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

Longitudinal study of CTX-M ESBL-producing E. coli strains on a UK dairy farm

The aim of this study was to investigate the bacterial strains and farm environment that may contribute to the persistence of ESBL-producing E. coli on a single UK dairy farm. A longitudinal study was conducted comprising 6 visits, between August and October 2010, followed by a further visit at approximately 69weeks after the initial visit. Faecal and environmental samples were collected from different parts of the farm. The persistence and extent of faecal shedding of ESBL E. coli by individual calves was also determined. Twenty two different PFGE types were identified. Four of these were persistent during the study period and were associated with serotypes: O98, O55, O141 and O33. The counts suggest that shedding in calf faeces was an important factor for the persistence of strains, and the data will be useful for parameterising mathematical models of the spread and persistence of ESBL strains within a dairy farm.

Fecal source tracking, the indicator paradigm, and managing water quality

Fecal source tracking is used because standard methods of measuring fecal contamination in water by enumerating fecal indicator bacteria (FIB) do not identify the sources of the contamination. This paper presents a critical review of source tracking with emphasis on the extent to which methods have been tested (especially in comparison with other methods and/or with blind samples), when methods are applicable, their shortcomings, and their usefulness in predicting public health risk or pathogen occurrence. In addition, the paper discusses the broader question of whether fecal source tracking and fecal indicator monitoring is the best approach to regulate water quality and protect human health. Many fecal source-tracking methods have only been tested against sewage or fecal samples or isolates in laboratory studies (proof of concept testing) and/or applied in field studies where the "real" answer is not known, so their comparative performance and accuracy cannot be assessed. For source tracking to be quantitative, stability of ratios between host-specific markers in the environment must be established. In addition, research is needed on the correlation between host-specific markers and pathogens, and survival of markers after waste treatments. As a result of the exclusive emphasis on FIB in legislation, monitoring has concentrated on FIB and lost sight of pathogens. A more rational approach to regulating water quality would start with available epidemiological data to identify pathogens of concern in a particular water body, and then use targeted pathogen monitoring coupled with targeted fecal source tracking to control them. Baseline monitoring of indicators would become just one tool among many.

Determining sources of fecal bacteria in waterways

The microbiological contamination of waterways by pathogenic microbes has been, and is still, a persistent public safety concern in the United States and in most countries of the world. As most enteric pathogens are transmitted through the fecal-oral route, fecal pollution is generally regarded as the major contributor of pathogens to waterways. Fecal pollution of waterways can originate from wastewater treatment facilities, septic tanks, domestic- and wild-animal feces, and pets. Because enteric pathogens are derived from human or animal sources, techniques capable of identifying and apportioning fecal sources have been intensively investigated for use in remediation efforts and to satisfy regulatory concerns. Pollution of human origin is of the most concern, since human feces is more likely to contain human-specific enteric pathogens. Fecal indicator bacteria have been used successfully as the primary tool for microbiologically based risk assessment. However measurement of fecal indicator bacteria does not define what pathogens are present, or define the sources of these bacteria. Microbial source tracking (MST) methods that have the ability to differentiate among sources of fecal pollution are currently under development. These methods will ultimately be useful for risk assessment purposes and to aid regulatory agencies in developing strategies to remediate microbiologically impaired waterways.

Phenotypic and genotypic characterization of human and nonhuman Escherichia coli

Estuarine waters receive fecal pollution from a variety of sources, including humans and wildlife. Escherichia coli is one of several fecal coliform bacteria that inhabit the intestines of many warm-blooded animals that sometimes contaminate water. Its presence does not specifically implicate human fecal input, therefore it is necessary to differentiate contamination sources to accurately assess health risks. E. coli were isolated from human sources (HS) and nonhuman sources (NHS) in the Apalachicola National Estuarine Research Reserve and analyzed for fatty acid methyl ester (FAME), O-serogroup, and pulsed-field gel electrophoresis (PFGE) profiles. For FAME and PFGE analyses, there was no relationship between profile and isolate source. Human source PFGE profiles were less diverse than NHS isolates, and conversely for FAME. In contrast, O-serogrouping showed less diversity for HS vs. NHS isolates, and the predominant HS O-serogroups differed significantly (P < 0.01) from those of NHS isolates.

