• Journal of Microbiology and Biotechnology
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• v.25 no.7
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• pp.1154-1162
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• 2015

The emergence of carbapenem resistance among Pseudomonas aeruginosa is an increasing problem in many parts of the world. In particular, metallo-$\beta$-lactamases (MBLs) and AmpC $\beta$lactamases are responsible for high-level resistance to carbapenem and cephalosporin. We studied the diversity and frequency of $\beta$-lactamases and characterized chromosomal AmpC $\beta$lactamase from carbapenem-resistant P. aeruginosa isolates. Sixty-one carbapenem-resistant P. aeruginosa isolates were collected from patients in a tertiary hospital in Daejeon, Korea, from January 2011 to June 2014. Minimum inhibitory concentrations (MICs) of four antimicrobial agents were determined using the agar-dilution method. Polymerase chain reaction and sequencing were used to identify the various $\beta$-lactamase genes, class 1 integrons, and chromosomally encoded and plasmid-mediated ampC genes. In addition, the epidemiological relationship was investigated by multilocus sequence typing. Among 61 carbapenem-resistant P. aeruginosa isolates, 25 isolates (41.0%) were MBL producers. Additionally, 30 isolates producing PDC (Pseudomonas-derived cephalosporinase)-2 were highly resistant to ceftazidime (MIC₅₀ = $256{\mu}g/ml$) and cefepime (MIC₅₀ = $256{\mu}g/ml$). Of all the PDC variants, 25 isolates harboring MBL genes showed high levels of cephalosporin and carbapenem resistance, whereas 36 isolates that did not harbor MBL genes revealed relatively low-level resistance (ceftazidime, p < 0.001; cefepime, p < 0.001; imipenem, p = 0.003; meropenem, p < 0.001). The coexistence of MBLs and AmpC $\beta$-lactamases suggests that these may be important contributing factors for cephalosporin and carbapenem resistance. Therefore, efficient detection and intervention to control drug resistance are necessary to prevent the emergence of P. aeruginosa possessing this combination of $\beta$-lactamases.

• Korean Journal of Veterinary Research
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• v.26 no.1
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• pp.79-85
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• 1986

This paper deals with the isolation of Salmonella on 3 herds during the period from May 1984 to May 1985. Isolated Salmonella were examined for serotypes, adhesive fimbriae, antibiotic susceptibility and detection of R plasmid. The results were as follows; Of total 1505 cattle, 24 Salmonella were isolated from 18 cattle (1.2%) and their serotypes were S. enteritidis (9 strains), S. derby(4 strains), S. infantis (1 strain), $C_1$ group(8 strains), $C_2$ group(1 strain) and untypable(1 strain). Twelve strains of Salmonella were isolated from 227 cattle with diarrhea and their serotypes were S. enteritidis(4 strains), S. derby(3 strains), S. infantis(1 strain), $C_1$ group(3 strains) and untypable(1 strain). The isolation rate of Salmonella in cattle varied from 1.6 to 0.9% in 3 herds, it was higher in summer and autumn and lower with the age. Of total 24 strains, 23 were adhesive type 1 fimbriae. Antibiotic susceptibility test of Salmonella isolated was performed by the agar dilution method, using 9 antibiotics as follows: ampicillin(Am), chloramphenicol(Cm), gentamicin(Gm), kanamycin(Km), nalidixic acid(Na), rifampicin(Rf), streptomycin(Sm), sulfadimethoxine(Su) and tetracycline(Tc). All the strains tested were susceptible to Am, Cm, Gm, Km, Na, Rf and Tc. Of total 24 strains, 23(95.8%) were resistant to Su and 14(58.3%) to Sm. Of the 23 resistant Salmonella strains, all the strains were found to carry R plasmid. Among them, two strains which had the R plasmid conferring SmSu resistance was transferable at $25^{\circ}C$ only.

