Dissemination of Plasmid-mediated qnr, aac(6')-Ib-cr, and qepA Genes Among 16S rRNA Methylase Producing Enterobacteriaceae in Korea

Plasmid-mediated quinolone resistance (PMQR) genes: qnr, aac(6')-Ib-cr, and qepA were investigated among 153 armA and 51 rmtB-positive transconjugants and their 204 clinical isolates of Enterobacteriaceae. Overall, qnrB4 and aac(6')-Ib-cr genes were identified in 52.3% (63 K. pneumoniae, 10 E. coli, 4 E. cloacae, and 3 E. aerogenes) and 24.8% (16 K. pneumoniae, 8 E. coli, 6 S. marcescens, 4 E. cloacae, 3 C. freundii and 1 K. oxytoca) of 153 armA-positive isolates, respectively. Four isolates of K. pneumoniae and two isolates of E. coli positive for armA co-harbored both qnrB4 and aac(6')-Ib-cr. The qepA gene was detected in 11.8% (5 E. coli and 1 K. pneumoniae) of 51 rmtB-positive clinical isolates and their transconjugants. Southern hybridization confirmed the co-localization of qepA and rmtB on a large conjugative plasmid of size between 90 to 170 kb. Inc replicon typing showed that qnrB4/6, aac(6')-Ib-cr, and qepA genes were principally disseminated by IncFIIAs, IncL/M, and IncF plasmids, respectively. This study constitutes the first report of the three known PMQR genes among the 16S rRNA methylase producing Enterobacteriaceae isolates of human origin from Korea.

Molecular characterization of bacterial endosymbionts of Acanthamoeba isolates from infected corneas of Korean patients

The endosymbionts of 4 strains of Acanthamoeba (KA/E9, KA/E21, KA/E22, and KA/E23) isolated from the infected corneas of Korean patients were characterized via orcein stain, transmission electron microscopic examination, and 16S rDNA sequence analysis. Double membrane-bound, rod-shaped endosymbionts were distributed randomly throughout both the trophozoites and cysts of each of Acanthamoeba isolates. The endosymbionts of KA/E9, KA/E22, and KA/E23 were surrounded by electron-translucent areas. No lacunae-like structures were observed in the endosymbionts of KA/E21, the bacterial cell walls of which were studded with host ribosomes. Comparative analyses of the 16S rDNA sequences showed that the endosymbionts of KA/E9, KA/E22 and KA/E23 were closely related to Caedibacter caryophilus, whereas the KA/E21 endosymbiont was assigned to the Cytophaga-Flavobacterium-Bacteroides (CFB) phylum. In the 4 strains of Acanthamoeba, the hosts of the endosymbionts were identified as belonging to the Acanthamoeba castellanii complex, which corresponds to the T4 genotype. Acanthamoeba KA/E21 evidenced characteristics almost identical to those of KA/E6, with the exception of the existence of endosymbionts. The discovery of these endosymbionts from Acanthamoeba may prove essential to future studies focusing on interactions between the endosymbionts and the amoebic hosts.

Genetic Diversity of Stenotrophomonas maltophilia Isolated from Clinical Specimens

Stenotrophomonas maltophilia is a multi-drug resistant pathogen that has been isolated with increasing frequency from the hospitalized patients. A total of 202 S. maltophilia was isolated from three university hospitals and analysed by molecular typing for an epidemiologic investigation. All isolates were tested by antimicrobial susceptibility, random amplified polymorphic DNA (RAPD) analysis, and pulsed-field gel electrophoresis (PFGE). The RAPD and PFGE patterns were recorded and analysed by the unweighted-pair group method with arithmetic average method. Two or more isolates were considered to be clonally related if their PFGE pattern exhibited > or =80% similarity. Trimethoprim/ sulfamethoxazole and ciprofloxacin were the most active antimicrobial agents tested. The majority of the isolates found to be genetically unrelated by PFGE. The genetically related isolates were recovered from the same patient. The result demonstrates a high genetic diversity of S. maltophilia isolates from clinical specimens. The clonal diversity of S. maltophilia from the hospitalized patients is partly due to the strains originated from the hospital environments, but not horizontal transfer between the patients

