산출을 위한 기초자료로 활용하고자 한다. 실험은 돈사 내 환기팬 및 열회수형 환기장치를 설치하여 세 가지 다른 조건에서 실험을 행하였다. 첫 번째, 환기팬 및 열회수형 환기장치를 가동하지 않은 상황(Test-1), 두 번째, 환기팬만 가동한 상황(Test-2), 그리고 마지막으로 열회수형 환기장치만 가동한 상황(Test-3), 세 가지 상황으로 구분하여 실시하였다. 열회수형 환기장치를 가동하였을 경우, 내부 상, 중, 하층부의 온도가 가장 균일한 것으로 나타났고, 상대습도 또한 일정하게 유지되는 것으로 나타났다. CO2 농도의 경우, 환기팬을 가동한 상황(Test-2)보다 다소 높았지만 시간이 지남에 따라 농도가 낮아지는 것으로 보아, 환기에 효과가 있다고 판단된다. 부유미생물의 경우는 밀폐된 상황(Test-1) 보다 오히려 높게 측정되었는데, 이는 열회수형 환기장치의 내부 교차오염 등에 의한 것으로 판단된다.