Antibiotic resistance and transmissible R-factors in the intestinal coliform flora of healthy adults and children in an urban and a rural community

OUP accepted manuscript

Escherichia coli has a rich history as biology's ‘rock star’, driving advances across many fields. In the wild, E. coli resides innocuously in the gut of humans and animals but is also a versatile pathogen commonly associated with intestinal and extraintestinal infections and antimicrobial resistance—including large foodborne outbreaks such as the one that swept across Europe in 2011, killing 54 individuals and causing approximately 4000 infections and 900 cases of haemolytic uraemic syndrome. Given that most E. coli are harmless gut colonizers, an important ecological question plaguing microbiologists is what makes E. coli an occasionally devastating pathogen? To address this question requires an enhanced understanding of the ecology of the organism as a commensal. Here, we review how our knowledge of the ecology and within-host diversity of this organism in the vertebrate gut has progressed in the 137 years since E. coli was first described. We also review current approaches to the study of within-host bacterial diversity. In closing, we discuss some of the outstanding questions yet to be addressed and prospects for future research.

Assessing Transmission of Antimicrobial-Resistant Escherichia coli in Wild Giraffe Contact Networks

There is growing evidence that anthropogenic sources of antibiotics and antimicrobial-resistant bacteria can spill over into natural ecosystems, raising questions about the role wild animals play in the emergence, maintenance, and dispersal of antibiotic resistance genes. In particular, we lack an understanding of how resistance genes circulate within wild animal populations, including whether specific host characteristics, such as social associations, promote interhost transmission of these genes. In this study, we used social network analysis to explore the forces shaping population-level patterns of resistant Escherichia coli in wild giraffe (Giraffa camelopardalis) and assess the relative importance of social contact for the dissemination of resistant E. coli between giraffe. Of 195 giraffe sampled, only 5.1% harbored E. coli isolates resistant to one or more tested antibiotics. Whole-genome sequencing on a subset of resistant isolates revealed a number of acquired resistance genes with linkages to mobile genetic elements. However, we found no evidence that the spread of resistance genes among giraffe was facilitated by interhost associations. Giraffe with lower social degree were more likely to harbor resistant E. coli, but this relationship was likely driven by a correlation between an individual's social connectedness and age. Indeed, resistant E. coli was most frequently detected in socially isolated neonates, indicating that resistant E. coli may have a selective advantage in the gastrointestinal tracts of neonates compared to other age classes. Taken together, these results suggest that the maintenance of antimicrobial-resistant bacteria in wild populations may, in part, be determined by host traits and microbial competition dynamics within the host.IMPORTANCE Antimicrobial resistance represents a significant threat to human health, food security, and the global economy. To fully understand the evolution and dissemination of resistance genes, a complete picture of antimicrobial resistance in all biological compartments, including natural ecosystems, is required. The environment and wild animals may act as reservoirs for anthropogenically derived resistance genes that could be transferrable to clinically relevant bacteria of humans and domestic animals. Our study investigated the possible transmission mechanisms for antimicrobial-resistant bacteria within a wild animal population and, more broadly, contributes to our understanding of how resistance genes are spread and maintained in natural ecosystems.

Mobile genetic elements of the human gastrointestinal tract: potential for spread of antibiotic resistance genes

The human intestine is an important location for horizontal gene transfer (HGT) due to the presence of a densely populated community of microorganisms which are essential to the health of the human superorganism. HGT in this niche has the potential to influence the evolution of members of this microbial community and to mediate the spread of antibiotic resistance genes from commensal organisms to potential pathogens. Recent culture-independent techniques and metagenomic studies have provided an insight into the distribution of mobile genetic elements (MGEs) and the extent of HGT in the human gastrointestinal tract. In this mini-review, we explore the current knowledge of mobile genetic elements in the gastrointestinal tract, the progress of research into the distribution of antibiotic resistance genes in the gut and the potential role of MGEs in the spread of antibiotic resistance. In the face of reduced treatment options for many clinical infections, understanding environmental and commensal antibiotic resistance and spread is critical to the future development of meaningful and long lasting anti-microbial therapies.