Molecular relationships between trimethoprim R plasmids obtained from human and animal sources

A total of 65 trimethoprim R plasmids (35 obtained from human strains and 30 from animal strains of Escherichia coli) were examined by the technique of restriction endonuclease fingerprinting. Plasmids belonging to incompatibility groups B, FII and I delta obtained from human and animal sources showed close similarities within each group. Plasmids belonging to incompatibility groups I alpha and P were also obtained from both human and animal sources, but there was no conclusive evidence of close relationships within the groups. Restriction endonuclease fingerprinting was found to be useful for obtaining information about the epidemiology of R plasmids. Its main limitation in this study related to broad host range plasmids of the P incompatibility group, some of which contained very few sites susceptible to cleavage by the restriction endonucleases tested.

The sub-specific differentiation of Escherichia coli with particular reference to ecological studies in young animals including man

It is possible to differentiate isolates of Escherichia coli using a number of techniques including the determination of the serotype, biotype and phage type and the profiles for resistance to antibacterial agents and toxic chemicals, intracellular enzymes, outer membrane proteins and plasmids and the production of enterotoxin and colicines. These methods have been used principally for the study of pathogenic E. coli and plasmid-mediated drug resistance. However they can also be used successfully for ecological purposes and the application of several of these techniques for the study of the ecology of E. coli in healthy young animals including man is described.

The effects of oxytetracycline on the intestinal Escherichia coli flora of newly weaned pigs

Four recently weaned pigs were dosed orally with oxytetracycline. This caused a rapid increase in the incidence of tetracycline resistance (TcR) among Escherichia coli isolates from the faecal flora. The isolates were differentiated further on the basis of O-serogroup, biotype and resistance pattern. There was no evidence that the administration of the antibiotic selected for a few TcR clones, but rather a relatively large number of TcR strains were identified during the dosing period. Using selective isolation media a proportion of these strains were demonstrated in the minority faecal Esch. coli flora before dosing, while the remainder were recognized for the first time after dosing commenced. The incidence of TcR among Esch. coli isolates also increased after weaning in other pigs which were not dosed with oxytetracycline or any other antibacterial agent. In a proportion of these animals this increase was associated with the dominance of a TcR enteropathogenic serotype (0149:K 91, K 88a, c) in the faecal Esch. coli flora which was probably ingested in small numbers before weaning. The source of other TcR strains was probably the environment in which each pig was placed after weaning.

Coliform numbers in the stomach and small intestine of healthy pigs following weaning at three weeks of age

In 60 weaned and 52 unweaned pigs, aged between 21 and 32 days, the number of coliform organisms in the gastric contents was found to be related to their pH value. The contents were generally more acidic in the weaned animals and contained fewer coliforms. Haemolytic coliform organisms were never identified among selected isolates examined from the gastric contents although in weaned animals the haemolytic enterotoxigenic Escherichia coli serotype 0149: K91, K88a,c (Abbotstown strain) was commonly recovered from the intestines. After weaning, this strain appeared to colonize the anterior small intestine from lower down the tract, and its presence was associated with an increase in the total coliform count at the site from which it was isolated. Rotaviruses were also more commonly detected in the intestinal contents of weaned than unweaned pigs, but their appearance after weaning appeared to be preceded by the proliferation of haemolytic E. coli. The presence of either or both of these potentially enteropathogenic organisms never induced diarrhoea, and although faecal water content increased significantly after weaning, this occurred independently of the presence of both agents.

