Intercontinental spread of a new antibiotic resistance gene on an epidemic plasmid

β-Lactam Resistance Gene NDM-1 in the Aquatic Environment: A Review

New Delhi Metallo-β-lactamase-1 (NDM-1) offers carbapenem antibiotics resistance that creates an evolving challenge in treating bacterial infections. NDM-1-bearing strains were observed in surface waters around New Delhi in 2010 and after then identified globally. The usage of antibiotics may hasten the growth of the NDM-1-producing bacteria, which pose severe hazards to human and animal health. The emergence of the NDM-1 in the aquatic environment is turning out to be a growing concern worldwide. NDM-1 gene conferring resistance to a widespread class of antibiotics has been observed in bacteria disseminated in animal production wastewaters, hospital sewage, domestic sewage, industrial effluents, wastewater treatment plants, drinking water, surface water, and even in groundwater. This review recapitulates the currently published research studies on the prevalence and geographical distribution of the NDM-1 gene in the aquatic environment, its habitats, and healthcare risk associated with NDM-1-producing bacteria, in addition to molecular techniques employed to reveal the occurrence of the NDM-1 in the aquatic environment, including conventional polymerase chain reaction, real-time qPCR, DNA hybridization, and microarray-based methods.

Conjugation Dynamics of Self-Transmissible and Mobilisable Plasmids into E. coli O157:H7 on Arabidopsis thaliana Rosettes

Many antibiotic resistance genes present in human pathogenic bacteria are believed to originate from environmental bacteria. Conjugation of antibiotic resistance conferring plasmids is considered to be one of the major reasons for the increasing prevalence of antibiotic resistances. A hotspot for plasmid-based horizontal gene transfer is the phyllosphere, i.e., the surfaces of aboveground plant parts. Bacteria in the phyllosphere might serve as intermediate hosts with transfer capability to human pathogenic bacteria. In this study, the exchange of mobilisable and self-transmissible plasmids via conjugation was evaluated. The conjugation from the laboratory strain Escherichia coli S17-1, the model phyllosphere coloniser Pantoea eucalypti 299R, and the model pathogen E. coli O157:H7 to the recipient strain E. coli O157:H7::MRE103 (EcO157:H7red) in the phyllosphere of Arabidopsis thaliana was determined. The results suggest that short-term occurrence of a competent donor is sufficient to fix plasmids in a recipient population of E. coli O157:H7red. The spread of self-transmissible plasmids was limited after initial steep increases of transconjugants that contributed up to 10% of the total recipient population. The here-presented data of plasmid transfer will be important for future modelling approaches to estimate environmental spread of antibiotic resistance in agricultural production environments.

Antibiotic Resistance and the Biology of History

Beginning in the 1940s, mass production of antibiotics involved the industrial-scale growth of microorganisms to harvest their metabolic products. Unfortunately, the use of antibiotics selects for resistance at answering scale. The turn to the study of antibiotic resistance in microbiology and medicine is examined, focusing on the realization that individual therapies targeted at single pathogens in individual bodies are environmental events affecting bacterial evolution far beyond bodies. In turning to biological manifestations of antibiotic use, sciences fathom material outcomes of their own previous concepts. Archival work with stored soil and clinical samples produces a record described here as 'the biology of history': the physical registration of human history in bacterial life. This account thus foregrounds the importance of understanding both the materiality of history and the historicity of matter in theories and concepts of life today.

The world's microbiology laboratories can be a global microbial sensor network

The microbes that infect us spread in global and local epidemics, and the resistance genes that block their treatment spread within and between them. All we can know about where they are to track and contain them comes from the only places that can see them, the world's microbiology laboratories, but most report each patient's microbe only to that patient's caregiver. Sensors, ranging from instruments to birdwatchers, are now being linked in electronic networks to monitor and interpret algorithmically in real-time ocean currents, atmospheric carbon, supply-chain inventory, bird migration, etc. To so link the world's microbiology laboratories as exquisite sensors in a truly lifesaving real-time network their data must be accessed and fully subtyped. Microbiology laboratories put individual reports into inaccessible paper or mutually incompatible electronic reporting systems, but those from more than 2,200 laboratories in more than 108 countries worldwide are now accessed and translated into compatible WHONET files. These increasingly web-based files could initiate a global microbial sensor network. Unused microbiology laboratory byproduct data, now from drug susceptibility and biochemical testing but increasingly from new technologies (genotyping, MALDI-TOF, etc.), can be reused to subtype microbes of each genus/species into sub-groupings that are discriminated and traced with greater sensitivity. Ongoing statistical delineation of subtypes from global sensor network data will improve detection of movement into any patient of a microbe or resistance gene from another patient, medical center or country. Growing data on clinical manifestations and global distributions of subtypes can automate comments for patient's reports, select microbes to genotype and alert responders.

Antimicrobial resistance among Enterobacteriaceae in South America: history, current dissemination status and associated socioeconomic factors

South America exhibits some of the higher rates of antimicrobial resistance in Enterobactericeae worldwide. This continent includes 12 independent countries with huge socioeconomic differences, where the ample access to antimicrobials, including counterfeit ones, coexists with ineffective health systems and sanitation problems, favoring the emergence and dissemination of resistant strains. This work presents a literature review concerning the evolution and current status of antimicrobial resistance threats found among Enterobacteriaceae in South America. Resistance to β-lactams, fluoroquinolones and aminoglycosides was emphasized along with description of key epidemiological studies that highlight the success of specific resistance determinants in different parts of the continent. In addition, a discussion regarding political and socioeconomic factors possibly related to the dissemination of antimicrobial resistant strains in clinical settings and at the community is presented. Finally, in order to assess the possible sources of resistant bacteria, we compile the current knowledge about the occurrence of antimicrobial resistance in isolates in South American' food, food-producing animals and off-hospitals environments. By addressing that intensive intercontinental commerce and tourism neutralizes the protective effect of geographic barriers, we provide arguments reinforcing that globally integrated efforts are needed to decelerate the emergence and dissemination of antimicrobial resistant strains.

