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 pigs were grouped as Inc FIV and three as Inc N. Eleven of 26 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 36 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.     

Comparative evaluation of biological properties of Salmonella typhimurium strains of different origin and genetic nature of resistance to antibiotics

The results obtained in the comparative study of the biological characteristics of Salmonella typhimurium strains of different origin are presented. The circulation of two biovariants differing in a number of biological characteristics, mainly in their susceptibility to antibiotics, has been shown. R-plasmids, mostly with the markers of resistance to tetracycline and with a molecular weight of 64 Md, have been isolated from "hospital" and "sporadic" strains possessing multiple antibiotic resistance.     

Antibiotic resistance and R-plasmids in food chain Salmonella: evidence of plasmid relatedness.

A large number of strains (1,783) belonging to 15 Salmonella serovars isolated, in Canada, from the three major links of the human food chain were screened for multiple antibiotic resistance and the presence of R-plasmids. Multiresistant strains occurred among animal feed, livestock, and human isolates at frequencies of 4, 22, and 14%, respectively. Conjugation analysis revealed that 58% of the isolates from feeds, 87% of those from livestock, and 89% of the human strains carried all or part of their resistance determinants extrachromosomally on R-plasmids. Conjugative plasmids representing nine different incompatibility groups were detected, with the Inc I alpha group being predominant. Within the limits of the parameters measured, certain of these plasmids show a degree of relatedness suggestive of a common ancestry.     

Characterization and mobilization of nonconjugative plasmids encoding resistance to streptomycin and sulfanilamide

Most of nonconjugative streptomycin (Sm)- and sulfanilamide (Su)- resistance of clinical isolates belonging to various species of Enterobacteriaceae and Pseudomonas were encoded by an Inc Q plasmid, molecular size of which was 5.5 Md. The SmSu plasmids were efficiently mobilized by Inc P plasmids between E. coli strains. Inc I group and Inc F group plasmids could mobilize the Inc Q plasmids at lower efficiencies. The Inc Q plasmid was also mobilized to various species of Enterobacteriaceae at high frequencies without accompanying the conjugative Inc P plasmid; as a result, most of the SmSu-resistant transconjugants were nontransferable. The above results may explain the wide distribution of nonconjugative SmSu strains among clinical isolates.     

Characterization of R-plasmids in environmental isolates ofsalmonella: Host range and stability

Four environmental isolates ofSalmonella, resistant to several drugs, were examined for plasmid carriage with four different plasmid DNA isolation procedures. The method of Birnboim and Doly gave the best results. Three of the strains possessed a single plasmid with molecular weights of 60 (kanamycin resistant), 44.5 (kanamcin resistant), and 23.4 Md (ampicillin and amoxicillin resistant); the other strain (resistant to tetracycline) harbored two plasmids of 69.8 and 2.2 Md. The 69.8 Md was the one responsible for resistance. All plasmids were fi^–, and the 44.5 Md Kc^r plasmid synthesized a sex pilus type F. Some properties related to the dissemination of R-plasmids, such as host range, transfer frequencies, and in vitro stability, were studied. Plasmids generally showed a wide host range and high stability in the transconjugants tested. It could be concluded that these plasmids may be widely disseminated in the environment studied.     

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 in263/954 (28%) of bovine isolates,59/441 (13%) of porcine isolates and15/177 (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 > 1024 mg Tp/1 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), IncF_***H (4 plasmids), IncH₂ (1 plasmid), IncIaP (10 plasmids), IncIdT (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.     

Incidence and transfer of R-plasmids at a hospital in Saudi Arabia

One hundred and fifty Gram-negative bacteria isolated from patient specimens at King Faisal Specialist Hospital were examined for their ability to transfer antibiotic resistance plasmids to a sensitive Escherichia coli recipient in conjugation and transformation experiments. Agarose gel electrophoresis was used to enumerate and size the R-plasmids found, and Southern DNA hybridization was used to assess similarities between antibiotic resistance plasmids from different bacteria and sources. Of the bacterial isolates tested 65% contained plasmids, 70% of these transferred antibiotic resistance to E. coli, and 40% transferred multiple, linked resistances on R-plasmids. DNA hybridization of these R-plasmids demonstrated widespread similarities between plasmids from different bacterial genera and from different hospital locations. In particular, a gene encoding ampicillin resistance appeared especially widespread, indicating that a transposon may be mediating transmission of this resistance.     