Trimethoprim resistance plasmids in Escherichia coli isolated from cases of diarrhoea in cattle, pigs and sheep

A total of 1572 isolates of Escherichia coli obtained from the faeces of young farm animals with diarrhoea over the period 1980-1983 were screened for resistance to trimethoprim (Tp). Resistance to Tp was detected in 263/954 (28%) of bovine isolates, 59/441 (13%) of porcine isolates and 15/177 (9%) of ovine isolates. Seventy-five resistant isolates from separate outbreaks of infection on farms within a 25 mile radius of Nottingham were examined in detail. Sixty-eight (91%) of the 75 isolates were resistant to greater than 1024 mg Tp/l and 34 (50%) of these 'highly resistant' isolates (45% of total resistant isolates) transferred their Tp resistance to E. coli K12. A further 13 (17%) isolates were demonstrated to carry non-self-transferable plasmids which were capable of being mobilized to E. coli K12 by the broad host range plasmid RP4. Thirty-one self-transferable Tp R plasmids were divided between the following incompatibility groups: IncB (14 plasmids), IncFII (4 plasmids), IncH2 (1 plasmid), IncI alpha (10 plasmids), IncI delta (1 plasmid) and IncP (1 plasmid). In terms of antibiotic resistance patterns and incompatibility properties, many of these plasmids closely resembled those isolated from human patients in the same area, suggesting that there may be a common pool of Tp R plasmids.

A comparison of the ecology of Escherichia coli in the intestine of healthy unweaned pigs and pigs after weaning

A total of 51 clinically healthy pigs (14 unweaned and 37 weaned) from five litters, and aged 21 to 35 d, were studied. Escherichia coli isolates from the duodenum, jejunum, ileum, caecum and colon were differentiated on the basis of O-serogroup, biotype and resistance pattern. The complexity of the flora was influenced considerably by the presence or absence of the enterotoxigenic serotype 0149: K91, K88a,c (Abbotstown strain). When it was absent the E. coli flora of both weaned and unweaned pigs was complex with up to 25 strains being identified. The majority of these E. coli strains identified in each pig were isolated from only one of the five intestinal sites sampled. On the other hand, when the enterotoxigenic strain was present (14 pigs) it tended to dominate the E. coli flora at all levels of the intestine and this dominance was reflected in a corresponding fall in the total number of E. coli strains isolated per pig.

The ecology of Escherichia coli in market calves fed a milk-substitute diet

Dynamic changes in the Escherichia coli population in the calf gut were studied over 21 days in a group of 18 intensively-reared market calves. Isolates were identified by O-serogrouping, biotyping and resistogram patterns. Seventy O-serogroups were identified among nearly 3000 E. coli isolates examined and these were subdivided into 416 strains by means of their biotype and resistogram. Seventy-five per cent of these strains were detected only once or twice, which points to the continual replacement of the E. coli flora with strains that showed low persistence in the gut. The rise in the frequency of antibiotic resistance observed during the study was not due to a change in the proportion of resistant to sensitive strains in the gut flora. It was a consequence of the displacement of the original flora by multiply-resistant strains, which presumably originated from the calves' environment.

The persistence of drug resistant Escherichia coli strains in the majority faecal flora of calves

Two groups of calves, one of three and the other of two animals, were purchased in markets and reared initially on a commercial veal unit for 1 month and 4 months respectively. They were then moved to the Veterinary School, Langford, and kept for a further 6 and 4 months respectively. The animals were sampled weekly and a continual turnover in the strains forming the majority Escherichia coli faecal flora was demonstrated for all calves. Antibacterial-drug resistance, as measured by an Antibiotic Resistance Index (ARI), increased after arrival on the veal unit and persisted at high levels during the whole of their stay. After moving to Langford the ARI fell. Initially there was a reduction in the average number of resistance determinants per resistant strain and then, after a delay of up to 8 weeks, by an increase in the proportion of isolates that were fully sensitive. The source of the sensitive strains was not ascertained, although their appearance was not associated specifically with either weaning or turning out to pasture.