Identification and characterization of the first Escherichia coli strain carrying NDM-1 gene in China

New Delhi metallo-β-lactamase-1 (NDM-1), an acquired class B carbapenemase, is a significant clinical threat due to its extended hydrolysis of β-lactams including carbapenems. In this study, we identified the first confirmed clinical isolate of Escherichia coli BJ01 harboring bla(NDM-1) in China. The isolate is highly resistant to all tested antimicrobials except polymyxin. bla(NDM-1), bla(CTX-M-57), and bla TEM-1 were identified in the isolate. bla(NDM-1) was transferable to E. coli EC600 and DH5α in both plasmid conjugation experiments and plasmid transformation tests. BJ01 was identified as a new sequence type, ST224, by multilocus sequence typing. Analysis of genetic environment shows complex transposon-like structures surrounding the bla NDM-1 gene. Genetic analysis revealed that the region flanking bla(NDM-1) was very similar to previously identified NDM-positive Acinetobacter spp. isolated in China. The findings of this study raise attention to the emergence and spread of NDM-1-carrying Enterobacteriaceae in China.

Antibiotic resistance: from Darwin to Lederberg to Keynes

The emergence and spread of antibiotic-resistant bacteria reflects both, a gradual, completely Darwinian evolution, which mostly yields slight decreases in antibiotic susceptibility, along with phenotypes that are not precisely characterized as "resistance"; and sudden changes, from full susceptibility to full resistance, which are driven by a vast array of horizontal gene transfer mechanisms. Antibiotics select for more than just antibiotic resistance (i.e., increased virulence and enhanced gene exchange abilities); and many non-antibiotic agents or conditions select for or maintain antibiotic resistance traits as a result of a complex network of underlying and often overlapping mechanisms. Thus, the development of new antibiotics and thoughtful, integrated anti-infective strategies is needed to address the immediate and long-term threat of antibiotic resistance. Since the biology of resistance is complex, these new drugs and strategies will not come from free-market forces, or from "incentives" for pharmaceutical companies.

Molecular dissection of an outbreak of carbapenem-resistant enterobacteriaceae reveals Intergenus KPC carbapenemase transmission through a promiscuous plasmid

Carbapenem-resistant Enterobacteriaceae (CRE) have emerged as major causes of health care-associated infections worldwide. This diverse collection of organisms with various resistance mechanisms is associated with increased lengths of hospitalization, costs of care, morbidity, and mortality. The global spread of CRE has largely been attributed to dissemination of a dominant strain of Klebsiella pneumoniae producing a serine β-lactamase, termed K. pneumoniae carbapenemase (KPC). Here we report an outbreak of KPC-producing CRE infections in which the degree of horizontal transmission between strains and species of a promiscuous plasmid is unprecedented. Sixteen isolates, comprising 11 unique strains, 6 species, and 4 genera of bacteria, were obtained from 14 patients over the first 8 months of the outbreak. Of the 11 unique strains, 9 harbored the same highly promiscuous plasmid carrying the KPC gene bla(KPC). The remaining strains harbored distinct bla(KPC) plasmids, one of which was carried in a strain of Klebsiella oxytoca coisolated from the index patient and the other generated from transposition of the bla(KPC) element Tn4401. All isolates could be genetically traced to the index patient. Molecular epidemiological investigation of the outbreak was aided by the adaptation of nested arbitrary PCR (ARB-PCR) for rapid plasmid identification. This detailed molecular genetic analysis, combined with traditional epidemiological investigation, provides insights into the highly fluid dynamics of drug resistance transmission during the outbreak. IMPORTANCE The ease of horizontal transmission of carbapenemase resistance plasmids across strains, species, and genera of bacteria observed in this study has several important public health and epidemiological implications. First, it has the potential to promote dissemination of carbapenem resistance to new populations of Enterobacteriaceae, including organisms of low virulence, leading to the establishment of reservoirs of carbapenem resistance genes in patients and/or the environment and of high virulence, raising the specter of untreatable community-associated infections. Second, recognition of plasmid-mediated outbreaks, such as those described here, is problematic because analysis of resistance plasmids from clinical isolates is laborious and technically challenging. Adaptation of nested arbitrary PCR (ARB-PCR) to investigate the plasmid outbreak facilitated our investigation, and the method may be broadly applicable to other outbreaks due to other conserved mobile genetic elements. Whether infection control measures that focus on preventing transmission of drug-resistant clones are effective in controlling dissemination of these elements is unknown.

Integrated Multilevel Surveillance of the World's Infecting Microbes and Their Resistance to Antimicrobial Agents

Microbial surveillance systems have varied in their source of support; type of laboratory reporting (patient care or reference); inclusiveness of reports filed; extent of microbial typing; whether single hospital, multihospital, or multicountry; proportion of total medical centers participating; and types, levels, integration across levels, and automation of analyses performed. These surveillance systems variably support the diagnosis and treatment of patients, local or regional infection control, local or national policies and guidelines, laboratory capacity building, sentinel surveillance, and patient safety. Overall, however, only a small fraction of available data are under any surveillance, and very few data are fully integrated and analyzed. Advancing informatics and genomics can make microbial surveillance far more efficient and effective at preventing infections and improving their outcomes. The world's microbiology laboratories should upload their reports each day to programs that detect events, trends, and epidemics in communities, hospitals, countries, and the world.

Associations among rhizobial chromosomal background, nod genes, and host plants based on the analysis of symbiosis of indigenous rhizobia and wild legumes native to Xinjiang

The associations among rhizobia chromosomal background, nodulation genes, legume plants, and geographical regions are very attractive but still unclear. To address this question, we analyzed the interactions among rhizobia rDNA genotypes, nodC genotypes, legume genera, as well as geographical regions in the present study. Complex relationships were observed among them, which may be the genuine nature of their associations. The statistical analyses indicate that legume plant is the key factor shaping both rhizobia genetic and symbiotic diversity. In the most cases of our results, the nodC lineages are clearly associated with rhizobial genomic species, demonstrating that nodulation genes have co-evolved with chromosomal background, though the lateral transfer of nodulation genes occurred in some cases in a minority. Our results also support the hypothesis that the endemic rhizobial populations to a certain geographical area prefer to have a wide spectrum of hosts, which might be an important event for the success of both legumes and rhizobia in an isolated region.