Polyresistant Enterobacteriaceae strains and their plasmids in a hospital. Medical and theoretical aspects

The properties and origin of multiple resistant strains of Enterobacteriaceae found in the intestine and nasopharynx of infants admitted to the hospital for premature infants were studied. The strains of E. coli of different serovars isolated at various periods contained similar conjugative R plasmids with a molecular weight of 80 Md belonging to the O incompatibility group controlling resistance to kanamycin and physically independent small plasmids controlling resistance to ampicillin (7 Md) and streptomycin-sulfanilamides (4 Md). Multiple drug resistance in the strains of K. pneumoniae was controlled by single large (100-120 Md) plasmid cointegrates with 6-8 resistance markers. Such cointegrates consisted of several potentially independent plasmids, sometimes dividing on transformation of plasmid DNA of the recipient strains of E. coli K12. The small plasmids controlling resistance to ampicillin and streptomycin-sulfanilamides similar to the respective plasmids of E. coli were the constant components of the plasmids cointegrates. The multiple drug resistance in the above strains was combined with high capacity for colonization in premature infants. The medical staff and mothers were the sources of bacterial strains with single plasmids controlling definite types of resistance. It is suggested that the multiple resistant strains of Enterobacteriaceae are formed in hospital as a result of accumulation of the plasmids or plasmid markers and selection. One of the conditions for successive acquisition of new plasmid markers by definite bacterial strains was their high capacity for colonization in patients, which provided constant contacts and genetic exchange of such strains with a wide range of immigrant strains during colonization in the newly admitted patients.     

Plasmids of Azospirillum brasilense

The cells from natural isolates of A. Brasilense were found to harbour 1 to 4 plasmids with the molecular masses within the 27-300 Md range. 100 Md plasmids are specific for this bacterial species. Strains isolated from the roots of cereals (wheat, maize, barley) have more heterogeneous plasmid composition as compared to the strains isolated from soil.     

Antibiotic sensitivity and the characteristics of transmissive R plasmids in Shigella belonging to various species]

Sensitivity of 241 Shigella strains isolated from patients at various regions of the USSR in 1975--1978 was tested with respect to 14 antibiotics by the method of serial dilutions. 90.5 per cent of the isolates proved to be resistant to the antibacterial drugs and the greater part of 75.9 per cent of them had multiple resistance. The resistance of the Shigella was most pronounced and frequent with respect to tetracycline, streptomycin, levomycetin, as well as ampicillin and carbenicillin. Gentamicin, cephaloridin, polymyxin M, kanamycin, monomycin, neomycin and rifampicin were highly active against the Shigella. More than 50 per cent of the isolates were sensitive to levomycetin, ampicillin and carbenicillin. Differences in the frequency of the resistant strains and the spectrum of the antibiotic resistance of different Shigella subgroups (species) were observed. The study of 173 multiple resistant Shigella strains showed that about 67 per cent of the strains had a capacity for transduction of the resistance markers into the recipient cells of E. coli. The conjugative R-plasmids were most frequent in Sh. boydii and Sh. sonnei (95 and 95 per cent respectively), less frequent in Sh. flexneri and Sh. newcastle (68 and 53 per cent respectively) and least frequent in the mannitol negative Shigella (25 per cent). The capacity for transduction of R-plasmids in the strains carrying the determinants of resistance to 2 or 3 antibiotics was higher than in the strains carrying the determinant of resistance to one antibiotic. The clinical Shigella strains tested mainly had transmissive R-plasmids of fi--character (79 per cent).     

Conjugative R-plasmid of facultative methylotrophic bacteria Pseudomonas sp. M

50 Md conjugative plasmid, designated pM3, has been found in the cells from natural isolates of Pseudomonas sp M. The plasmid determines the resistance to tetracycline and streptomycin and is capable of conjugative transfer between the cells of Pseudomonas and Escherichia coli. The conjugative derivatives of pM3 deleted for 14 Md of molecular mass were isolated after acridine dyes treatment of cells harbouring plasmid pM3. The discovered plasmid was not shown to belong to IncP1 incompatibility group.     

Conjugative plasmids of Salmonella strains resistant to antibiotics

Plasmid DNA profile and conjugative R-plasmids were detected in Salmonella clinical isolates. The study revealed that drug resistance of Salmonella clinical strains of different serovars was determined by R-plasmids with a mol. wt. of 60-90 kD, carrying a certain spectrum of resistance to antibiotics. 9 types of conjugative plasmids, differing in their mol. wt. and resistance markers, were detected.     

