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Biomedical subjects

M Hinton

Publications and source records attributed to M Hinton.

At least 55 records · Page 3Linked to original sources
PubMed1986

The ecology of Escherichia coli in animals including man with particular reference to drug resistance.

The phenomenon of drug resistance among bacteria, particularly Escherichia coli, has been a major research interest of the University of Bristol's departments of microbiology and veterinary medicine during the past 15 years. Tens of thousands of E coli isolates from man and farm animals have been examined in studies of both the ecology of the species and the epidemiology of their resistance to therapeutic antibacterial agents. The principal findings obtained in these investigations are described.

Animals↗
PubMed1986

Speciation, serotyping, antimicrobial sensitivity and plasmid content of Proteeae from the environment of calf-rearing units in South West England.

A survey was undertaken of the occurrence, serotype, antimicrobial sensitivity and plasmid content of members of the tribe Proteeae in the environment of two calf-rearing units in the county of Avon in South West England. Examples of the following species were found: Proteus mirabilis, Prot. vulgaris, Prot. vulgaris Biogroup 2, Morganella morganii, Providencia stuartii, Prov. alcalifaciens and Prov. rettgeri. A wide range of serotypes was found, many having been previously reported from nosocomial isolates. A total of 15% of isolates carried plasmids; six pairs of isolates were identified which had identical serotypes but different patterns of plasmid carriage. The antimicrobial sensitivity of the isolates was generally similar to isolates of Proteeae from humans. Although no truly aminoglycoside-resistant isolates were found, some isolates of Prov. stuartii and Prov. rettgeri had MIC's higher than the other isolates to gentamicin and netilmicin, suggesting the presence of low levels of the enzyme AAC 2'. The study demonstrates that there is a considerable diversity of species and types of Proteeae associated with calves and their environment. It seems likely that a potential cause of colonization of the human gut by Proteeae is the consumption of meat.

Animals↗
PubMed1986

Preliminary observations on the influence of antibiotics on the ecology of Escherichia coli and the enterococci in the faecal flora of healthy young chickens.

Two separate replicated experiments are described. In the first the influence of oxytetracycline on the Escherichia coli flora was assessed, while in the second the effect of tylosin on the enterococci was investigated. In both experiments the administration of the antibiotic was associated with an increase in the average proportion of isolates resistant to the agent although in experiment 1 the agent had no apparent influence on either the total number of E. coli strains, differentiated by biotype and resistance pattern, or the number of 'new' strains per sampling. On the other hand significant differences were noted between the two replicates and also in relation to the age of the birds. In the second experiment fewer enterococcal strains were isolated from the birds dosed with tylosin but since fewer strains on average were isolated from the samples collected prior to dosing it is probable that this difference was due to factors other than the influence of the antibiotic. The enterococci were speciated and the two most commonly isolated were Streptococcus faecalis and S. faecium. The isolation rate of each was expressed as a proportion of the total number of enterococcal isolates per sample and when considered in relation to both dosing and the age of the bird the interaction dosing X age was statistically significant for both species. However, the differences did not appear particularly great and it was possible that the differences were of no practical importance from an ecological point of view.

Animals↗
PubMed1985

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.

Animals↗
PubMed1985

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.

Age Factors↗
PubMed1985

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.

Animals↗
PubMed1985

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.

Animal Feed↗
PubMed1985

The ecology of Escherichia coli in calves reared as dairy-cow replacements.

A continual turn-over in the strains forming the majority of faecal Escherichia coli flora was demonstrated in 16 calves reared as dairy cow replacements. The incidence of antibiotic resistance among isolates, as measured by an Antibiotic Resistance Index (ARI), changed markedly with the age of the calf. The value was low initially, when the calves were 1-2 days old and housed with adult animals. It then rose rapidly during the first week after the animals had been weaned and moved into nursery pens. This change in ARI was associated with the isolation of strains resistant to four or five of the six drugs included in the sensitivity test. The ARI then fell from the third week to low levels by the time that the calves were five months of age. This fall was due to the isolation of an increasing proportion of sensitive E. coli strains. These differed from the sensitive strains which had colonized the calves in the early days of life so demonstrating that the change was not due to the reemergence of strains identified several weeks previously. The source of E. coli strains was presumed to be the calfs' environment but further investigations are required to prove this conclusively.