Molecular Determinants of Affinity for Aminoglycoside Binding to the Aminoglycoside Nucleotidyltransferase(2‘ ‘)-Ia

One of the most commonly occurring aminoglycoside resistance enzymes is aminoglycoside 2''-O-nucleotidyltransferase [ANT(2'')]. In the present study molecular determinants of affinity and specificity for aminoglycoside binding to this enzyme are investigated using isothermal titration calorimetry (ITC). Binding of aminoglycosides is enthalpically driven accompanied by negative entropy changes. The presence of metal-nucleotide increases the affinity for all but one of the aminoglycosides studied but has no effect on specificity. The substituents at positions 1, 2', and 6' are important determinants of substrate specificity. An amino group at these positions leads to greater affinity. No correlation is observed between the change in affinity and enthalpy. At the 2' position greater affinity results from a more negative enthalpy for an aminoglycoside containing an amino rather than a hydroxyl at that position. At the 6' position the greater affinity for an aminoglycoside containing an amino substituent results from a less disfavorable entropic contribution. The thermodynamic basis for the change in affinity at position 1 could not be determined because of the weak binding of one of the aminoglycoside substrates, amikacin. The effect of increasing osmotic stress on affinity was used to determine that a net release of approximately four water molecules occurs when tobramycin binds to ANT(2''). No measurable net change in the number of bound water molecules is observed when neomycin binds the enzyme. Data acquired in this work provide the rationale for the ability of ANT(2'') to confer resistance against kanamycins but not neomycins.

Enzyme−Substrate Interactions with an Antibiotic Resistance Enzyme: Aminoglycoside Nucleotidyltransferase(2‘ ‘)-Ia Characterized by Kinetic and Thermodynamic Methods

Aminoglycoside nucleotidyltransferase(2'')-Ia is one of the most often detected enzymes in aminoglycoside-resistant bacteria. Despite its prevalence, little biochemical and biophysical work has been reported for this enzyme. In the current study, substrate specificity and temperature dependence of k(cat) are determined by kinetic assays. Dissociation constants and thermodynamic properties of enzyme-substrate complexes are determined by isothermal titration calorimetry, electron paramagnetic resonance, and fluorescence spectroscopy. Kinetic studies show that aminoglycosides with 2'-NH(2) are better substrates (higher k(cat)/K(m)) than ones with 2'-OH when magnesium(II) is used as the catalytically required divalent cation. The activity is reduced 10-fold for substrates with 2'-NH(2) when manganese(II) replaces magnesium as the required metal. However, kanamycin A, which has a 2'-OH, shows a much smaller decrease in activity when manganese substitutes for magnesium as the divalent cation. Temperature dependence studies show the activation energy of catalysis to be 19.2 kcal/mol and the temperature optimum between 30 and 32 degrees C. The binding of the aminoglycoside substrate tobramycin to the enzyme occurs with a favorable enthalpy which compensates for a large entropic penalty to yield a negative DeltaG value for the complex formation. Enthalpy of binding is less exothermic in the presence of metal-nucleotide. However, due to the more favorable entropy, a more favorable DeltaG is observed for the formation of the enzyme-metal-nucleotide:aminoglycoside complex. Tobramycin binds to ANT(2' ') with a dissociation constant of 0.6 microM, which is further reduced by 3-fold when metal-nucleotide is present. Binding of ATP to the enzyme is determined to be very weak in the absence of a divalent cation, and becomes 2 orders of magnitude tighter when magnesium or manganese is present. Binding studies also show that, in addition to binding to the enzyme in the form of metal-nucleotide complex, a second catalytically required metal binds to an additional site on the enzyme.

Antibiotic utilisation in community practices: guideline concurrence and prescription necessity

PURPOSE

To evaluate the indications, concurrence with prescribing guidelines and potential necessity for antibiotic (AB) prescriptions written in community practice.

METHODS

We reviewed the charts of all patients with infection-related illnesses seen by family physicians during two random days of regular practice between 1 Oct 1997 and 30 Jan 1998. Guideline concurrence of AB prescribing was assessed using regional AB prescribing guidelines. Likelihood of AB indication for respiratory tract infections was assessed using published clinical practice guidelines for determination of likely viral versus bacterial etiology.

RESULTS

Of 4218 visits captured, 949 (22%) were for newly acquired infections. Sixty four percent (n=604) of consultations for newly acquired infections resulted in an AB prescription. Based on the doctors' diagnoses, 61% of AB prescriptions were concurrent with prescribing guidelines, 10% were for the wrong drug, 20% were not indicated and in 10% of cases a lower line AB was available. For respiratory tract infections, 12% of these infections were likely bacterial, whereas the physicians determined that 56% were bacterial.

CONCLUSIONS

A large proportion of ABs administered in community practices were not in concurrence with community AB prescribing guidelines. Improvements can be made in AB choice and in decisions about likely viral etiology for respiratory tract infections.

Homologies among three Bacillus licheniformis plasmids and molecular characterization of their replication module

To assess to what extent three Bacillus licheniformis plasmids had the same molecular organization a physical map of the 9.34, 8.40 and 7.90 kb plasmids was achieved by using seventeen restriction enzymes. Southern hybridization was performed on plasmids using restriction fragments of the smallest plasmid as probes. Data from different hybridization patterns show a close homology among the three plasmids hypothesizing a similar molecular organization. The lack of plasmid diversity observed, seem to support the hypothesis of a similar phylogeny among these plasmids. This investigation provides more information concerning phylogeny, interrelationships and level of diversity among Bacillus plasmids and a molecular characterization of three plasmids useful for the construction of cloning vectors.