A brief multi-disciplinary review on antimicrobial resistance in medicine and its linkage to the global environmental microbiota

The discovery and introduction of antimicrobial agents to clinical medicine was one of the greatest medical triumphs of the 20th century that revolutionized the treatment of bacterial infections. However, the gradual emergence of populations of antimicrobial-resistant pathogenic bacteria resulting from use, misuse, and abuse of antimicrobials has today become a major global health concern. Antimicrobial resistance (AMR) genes have been suggested to originate from environmental bacteria, as clinically relevant resistance genes have been detected on the chromosome of environmental bacteria. As only a few new antimicrobials have been developed in the last decade, the further evolution of resistance poses a serious threat to public health. Urgent measures are required not only to minimize the use of antimicrobials for prophylactic and therapeutic purposes but also to look for alternative strategies for the control of bacterial infections. This review examines the global picture of antimicrobial resistance, factors that favor its spread, strategies, and limitations for its control and the need for continuous training of all stake-holders i.e., medical, veterinary, public health, and other relevant professionals as well as human consumers, in the appropriate use of antimicrobial drugs.

Commensal Escherichia coli of healthy humans: a reservoir for antibiotic-resistance determinants

This study examined in detail the population structure of Escherichia coli from healthy adults with respect to the prevalence of antibiotic resistance and specific resistance determinants. E. coli isolated from the faeces of 20 healthy adults not recently exposed to antibiotics was tested for resistance to ten antibiotics and for carriage of integrons and resistance determinants using PCR. Strain diversity was assessed using biochemical and molecular criteria. E. coli was present in 19 subjects at levels ranging from 2.0×104 to 1.7×108 c.f.u. (g faeces)−1. Strains resistant to one to six antibiotics were found at high levels (>30 %) in only ten individuals, but at significant levels (>0.5 %) in 14. Resistant isolates with the same phenotype from the same individual were indistinguishable, but more than one susceptible strain was sometimes found. Overall, individuals harboured one to four E. coli strains, although in 17 samples one strain was dominant (>70 % of isolates). Eighteen strains resistant to ampicillin, sulfamethoxazole, tetracycline and trimethoprim in 15 different combinations were observed. One resistant strain was carried by two unrelated individuals and a susceptible strain was shared by two cohabiting subjects. Two minority strains were derivatives of a more abundant resistant strain in the same sample, showing that continuous evolution is occurring in vivo. The trimethoprim-resistance genes dfrA1, dfrA5, dfrA7, dfrA12 or dfrA17 were in cassettes in a class 1 or class 2 integron. Ampicillin resistance was conferred by the bla TEM gene, sulfamethoxazole resistance by sul1, sul2 or sul3 and tetracycline resistance by tetA(A) or tetA(B). Chloramphenicol resistance (cmlA1 gene) was detected only once. Phylogenetic groups A and B2 were more common than B1 and D. Commensal E. coli of healthy humans represent an important reservoir for numerous antibiotic-resistance genes in many combinations. However, measuring the true extent of resistance carriage in commensal E. coli requires in-depth analysis.

Evaluation of a rapid screening method for detection of antimicrobial resistance in the commensal microbiota of the gut

The assessment of antimicrobial resistance among commensal bacteria is an indicator of the spread of antimicrobial resistance. Rapid screening methods for detection of antimicrobial-resistant faecal Escherichia coli directly on MacConkey plates have been successfully adopted but suffer from lack of standardisation. The purpose of this study was to evaluate a direct plating method (DPM) for detection of antimicrobial-resistant faecal E. coli and to compare it with a conventional method. Faecal samples were collected from 71 healthy children from Peru and Bolivia. In the DPM, a faecal swab was directly plated onto a MacConkey agar plate and antimicrobial disks were applied onto the seeded plate. Raw data were obtained by direct reading of the plate and were subjected to confirmatory analysis. Good concordance between the DPM and a conventional method was observed in detecting carriage of resistant E. coli, with a higher sensitivity for the DPM. Analysis of the results allowed interpretive criteria to be defined for DPM raw data. The DPM showed good sensitivity and specificity at very low cost (ten times cheaper than the conventional method) to investigate the faecal carriage of drug-resistant E. coli. It may represent a useful tool to conduct large-scale resistance surveillance studies and to monitor resistance control programmes cost effectively, particularly in low-resource countries.

