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Detection and characterization of class 1 integrons in enterohemorrhagic Escherichia coli.

Enterohemorrhagic Escherichia coli (EHEC) strains isolated from humans, cattle, and food and belonging to serogroups O26 (7 strains), O111 (19 strains), and O157 (70 strains) were examined for susceptibility to 11 antimicrobial drugs. Fifty-nine strains showing resistance to at least one of the drugs were examined by PCR for the presence of class 1 integrons, which were identified in 17 strains. Integrons were found more frequently in strains belonging to serogroups O111 and O26 than in the O157 isolates. DNA sequence analysis demonstrated that most of the integrons contained the aadA1 gene cassette conferring resistance to streptomycin/ spectinomycin, alone or associated with the drfA1 gene cassette conferring resistance to trimethoprim. One integron, identified in a O157:H7 strain, carried the aadA2 and dfrA12 gene cassettes, conferring resistance to streptomycin/spectinomycin and trimethoprim, and the open reading frame F (OrfF) encoding unknown functions. Most of the integrons were carried by Tn21 derivative transposons and were transferable by conjugation to an E. coli K-12 strain. In conclusion, integrons and antibiotic resistance genes can be frequently found in EHEC strains, particularly E. coli O111 and E. coli O26, and their presence could complicate therapeutic trials.

Animals↗

Diversity in antimicrobial resistance and other characteristics among Salmonella typhimurium DT104 isolates.

Multiresistant Salmonella enterica subspecies enterica serovar Typhimurium definitive type 104 (S. Typhimurium DT104 or DT104) bacteria are important pathogens in animals and humans. DT104 isolates are often called pentaresistant strains that spread clonally. The purpose of this study was to determine phenotypic, genotypic, and epidemiologic characteristics of 175 S. Typhimurium DT104 strains isolated from food-producing animals in Canada. More than 90% of the isolates were resistant to ampicillin (Amp), chloramphenicol (Chl), florfenicol (Flo), sulfisoxazole (Sul), and tetracycline (Tet), 53% of the isolates were additionally resistant to spectinomycin (Spc) and streptomycin (Str), and 28% to kanamycin (Kan) and neomycin (Neo). Sixty-one percent of the strains harbored a single 60-MDa plasmid, 21% contained 60- and 2.0-MDa plasmids, and 4% had 60, 4.6- and 2.0-MDa plasmids. Resistance to Kan and Neo was encoded by the aminoglycoside aphA-1 gene on 2.0-MDa plasmids, whereas resistance to trimethoprim (Tmp) and Sul was encoded by the dhfrIb gene on 4.6-MDa plasmids. Polymerase chain reactions (PCR) showed the presence of integrons with the ant (3")-Ia aminoglycoside adenyltransferase and the bla(PSE-1) beta-lactamase gene cassettes, and the presence of the flost gene in all but one strain resistant to Spc and Str, Amp, and Chl and Flo, respectively. DT104 isolates from cattle at six feedlots represented a separate clone; they were sensitive to Str and Spc and lacked the ant (3")-Ia gene. Pulsed-field gel electrophoresis (PFGE) using Bln I, Spe I, and Xba I resulted in 15, 12, and 8 PFGE patterns, respectively. In summary, we observed considerable diversity in phenotypic, genotypic, and epidemiological characteristics among the DT104 isolates.

Animals↗

Integron-associated antibiotic resistance in enteroaggregative and enteroinvasive Escherichia coli.

Ten enteroinvasive (EIEC) and 25 enteroaggregative (EaggEC) E. coli strains isolated from Senegalese patients were analyzed for their integron content. All strains were resistant to at least two antibiotics. Four EIEC and 15 EaggEC were found to carry a class 1 integron. An identical integron carrying a single dfrA5 cassette, conferring resistance to trimethoprim, was identified in all four EIEC strains. Five EaggEC strains harbored an integron with a single cassette, dfrA7, while the remaining 10 strains carried two integrons, one with a single cassette, aadA1a conferring resistance to streptomycin and spectinomycin, and the second one bearing two cassettes, dfrA13 and oxa5, the later being a beta-lactam resistance cassette. The presence of these integrons is worrying, because trimethoprim is largely used for diarrheal disease therapy in Africa. Thus, the presence of integrons in diarrheagenic strains is of public health importance because a limited number of antibiotics are available in developing countries.