The traveller and emerging infections: sentinel, courier, transmitter

The movement of populations shapes the patterns and distribution of infectious diseases globally. The consequences of travel are seen in the traveller and in places and populations visited and may persist long after travel. The traveller can be seen as an interactive biological unit who picks up, processes, carries and drops off microbial genetic material. A traveller can introduce potential pathogens in the absence of signs or symptoms of illness. Travellers can serve as a sentinel population; study of them can provide insights into the presence and level of risk of transmission of infections in other geographical regions. Travellers can also be seen as couriers who inadvertently ferry pathogens and microbial genetic material to regions where researchers can carry out detailed analyses that can help to map the location and movement of strains, genotypes and resistance patterns. The laboratory plays a key role in the identification and characterization of pathogens, which can inform management of individual patients and the public health response. The connectedness and mobility in the world today facilitate the emergence of infectious diseases in humans and also in animals and plants. Many traditional barriers have been breached by travel, roads and technology. Population size and density favour spread of many infections. The rapid generation time of microbes and their capacity to adapt to changes in the physico-chemical and immunological environment will pose continuing challenges.

Mercury resistance determinants related to Tn21, Tn1696, and Tn5053 in enterobacteria from the preantibiotic era

Three mer transposons from the Murray collection of preantibiotic enterobacteria show >99% sequence identity to current isolates. Tn5073 is most closely related to Tn5036 and Tn1696, and Tn5074 is most closely related to Tn5053. Tn5075 is most closely related to Tn21 but lacks integron In2 and is flanked by insertion elements.

Emergence, spread, and environmental effect of antimicrobial resistance: how use of an antimicrobial anywhere can increase resistance to any antimicrobial anywhere else

Use of an antimicrobial agent selects for overgrowth of a bacterial strain that has a gene expressing resistance to the agent. It also selects for the assembly and evolution of complex genetic vectors encoding, expressing, linking, and spreading that and other resistance genes. Once evolved, a competitive construct of such genetic elements may spread widely through the world's bacterial populations. A bacterial isolate at any place may thus be resistant-not only because nearby use of antimicrobials had amplified such a genetic construct locally, but also because distant use had caused the construct or its components to evolve in the first place and spread there. The levels of resistance at any time and place may therefore reflect in part the total number of bacteria in the world exposed to antimicrobials up until then. Tracing the evolution and spread of such genetic elements through bacterial populations far from one another, such as those of animals and humans, can be facilitated by newer genetic methods.

Generally overlooked fundamentals of bacterial genetics and ecology

Several important aspects of the antimicrobial resistance problem have not been treated extensively in previous monographs on this subject. This section very briefly updates information on these topics and suggests how this information is of value in assessing the contributions of human and agricultural use of antimicrobial agents on the problem of increasing antimicrobial resistance. The overall themes are (1) that propagation of resistance is an ecological problem, and thus (2) that ameliorating this problem requires recognition of long-established information on the commensal microbiota of mammals, as well as that of recent molecular understanding of the genetic agents involved in the movement of resistance genes.

A decade of antimicrobial susceptibilities at the University of Kentucky Hospital

OBJECTIVE

To determine the antimicrobial susceptibility rates for key antimicrobial agents and selective bacterial pathogens in the decade of the 1990s.

METHODS

Data from 1990 to 2000 from the University of Kentucky Clinical Microbiology Laboratory were analyzed by linear regression analysis to identify agents and pathogens that show a decline in susceptibility. For selected pathogens and antimicrobial agents, predictions were made for further declines in susceptibility for 2005 and 2010.

RESULTS

Significant declines in susceptibility to selected antimicrobial agents were found for Pseudomonas aeruginosa, Klebsiella pneumoniae, Enterobacter cloacae, Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis, and Streptococcus pneumoniae. Further declines were predicted for 2005 and 2010.

CONCLUSIONS

Examination of susceptibility rates over time in a university hospital medical center provides useful data for future planning. In our institution, antimicrobial susceptibility rates have significantly declined during the 1990s for certain antimicrobial agents and bacterial pathogens. We are attempting to change our antimicrobial use patterns through formulary manipulation and clinician education, which may retard or prevent such declines in the future.

The rise and fall of antimicrobial resistance

Antimicrobial resistance is a growing problem in nearly every infectious disease, but the extent and rate of increase of the problem varies widely with different pathogen-drug combinations. The rate of increase of resistance depends primarily on the availability of resistant variants and the intensity of selection imposed by antimicrobial treatment (appropriately measured). Declines in resistance following antimicrobial control measures are typically faster in hospital-acquired infections than in community-acquired ones, probably owing to the dependence in the latter case on the fitness cost of resistance. Open questions and approaches for testing the hypotheses proposed here are outlined.

Dissemination of antibiotic-resistant bacteria across geographic borders

The development of antibiotic-resistant (AR) bacteria in any country is of global importance. After their initial selection and local dissemination, AR bacteria can be transferred across international borders by human travelers, animal and insect vectors, agricultural products, and surface water. The sources and routes of importation of strains of AR bacteria are most often unknown or undetected, because many bacteria carrying resistance genes do not cause disease, and routine surveillance often does not detect them. Control of international dissemination of AR bacteria depends on methods to reduce selection pressure for the development of such bacteria and improved surveillance to detect their subsequent spread.