Potential impact of increased use of biocides in consumer products on prevalence of antibiotic resistance

There has recently been much controversy surrounding the increased use of antibacterial substances in a wide range of consumer products and the possibility that, as with antibiotics, indiscriminate use of biocides might contribute to the overall pattern of susceptibility in the general environment and in the clinic. Such speculation, based on the isolation of resistant mutants from in vitro monoculture experiments, is not reflected by an emergence of biocide-resistant strains in vivo. This review provides a broad coverage of the biocide and resistance literature and evaluates the potential risks, perceived from such laboratory monoculture experiments, against evidence gathered over 50 years of field studies. An explanation for the continued effectiveness of broad-spectrum biocidal agents against the decline in efficacy of therapeutic agents is provided based on the fitness costs of resistance and the ubiquity of naturally occurring substances that possess antibacterial effect. While we conclude from this review of the literature that the incorporation of antibacterial agents into a widening sphere of personal products has had little or no impact on the patterns of microbial susceptibility observed in the environment, the associated risks remain finite. The use of such products should therefore be associated with a clear demonstration of added value either to consumer health or to the product life. Hygienic products should therefore be targeted to applications for which the risks have been established.

Multiple antibiotic resistance patterns of Escherichia coli isolates from swine farms

Antibiotic resistance of Escherichia coli from sows and pigs was determined to compare patterns between pigs of various ages and degrees of antibiotic use. Resistance patterns differed between farm types and pigs of differing ages, indicating that pig age and degree of antibiotic use affect resistance of fecal E. coli.

The prevalence of antibiotic-resistant faecal Escherichia coli in healthy volunteers in Venezuela

Faecal samples were collected from healthy volunteers in two regions in Venezuela, the village of Grulla (n = 195) and the city of Mérida (n = 181), and analysed for the prevalence of antibiotic resistant faecal Escherichia coli as well as the antibiotic susceptibility of the strains isolated. The highest prevalences of resistance were observed for amoxicillin, oxytetracycline, sulfamethoxazole and trimethoprim. The percentages found for Grulla were 46, 38, 44 and 30%, respectively; for Mérida 39, 65, 56 and 36%, respectively. In Mérida, a significantly higher prevalence of resistance for oxytetracycline was found (P < 0.05). Significant differences in the distribution of the MIC values between Grulla and Mérida were observed for amoxicillin, chloramphenicol and oxytetracycline (P < 0.05). In Grulla, the most frequent pattern was resistance to amoxicillin only and in Mérida to oxytetracycline only. Amoxicillin resistance was due to production of TEM1 beta-lactamase.

Associations among antimicrobial drug treatments and antimicrobial resistance of fecal Escherichia coli of swine on 34 farrow-to-finish farms in Ontario, Canada

Logistic regression was used to model associations between antimicrobial treatment and resistance among fecal Escherichia coli of finisher pigs at the farm level. Four sets of potential risk factors representing different levels of refinement of antimicrobial use on farms were modelled on resistance to antimicrobials. Final models for each antimicrobial were constructed from treatment and management variables significant on initial screening, and corrections for overdispersion were made. In general, in-feed antimicrobial treatment of pigs was more consistently associated with an increased risk of resistance than individual-animal treatment. Antimicrobial treatment in starter rations was significant in final models of resistance to ampicillin, carbadox, nitrofurantoin, sulfisoxizole, and tetracycline. Treatment in grower-finisher rations was significantly associated with resistance to ampicillin, spectinomycin, sulfisoxizole, and tetracycline. There was little evidence that in-feed antimicrobials increased the risk of resistance to gentamicin, which is a drug used only for individual-pig treatment in this study population. These results suggest that antimicrobial medication of rations of post-weaning pigs selects for and maintains antimicrobial resistance among E. coli of finisher pigs. Although resistance was common on farms that did not medicate rations of post-weaning pigs, the results indicate that antimicrobial use does increase the risk of resistance to the antimicrobials studied.

Screening for antimicrobial resistance in fecal samples by the replica plating method

Replica plating can be used for the detection of antibiotic resistance in normal flora. We have evaluated this application of the replica plating method by comparing it with a five-colony method. The replica plating method uses a single plate for each antibiotic, with a concentration just above that for borderline resistance. By the five-colony method, five colonies per sample were picked, chosen to represent all different colony morphologies present, and MICs were determined by a standard agar dilution method. The gram-negative, aerobic floras of 131 fecal samples were screened for resistance to ampicillin, cefuroxime, nalidixic acid, trimethoprim, sulfamethoxazole, and tetracycline by both methods. The rate of resistance detection by the two methods did not differ statistically for any of the antibiotics tested. The breakpoint concentrations used for the replica plates in the study gave results similar to those produced by the agar dilution method and the breakpoint values of the National Committee for Clinical Laboratory Standards and can thus be recommended. As the only currently used resistance detection method, replica plating facilitates an exact determination of the percentage of resistant colonies/total number of colonies (between 1 and 100%) in a sample. This revealed an uneven distribution, with only 23% of the samples having resistance frequencies in the range of 10 to 85%; usually, the resistant flora either was a small minority or was very dominant in samples with resistance. This phenomenon was present for all of the antibiotics.