Animals↗
PubMed1985

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.

Animals↗
PubMed1985

The influence of flumequine on the resistance of the coliform flora of chickens to the agent.

Flumequine (1 g/l) was administered to healthy young chickens in the drinking water for 5 days. A transient increase in the incidence of resistance to flumequine (4 micrograms/ml) was recorded in faecal coliform isolates after administration. Cross-resistance with nalidixic acid was demonstrated, but there was no evidence of cross-resistance to ampicillin, chloramphenicol, kanamycin, streptomycin, sulphadiazide, tetracycline and trimethoprim.

Animals↗
PubMed1984

Parasitic liver damage in lambs with particular reference to the migrating larvae of Ascaris suum.

It has been suggested that the larvae of the pig nematode Ascaris suum is a possible cause of rejection of lambs' livers in the abattoir. However, this assertion was not substantiated in an experimental study in which lambs were dosed with infective A suum eggs. This produced, at the worst, small trivial lesions (up to 2 mm diameter) which would probably have been missed at meat inspection under commercial conditions. No evidence of ascarid lesions was observed in the livers of 5873 lambs and hoggs slaughtered between June and August. The most important causes of rejection were lesions caused by Cysticercus tenuicollis and migrating Fasciola hepatica, and these accounted for 90 and 8 per cent, respectively, of 1337 livers rejected either totally or partially by the meat inspectors.

Abattoirs↗
PubMed1984

Further observations on the excretion of salmonella in the faeces of calves fed milk substitute.

Swabs of rectal faeces were obtained daily for 28 days from 90 calves reared in five batches during the summer of 1983. The calves were purchased unweaned in markets and fed a milk-substitute diet. Salmonella typhimurium phage type DT204c was isolated from calves in four batches and Salmonella newport from one. When the data from the 90 calves were considered together the incidence of salmonellas, excretion rose to peak between 5 and 7 days after purchase before declining to low levels during the fourth week. Salmonella was isolated from 55 (61%) calves; 30 were positive on up to four occasions while 21 and 4 animals respectively were positive between 5 and 11 and 15 and 20 times. In the majority of animals infection was probably subclinical since treatment with antibacterial drugs and excretion of S. typhimurium coincided in four calves only.

Animal Feed↗
PubMed1984

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.

Animals↗
PubMed1983

The excretion of Salmonella typhimurium in the faeces of calves fed milk substitute.

A total of 495 calves in 16 batches were examined (117 calves in 4 batches in 1979 and 378 in 12 batches in 1982). They were purchased in markets, transported by road to a farm in Somerset and reared on a milk substitute diet for a period of up to five weeks. Salmonella typhimurium phage type DT 193 was endemic in 1979 and phage type DT 204c in 1982. The mortality rates in the two years were 9.4% and 1.9% respectively. The causes of death were not investigated although the majority were probably due to salmonellosis. The rate of isolation of S. typhimurium from the rectal faeces of calves in all groups was either zero or relatively low on arrival. It rose to a peak (which was higher in 1979) in the second or third weeks before declining to low levels by the end of the fourth week of residence on the farm. Data from 162 calves, examined twice weekly for four weeks in 1982, indicated that the distribution of infected calves, based on the number of times that S. typhimurium was isolated from each, was not random. The calves could be assigned to two main categories; those from which the organism was never isolated and those from which it was isolated at least twice. This suggested that salmonella infected calves actively excreted the organism. The association between salmonella excretion and medication of sick animals with antibacterial drugs was strongest during the second week. Over the four-week period nearly 40% of the calves found to be excreting S. typhimurium were not treated, indicating a high incidence of subclinical infection. Salmonella excretion by the calves followed a regular pattern and infection was self-limiting within five weeks. The peak in the salmonella excretion rate and the mortality rate were higher in 1979 when phage type DT 193 was the endemic strain. However, in 1982 the calves received 100 p.p.m. furazolidone in their milk ration during the first week of their stay on the farm, and this may have contributed to the differences noted between the two years.

Animal Feed↗