Effects of yoghurt intake on plasmid transfer and colonisation with transconjugants in the digestive tract of mice associated with human faecal flora

This study deals with the effects of yoghurt intake on wild-type and recombinant plasmid transfer from an exogenous Escherichia coli K12-derivative donor strain to an endogenous recipient strain in the digestive tract of mice associated with human faecal flora. We showed that the self-transmissible plasmid R388 was efficiently transferred to recipient strain PG1 in mice associated with human faecal flora (HFF-PG1) and that the resulting transconjugants (PG1-R388) became established at a high and maximal population level without any selective pressure. Using HFF-PG1 mice made it possible to determine whether yoghurt consumption decreases R388 transfer efficiency and the ability of transconjugant PG1-R388 to successfully colonise the digestive tract. Results indicated that yoghurt consumption had two effects: it reduced the efficacy of plasmid transfer 10-fold and decreased the transconjugant PG1-R388 population density 100-fold, compared to the control group. We also describe another HFF mouse model in which recipient PG1 was replaced by EM0 with which no plasmid transfer was observed. This model made it possible to demonstrate the potential promoting effect of yoghurt intake on transconjugant formation and establishment. Our results indicated no yoghurt effect; no transconjugants appeared in the digestive tract of HFF-EM0 mice fed on yoghurt or on standard food. In both mouse models, HFF-PG1 and HFF-EM0, yoghurt intake did not promote the mobilisation of either the non-self-transmissible plasmid pUB2380 or the recombinant plasmid pCE325.

Antibiotic dispensing by drug retailers in Kathmandu, Nepal

OBJECTIVES To assess over-the-counter antimicrobial dispensing by drug retailers in Kathmandu, Nepal, for rationality, safety, and compliance with existing government regulations.

METHODS

Standardized cases of dysuria in a young adult male and acute watery diarrhoea in a child were presented by a mock patient to retailers at 100 randomly selected pharmacies. Questions asked by retailers and advice and medications given at their initiative were recorded.

RESULTS

All retailers engaged in diagnostic and therapeutic behaviour beyond their scope of training or legal mandate. Historical information obtained by retailers was inadequate to determine the nature or severity of disease or appropriateness of antimicrobial therapy. 97% (95% CI = 91.5-99.4%) of retailers dispensed unnecessary antimicrobials in diarrhoea, while only 44% (95% CI = 34.1-54.3%) recommended oral rehydration therapy and only 3% (95% CI = 0.6-8.5%) suggested evaluation by a physician. 38% (95% CI = 28.5-48.2%) gave antimicrobials in dysuria, yet only 4% (95% CI = 1.1-9.9%) adequately covered cystitis. None covered upper urinary tract or sexually transmitted infections, conditions which could not be ruled out based on the interviews, and only 7% (95% CI = 2.9-13. 9%) referred for a medical history and physical examination necessary to guide therapy.

CONCLUSIONS

Although legislation in Nepal mandates a medical prescription for purchase of antibiotics, unauthorized dispensing is clearly problematic. Drug retailers in our study did not demonstrate adequate understanding of the disease processes in question to justify their use of these drugs. Risks of such indiscretion include harm to individual patients as well as spread of antimicrobial resistance. More intensive efforts to educate drug retailers on their role in dispensing, along with increased enforcement of existing regulations, must be pursued.

Isolation of broad-host-range replicons from marine sediment bacteria

Naturally occurring plasmids isolated from heterotrophic bacterial isolates originating from coastal California marine sediments were characterized by analyzing their incompatibility and replication properties. Previously, we reported on the lack of DNA homology between plasmids from the culturable bacterial population of marine sediments and the replicon probes specific for a number of well-characterized incompatibility and replication groups (P. A. Sobecky, T. J. Mincer, M. C. Chang, and D. R. Helinski, Appl. Environ. Microbiol. 63:888-895, 1997). In the present study we isolated 1.8- to 2.3-kb fragments that contain functional replication origins from one relatively large (30-kb) and three small (<10-kb) naturally occurring plasmids present in different marine isolates. 16S rRNA sequence analyses indicated that the four plasmid-bearing marine isolates belonged to the alpha and gamma subclasses of the class Proteobacteria. Three of the marine sediment isolates are related to the gamma-3 subclass organisms Vibrio splendidus and Vibrio fischeri, while the fourth isolate may be related to Roseobacter litoralis. Sequence analysis of the plasmid replication regions revealed the presence of features common to replication origins of well-characterized plasmids from clinical bacterial isolates, suggesting that there may be similar mechanisms for plasmid replication initiation in the indigenous plasmids of gram-negative marine sediment bacteria. In addition to replication in Escherichia coli DH5alpha and C2110, the host ranges of the plasmid replicons, designated repSD41, repSD121, repSD164, and repSD172, extended to marine species belonging to the genera Achromobacter, Pseudomonas, Serratia, and Vibrio. While sequence analysis of repSD41 and repSD121 revealed considerable stretches of homology between the two fragments, these regions do not display incompatibility properties against each other. The replication origin repSD41 was detected in 5% of the culturable plasmid-bearing marine sediment bacterial isolates, whereas the replication origins repSD164 and repSD172 were not detected in any plasmid-bearing bacteria other than the parental isolates. Microbial community DNA extracted from samples collected in November 1995 and June 1997 and amplified by PCR yielded positive signals when they were hybridized with probes specific for repSD41 and repSD172 replication sequences. In contrast, replication sequences specific for repSD164 were not detected in the DNA extracted from marine sediment microbial communities.

Rhizobium gone native: unexpected plasmid stability of indigenous Rhizobium leguminosarum

Lateral transfer of bacterial plasmids is thought to play an important role in microbial evolution and population dynamics. However, this assumption is based primarily on investigations of medically or agriculturally important bacterial species. To explore the role of lateral transfer in the evolution of bacterial systems not under intensive, human-mediated selection, we examined the association of genotypes at plasmid-encoded and chromosomal loci of native Rhizobium, the nitrogen-fixing symbiont of legumes. To this end, Rhizobium leguminosarum strains nodulating sympatric species of native Trifolium were characterized genetically at plasmid-encoded symbiotic (sym) regions (nodulation AB and nodulation CIJT loci) and a repeated chromosomal locus not involved in the symbiosis with legumes. Restriction fragment length polymorphism analysis was used to distinguish genetic groups at plasmid and chromosomal loci. The correlation between major sym and chromosomal genotypes and the distribution of genotypes across host plant species and sampling location were determined using chi2 analysis. In contrast to findings of previous studies, a strict association existed between major sym plasmid and chromosomal genetic groups, suggesting a lack of successful sym plasmid transfer between major Rhizobium chromosomal types. These data indicate that previous observations of sym plasmid transfer in agricultural settings may seriously overestimate the rates of successful conjugation in systems not impacted by human activities. In addition, a nonrandom distribution of Rhizobium genotypes across host plant species and sampling site demonstrates the importance of both factors in shaping Rhizobium population dynamics.