Resistance in faecal Escherichia coli isolated from pigfarmers and abattoir workers

Faecal samples collected from three populations of healthy adult volunteers (290 pigfarmers, 316 abattoir workers, 160 (sub)urban residents) living in the south of The Netherlands were analysed for the prevalence and degree of antibiotic resistance of Escherichia coli. Significant differences in prevalence of resistance to amoxicillin, neomycin, oxytetracycline, sulfamethoxazole and trimethoprim were observed. The pigfarmers showed the highest percentages of resistance and the (sub)urban residents the lowest. In contrast no significant differences in high degrees of resistance were observed, except for neomycin. Although both pigfarmers and abattoir workers have regular contact with pigs differences in prevalences of resistance were observed. However, because abattoir workers with intensive and less intensive pig(carcass) contact did not show significant differences, this is probably not the only important source of resistant E. coli in pigfarmers. The high antibiotic use by pigfarmers (5%) and abattoir workers (8%) than by (sub)urban residents (0%) did not result in significantly different resistance percentages.

Positive correlation between the age of patients and the degree of antimicrobial resistance among urinary strains of Escherichia coli

We have studied the resistance of urinary strains of Escherichia coli in relation to patients' age. A total of 4146 samples of urine was collected during 1984-1990 from patients staying in an acute care university hospital and in a long-term care city hospital in Finland. In the city hospital, the proportion of strains resistant to either ampicillin, trimethoprim, sulphonamides, or to all of these simultaneously (multi-resistant), correlated with increase in age of the patients. In the university hospital, a clear increase was observed in trimethoprim-resistant and multiresistant isolates. Such correlation with age was not observed among catheterised patients in either hospital. Whether this is due to cumulative lifetime use of antimicrobials remains to be studied. We conclude that the incidence of resistant strains of E. coli correlates with patients' age among both chronic and acute care patients who are not catheterised. This is important in the choice of empirical treatment for urinary tract infections of elderly people.

Carriage of antibiotic-resistant Escherichia coli by healthy volunteers during a 15-week period

Escherichia coli strains (n = 678 and n = 670) isolated from faecal samples from 90 and 93 healthy volunteers of two cities, Weert and Roermond respectively, were analysed for their susceptibility to 12 antimicrobial agents during a 15-week period. Significant differences between both cities in the distribution of the MIC values were observed for apramycin, chloramphenicol, kanamycin, neomycin, nitrofurantoin, sulfamethoxazole and trimethoprim. For Weert (n = 678) the antibiotic resistance percentages varied from 0.4% for nalidixic acid to 26.7% for sulfamethoxazole. For Roermond (n = 670) the figures varied from 0.6% for nitrofurantoin to 37.5% for sulfamethoxazole. Resistance to amoxicillin/clavulanate was not found in either city. The most frequent pattern was resistance to sulfamethoxazole only, followed by resistance to oxytetracycline, streptomycin and sulfamethoxazole. In each individual there was only a small variation in resistance patterns of the isolates, i.e. the majority had one (n = 51) or two (n = 63) patterns with a maximum of five during the 15-week period. A fully susceptible pattern was found in the strains from 38 individuals.

Antibiotic sensitivity of enteric pathogens in Vietnam

The in vitro antimicrobial susceptibilities of 675 common enteropathogenic isolates from faecal specimens of patients with diarrhea (E. coli, Shigella, Salmonella and V. cholerae), and 568 E. coli isolates from faecal flora of healthy persons, which were collected as part of a National antibiotic resistance surveillance in Vietnam, were determined. The agar dilution method was used for the following nine antibiotics: ampicillin, doxycycline, chloramphenicol, gentamicin, nalidixic acid, kanamycin, trimethoprim, trimethoprim in combination with sulfamethoxazole (1/20), and sulfisomidin. Gentamicin was the most active of the antibiotics tested against all bacterial species with MICs in the range 0.125-4 mg/l. All strains were susceptible to nalidixic acid (0.125-8 mg/l) and more than 90% were susceptible to kanamycin. Among E. coli and Shigella isolates from patients the frequencies of resistance to commonly used antibiotics were high: ampicillin 73% and 84%, doxycycline 83% and 94%, chloramphenicol 71% and 91%, sulfisomidin 82% and 92%, respectively. Resistance to trimethoprin, as well as to the combination with sulfamethoxazole was found in 21% and 23%, respectively. The frequencies of multiple resistance (resistance to three or more antibiotics) were also high (77% and 89%, respectively). Less than 10% of Salmonellae and V. cholerae isolates were resistant to ampicillin, sulfisomidin or trimethoprim. Among E. coli from healthy people the frequencies of resistance were lower than in isolates from patients: ampicillin 23%, doxycycline 40%, chloramphenicol 21% and sulfisomidin 34%. However, the same patterns of multiple resistance were found in both groups.