Chromosome Mapping↗

Spread of a methicillin-resistant and multiresistant epidemic clone of Staphylococcus aureus in Argentina.

One hundred forty-eight recent methicillin-resistant Staphylococcus aureus (MRSA) isolates collected from 13 hospitals in Argentina were examined for antibiotic susceptibility and clonal type, using hybridization with DNA probes specific for mecA and Tn554, and pulsed-field gel electrophoresis (PFGE) of chromosomal SmaI digests. The majority of the isolates (62.2%) shared the common PFGE B pattern and carried variants of mecA and Tn554 polymorphs characteristic of an MRSA clone widely spread in Brazilian hospitals. Similarly to the Brazilian isolates, the MRSA clone recovered in the Argentinian hospitals (XI::B::B) and its close relatives (XI::B'::B, XI::AA::B, XI::M::B, XI::omega omega::B, and III::W::B) showed susceptibility to spectinomycin and resistance to numerous antibacterial agents, including beta-lactams, tetracycline, aminoglycosides, macrolides, trimethoprim/sulfamethoxazole, ciprofloxacin, and fosfomycin, and more than 60% of the isolates were also resistant to chloramphenicol and rifampin. The XI::B::B MRSA clone represented the majority of isolates recovered in most of the hospitals, nine of which were located in the city of Buenos Aires, three in the province of Buenos Aires, and one in the province of Tucumán, 1,312 km northwest of the city of Buenos Aires. The observations document further geographic expansion of this South American MRSA clone across national boundaries.

Anti-Bacterial Agents↗

Characterization of aminoglycoside resistance genes and class 1 integrons in porcine and bovine gentamicin-resistant Escherichia coli.

A total of 78 gentamicin-resistant Escherichia coli strains from swine (27) and cattle (51) were characterized by phenotypic resistance, presence of selected aminoglycoside resistance genes, class 1 integrons and gene cassettes, and pulsed-field gel electrophoresis. Gentamicin resistance was mainly encoded by the ant(2'')-I gene that was found in 76% of all the strains investigated, whereas the aac(3)-IIa gene was found in 14%. The ant(2'')-I gene was predominant in strains from cattle, whereas the porcine strains contained both ant(2'')-I, aac(3)-IIa, and the aac(3)-IVa genes. The pulsed-field gel electrophoresis (PFGE) investigation indicated a close clonal relationship in half of the bovine strains whereas the remaining E. coli were unrelated. Among the E. coli investigated, 20% contained class 1 integrons. Genes encoding resistance to trimethoprim (dhfrI, dhfrIb, and dhfrVII), gentamicin, tobramycin, and kanamycin (ant(2'')-Ia streptomycin and spectinomycin (ant(3'')-Ia) and streptothricin (sat1) were identified as gene cassettes. The most prevalent gene cassettes were ant(3'')-Ia (11 isolates) and the dhfrI (nine isolates).

Animals↗

Similarity of antibiotic resistance patterns and molecular typing properties of methicillin-resistant Staphylococcus aureus isolates widely spread in hospitals in New York City and in a hospital in Tokyo, Japan.

One hundred and forty-three single-patient methicillin-resistant Staphylococcus aureus (MRSA) isolates collected during April-June, 1997, and February, 1998, in a hospital in Tokyo, Japan, were characterized by molecular typing techniques that involved hybridization of ClaI restriction digests with the mecA- and Tn554-specific DNA probes and determination of macrorestriction patterns of SmaI-digested chromosomal DNA by pulsed-field gel electrophoresis (PFGE). A large proportion (76%) of the isolates carried the mecA polymorph I, Tn554 pattern A, and PFGE pattern A (clonal type I:A:A), which was the same as the clonal type of an MRSA widely spread in hospitals in New York City and hospitals in neighboring New Jersey, Connecticut, and Pennsylvania. Also similarly to the New York clone, most of the MRSA isolates from the Japanese hospital were resistant to penicillin, ciprofloxacin, erythromycin, tetracycline, and high concentrations (500 microg/ml) of spectinomycin, but were susceptible to chloramphenicol, sulfamethoxazole-trimethoprim, and rifampin. All of the 143 MRSA isolates had vancomycin MICs < or = 2 mg/L.