Homology among nearly all plasmids infecting three Bacillus species

We have surveyed naturally occurring plasmids in strains of Bacillus subtilis and the closely related species B. mojavensis and B. licheniformis. Previous studies have failed to find host-benefitting functions for plasmids of these species, suggesting that these plasmids are nonmutualistic. Only one type of plasmid was found in each plasmid-bearing strain, suggesting that most of the plasmids infecting these Bacillus species are in the same incompatibility group. A sample of 18 plasmids from these species ranged in size from 6.9 to 16 kb, with all but 6 plasmids falling into three size groups. These groups differed in the sizes of their host ranges and geographical ranges. All but 1 of the 18 plasmids from these three host species are homologous with one another. The cryptic plasmids from these three species are far less diverse than are plasmids (from other species) that are known to benefit their bacterial hosts. The low-level diversity among these cryptic plasmids is consistent with the hypothesis that host-benefitting adaptations play an important role in fostering the coexistence of plasmid populations, but other explanations for the low-level plasmid diversity are possible. Comparison of the phylogenies of the plasmids with those of their hosts suggests that Bacillus plasmids are horizontally transferred in nature at a low rate similar to that found for the colicin plasmids of Escherichia coli.

Detection and surveillance of antimicrobial resistance

The clinical microbiology laboratory is strategically positioned to recognize changing patterns in bacterial resistance to antimicrobials. This requires the application of accurate testing methods and a methodological survey of drug-resistance patterns among clinically important bacteria. This information can be assembled into comprehensive international databases, using a common format to facilitate monitoring.

Genetic and molecular R-plasmid analysis of Enterobacteriaceae hospital strains at Children's Hospitals of the former USSR

R-plasmids from Enterobacteriaceae clinical strains, mainly Klebsiella and Serratia, isolated at different neonatal and children's hospitals of different cities of the former USSR for 10 years, were studied for their possible influence on the bacterial host phenotype. Hospital R-plasmids of stable inheritance persisted in hospitals from 2 to 7 years and were disseminated among strains of different genera (Klebsiella, Serratia, Enterobacter) and among different units. The data showed a possibility of long-term molecular rearrangements of R-plasmids in the hospital settings and an acquisition of genetic determinants encoding enterotoxin production. A novel R-plasmid encoding cytotoxicity to HEp-2 cells involved in two nosocomial outbreaks due to K. pneumoniae strains was reported. K. pneumoniae population heterogeneity was evaluated by using the plasmid parameters of strains. Their heterogeneity of a bacterial population was significantly lower during nosocomial outbreaks than in interepidemic periods.

Risk factors for acquisition of multiply drug-resistant gram-negative bacteria

Some bacteria are naturally resistant to many antibiotics and most can become multiply resistant. Multiply resistant gram-negative bacteria have proved a particular problem over the last 30 years, but the development of new agents has lessened their significance for most clinicians. Now, however, clinical practice is threatened by the lack of new classes of antibiotics, the widespread emergence of resistance and the advent of plasmid-mediated cephalosporinases by which the spread of resistance is likely to be rapid. Increased use of prophylaxis in immunosuppressed and intensive care patients is likely to aggravate the problem, as is the use of new broad-spectrum agents in the community. More directed and restricted antibiotic use and better education of patients and prescriber are necessary to contain the problem of antibiotic resistance. Improved surveillance of sensitivity trends is essential. Many outbreaks also are associated with poor infection control techniques. The cost of outbreaks due to multiply resistant organisms and lack of compliance with infection control procedures needs to be properly studied. While many predisposing factors for the acquisition of these organisms and the development of infection are understood, the multifactorial nature of illness in many patients complicates the issue, necessitating further study of risk factors and preventative and therapeutic measures.

Plasmid diversity in Escherichia coli isolated from processed poultry and poultry processors

Plasmids of bacteria selected from different bacterial populations because they shared a distinctive antimicrobial resistance phenotype have sometimes had identical restriction fragments. Such identical plasmids are thought to belong to small and thus epidemic clones because the plasmid content of unselected resistant isolates has seemed diverse. To survey this presumed diversity and its implications for the lineage of resistance plasmids we examined the transferability, sizes and EcoR1 restriction fragment sizes of plasmids in both Escherichia coli isolated randomly from poultry raised by 16 growers as they were being processed through two plants and in isolates from the urine of women processing poultry in those plants. Forty two (24%) of 175 resistant isolates from poultry of 16 growers and 9 (26%) of 34 resistant isolates from the poultry processors transferred resistance conjugatively to varied combinations of antimicrobials. No poultry isolate had both the same expressed and the same transferred combination as any processor's isolate. The DNA bands which could be discerned in electrophoresis gels of restricted or unrestricted plasmid extracts of isolates or their transconjugants from 156 of the poultry and 24 of the poultry processors appeared diverse. Pairs of related-appearing plasmids were seen in consecutive isolates of poultry from each of two growers and in one pair from different growers. One set of identical-appearing plasmids was seen in 3 consecutive isolates from poultry of one grower, others in 2 consecutive isolates from a second grower's poultry, in 2 non-consecutive isolates of a third grower's, and in single isolates from poultry of 2 different growers. None of the plasmids from any of the human isolates appeared related to those from any other human isolate or to those of any poultry isolate. These results indicate that resistance plasmids are highly diverse and that all but two of the exceptions to complete diversity in the isolates surveyed here could be ascribed to cross colonization within flocks of individual poultry growers. Also, while none of the plasmids in the poultry isolates appeared ancestral to any of plasmids in the poultry processors' isolates, their diversity indicates that those sampled plasmids would be only a very small fraction of the total number of different plasmids in bacteria colonizing poultry processed at that time or earlier.