The carriage of Escherichia coli resistant to antimicrobial agents by healthy children in Boston, in Caracas, Venezuela, and in Qin Pu, China

BACKGROUND AND METHODS

The healthy members of a community represent its largest reservoir of bacteria resistant to antimicrobial agents. We compared the resistance to eight agents of Escherichia coli in stool samples from untreated, healthy children in cities on three continents.

RESULTS

When screened by a selective method that detected 1 resistant colony in 10,000 colonies, nearly half the children in Boston (18 of 39) had no resistant colonies--a finding consistent with the findings of other surveys performed in developed countries. However, all but 1 of 41 children screened in Caracas, Venezuela, and all but 2 of 53 in Qin Pu, China, carried resistant strains. Only 1 child in Boston but 25 in Caracas and 34 in Qin Pu carried strains resistant to trimethoprim. None of the children in Boston or Caracas but 17 in Qin Pu carried strains resistant to gentamicin. Among 10 colonies selected randomly from each stool sample, the average frequency of resistance in Caracas was 3.6 times greater than in Boston, and that in Qin Pu was 5.3 times greater. There was resistance to five or more antimicrobial agents in 20 percent of the Qin Pu strains and in 6 percent of the Caracas strains but in none of the Boston strains.

CONCLUSIONS

In addition to clinical isolates, as reported previously, the bacteria that colonize health children in the community may be resistant far more often in some regions than in others. A low rate of carriage of antimicrobial resistance in the community should become a public health goal.

High frequency of antimicrobial resistance in human fecal flora

The frequency of resistance to seven different antimicrobial agents was examined in the aerobic gram-negative gut flora of over 600 individuals from hospitals, from laboratories where antibiotics were used, and from urban and rural communities. In a majority (62.5%) of fecal samples from people without a recent history of taking antibiotics, 10% or more of the total organisms were resistant to at least one of the antibiotics. In about 40% of the samples, resistance to more than one drug was present at this level. More than one-third of the samples contained resistant organisms comprising 50% or more of the total flora examined. Organisms with coresistance to multiple drugs were found frequently. Individuals taking antibiotics produced more samples with a higher proportion (greater than 50%) of resistant bacteria, and these samples also had a significantly greater number of different resistance determinants. This extensive study revealed a high prevalence of resistant bacteria in the gut flora of ambulatory and hospitalized individuals whether or not they were taking antibiotics.

Effect of age and housing location on antibiotic resistance of fecal coliforms from pigs in a non-antibiotic-exposed herd

The relationship of age and housing location to single antibiotic resistance, multiple antibiotic resistance, and resistance patterns of fecal coliforms obtained during a 20-month period from pigs in a herd that was not exposed to antibiotics for 126 months was determined. Bacteria resistant to single and multiple antibiotics were isolated more frequently (P less than 0.01) from pigs under 7 months of age. A greater proportion of isolates from pigs over 6 months of age was sensitive to the 13 antimicrobial agents tested (P less than 0.01), while a smaller proportion showed resistance to single (P less than 0.05) and multiple (P less than 0.01) antibiotics. More than 80% of the resistant isolates were resistant to tetracycline, streptomycin, or sulfisoxazole. Resistance was greater (P less than 0.01) for pigs in the finishing unit than for those on pasture. Resistance to ampicillin, carbenicillin, and tetracycline was greater (P less than 0.05) for pigs in the finishing unit than for those in the farrowing house. More isolates from pigs on pasture were sensitive to all antimicrobial agents tested (P less than 0.01). A greater proportion of isolates from pigs in the finishing unit showed resistance to a single antibiotic (P less than 0.01). The data from this study suggest that exposure to antibiotics is not the only factor that influences the prevalence of bacteria that are resistant to single and multiple antibiotics in the feces of domestic animals and that considerable research is needed to define the factors influencing antibiotic resistance in fecal bacteria.