• Korean Journal of Veterinary Research
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• v.48 no.3
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• pp.295-303
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• 2008

One hundred and sixty nine Escherichia (E.) coli strains isolated from fecal samples of aquatic birds in Geumho river basin and Dalseong park were tested by agar dilution method to determine their susceptibility patterns to 14 antimicrobial agents. The distribution of tetracycline resistance determinants (tetA, tetB, tetC, tetD and tetE) were also examined by PCR in 76 tetracycline-resistant ($TC^r$) E. coli isolates. The high resistance was observed in tetracycline, cephalothin and ampicillin (45.0~36.7%). Resistance of E. coli isolates derived from Dalseong park to tetracycline, cephalothin, ampicillin and streptomycin (65.7~44.8%) were significantly higher than those isolated from Geumho river basin (31.4~14.7%). About seventy percent (70.4%) of the strains isolated were resistant to one or more drugs tested. Thirty (39.5%) of 76 $TC^r$ E. coli isolates which were resistant to one or more drugs transferred all or a part of their resistance patterns to the recipient strain of E.coli J53 by conjugation. All of $TC^r$ E. coli isolates contained at least one or more of 5 tet genes examined. The most common genes found in these isolates were tetA (60.6%) and followed by tetB (7.9%) and tetC (1.3%). However, tetD and tetE were not found in any of the isolates tested. Twenty one (27.6%) of $TC^r$ E. coli isolates had two determinants, tetA/tetB (20 strains), tetA/tetC (1 strain). And two strains (2.6%) contained three determinants (tetA/tetB/tetC).

• Korean Journal of Agricultural Science
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• v.41 no.2
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• pp.135-139
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• 2014

Pathogenic E. coli associated post-weaning diarrhea (PWD) and edema disease are common diseases in commercially-housed weanling pigs. An enterotoxigenic E. coli (ETEC) oral challenge model has been used to mimic the physiological responses observed in commercial conditions. However, an oral challenge procedure has two major limitations: (1) the ETEC cell density is unknown at the point of oral inoculation, and (2) blending ETEC with traditional TSB (trypticase soy broth) is not palatable and hence decreases acceptability by piglets. Therefore, the purposes of this study were to (1) establish a regression equation that can be used for estimation of ETEC concentration in dilution media using the spectrophotometric measurement of cell density; and (2) examine survival of ETEC after blending either with TSB, sweetener or dextrose. A strain of ETEC (serogroup beta-hemolytic E. coli O149; K91; F4; toxins LT, STa, STb) was grown in TSB for 3.5 hours, centrifuged, the supernatant was discarded, and the ETEC pellet was then blended either with TSB (100 mL), sweetener (60 mL TSB + 40 mL fruit flavored concentrate), or dextrose (50 mL TSB + 50 mL dextrose; 0.5g/mL dextrose). Cell density was measured using the colorimetric method and also plated on a 5% sheep blood agar for counting of ETEC colony forming units at 0, 5, 35, 65 and 125 min after blending. The optical density at 600 nm explained 83% of ETEC colony forming units, indicating that the established linear equation (y= 6E+08x - 4E+07, P<0.004) can be used for robust quantification of ETEC cell density in TSB, sweetener and dextrose media. When ETEC was blended with sweetener and dextrose, survival of ETEC was decreased by 45% and 72% within 5 min post-blending. Therefore, further research is required to find out the suitable medium that has potential to improve palatability without compromising survival of ETEC.