Mercury released from dental "silver" fillings provokes an increase in mercury- and antibiotic-resistant bacteria in oral and intestinal floras of primates

In a survey of 640 human subjects, a subgroup of 356 persons without recent exposure to antibiotics demonstrated that those with a high prevalence of Hg resistance in their intestinal floras were significantly more likely to also have resistance to two or more antibiotics. This observation led us to consider the possibility that mercury released from amalgam ("silver") dental restorations might be a selective agent for both mercury- and antibiotic-resistant bacteria in the oral and intestinal floras of primates. Resistances to mercury and to several antibiotics were examined in the oral and intestinal floras of six adult monkeys prior to the installation of amalgam fillings, during the time they were in place, and after replacement of the amalgam fillings with glass ionomer fillings (in four of the monkeys). The monkeys were fed an antibiotic-free diet, and fecal mercury concentrations were monitored. There was a statistically significant increase in the incidence of mercury-resistant bacteria during the 5 weeks following installation of the amalgam fillings and during the 5 weeks immediately following their replacement with glass ionomer fillings. These peaks in incidence of mercury-resistant bacteria correlated with peaks of Hg elimination (as high as 1 mM in the feces) immediately following amalgam placement and immediately after replacement of the amalgam fillings. Representative mercury-resistant isolates of three selected bacterial families (oral streptococci, members of the family Enterobacteriaceae, and enterococci) were also resistant to one or more antibiotics, including ampicillin, tetracycline, streptomycin, kanamycin, and chloramphenicol. While such mercury- and antibiotic-resistant isolates among the staphylococci, the enterococci, and members of the family Enterobacteriaceae have been described, this is the first report of mercury resistance in the oral streptococci. Many of the enterobacterial strains were able to transfer mercury and antibiotic resistances together to laboratory bacterial recipients, suggesting that the loci for these resistances are genetically linked. Our findings indicate that mercury released from amalgam fillings can cause an enrichment of mercury resistance plasmids in the normal bacterial floras of primates. Many of these plasmids also carry antibiotic resistance, implicating the exposure to mercury from dental amalgams in an increased incidence of multiple antibiotic resistance plasmids in the normal floras of nonmedicated subjects.

Correlation between aminoglycoside resistance profiles and DNA hybridization of clinical isolates

DNA hybridization data and aminoglycoside resistance profiles (AGRPs) were determined for 4,088 clinical isolates from three studies (United States, Belgium, and Argentina). The correlation between susceptibility profiles and hybridization results was determined with nine DNA probes. For each of the seven aminoglycoside resistance profiles which we were able to test, the data suggested at least two distinct genes could encode enzymes which lead to identical resistance profiles. Furthermore, the DNA hybridization data showed that individual strains carried up to six unique aminoglycoside resistance genes. DNA hybridization revealed interesting differences in the frequencies of these genes by organism and by country.

Contemporary challenges for hospital epidemiology

According to conventional wisdom, it is time for hospital epidemiologists to look beyond traditional infection control responsibilities and to shoulder an "expanded role," including quality assurance, risk management, and pharmacoepidemiology. Some see this as a matter of survival as the profession reacts to potent external forces that seek to curb the cost of health care while assuring quality service. Infection control specialists, it is argued, have the epidemiologic skills to measure adverse outcomes of hospitalization, adjust for confounding variables, and evaluate the impact of targeted interventions. Before embracing these new responsibilities, however, it should be noted that many hospital epidemiologists would require additional training in basic epidemiologic principles. Although hospital epidemiologists may seek a leadership role in hospital quality assurance and health policy research, they have generally not been innovators in these fields, even in some specific areas relevant to infection control. For example, while hospital epidemiologists have begun to consider severity of illness as a potential confounder in epidemiologic analyses, they have not participated in the development or validation of any of the most widely used indicators. For those hospital epidemiologists who wish to capitalize on their traditional background in infectious diseases, contemporary infection control provides numerous challenges. For example, the epidemiology of many common nosocomial infections, such as bacterial pneumonia in immunocompromised hosts, remains to be defined. Hospital epidemiologists need to incorporate a variety of sophisticated microbiologic methods into their practice to help them trace the spread of nosocomial pathogens. Finally, they should collaborate more closely with clinical and bench investigators in a number of areas, including microbial pathogenesis, immunology, and biotechnology.

Nosocomial spread of an amikacin resistance gene on both a mobilized, nonconjugative plasmid and a conjugative plasmid

Resistance to amikacin among members of the family Enterobacteriaceae at a hospital in Venezuela rose from 2% in 1979 to 5% in 1984 and 10% in 1985 as amikacin usage rose 20-fold to exceed gentamicin usage. Resistance to gentamicin remained at 25 to 27%. We examined the plasmids from 21 isolates obtained in 1984 and 1985. Nine of eleven in 1984 and three of ten in 1985 carried aacA and sul on a 3.8-kb BamHI fragment of pBWH300, a 10.4-kb nonconjugative plasmid that had been mobilized into strains of six species by at least two different coresident conjugative plasmids. Six 1985 isolates of two species carried these genes on a similar BamHI fragment of the 104-kb conjugative plasmid pBWH303. One isolate in 1984 and one in 1985 carried the 69-kb conjugative plasmid pBWH301, which had aacA as the promoter-proximal gene of an operon that also encompassed the cat and aadB resistance genes. Another conjugative plasmid, pBWH302, was found in a single isolate. It carried a different aacA allele on the functional transposon Tn654, which appeared to be closely related to Tn1331, a transposon previously isolated in Argentina and Chile. Increased selection may thus have led to dissemination of an endemic aacA allele on two endemic plasmids, one spread by mobilization, with occasional intrusion of additional aacA alleles from outside.