Antimicrobial Resistance and Integrons Found in Commensal Escherichia coli Isolates from Healthy Humans

The emergence and spread of antimicrobial resistance among the pathogenic and commensal Enterobacteriaceae are of great concern worldwide. We characterized the antimicrobial resistance and integrons found in commensal Escherichia coli from healthy humans in the community. Class 1 integrase (intl1) and class 2 integrase (intl2) genes were identified in 22 (13.3%) and 2 (1.2%) of 165 E. coli isolates, respectively. dfrA17-aadA5 and dfrA1-aadA2 were the most common class 1 integrons. The prevalence of each type of class 1 integron among commensal E. coli isolates during 2001~2003 was similar to that of clinical E. coli isolates from hospital-acquired infections during 1994~1999. The resistant rates of commensal E. coli isolates carrying intl1 to ampicillin, streptomycin, gentamicin, sulfamethoxazole, trimethoprim, chloramphenicol, and tetracycline were significantly higher than those of intl1-negative E. coli isolates (p<0.05). Integrons were directly associated with multidrug resistance in commensal E. coli isolates. It is hypothesized that multidrug-resistant Enterobacteriaceae from hospital-acquired infections are a potential reservoir for integrons associated with resistance genes found in commensal E. coli isolates in the community

Epidemiology of Shigellosis in Korea

Shigellosis is an acute diarrheal disease caused by bacteria of the genus Shigella. Following the occurrence of a large outbreak of shigellosis as well as sporadic cases since 1998, shigellosis has been a major health problem in Korea. There have been major changes in epidemiology during the last five decades concerning shigellosis in terms of total incidence of shigellosis, prevalence of certain serogroups, selection of specific clones, and introduction of new Shigella clones. S. dysenteriae was the most prevalent species until the early twentieth century, S. flexneri was the most prevalent until the late 1980s, and S. sonnei has been the most prevalent since 1990. Diverse serotypes of S. dysenteriae (4 serotypes), S. flexneri (8 serotypes), and S. boydii (4 serotypes) were found during the Korean War and many of these Korean endemic Shigella strains circulated in the community until the late 1970s. However, the endemic strains of S. dysenteriae, S. boydii, and S. sonnei disappeared in the late 1980s. A new clone of S. sonnei that was introduced between the late 1980s and the early 1990s was responsible for a large proportion of shigellosis in recent years. S. flexneri serotype 4a was the most frequently found during the Korean War and then the incidence of S. flexneri 2a gradually increased with time. S. flexneri isolates detected from 1991 to 1997 were all serotype 2a. However, the diverse clones of S. flexneri reemerged in Korea since 1999. It has not been determined whether the S. flexneri strains from the 2000s were the descendants of the Korean endemic strains or imported new strains, but the PFGE patterns were different between S. flexneri strains from the 1980s and 2000s. The widespread of new S. sonnei strains and the persistence of S. flexneri strains are responsible for the endemicity of shigellosis in Korea.

Prevalence of Specific Clone of Salmonella enterica Serovar Typhimurium Clones in the Swine Population of Kyungpook Province During 1998 to 2000

A total of 40 Salmolella enterica serovar Typhimurium (S. typhimurium) strains were isolated from clinical specimens of swine at 10 farms in Kyungpook province from 1998 to 2000. We investigated the clonal relationship of S. typhimurium isolates by antimicrobial susceptibility, plasmid profile, and Southern hybridization analysis with tetA, and pulsed-field gel electrophoresis (PFGE). All S. typhimurium isolates showed identical biochemical characteristics and were resistant to tetracycline, streptomycin, and sulfamehtoxazole. They were classified into 5 groups by antimicrobial resistance patterns. S. typhimurium isolates carried 3 to 5 plasmids and were classified into 5 groups by plasmid profiles. Southern hybridization showed that tetA gene was located in 21 kb of plasmid. S. typhimurium isolates from 9 different farms showed identical or similar PFGE patterns, which indicates clonal origin of the strains. All S. typhimurium isolates, except one isolate from 1998, seemed to belong to be one clone by the combination of three epidemiological typing methods. These data demonstrated that a specific clone of Salmolella enterica serovar Typhimurium was widely spread in swine farms in Kyungpook province.