Aged↗

In vitro susceptibility of Helicobacter pullorum strains to different antimicrobial agents.

The in vitro activity of 13 antimicrobial agents against 23 Helicobacter pullorum strains from poultry (21) and human (two) origin, and one human H. canadensis strain was tested by the agar dilution method. With the H. pullorum strains, monomodal distributions of Minimum Inhibitory Concentrations (MICs) were seen with lincomycin, doxycycline, gentamicin, tobramycin, erythromycin, tylosin, metronidazole, and enrofloxacin in concentration ranges considered as indicating susceptibility in other bacteria. The normal susceptibility level for nalidixic acid was situated at or slightly above the MIC breakpoints proposed for Campylobacteriaceae. Ampicillin, ceftriaxone, and sulphamethoxazole-trimethoprim showed poor activity against H. pullorum. For the H. canadensis strain, a similar susceptibility pattern was seen, except for nalidixic acid and enrofloxacin, whose MIC of >512 and 8 microg/ml, respectively, indicated resistance of this agent. With spectinomycin, a bimodal distribution of the MICs was noted for the tested strains; eight H. pullorum isolates originating from one flock showed acquired resistance (MIC>512 microg/ml).

Anti-Infective Agents↗

Therapy for gonococcal infections: options in 1989.

The choice of therapy for Neisseria gonorrhoeae infections is complicated by antibiotic resistance and by the varying efficacy of some antibiotics at different anatomic sites of infection. Ceftriaxone (a single intramuscular dose of 250 mg) is a simple, effective, and generally well-tolerated choice for uncomplicated N. gonorrhoeae infection at all anatomic sites. Alternatives include single-dose oral regimens of ciprofloxacin, norfloxacin, and cefuroxime axetil as well as single-dose intramuscular regimens of spectinomycin, ceftizoxime, and cefotaxime. The addition of doxycycline (100 mg orally twice a day for 7 days) is recommended for presumptive treatment of chlamydial coinfection. Tetracyclines should not be used as sole therapy for gonococcal infection because of gonococcal resistance.

Anti-Bacterial Agents↗

Epidemiology of penicillin-resistant Neisseria gonorrhoeae isolated in Taiwan, 1960-1990.

The epidemiology of penicillin-susceptible Neisseria gonorrhoeae isolated in Taiwan from 1960 to 1990 is summarized. The isolation of N. gonorrhoeae less sensitive to penicillin (i.e., with intrinsic resistance) was first reported in 1960. The rate at which organisms less sensitive to penicillin (MIC, greater than or equal to 0.5 microgram/mL) were isolated increased to 17%, 50%, 80.1%, and 88.8% in 1967, 1975, 1984, and 1990, respectively. Penicillinase-producing N. gonorrhoeae (PPNG) first appeared in Taiwan in late 1976, and the first six strains of PPNG isolated were from United States military servicemen who had relocated from Southeast Asia. The percentage of PPNG strains rose to 37.82% in 1982, and has remained high (50%-62%) since 1983. In the present study, resistance of N. gonorrhoeae to spectinomycin (MIC, greater than 32 micrograms/mL), third-generation cephalosporins (MIC, greater than 4 micrograms/mL), or quinolones (MIC, greater than 4 micrograms/mL) has not been found. Strains requiring arginine, hypoxanthine, and uracil for growth, which frequently cause disseminated gonococcal infections, were not isolated. PPNG strains tended to be of the prototrophic auxotype (55%); non-PPNG strains were mostly of the proline-requiring auxotype (48.8%). Two kinds of R plasmids were isolated in the PPNG strains: the 4.4-MD Asian type (82%-95%) and the 3.05-MD Toronto type (5%-18%). All of the PPNG strains possessing Toronto R plasmid were of the same auxotype/serotype (prototrophic/IB). Evidence suggests that the Asian-type R plasmid was imported into Taiwan in 1976, while the Toronto-type R plasmid may have first emerged in Taiwan in 1983.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial Typing Techniques↗

Drugs of choice for the treatment of uncomplicated gonococcal infections.