[Contribution to the discussion on the release of transgenic organisms. II. Ecologic aspects]

Problems which might be caused by the release of transgenic organisms are discussed from the viewpoint of genetics, population genetics and ecology. On this background, the differences between "classical" methods to recombine genetic information and the more recent ones of gene engineering are pointed out and the predictability of gene interactions is discussed. Moreover, the possibility of uncontrolled reproduction of released transgenic organisms and the distribution of manipulated genes are demonstrated on the basis of our knowledge on nontransgenic organisms. Finally, the problems of risk assessment are emphasized.

Antibiotic availability and use: consequences to man and his environment

Antibiotics are the cornerstone of therapy for infectious diseases affecting people living worldwide. The ability of these agents to cure infections, with little if any harm to the host, has helped to propagate their designation as "miracle drugs". This idea has continued throughout the past four decades and into the present one. To a large extent, this concept has led to the inappropriate use of these agents. The consequence of this misuse affects not only the individuals taking antibiotics, but indirectly others who may subsequently need antibiotics, but find that the infecting pathogen is resistant. This phenomenon results from the strong selective environmental effect of these drugs for resistant bacteria. Resistant pathogens have emerged and spread worldwide. In response to this global health problem, the Alliance for the Prudent Use of Antibiotics was established. This international network of concerned prescribers and users aims to improve antibiotic use and eliminate inappropriate use worldwide. Prudent use of antibiotics will not only curtail health care costs and the potential side effects to the individual taking these drugs, but also diminish the wide ecologic effects leading to selection of antibiotic resistant forms of common disease-causing agents.

Spreading of streptomycin antibiotic resistance gene in Escherichia coli plasmids demonstrated by Southern blot analysis

Plasmids from E. coli strains of 38 donors were transconjugated to common recipient SY663 Escherichia coli K12. The restriction patterns of the isolated plasmids were highly heterogenous. However, the streptomycin (Sm) resistance genes of the plasmids were identical or closely homologous in 29 of the 33 plasmids conferring Sm resistance. These data were based on Southern blot analysis, using the Sm resistance gene (encoding aminoglycoside phosphoryl transferase) as probe cut out from pBP1 plasmid. Our data suggest an extensive spreading of streptomycin resistance gene of this type.

Nucleotide sequence analysis of 2''-aminoglycoside nucleotidyl-transferase ANT(2'') from Tn4000: its relationship with AAD(3'') and impact on Tn21 evolution

Aminoglycoside 2''-O-nucleotidyltransferase (AAD(2'')) mediates bacterial resistance to dibekacin, gentamicin, kanamycin, sisomicin and tobramycin. Its coding sequence, aadB, is part of Tn21-related transposon, Tn4000. Nucleotide sequence analysis revealed the presence of an open reading frame capable of specifying a protein of 177 amino acids with a calculated molecular weight of 21,240. The predicted amino acid sequence revealed up to 27% homology to that of three nucleotidyltransferases of type AAD(3''), which are widely distributed among Gram-negatives, and to the AAD(9) from Staphylococcus aureus transposon Tn554. The regions flanking aadB suggest that its insertion into Tn21 arose from a site-specific recombination event adjacent to the aadA gene.

Functional and structural map of pLST1000: a multiresistance plasmid widely distributed in Enterobacteriaceae

pLST1000, an 80-kb plasmid found in Enterobacteriaceae in North and South America, harbors the aadB and several other resistance genes. We suggested earlier that, because of its widespread distribution, pLST1000 could act as a carrier plasmid, bringing the aadB gene to new locations. This paper presents the restriction enzyme recognition site and functional map of the plasmid. The resistance genes lie in a discreet region. The aadB and aadA genes form an operon with the aadB gene promoter proximal. This operon is flanked by bla-TEM and bla-OXA2 genes, the former located in a functional Tn3-like transposon. This arrangement is similar to that of relatives of the transposon TN21, where additional resistance genes are precisely inserted in recombinational "hot spot" sequences that flank the aadA gene. We were not able to demonstrate transposition of the aadB gene in Escherichia coli. A sul gene and mer operon lie beyond the bla-OXA2 gene. The transfer genes form a single region, defined by insertions of Tn5-132 that give the Tra- phenotype.

Molecular epidemiology of OHIO-1 beta-lactamase

A total of 31 plasmids, all bearing a gene that encodes a novel, plasmid-mediated Richmond-Sykes class III beta-lactamase designated OHIO-1 and a gene that encodes aminoglycoside 2"-adenyltransferase, have been collected from hospitals in Ohio. By using restriction endonuclease digestion and Southern hybridization, we were able to demonstrate that all these plasmids have a common genetic origin.

Veterans Administration Hospital ANT(2") plasmid in Dallas, Tex

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New microbiological techniques for hospital epidemiology

Infection control teams rely on microbiology laboratories for accurate, reproducible data to trace the spread of microorganisms in the hospital. Since few problems are recognized immediately, laboratories should save important nosocomial pathogens so that outbreak strains will be available for analysis by more sophisticated techniques, particularly since automation has reduced the amount of epidemiologically useful data generated by routine procedures. Traditional supplemental reference procedures include phage typing, biotyping, serotyping and bacteriocin typing. Recently, analysis of antibiotic resistance determinants has provided the hospital epidemiologist with additional tools. Resistant strains have been characterized by their production of specific antibiotic inactivating enzymes. Agarose gel electrophoresis and restriction endonuclease analysis of plasmid DNA have permitted precise characterization of nosocomial strains, and the spread of antibiotic resistance genes can now be followed by sensitive and specific DNA probes. DNA probes also show promise for distinguishing nosocomial strains bearing known virulence factors from strains with less pathogenic potential. Molecular genetics techniques have found an additional role in elucidating the epidemiology of nosocomial viruses, especially the herpesviruses.

More than one DNA sequence encodes the 2''-O-adenylyltransferase phenotype

Biochemical and phenotypic assays indicate that three enterobacterial R plasmids isolated in a single hospital encode 2''-O-adenylyltransferase [ANT(2'')], and an ANT(2'')-specific probe was developed from one plasmid. Southern hybridization revealed the three plasmids to be unrelated and, further, showed their ANT(2'')-encoding genes to be different.