Degradation of the Retinoblastoma Tumor Suppressor Protein by the Human Papillomavirus-16 E7 Variants

Human papillomavirus type 16 (HPV-16) plays an etiological role in benign and malignant epithelial tumors. A critical event in HPV transformation of human cells is the inactivation of retinoblastoma protein (pRB) by the E7 protein. The metabolic half-life of pRB is decreased in cells that express high-risk HPV E7 proteins. The present study investigated the frequency of HPV-16 E7 variants in Korean women and compared the pRB degradation activity of E7 variant proteins. Of the 40 HPV-positive specimens from a total of 91 tissue specimens, 21 HPV-16 positive specimens were studied by sequencing analysis to determine the variation of E7 gene. The most frequent E7 variant was N29S (57%). The HPV-16 E7 variant was more prevalent in invasive cervical cancer tissue specimens than in those from low grade clinical stage. The degradation of pRB in HaCaT cells by HPV-16 E7 variant proteins was investigated by western blot analysis. There was no significant difference in pRB degradation activity between the HPV-16 E7 prototype protein and E7 variant proteins. The pRB degradation activity did not differ among HPV-16 E7 variants. These results suggest that the E7-induced degradation of pRB is important in cervical tumorigenesis; however, there was no relation between the pRB degradation activity and the variations in HPV-16 E7 protein among Korean women.

Molecular Epidemiology of Nalidixic Acid Resistance in Shigella sonnei Isolates

Twenty-six nalidixic acid-resistant Shigella sonnei strains isolated from 1982 to 2001 and 56 nalidixic acid-resistant mutants induced by quinolone drugs from susceptible wild strains were analyzed by sequencing the gyrA gene. All the 22 nalidixic acid-resistant isolates from 1998 to 2001 showed identical amino acid substitution of Ser to Leu (TCG --> TTG) at codon 83 while 7 different mutation types were detected in artificially induced nalidixic acid-resistant mutants. Asp87 (GGC) type was observed most commonly among mutants induced by nalidixic acid while Ser83 (TTG) type was common among mutants induced by ciprofloxacin or norfloxacin. All the isolates collected between 1998 and 2001 showed identical or nearly identical pulsed-field gel electrophoresis pattern. These results suggest that the explosive increase of S. sonnei infection after 1998 was mainly due to the spread of restricted number of clones resistant to nalidixic acid.

Clonal Types and Antimicrobial Susceptibilitiy Patterns in Methicillin-Resistant Staphylococcus aureus Isolates from a Korean Hospital

A total of 54 non-duplicate methicillin-resistant Staphylococcus aureus (MRSA) isolates from clinical specimens and 3 MRSA isolates from healthy medical staffs were obtained from Kyungpook National University Hospital. They were analyzed for clonal types by multilocus sequence typing, protein A gene (spaA) typing, the staphylococcal cassette chromosome mec (SCCmec) typing, and pulsed-field gel electrophoresis (PFGE). The MRSA isolates were examined for antimicrobial susceptibility. Clinical MRSA isolates were classified into 4 clonal complexes, 4 sequence types (STs), 5 spaA types, 4 PFGE patterns, and 3 SCCmec types with variants. On the basis of ST, ST239 (n=25) and ST5 (n=24) were the most frequently encountered. MRSA isolates belonging to ST239 were genotypically homogenous, while those belonging to ST5 showed variations in spaA and SCCmec types. Of the 3 MRSA isolates from healthy medical staffs, one was genotypically identical to MRSA isolates belonging to ST5 and the other two ST239. All MRSA isolates were susceptible to vancomycin and teicoplain. Only 4% of isolates were resistant to rifampin, while 91% of isolates were resistant to ciprofloxacin. The resistance rate of MRSA isolates belonging to ST239 against trimethoprim-sulfamethoxazole (SXT) was significantly higher than that of the isolates belonging to ST5 (76% vs 0%, p<0.001). In summary, ST239 and ST5 were responsible for most MRSA infections and healthy medical staffs also carried these MRSA strains. The susceptibility of the ST239 clone against SXT, which was commonly used for oral therapy to treat MRSA infection, was significantly different from the ST5 clone.