Resistance of Neisseria gonorrhoeae to antimicrobial agents continues to spread and intensify. Choosing an antimicrobial regimen requires knowledge of the comparative efficacy of candidate regimens, as delineated in properly conducted clinical trials; their activity against N. gonorrhoeae in vitro; and their pharmacokinetics and toxicity. We tabulated the results of trials of single-dose antimicrobial therapy for uncomplicated gonococcal infection published after 1980. Thirty regimens comprising 21 antimicrobial drugs have been shown to be highly effective for rectal and urogenital infections; the agents involved are cefixime, cefodizime, cefotaxime, cefoxitin, ceftizoxime, ceftriaxone, cefuroxime, cefuroxime axetil, ciprofloxacin, fleroxacin, norfloxacin, ofloxacin, pefloxacin, temafloxacin, azithromycin, aztreonam, netilmicin, rifampin plus erythromycin stearate, sisomicin, and spectinomycin. Few regimens have been shown to be highly effective against pharyngeal infections. Among those antimicrobial agents available for the treatment of uncomplicated gonococcal infections in the United States, ceftriaxone (125 mg), cefixime (400 mg), ciprofloxacin (500 mg), and ofloxacin (400 mg) appear to offer the best balance of proven efficacy and safety.

Anti-Bacterial Agents↗

Antimicrobial resistance in Neisseria gonorrhoeae.

The changing patterns of antimicrobial resistance in Neisseria gonorrhoeae have been reviewed regularly since the introduction of antimicrobial therapy in the 1930s. At present, ceftriaxone, fluoroquinolones, and spectinomycin have remained efficient as single-dose treatment of gonorrhea worldwide. To ensure that limited resources can be used in the best possible way, continuous surveillance of gonococcal resistance to antimicrobials is needed.

Chromosomes, Bacterial↗

Genetics of Chlamydomonas reinhardtii diploids. II. The effects of diploidy and aneuploidy on the transmission of non-Mendelian markers.

The transmission of two non-Mendelian drug resistance markers has been studied in crosses of Chlamydomonas reinhardtii involving diploids and aneuploids with different mating type genotypes. Under normal laboratory conditions for gametogenesis, mating and zygote maturation, the transmission pattern of the non-Mendelian markers sr-u-1 (resistance to streptomycin) and spr-u-1-27-3 (resistance to spectinomycin) is primarily determined by the mating type genotypes of the parental cells. Our results confirm and expand an earlier observation suggesting that an apparent codominant function of the female (mt+) allele in regulating chloroplast gene transmission in meiosis appears to be distinct and separate from its recessive function in regulating mating behavior. The chloroplast DNA complement (as indexed by the number of extranuclear DNA-containing bodies) may exert a secondary effect on the transmission of these markers. Within a mating type group (mt+/mt- or mt-/mt-) a cell line with more chloroplast DNA tended to transmit its non-Mendelian markers more frequently than a cell line with less chloroplast DNA.

Aneuploidy↗

Homeologous plastid DNA transformation in tobacco is mediated by multiple recombination events.

Efficient plastid transformation has been achieved in Nicotiana tabacum using cloned plastid DNA of Solanum nigrum carrying mutations conferring spectinomycin and streptomycin resistance. The use of the incompletely homologous (homeologous) Solanum plastid DNA as donor resulted in a Nicotiana plastid transformation frequency comparable with that of other experiments where completely homologous plastid DNA was introduced. Physical mapping and nucleotide sequence analysis of the targeted plastid DNA region in the transformants demonstrated efficient site-specific integration of the 7.8-kb Solanum plastid DNA and the exclusion of the vector DNA. The integration of the cloned Solanum plastid DNA into the Nicotiana plastid genome involved multiple recombination events as revealed by the presence of discontinuous tracts of Solanum-specific sequences that were interspersed between Nicotiana-specific markers. Marked position effects resulted in very frequent cointegration of the nonselected peripheral donor markers located adjacent to the vector DNA. Data presented here on the efficiency and features of homeologous plastid DNA recombination are consistent with the existence of an active RecA-mediated, but a diminished mismatch, recombination/repair system in higher-plant plastids.

Base Sequence↗

A hospital outbreak of multiresistant Salmonella typhimurium belonging to phage type 193.