The resistance to chemotherapeutic agents of Escherichia coli from domestic dogs and cats

The prevalence of antibiotic resistant Escherichia coli in the rectal flora of 168 healthy dogs and 93 cats in the Brisbane area was investigated. Rectal swabs were plated on MacConkey agar with and without antibiotics, and 690 isolates confirmed as faecal E. coli were tested for resistance to tetracycline, streptomycin, chloramphenicol, ampicillin, neomycin, furazolidone and sulphanilamide. Resistant isolates were obtained from 101 (60%) of the dogs and 24 (26%) of the cats sampled. A high percentage of the isolates was resistant to tetracycline, streptomycin, ampicillin and sulphanilamide. Multiple resistance to 3 or more of the drugs was exhibited by the majority of isolates and a total of 31 different multiple resistance patterns was demonstrated. Of the 50 strains tested for transfer of resistance, 30 (60%) transferred some or all of their resistance determinants to an E. coli K12F - recipient.

Prevention of drug-resistant Escherichia coli colonization in chickens by treatment with a faecal fluid

This study was performed to prove that intestinal colonization in chickens by resistant Escherichia coli strains present in the environment might be prevented when faeces in which sensitive E. coli strains were dominant was administered to newly hatched chicks. The appearance of resistant E. coli strains was markedly reduced. Escherichia coli O49:H12 was the sensitive E. coli strain which formed the major colonizer in the intestinal tract. In young chickens, this strain persisted as a major component, and even when it was a minor colonizer in the faecal fluid administered, it appeared as a major component soon afterwards. This strain is considered to be a good colonizer in the gut of young chickens.

Plasmids encoding trimethoprim resistance in bacterial isolates from man and pigs

Trimethoprim (Tp) resistant Gram negative bacteria were isolated from humans and pigs. The bacterial hosts were characterized by their resistance pattern and biotype. The presence of transferable Tp plasmids was demonstrated in 86% of 59 porcine isolates and 37% of 49 human isolates. The Tp R-plasmids carried a diversity of resistance determinants such as Tc, Cm, Sp, Sm and Su. Incompatibility tests distinguished two major groups, Inc FIV and Inc N. Thirty of 99 Tp R-plasmids isolated from humans were grouped as Inc FIV and eight as Inc N. The results of molecular weight determination of Tp R-plasmids performed by agarose gel electrophoresis were consistent with the existence of two groups--larger R-plasmids (76 to 104 Md) belonging to Inc FIV and lower molecular weight R-plasmids (25 to 35 Md) belonging to Inc N. Results from this study indicate that the Tp R-plasmids isolated in Perth have evolved independently from those described in Europe and the United Kingdom. There is also evidence for their local spread between Escherichia, Klebsiella, Enterobacter, Citrobacter and Acinetobacter from man and animals.

Genetic transfer of antimicrobial resistance and enterotoxigenicity among Escherichia coli strains

To understand the role of enterotoxin (Ent) plasmids in epidemics of enterotoxigenic (ET) Escherichia coli diarrhea in the United States, we studied the genetics of Ent plasmids in relation to E. coli serotypes and R plasmids. Twenty-nine ET E. coli strains, including all epidemic isolates available at the Centers for Disease Control, Atlanta, Ga. (CDC), were assessed for the ability to transfer antimicrobial resistances (if present) by conjugation, to mobilize a nonconjugative R plasmid, and to cotransfer enterotoxigenicity with R determinants. Of the 12 ET E. coli strains isolated in the United States, 5 were able to transfer R plasmids; one strain cotransferred detectable enterotoxigenicity. Another four U.S. isolates were able to mobilize plasmid DNA, but no toxin production was detected in transconjugants. Of 17 resistant ET E. coli from South Asia, 13 were able to transfer R plasmids; 5 of those 13 cotransferred detectable Ent plasmids. In all, 22 ET E. coli strains (76%) were able to initiate conjugation and genetic transfers. Six of these strains (20%) were able to cotransfer enterotoxigenicity with a conjugative R plasmid at a detectable frequency. One of the six strains transferred R and Ent determinants on a single plasmid. These data are addressed in relation to the observed immobility of Ent and R during outbreaks of ET E. coli, the efficacy of prophylactic tetracycline, and the worldwide occurrence of a limited number of ET E. coli serotypes.