• Korean Journal of Pharmacognosy
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• v.45 no.2
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• pp.168-173
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• 2014

The aim of this study was to evaluate the anti-helicobacter activity of the ethanol extract of Sohamhyoongtang (Coptidis Rhizoma, Pinelliae Tuber and Trichosanthis Semen) and Coptidis Rhizoma total alkaloids, which is one of the components of Sohamhyoongtang. Crude ethanol extract of Sohamhyoongtang (ESHHT) and Coptidis Rhizoma total alkaloids (CRTA) were used for this experiment. Five different types of H. pylori (including H. pylori 26695) were used as test strain. To determine anti-helicobacter activity, minimum inhibitory concentration (MIC) was determined by agar dilution method. The effect of ESHHT and CRTA on the gene expression of H. pylori was investigated by quantitative realtime-PCR (qRT-PCR). MICs of ESHHT against five H. pylori strains were $250{\sim}500{\mu}g/ml$ and MICs of CRTA against five H. pylori strains were $50{\sim}200{\mu}g/ml$. Four representative virulence genes of H. pylori, cagA, ureA, ureB and ureI were tested as target genes for qRT-PCR. According to the qRT-PCR results, both ESHHT and CRTA markedly repressed the expression of cagA gene of H. pylori 26695 (6.91 and 20 folds respecively). These results showed that the ESHHT and CRTA demonstrated antihelicobacter properties, suggesting their potential use in gastritis or duodenal ulcer.

• Korean Journal of Veterinary Research
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• v.19 no.1
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• pp.75-83
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• 1979

The sensitivities of 270 pathogens (124 Streptococci, 118 Staphylococci, 10 Corynebacterium pyogenes and 18 Escherichia coli) isolated from clinical or subclinical cases of bovine mastitis during lactation to 11 antibiotics were determined by the agar plate dilution method. All cultures of Streptococci were inhibited at $1.56{\mu}g/ml$ of ampicillin and 1.56 units/ml of penicillin G. Most of the cultures were inhibited at $3.125{\mu}g/ml$ of leukomycin, but were resistant to kanamycin, streptomycin, chloramphenicol, erythromycin and colistin at concentration of $12.5{\mu}g/ml$. More than 93% of the Staphlococcal cultures were sensitive to kanamycin, leukomycin, ampicillin, tetracycline, ledermycin and minocycline at concentrations of $12.5{\mu}g/ml$ or less, and sensitive to penicillin at concentration of 3.125 units/ml, but for more than 71% of the cultures to chloramphenicol, erythromycin and colistin the concentrations required to inhibit growth were 100 ${\mu}g/ml$ or higher. All 10 cultures of Corynebacterium pyogenes were inhibited by leucomycin, ampicillin and minocycline at concentration of $1.56{\mu}g/ml$ and by penicillin G at concentration of 0.78 units/ml, but all the cultures required at least $400{\mu}g/ml$ or higher of streptomycin, erythromycin and colistin for inhibition. More than 83% of E. coli cultures were sensitive to erythromycin and minocycline at concentration of $12.5{\mu}g/ml$, but resistant to leucomycin and chloramphenicol at concentration of $100{\mu}g/ml$.

• The Korean Journal of Food And Nutrition
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• v.27 no.2
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• pp.213-218
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• 2014

The enterotoxin production and antimicrobial susceptibility on hemolytic strains from stools of diarrheal pigs was investigated in this study. Through morphological observation, gyrB nucleotide sequence, and API kit analysis, the selected potential pathogenic strain BY06 was identified as Bacillus cereus. Because the characteristic of enterotoxin symptoms were widely caused by Bacillus cereus strains, a PCR test was carried out in order to check the enterotoxin genes (hblA) in this strain. According to the results, this strain was an enterotoxin positive strain containing the hblA gene. The minimum inhibitory concentrations of 10 different antimicrobial agents were screened by the agar dilution test, indicating that this strain was resistant to penicillin G and intermediate to erythromycin; however, it susceptible to cephalothin, vancomycin, clindamycin, fusidic acid, gentamicin, ciprofloxacin, tetracycline and rifampin. These results suggest that the B. cereus BY06 isolated from pig feces has a potential risk of producing enterotoxin and is resistant to penicillin G, but susceptible to various antimicrobial agents.