Epidemiologic analysis of Ampicillin Resistance in Shigella sonnei Isolates by blaTEM Hybridization

Forty-seven ampicillin-resistant R plasmids derived from 218 Shigella sonnei isolates from Daegu and Gwangju areas from 1980 to 2000 were epidemiologically compared by fragments of restriction endonuclease patterns by EcoRI and SmaI, and by Southern hybridization with a blaTEM-1 probe. All the ampicillin-resistant strains isolated in the 1980S carried a conjugative R plasmid responsible for multiple resistance other than ampicillin, and an ampicillin-resistance plasmid. Ampicillin-resistant strains isolated in the 1990S harbored single conjugative R plasmid encoding ampicillin resistance along with variable antimicrobial resistances. The restriction endonuclease digestion patterns and Southern hybridiztion analysis of conjugative R plasmids showing identical resistance pattern and a same size showed different fragment and Western blotting patterns according to different isolation years and areas, while identical patterns were observed among the plasmids derived from a same isolation year and area. These findings suggest that ampicillin resistance among S. sonnei isolates was due to introduction of ampicillin-resistant R plasmids originated from different sources.

Molecular Epidemiology of Shigella sonnei Isolated from 1994 to 1999 in Daegu area

A total of 78 Shigella sonnei strains isolated from 1994 to 1999 in Daegu were screened by biochemical test, antimicrobial susceptibility test, plasmid profiling, and epidemiologic analysis. Among them, 26 representative strains with different properties were selected and their molecular epidemiological characteristics were studied. Among the 78 strains, two strains did not ferment raffinose and another two strains did not produce colicin. The 26 selected strains were differentiated into 15 plasmid profiles, 11 antimicrobial, 14 enterobacterial repetitive intergenic consensus sequencebased PCR (ERIC-PCR) pattern, 10 pulsed-field gel electrophoresis (PEGE) pattern types. When all of the typing methods were combined, the strains could be differentiated into 15 types. However, significant correlation among different testing methods was not observed. PEGE analysis indicated that all the strains tested were related despite minor genotypic and phenotypic differences. Our data could not address whether these genetic diversity of strains is due to different circulating strains originated from a number of clone or due to minor genetic variation.

Epidemiologic analysis of Shigella sonnei Isolates by using Antimicrobial Resistance Gene Probes

Thirty-four Shigella sonnei isolates from 6 outbreaks and sporadic cases from May 1999 until January 2000 in Daegu and 9 regions of Gyeongsangbuk-Do were epidemiologically analyzed by plasmid profiling, pulsed-field gel electrophoresis (PFGE), and hybridization with 2 antimicrobial resistance gene probes, tetA and dfrA1. In outbreak cases, resistance pattern in all of the strains was identical: they were resistant to tetracycline (Tc), streptomycin (Sm), sulfisomidine (Su), trimethoprim (Tp), and nalidixic acid (Na). In sporadic cases, Tc, Sm, Su, Na, ampicillin (Ap), and kanamycin (Km) pattern and TcSmSuTpApNa pattern were additionally observed. Isolates from the same outbreak showed identical plasmid profile and PFGE pattern. Most of different outbreak strains and sporadic strains showed different plasmid profiles, and identical or different PFGE patterns, while all of the isolates shared common tetA gene on a non-conjugative 18.3 kbp R plasmid carrying resistance to tetracycline, streptomycin, and sulfisomidine, and dfrA1 gene on the chromosome. Non-conjugative R plasmids derived from all of the isolates were confirmed to be identical by the Southern hybridization analysis of restriction endonuclease treated or non-treated plasmid profiles using the tetA probe. The same strains also reacted with dfrA1 probe at the same-sized DNA fragment (60 kbp) on pulsed-field gel electrophoresis of total genomic DNA. Our findings suggested that epidemic strains of Shigella sonnei prevalent in the Daegu and Gyeongsangbuk-Do area during the test period should have originated from an identical or closely related strain source although most of strains did not show the same plasmid profile and PFGE pattern.