The persistence of drug resistant Escherichia coli in the intestinal flora of healthy broiler chicks

Antibacterial drugs (oxytetracycline, streptomycin and sulphonamides) were included in the drinking water of healthy broiler chicks from the sixth to the twentieth day of life to select a resistant gut flora. On the twenty-first day the birds were divided into three groups and reared in separate rooms until 100 days of age. One group was housed in cages with wire floors while the others were reared on litter. Faeces from adult hens were added regularly to the litter of one of these groups to determine its effect on the gut flora of the chicks. The ecology of Escherichia coli was studied using O-serotyping, biotyping and antibacterial drug resistogram typing. The proportion of E. coli in the dominant faecal flora resistant to two to four antibacterial drugs increased with time to reach a peak several days after the drugs were withdrawn. Thereafter, the level of drug resistance in the E. coli declined equally in all three groups. The majority of organisms with multiple resistance were derived from biotypes of O-serotypes initially resistant to only one drug and were identified before the drugs were administered. The decline in the level of resistance in the dominant faecal flora after the fourth week was due to the appearance of either new O-serotypes or new biotypes of O-serotypes previously shown to be multiply resistant, and which were either sensitive or resistant to only one drug. It is probably that these new strains were derived from the food since several O-serotypes appeared simultaneously in all three groups of birds.

The survival of multi-antibacterial drug-resistant Escherichia coli and Salmonella typhimurium in stored static slurry from a veal calf unit

Salmonella typhimurium phage type DT 193 survived in small numbers, in stored static slurry derived from veal calves, for the 7-week period of observation. The viable coliform count fell by 1 1/2 logs during the first 2 weeks of storage, thereafter there were only relatively small fluctuations in the coliform population. In all 735 of 752 Escherichia coli isolates examined from eight samples of slurry were resistant to 3-6 antibacterial drugs. There was no dramatic change in the overall level of drug resistance amongst the E. coli with time. Chloramphenicol resistance was recorded in 400 (55%) of the E. coli. It was always associated with multiple resistance, with 96% of the strains being resistant to 5 or 6 drugs, although the proportion of isolates of each of the ten most prevalent O-serotypes resistant to chloramphenicol was variable and ranged between none and 97.5%. The use of biotyping together with O-serotyping indicated that the E. coli population was extremely complex, although certain components of the population remained relatively stable within the dominant flora with time since several of the more common O-serotype/biotype combinations were isolated from more than half of the eight slurry samples examined.

Spread of R-plasmids among Escherichia coli causing urinary tract infections

The incidence of multiple-antibiotic resistance among Escherichia coli isolated from urinary tract infections at Charing Cross Hospital, London, increased over the last 10 years, and its distribution was related to O-type. Among strains of the eight O-types most frequently causing such infections at this hospital, O4, O9, and O18 had a high incidence of multiple resistance (35, 22, and 19%, respectively); O2 and O6 had a intermediate incidence (14 and 11%, respectively); and O7, O1, and O75 had a low incidence (8, 6, and less than 3%, respectively). This nonrandom distribution appears to be a consequence of unequal plasmid recipient ability. After overnight mating with antibiotic-resistant donors, R-plasmid infection frequencies among antibiotic-sensitive urinary tract isolates differed by up to 10(5)-fold, and such differences were correlated with the variation in the incidence of antibiotic resistance among the O-types. The inherent differences in the ability to achieve significant R-plasmid spread, which appear to be determined by the host, not the plasmid, may be compounded in some cases by the inhibition of potential mating partners by colicin production.