• Journal of the korean academy of Pediatric Dentistry
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• v.11 no.1
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• pp.75-89
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• 1984

A total of 141 strains of Streptococcus mutans were isolated from dental plaques of 153 subjects. Eighty-two children with caries-experience, 18 caries-free children and their mothers were participated. All isolates were examined for their serotypes by immunodiffusion method with 7 reference sera and their antibiotic susceptibilities to 7 antibiotics by agar dilution method using 7 kinds of antibiotics, and were compared their results by caries experience (DMFT ratio) and by intrafamilial levels. 1. Isolation rate of Streptococcus mutans were greater in samples of carious teeth than those of sound teeth, and in mothers than in children. 2. Multiple serotypes of Streptococcus mutans were occasionally found in a single samples. 3. Of the total 141 isolates (83 isolates from children, and 58 from their mothers), type c isolates were most prevalent (63.8%). Type d,e and f were found, comprizing 14.9%, 10.6% and 6.4% respectively. Serotype g, a and untypable strain were also found but far lower frequencies (2.8-0.7%), and type b was detected. 4. These results suggest that there are no significant correlation among the distribution of serotypes, antibiotic susceptibilities, caries experience and intrafamilial relationships. 5. Most of isolates were susceptible to chloramphenicol (100%), penicillin (95.7%), ampicillin (94.3%), and gentamicin (92.2%), but about one-third isolates were resistant to cephaloridine (27%), streptomycin (33.3%) and kanamycin (47.6%), resulting that 91 strains (64.5%) among 141 isolates were resistant to one or more drugs used. 6. Of the 91 resistant strains, 20 different resistant patterns were observed, and the most frequently encountered patterns were KM, SM and CE.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.42 no.4
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• pp.322-328
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• 2009

Three-hundred and sixteen Escherichia coli strains from seawater, and a variety of farmed fishes, including oliver flounder (Paralichthys olivaceus), black rock fish (Sebastes schlegeli), red sea bream (Pagrus major) and sea bass (Lateolabrax japonicus) between May to October in 2004, were tested by agar dilution method to determine their susceptibility patterns to 17 antimicrobial agents. Overall, 92.1% of Escherichia coli isolates from samples showed antimicrobial resistance to at least one antimicrobial agent and the multiple resistance was seen in 173 isolates (54.7%). The resistance of E. coli isolates to tetracycline (74.1%) was highest, followed by cephalothin (69.9%), doxycycline (66.5%), streptomycin (47.2%), ampicillin (46.2%), cefazolin (31.6%), enrofloxacin (31.0%). norfloxacin (28.2%). The most frequent resistance pattern was TE-D-CF-CIP-ENO-NOR-AM-S-C-SXT-AmC-CZ (14.7%), followed by CF (6.2%), TE (5.1%), TE-CF (4.5%) in 177 isolates from fishes and TE-D-CF (7.2%) followed by TE-D-CF-S (5.8%), CF and TE-D-S (3.6%) in 139 isolates from seawater.

• Korean Journal of Microbiology
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• v.38 no.4
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• pp.306-311
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• 2002

PCR of the mecA gene for the rapid detection of methicillin-resistant staphylococci was perfomed and compared with the antibiotic sensitivity test. A total of 43 strains of staphylococi from clinical specimens were used in this study. An antibiotic sensitivity test by the agar dilution method of NCCLS (The National Commitee for Clinical Laboratory Standard) was performed for the strains. Among them, 39 isolates were methicillin-resistant (MRS), and 4 isolates were methicillin-susceptible (MSS). With the exception for one strain (Staphylococcus cohnii, HRC2-4), all MRS strains amplified the expected 533 bp fragments of the mecA gene by PCR, However, one strain (Staphylococcus aureus, HSA1-10) that was classified as a sensitive strain by the antibiotic sensitivity test was mecA positive by PCR. All 35 methicillin-resistant Staphylococcus aureus (MRSA) strains were mecA positive, but overall, concordance between the results of the mecA PCR and antibiotic sensitivity test was 95.6%.