Genomic Analysis of Human Papillomavirus Type 16 in Cervical Cancer

To study the correlation of human papillomavirus (HPV) infection with clinical stage in cervical abnormalities, 17 cases of normal cervical tissue and 69 cases of abnormal cervical tissue (cervical intraepithelial neoplasia and invasive cervical cancer) was examined by PCR with HPV-specific consensus primers. One case (5.9%) of normal cervical tissue and 42 cases (60.9%) of abnormal cervical tissues harbored HPV. To investigate the integration of HPV genome in 24 cases of HPV 16 positive cervical cancer, E2 gene of HPV 16 was amplified. Integration of HPV 16 was found in 7 cases (29.2%) with E2 disruption. All samples with E2 disruption were from invasive cervical cancer. A multiplex PCR for the mapping of integrated HPV 16 genome with an anchor primer and indicator primers showed that 11 cases (45.8%) were disrupted somewhere in HPV genome but E6, E7, and LCR regions were conserved in all cases. Seven types of integrated HPV genome from long- (7,062 bp) to short-conserved type (3,204 bp) with various deletions were detected by the multiplex PCR. These results show that integration can be detected more accurately by multiplex PCR than by E2 PCR, and E2 disruption is not a critical event of integration

Comparison of Epidemiological Typing Methods for Shigella sonnei

No abstract available.

Use of R plasmid and bla Gene for Epidemiological Fingerprinting of Clinical Isolates of Enterobacteriaceae resistant to beta- lactam Antibiotics

Clinical isolates of Enterobacteriaceae (189 Klebsiella, 61 Enterobacter, 32 Serratia, 19 E. coli, 7 Proteus, and 3 Citrobacter) from one university hospital were epidemiologically analyzed by using transferable R plasmids resistant beta-lactam antibiotics including broad-spectrum cephalosporins. About 30% of E. cloacae and S. marcescens and about 5% of K. pneumoniae were resistant to one or more broad-spectrum j3-lactam antibiotics including cefotaxim, ceftazidime, aztreonam, or cefoxitin but all isolates of E. aerogenes, K oxytoca, and P. mirabilis were susceptible. Thirty-six conjugative R plasmids including 8 plasmids resistant expanded-spectrum cephalosporins were obtained from multiple resistant K. pneumoniae (19), E. cloacae (9), E. coli (4), and C. freundii (1). Thirty-one plasmids were subjected to R plasmid analysis and classified 20 different plasmid types. Among them 5, 2, and 2 plasmids belong to 3 different types respectively showed identical molecular size, endonuclease fragment pattern by Southem hybridization pattern by TEM-1 probe, pI value by isoelctric focusing, and also identical antibiogram and biotype of wild strains harboring plasmids. But all of plasmids resistant to cefotaxim, ceftazidime, aztreonam or cefoxitin showed different palsmid anlysis patterns. These results indicate that the epidemic strains of 3 clonal types had been present in this hospital and anlysis using transferable R plasmid and bla gene can be used to discriminate multi-resistant clinical isolates of Enterobacteriaceae.