Effect of chlorination on antibiotic resistance profiles of sewage-related bacteria

A total of 1,900 lactose-fermenting bacteria were isolated from raw sewage influent and chlorinated sewage effluent from a sewage treatment plant, as well as from chlorinated and neutralized dilute sewage, before and after a 24-h regrowth period in the laboratory. Of these isolates, 84% were resistant to one or more antibiotics. Chlorination of influent resulted in an increase in the proportion of bacteria resistant to ampicillin and cephalothin, the increase being most marked after regrowth occurred following chlorination. Of the other nine antibiotics tested, chlorination resulted in an increased proportion of bacteria resistant to some, but a decrease in the proportion resistant to the remainder. Multiple resistance was found for up to nine antibiotics, especially in regrowth populations. Identification of about 5% of the isolates showed that the highest proportion of Escherichia coli fell in untreated sewage. Some rare and potentially pathogenic species were isolated from chlorinated and regrowth samples, including Yersinia enterocolitica, Yersinia pestis, Pasteurella multocida, and Hafnia alvei. Our results indicate that chlorination, while initially lowering the total number of bacteria in sewage, may substantially increase the proportions of antibiotic-resistant, potentially pathogenic organisms.

Resistance of Escherichia coli in faeces and the use of antimicrobial agents in the treatment of hospital patients

Resistance of faecal Escherichia coli to ampicillin, tetracycline, sulphamethoxazole and gentamicin was studied in patients admitted to seven different departments in two hospitals. The resistance of ampicillin, tetracycline and sulphamethoxazole in the seven patient groups was 27-57%, 26-56% and 35-63%, respectively. Resistance to gentamicin was found in only one department. An E. coli flora predominantly resistant to ampicillin, tetracycline or sulphamethoxazole (greater than 50% of the E. coli strains in a faecal sample resistant) was found in 10-38%, 4-30% and 21-35% of the samples. A cross-sectional study focusing on the influence of the use of antimicrobial agents on the occurrence of resistant strains revealed a positive correlation between the annual turnover of broad-spectrum penicillins in various departments and the occurrence of predominantly ampicillin-resistant E. coli strains in these departments.

Incidence of lysogeny, colicinogeny, and drug resistance in enterobacteria isolated from sewage and from rectum of humans and some domesticated species

Enterobacteria were isolated by streaking swabs of sewage and rectal swabs from human volunteers from domesticated animals. Thirty strains of human origin were identified as Escherichia coli. Out of 1,367 rectal isolates of animal origin, 21% were lysogenic (phi+), 29% were colicinogenic (col+), and 7% were col+ phi+. Out of 85 rectal samples more than 60% harbored variable numbers of col+ or phi+ bacteria. Lysogens harboring homoimmune prophages were detectable in six out of eight human subjects in sequential samples taken at weekly intervals. Chickens in Hong Kong are fed on antibiotic-containing feeds; the avian isolates contained the highest frequency (98%) of drug-resistant bacteria, whereas only 39% of the bovine and 61% of the human isolates were drug resistant. Transmissible drug resistance was demonstrable in sewage isolates and those from animal sources; the highest frequency (58%) of resistance donors was shown by the avian isolates, and the lowest (9%) was shown by the bovine isolates. Unselected marker analysis has shown that a vast majority of multiply resistant donors of diverse origins are able to transmit multiple resistance.

Drug resistance and R plasmids in Escherichia coli strains isolated from imported pet birds

Drug resistance in Escherichia coli strains isolated from pet birds (mynahs, macaws, finches, common bengals, parrots, and flamingos) imported into Japan from 10 foreign countries in 1977 and 1978 was investigated. Of the 309 strains isolated from 127 pet birds in the Animal Quarantine Service, 232 (75.1%) were drug resistant. Furthermore, strains resistant to oxytetracycline hydrochloride, dihydrostreptomycin, and sulfadimethoxine were relatively common. Resistance patterns varied from single to sextuple resistance, and 148 (63.8%) of the resistant strains had conjugative R plasmids. These results suggest that the high incidence of drug resistance and R plasmids in E. coli strains isolated from these pet birds may be a reflection of the prophylactic use of antibiotics for the prevention of diseases which increasingly occur with importation of the birds. Furthermore, the results suggest that the birds may be potential reservoirs of drug-resistant E. coli for families who raise and have intimate contact with such birds.