An outbreak of nosocomial infection was caused by strains of Salmonella typhimurium phage type 193 that were resistant to ampicillin, chloramphenicol, neomycin-kanamycin, streptomycin, spectinomycin, sulfonamides, tetracyclines, trimethoprim, and nalidixic acid. Resistances to drugs other than nalidixic acid were specified by plasmids, and, on the basis of phage typing and plasmid characterization studies, the multiresistant phage type 193 strains were determined to be clonal. In a two-year period, 488 patients infected with these bacteria were identified. An investigation in a pediatric surgical ward, where the outbreak was particularly severe, showed that patients exposed to antibiotics were more likely to be colonized with the epidemic strain and that young debilitated patients were more liable to show clinical signs of infection. Epidemiologic studies suggested that cross infection via the hands of the ward staff was the likely means of propagation of the epidemic.

Anti-Bacterial Agents↗

Neisseria gonorrhoeae recombinant strains expressing hybrid serological reactivities of outer membrane proteins IA and IB.

The inheritance of epitopes of protein I, the principal protein of the outer membrane of Neisseria gonorrhoeae, was investigated by DNA-mediated transformation. Protein I transformants were isolated by selection for the linked spectinomycin-resistance determinant. Twelve monoclonal antibodies used in coagglutination tests identified epitopes of the two forms of protein I (P.IA and P.IB). A given gonococcal culture from patients expresses epitopes of either P.IA or P.IB and rarely, if ever, exhibits hybrid P.IA/P.IB reactivities. Nevertheless, we found 35 P.IA/P.IB recombinants among 1506 transformants. Transmission by DNA of the hybrid reactivities and the apparent molecular mass characteristic of a given P.IA/P.IB species verified the genetic basis of the phenotypic changes. A recombinant that expressed six P.IA and two P.IB epitopes is of interest as a possible component of a gonococcal vaccine, because one or more of these epitopes are shared with 99.8% of a worldwide collection of 1858 clinical strains.

Agglutination Tests↗

Drug resistance and adherence to human intestines of enteroaggregative Escherichia coli.

Clinical isolates of enteroaggregative Escherichia coli (EAggEC) were tested for their in vitro susceptibilities to 27 antimicrobial agents. Marked drug resistance was observed with sulfamethoxazole, ampicillin, and chloramphenicol in contrast to such antimicrobial agents as cefixime, sparfloxacin, and ciprofloxacin. One of the EAggEC strains carried a plasmid that conferred on its host resistance to ampicillin, tetracycline, sulfamethoxazole, streptomycin, and spectinomycin and an ability to adhere to child ileal villi or HeLa cells in the characteristic aggregative pattern. This plasmid also mediated D-mannose-resistant hemagglutinin production and bacterial clump formation (autoagglutination). The data demonstrate appearance of marked drug resistance and an intestine-adherence and drug-resistance plasmid in the newest category of diarrheagenic E. coli.

Anti-Bacterial Agents↗

Aminoglycoside-modifying enzyme content of a multiply resistant strain of Streptococcus faecalis.

Streptococcus faecalis strain BM6217 was resistant to high levels of all the clinically useful aminoglycoside antibiotics. This broad aminoglycoside resistance was mediated by constitutively synthesized phosphotransferase, acetyltransferase, and adenylyltransferase activities. It was inferred that phosphorylation occurred at the 3', 5", and 2"-hydroxyl groups, acetylation at the 6'-amino group, and adenylylation, probably, at the 6-hydroxyl group of the aminoglycosides. Strain BM6217 remained susceptible to the aminocyclitol spectinomycin but the combination of penicillin G with that antibiotic appeared antagonistic to this strain.

Aminoglycosides↗

A follow-up survey of transferable, plasmid-encoded trimethoprim resistance in a general hospital (1975-1983).

Urinary isolates of bacteria resistant to trimethoprim were collected at the Whittington Hospital, London, during five three-monthly periods during 1975, 1977, 1979, 1981, and 1983. Seventy-six transferable trimethorpim-resistant isolates so obtained were examined for their antibiotic resistance patterns, trimethoprim resistance (TpR) levels and plasmid molecular weights. Overall between 1975 and 1983 the frequency of transferable TpR rose from 10% to 40% of trimethoprim-resistant isolates, caused mainly by an increasing number of Escherichia coli isolates which cotransferred antibiotic resistance to trimethoprim, streptomycin and spectinomycin. From 1975-1979 the rise in the frequency of transferable TpR was due to a gradual increase amongst in-patient isolates but since 1979 transferable TpR rose rapidly due to a ten-fold increase in out-patient isolates.

Cross Infection↗