Clonal analysis of methicillin-resistant Staphylococcus aureus strains in Korea

In this study, the distribution of the mec regulator genes and the presence of the mutation in mecI gene and mec promoter region among 50 MRSA clinical isolates derived from a single university hospital in Korea were analyzed. Among 50 MRSA strains, 13 strains had a deletion of mecI gene, and 37 strains were found to have mutations in mecI gene or mecA promoter region corresponding to a presumptive operator of mecA, i.e., the binding site of the repressor protein. Furthermore, in order to track the evolution of methicillin-resistant Staphylococcus aureus (MRSA) distributed in Korea, we determined the MRSA clonotype by combined use of genetic organization patterns of mec regulator genes, ribotype, and coagulase type. As the result, 48 of 50 MRSA strains could be classified into four distinct clones. Clonotype I is characterized by the coagulase type 3, deletion of mecI gene, and ribotype 1 shared by NCTC10442, the first reported MRSA isolate in England (9 strains). Clonotype II is characterized by the coagulase type 4, C to T substitution at position 202 of mecI gene, and ribotypes 2, 3 and 4 shared by 85/3619 strain isolated in Austria (10 strains). Clonotype III is characterized by the coagulase type 2, mutations of mecA promoter region and/or mecI, and ribotypes 4, 5, and 6 shared by N315 strain isolated in Japan (25 strains). Clonotype IV is characterized by the coagulase type 4, deletion of mecI gene, and ribotype 7 (4 strains). The clonality of two strains could not be determined due to their undefined ribotype.

Antimicrobial resistance and molecular epidemiologic characteristics of Stenotrophomonas maltophilia isolated from clinical specimens

Sixty-eight clinical isolates of Stenotrophomonas maltophilia from inpatients of 2 university hospitals in Taegu were epidemiologically analyzed by using the minimum inhibitory concentrations of 25 antimicrobial drugs, biochemical reaction, pulsed-field gel elctropgoresis (PFGE), and PCR with enterobacterial repetitive intergenic consensus sequences as primer (ERIC-PCR). 1. All the strains were susceptible to minocycline. More than 57% were susceptible to sulfisomidine (Su), ciprofloxacin (Ci), Ofloploxacin (Of), nalidixic acid (Na), and chloramphenicol (Cm), and 19apprx35% to ceftazidime (Cd), trimethoprim (Tp), Ticacillin-clavulanic acid, and cefoperazone-sulbactam. Most isolates were resistant to beta-lactam antibiotics such as ampicillin (Ap), carbenicillin (Cb), cefotaxim (Ct), cefoxitin (Cx), and aminoglycosides including gentamicin (Gm), tobramycin (Tb), amikacin (Ak). 2. All the isolates were multiply resistant of 5 to 17 drugs and showed 40 different resistance pattern types. 3. All the strains showed very similar biochemical reactions except beta-galactosidase and nitrate reduction test. Fourteen strains selected randomly were classified 10 different pattern type by PFGE and ERIC-PCR. These two methods showed identical result. Four strains isolated from wound in 1994 showed similar MIC pattern and identical API 20NE profile, PFGE, and ERIC-PCR pattern indicating episodes of cross-infection among patients. These results indicate that PFGE or ERIC-PCR profile has comparable discriminatory power for epidemiological typing of S. maltophilia.

Molecular Genetic Characteristics of Trimethoprim Resistance in Clinical and Normal Fecal Isolates of Escherichia coli