R-plasmid transfer frequencies from environmental isolates of Escherichia coli to laboratory and fecal strains

Multiple-drug-resistant strains of Escherichia coli were isolated from the water at an estuarine site. They represented about 8.3% of the total E. coli population. Fifty-five strains, representing each of the 32 resistance patterns identified, were mated with an E. coli K-12 F- strain. Matings were performed on membrane filters, and the cells were washed to remove any colicins produced by the donors. Thirty-one strains, about 5% of the mean E. coli density in the samples, transferred drug resistance and, hence, posessed conjugative R plasmids. Of these, 80% transferred drug resistance at a frequency of about 10(-4) or less. Nine environmental R+ strains were mated with three fecal recipients. The R-plasmid transfer frequencies to the fecal strains from the environmental donors correlated well with those from a derepressed K-12 R+ laboratory donor. The R+ X K-12 F- lac- transconjugants from 16 environmental strains were "backcrossed" to a lac+ K-12 F- strain. All transfer frequencies were higher in the backcrosses than in the original matings from the environmental donor. Furthermore, 7 of 13 different transconjugants, which accepted plasmids at repressed frequencies of less than 10(-3), donated them at frequencies greater than 10(-2). This suggests that these were derepressed plasmids in a repressed host.

Incidence of R-plasmids in fecal flora of healthy household dogs

Rectal swabs were taken from healthy household dogs that, insofar as could be determined, had not received antimicrobial drugs. Tetracycline-resistant coliforms comprised 80 to 100% of the total number of coliforms in 61 (65%) of the 94 dogs sampled. The median number of other resistance determinants possessed by these tetracycline-resistant coliforms was 5.1. Of the tetracycline-resistant strains studied, 97% were resistant to streptomycin; 76% were resistant to sulfonamides; 59% were resistant to ampicillin; 59% were resistant to kanamycin/neomycin; and 40% were resistant to chloramphenicol. A total of 64% of the strains was shown to transfer resistance by conjugation or by the aid of the sex factor F. Of the strains transferring resistance, 33% were found to transfer all of their resistance determinants.

A comparative study of gram-negative aerobic bacilli in the faeces of babies born in hospital and at home

Examination of the faeces of 50 babies born at home showed that bottle-fed babies carried significantly more Klebsiella, Proteus and Pseudomonas spp. and antibiotic-resistant Escherichia coli than did breast-fed babies. Bottle-fed babies born in hospital had a less mixed faecal flora than bottle-fed babies born at home. The possibility that bacterial contamination of home-prepared feeds may account for these differences requires investigation.

Changes in intestinal flora of farm personnel after introduction of a tetracycline-supplemented feed on a farm

A prospective study was undertaken to determine whether feeding farm animals antibiotics in feed caused changes in the intestinal bacterial flora of farm dwellers and their neighbors. Chickens were fed tetracycline-supplemented feed (tet-feed), and, as expected, within one week their intestinal flora contained almost entirely tetracycline-resistant organisms. Increased numbers of resistant intestinal bacteria also appeared, but more slowly, in farm members, but not their neighbors. Within five and six months, 31.3 per cent of weekly fecal samples from farm dwellers contained greater than 80 per cent tetracycline-resistant bacteria as compared to 6.8 per cent of the samples from the neighbors (P less than 0.001). Seven of the 11 farm members, but only three of the 24 neighbors, had two or more fecal samples containing greater than 80 per cent tetracycline-resistant coliforms (P less than 0.01). These resistant bacteria contained transferable plasmids conferring multiple antibiotic resistances. Selective pressure by tet-feed for antibiotic-resistant bacteria in chickens extends to human beings in contact with chickens and the feed.

Antibiotic resistance among coliform and fecal coliform bacteria isolated from sewage, seawater, and marine shellfish

Seawater and shellfish samples collected in the vicinity of a marine sewage outfall were examined for the incidence of antibiotic resistance among coliform and fecal coliform bacteria over a 2-year period. Seventy percent or more of these two groups of bacteria from both sources were resistant to one or more antibiotics. Forty-five percent of the isolates resistant to streptomycin or tetracycline were capable of transferring all or part of their resistance pattern to an antibiotic-susceptible strain of Escherichia coli K-12.