Antibiotic resistance and R-factors in the fecal coliform flora of urban and rural dogs

The incidence of antibiotic-resistant fecal coliforms in the rectal flora of 106 healthy dogs in the Galway area was investigated. As far as could be determined, none of the dogs had received antimicrobial drugs. Half of the dogs sampled were from homes within the city boundaries, whereas the remainder were from farms within a 40-mile (24.8-km) radius of the city. Of the dogs sampled, 47 had a highly susceptible fecal coliform flora, with less than 1% of the coliform population resistant to any of the four test antibiotics. Fecal coliforms resistant to one or more of the test drugs comprised between 40 and 100% of the total fecal coliform population of 36% of the rural dogs and 13% of the urban dogs sampled. Of the 473 resistant Escherichia coli isolates studied, the highest number of associated resistance determinants encountered was 5, with a medium number of 2.5. Of the E. coli isolates from rural dogs, 52% were resistant to three or more antibiotics compared with 37% of the isolates from urban dogs. A total of 64% of the isolates were shown to transfer some or all of their resistance determinants by conjugation. The transferability of ampicillin (77%) and chloramphenicol (70%) resistance determinants was higher than that of streptomycin (40%) or tetracycline (44%).

Persistence of plasmid-carrying tetracycline-resistant Escherichia coli in a married couple, one of whom was receiving antibiotics

This paper describes an extension to an earlier account of the coliform flora carried by a married couple, one of whom was taking tetracycline for prolonged periods. The latter phase of this study was notable for the following: first, certain tetracycline-resistant Escherichia coli O antigen types persisted in one of the participants for several weeks after tetracycline was withdrawn; second, a course of ampicillin led to replacement of the tetracycline-resistant flora by one that was ampicillin resistant, but the end of the ampicillin course led to the reappearance of the tetracycline-resistant line, even though no tetracycline was being taken; and third, the tetracycline-sensitive O75 E. coli, which appeared toward the end of the survey, had not lost their plasmid but carried a derivative in which the tetracycline resistance gene(s) had been inactivated by the insertion of an extra piece of deoxyribonucleic acid with a molecular weight of about 1 megadalton.

Adhesion of commensal bacteria to the large intestine wall in humans

Biopsies taken during colonoscopic examination of the human large bowel were used to examine the relationship of the commensal bacterial to the mucosal epithelial cell surface. Bacteria were seen adhering to the exposed epithelial cell surface and also to the mucus sheet. Isolation of aerobic organisms showed that Escherichia coli are closely associated with the gut wall throughout the large intestine. One strain of E. coli predominated in each biopsy, and this strain was present along the whole length of bowel. Adhesion of bacteria to the gut wall does occur in vivo and may be one of the factors involved in the ability of an organism to colonize and persist.

Plasmid carriage and the serum sensitivity of enterobacteria

The carriage of a range of plasmids by rough, serum-sensitive laboratory strains of Escherichia coli made no difference to their reactivity in human serum as determined by two methods. Plasmid-carrying enterobacteria isolated from polluted river water gave a variety of responses to serum. Smooth E. coli river isolate C8 was killed by serum but only after a delay of 1 h, and curing of antibiotic resistance and colicin determinants from this strain led to a small but significant increase in serum sensitivity. Plasmids from eight strains were transferred by conjugation to a cured derivative of C8 (C8(-)Nal(R)), and in six cases a significant increase in the serum resistance of the progeny was observed. Plasmid-mediated enhancement of resistance was particularly marked with plasmids R1 and NR1, and a round of replication mutant of NR1 conferred greater resistance than did the normal R factor. However, R1 and NR1 were unable to modify the serum response of a cured strain (P21(-)Nal(R)) derived from promptly serum-sensitive isolate P21. These findings suggest that lipopolysaccharide O-side chains, the cell surface components responsible for the delay in serum killing, are essential for the expression of plasmid factors that modify sensitivity to serum. Examination of K(A)(-) variants of two isolates indicated that the K(A) antigen has only a marginal effect on the serum response.