One hundred and thirty trimethoprim-resistant R plasmids derived from of Escherichia coli isolated from clinical specimens and feces of healthy collegians were examined for incompatibility, EcoRI endonuclease restriction fragment pattern, and Southern hybridization with DHFR I, II, III, V, and VII probe. 1. Most trimethoprim-resistant R plasmids were resistant to ampicillin, tetracycline, chloramphenicol, gentamicin, and kanamycin, and showed multiple drug resistance and various antimicrobial resistance patterns. 2. Trimethoprim-resistant R plasmids ranged from 90 to 50 kilobase and 42.3% of R plasmids tested were classified to incompatibilty group Inc FI, Inc FII or Inc FIV, 3. Among 48 random selected R plasmids from various origin, 14 R plasmids (including 9 of 14 Inc FII plasmids and 3 of 14 Inc FI plasmids) hybridized with DHFR VII oligonucleotide probe but others did not respond to any of DHFR probes used. 4. Most R plasmids showed various EcoRI endonuclease fragments and different reaction sites by Southern hybridization. Six plasmids showed identical or nearly identical molecular weight, EcoRI endonuclease fragment patterns and different sites of Southern hybridization. But 2 Inc FII plasmids derived from urine and feces showed identical pattern. These findings, if confirmed by further studies, suggest that normal flora E. coli can act as reservoir of resistant genes and, consequently, as a factor in the dissemination of these genes among enteric pathogens and need to be examined further.

Mutation of gyrA in Quinolone-Resistant Clinical Isolates of Escherichia coli

To study the gyrA mutations of E. coli from clinical specimens, 410 strains were isolated from 1994 to 1997 in Kyungpook National Vniversity hospital. Antimicrobial susceptibility tests, PCR and sequencing of gyrA, and in vitro induction of quinolone resistance were done. The frequency of quinolone resistant E. coli strains increased constantly during 1994 through 1996. Quinolone-resistant strains were more often resistant to unrelated antibiotics than quinolone-susceptible strains (chi-square test, p Leu (TCG -> TIG) at codon 83. In addition, four different types of amino acid substitution affecting codon 87 (Asp) were detected, 1) type I: Asn (GAC -> AAC); 2) type II: Tyr (GAC -> TAC); 3) type III: Oly (GAC -> GGC); 4) type IV: His (GAC -> CAC). The mutation of type IV has not been reported previously in quinolone-resistant E. coli strains. It is thought that the specific amino acid substitution probably affects minimum inhibitory concentrations (MIC) of quinolones because the MICs of ciprofloxacin, norfloxacin, and ofloxacin in type II were significantly higher than those of type I. By in vitro induction, MICs to quinolone-susceptible strains resulted in the increase in the MICs of all quinolones tested by 2- to 2048-fold. The induced mutants by quinolones had amino acid substitutions at codon 83, SerLeu or Asp87Asn, Gly or Tyr. Alteration of Ser83 results in the most effective increase in the MIC of quinolone such as NAL and alterations of Asp87 result in the effective increase of MIC of fluoroquinolone. These results suggest that the continuous use of quinolones might induce the specific amino acid substitution at gyrA.

Epidemiology of Serratia marcescens Isolates by Transferable Resistance Gene Analysis

Conjugative R plasmids derived from 74 clinical isolates of Serratia marcescens were epidemiologically analyzed for antimicrobial resistance, EcoRI restriction endonuclease analysis and Southern hybridization with DHFR, TEM and SHV probe. 1. Resistance frequency of isolates against various B-lactam antibiotics was changed by year. 2. Twenty (27%) resistant strains transferred 32 R plasmids to E. coli or Klebsiella by mixed culture. Most strains isolated from 1994 to 1996 transferred only trimethoprim resistance but most strains isolated from 1997 did resistances against gentamicin (Gm) and B-lactams including ampicillin (Ap), carbenicillin (Cb), cefazolin (Cz), cefaloridine (Cl), cefamandole (Cn). 3. Ten plasmids of GmApCbCzC1Cn or GmApCbCzC1 pattern and 3 plasmids of TcSuGmTbApCbCzC1 pattern respectively showed identical EcoRI restriction endonuclease digestion patterns and hybridized fragment patterns with TEM-1 probe by Southern hybridization. These results indicate that the epidemic plasmids carrying blamM gene were present in this hospital in 1997 and molecular genetic analysis of R plasmids can be used to discriminate S. marcescens isolates for epidemiologic studies.