The incidence of antibiotic resistance among coliform bacteria isolated from food

Three-hundred-and-seventy-eight strains of coliform bacteria were isolated from specimens of commonly sold milk and food products. Klebsiella and Enterobacter spp. were predominating. Resistance to sulphonamides, streptomycin, and chloramphenicol occurred in only 5, 1, and 2 strains, respectively. No tetracycline-resistant strains were found. Two-hundred-and-two strains (54 %) were resistant to ampicillin. In genetic crosses with a sensitive strain of E. coli Κ 12 W 3132 transmissible R factors could not be demonstrated in any of the resistant coliform strains.

It is concluded that food is not a significant source of antibiotic resistant enteric bacteria. It may, however, be suggested that food is a source of potentially pathogenic gram-negative bacteria which points out the importance of strict hygienic surveillance of food production.

Incidence of antibiotic resistance and transmissible R factors in the gram-negative bowel flora of hospital patients on admission

Stool specimens obtained on admission of 95 patients to a male urological ward were examined quantitatively for antibiotic-resistant gram-negative aerobic bacteria. All patients excreted resistant strains of some kind; 67% resistant Escherichia coli strains. Organisms resistant to sulphonamides, tetracyclines, and streptomycin occurred at a frequency of 10(-3)-10(-4). Ampicillin resistance was encountered most frequently, i.e. greater than 10(-2), whereas organisms resistant to chloramphenicol were found less often (10(-6)). Transmissible R factors were demonstrated in 53/121 (44%) resistant E. coli strains. A connection between tetracycline resistance and ability to transfer resistance was demonstrated. Resistance to chloramphenicol did not occur as a single resistance trait but was transferred from all strains resistant to this antibiotic.

Distribution of R plasmids among the O-antigen types of Escherichia coli isolated from human and animal sources

The O-antigen types of 600 independently isolated Escherichia coli strains from human feces have been determined, and the types have been related to the antibiotic resistance patterns of the strains. The relative abundance of each O-antigen type differed in the susceptible and resistant series of strains. The majority (86%) of the resistant strains carried R plasmids. Resistant E. coli (20.3%) were found associated with O-antigen types 8, 9 and 101, whereas the susceptible strains covered a wide range of O-antigen types. Examination of 174 resistant strains isolated from calf feces also showed a prevalence of O-antigen types 8, 9, 101 (24.1%), and it seems probable that strains expressing these three O-antigen types commonly carry R plasmids in the alimentary tracts of man and calves. The number of strains not typeable with the O sera available were similar in the human (12.5%) and the calf (11.5%) series. There are no grounds for distinguishing "human" from "calf" E. coli on the basis of their O-antigen reactions.

Potential for in vivo acquisition of R plasmids by one strain of Vibrio cholerae biotype El tor

The feces of five patients admitted to a hospital during an outbreak of cholera in Melbourne, Australia, in November 1972, were examined for the presence of tetracycline-resistant coliforms and tetracycline-resistant strains of Vibrio cholerae. Despite the abundance of tetracycline-resistant coliforms able to transfer this resistance to other strains of Escherichia coli, no tetracycline-resistant strains of V. cholerae were detected. In vitro transfer experiments using the V. cholerae strain responsible for the outbreak as recipient revealed that it was a particularly poor host for most R plasmids.

Survival of R+ Escherichia coli in sea water

The survival of Escherichia coli strains in sea water appears not to be affected by the possession of an R(+) factor. Sea water induces no detectable curing of R(+)E. coli.

Drug-resistant Escherichia coli and Klebsiella-Enterobacter in healthy adults in Thailand and the effect of antibiotic administration

Antibiotic-resistant strains of Escherichia coli and, to a lesser extent, Klebsiella-Enterobacter were common in serial samples of the normal intestinal flora of healthy young adults in Thailand, and the resistance often was to multiple drugs and was transferable. Antibiotic administration promoted dominance of the flora by drug-resistant organisms regardless of the drug regimen and the predrug susceptibility pattern of the flora. The normal pattern was regained slowly after the cessation of drug administration.

Effect of oral tetracycline on the occurrence of tetracycline-resistant strains of Escherichia coli in the intestinal tract of humans

Serial samples of feces from normal human subjects were analyzed for tetracycline-resistant strains of Escherichia coli. Subjects were found to be excreting tetracycline-resistant strains in amounts fluctuating with time. Ingestion of tetracycline increased both the number of individuals excreting tetracycline-resistant strains of E. coli and the proportion of the total E. coli isolates resistant to the antibiotic.