Escherichia coli antibodies in patients with inflammatory bowel disease

Sera from 30 patients with inflammatory bowel disease (IBD) (16 with Crohn's disease (CD) and 14 with ulcerative colitis (UC) were assayed for the presence of antibodies against 159 Escherichia coli O-antigens and compared with sera from 16 matched control subjects. The majority of patients with IBD had agglutinating antibodies to a higher number of Escherichia coli O-antigens and in higher titres than the control group. The number of positive agglutinins was O-33 mean 13.8 in CD, O-26 mean 7.9 for UC, and O-7 mean 1.5 in controls. Eight patients with IBD and arthropathy had antibodies to fewer O-antigens (O-7 mean 3.2). The antibodies were in the IgG and IgM, in titres corresponding to original values. No specific O-serotypes were associated with IBD. Common serotypes, R-plasmid carrying serotypes, and those associated with shigella-like adult diarrhoea were detected. O14 was detected only in five patients and O119 in none. There was no correlation between the number of Escherichia coli agglutinins and the site and severity of the disease or type of therapy. It is suggested that the presence of the high numbers of Escherichia coli antibodies is secondary to the disease process and is unlikely to be causally involved in the pathogenesis of the disease, but may play a role in the perpetuation of the disease and in the extraintestinal complications.

Spread of a single plasmid clone to an untreated individual from a person receiving prolonged tetracycline therapy

The aerobic gram-negative intestinal flora of two individuals living in close proximity was followed for 17 months. One of these persons was receiving a prolonged tetracycline treatment for acne vulgaris and was colonized by tetracycline-resistant Escherichia coli strains throughout the survey. The other person studied received no antibiotics during the period in question, but was frequently found to excrete a number of E. coli strains harboring tetracycline-resistant plasmids. The two E. coli strains (O75.H7 and O23.H16) excreted from both persons most frequently were indistinguishable, and so were the R-plasmids they carried. This suggests that R-plasmid-carrying E. coli may spread from individuals under treatment to close relatives that have not been treated.

R-plasmid transfer in vivo in the absence of antibiotic selection pressure

The persistence of an O18 Escherichia coli strain resistant to tetracycline, streptomycin, and sulfonamide has been followed in the fecal flora of a single individual over a period of 9 months. The strain in question carrying an R plasmid was detectable from the beginning of the survey, but it was only after a 10-day period of tetracycline therapy that it reached an all but permanent dominance in the fecal flora. No transfer of the R plasmid carried by the strain to any other coliform could be detected for 202 days after the end of tetracycline treatment. At this point, however, an O88 E. coli carrying the same plasmid as the O18 strain appeared briefly as a predominant component of the flora. The two plasmids isolated from the O18 and the O88 E. coli strains have been characterized in molecular terms and found to be similar. This suggests that R-plasmid transfer between two E. coli strains occurred in an individual who was living a normal daily life and who was not receiving antibiotics.

Plasmid-mediated resistance to the bactericidal effects of normal rabbit serum

An Escherichia coli K-12 strain bearing the plasmids R1 or R100 was more resistant to the bactericidal activity of normal rabbit serum than was the same strain without a plasmid. When the plasmid R100 was transferred to several K-12 strains, the strains acquired resistance to serum bactericidal activity.

Escherichia coli in a maternity ward

The Escherichia coli isolated from faecal and nasal swabs from all babies present in a maternity ward were serotyped and their anbitiotic resistance patterns and fermentation characteristics with six carbohydrates were determined. These were compared with E. coli isolated from hands and clothing of attendants and samples of ward air. The results suggest that mothers may be the primary source of E. coli in the ward but the colonized babies themselves provide the main reservoir of nursery E. coli. As most of these serotypes of E. coli were found on the attendant's hands or clothing or in the air, it is difficult to assess transmission routes for E. coli, particularly as some strains appear to possess a greater inherent ability to colonize babies than others. By the use of markers other than O antigens it was possible to characterize strains to a far greater extent.

Control of infectious diseases

A total of 655 Escherichia coli strains from various clinical sources were O-antigen typed, and the serological properties were correlated with R-plasmid carriage. Of the 655 strains, 224 were resistant to one or more antibiotics and 148 of these carried R plasmids. The distribution of O-antigen types among the susceptible strains was similar to that reported previously by others in England. The O-antigen types among the R⁺ strains showed some similarities to those found in susceptible strains, but O-antigen types O8, O9, O17, O18 and, perhaps, O101 and O107 were more common in the R⁺ than in the susceptible series. There is therefore some overlap between the O-antigen types of E. coli prevalent in R⁺ strains from clinical cases and from human and animal fecal sources.