In vitro and in situ conjugal transfer of an R-plasmid among enterobacteriaceae species isolated from meat samples

Abstract An R-plasmid donor strain of Escherichia coli isolated from a meat sample was mated with potential bacterial recipients belonging to the family Enterobacteriaceae isolated from ground beef and chicken samples. Nine different strains having different plasmid profiles were used as recipients in broth conjugation experiments. The recipients were identified as Enterobacter cloacae, Hafnia alvei, E. coli, Klebsiella pneumoniae and K. oxytoca . Of 1250 ampicillin resistant, tetracycline sensitive colonies tested, the incidence of recipients was estimated to be 3% (in ground beef) and 11% (in chicken) of the bacteria population. Two of the recipients, E. coli and K. Oxytoca also behaved as donors and transferred their R-plasmids to a laboratory recipient strain of E. coli K12-711. In vitro R-plasmid transfer frequencies varied within a wide range, from 10⁻² to 10⁻⁷ among recipients. Generally, frequencies of plasmid transfer were highest at 30°C and declined with decreasing temperature. Three of the recipient isolates, E. cloacae, H. alvei and E. coli displayed transfer of R-plasmids at 10°C in broth matings. Similar trends in R-plasmid transfer frequencies also were observed under in situ mating conditions in raw ground beef and pasteurized milk samples.     

Antibiotic resistance of Shigella in different regions of the USSR]

Shigella were most sensitive to polymyxin ceporin, ampicillin, neomycin and furazolidone and resistant to chloramphenicol, tetracycline and streptomycin. Shigella resistant simultaneously to two or three drugs mainly to tetracycline + chloramphenicol, tetracycline + streptomycin and tetracycline + chloramphenicol + streptomycin were most frequent. The frequency of the Shigella strains carrying R-plasmids increased from 28 per cent in 1969--1970 to 72.6 per cent in 1977. The Shigella strains isolated during the dysentery outbreak in 1973--1977 carried the R-factor controlling resistance to tetracycline + chloramphenicol, tetracycline + chloramphenicol + streptomycin, tetracycline + chloramphenicol + streptomycin + neomycin. Interaction between separate biochemical types, colicinogenicity and drug resistance classes was found in the Shigella isolates. The data on the effect of antibiotic (tetracyclines) intensive use in stock-raising defining wide spread of the R-plasmids controlling resistance to these drugs were obtained.     

Plasmid-linked drug resistance in Salmonella typhimurium in Kuwait

A total of 143 strains of S. typhimurium isolated from clinical cases in Kuwait were investigated for drug resistance. Multidrug resistance (3 or more drugs) was seen in 76.9% of the strains. The common resistance patterns were ASuT (16), AKSuT (20), ASSuT (14), CKSSuT (14), ACKSSuT (10), ACGKSSuT (15) and ACKGSSuTTm (8). MIC of resistant strains was usually high. Sixteen isolates were examined for the transferability of the resistance. All had R-plasmids, both autotransferable and non-autotransferable which could be mobilised by factor X.     

Molecular Typing of CTX-M-Producing Escherichia coli Isolates from Environmental Water,Swine Feces,Specimens from Healthy Humans,and Human Patients

CTX-M-producing Escherichia coli is the predominant type of extended-spectrum β-lactamase (ESBL)-producing E. coli worldwide. In this study, molecular typing was conducted for 139 CTX-M-producing E. coli isolates, phenotypically positive for ESBLs, isolated from environmental water, swine, healthy humans, and hospitalized patients in Hangzhou, China. The antibiotic resistance profiles of the isolates for the cephalosporins and fluoroquinolones were determined. The isolates showed 100% resistance to cefotaxime and ceftriaxone while maintaining relatively high susceptibility to cefoxitin, cefepime, and ceftazidime. A total of 61.9% (86/139) of the isolates, regardless of origin, showed high resistance to fluoroquinolones. PCRs and DNA sequencing indicated that bla_CTX-M-14 was the most prevalent CTX-M-9 group gene and that bla_CTX-M-15 and bla_CTX-M-55 were the dominant CTX-M-1 group genes. Isolates from all sources with CTX-M types belonging to the CTX-M-1 or CTX-M-9 group were most frequently associated with epidemics. Molecular homology analysis of the isolates, conducted by phylogenetic grouping, pulsed-field gel electrophoresis (PFGE), and multilocus sequence typing (MLST), demonstrated that the dominant clones belonged to B2-ST131, D-ST648, D-ST38, or A-CC10. These four sequence types (STs) were discovered in E. coli isolates both from humans and from environmental water, suggesting frequent and continuous intercompartment transmission between humans and the aquatic environment. Seven novel sequence types were identified in the current study. In conclusion, this study is the first to report the molecular homology analysis of CTX-M-producing E. coli isolates collected from water, swine, and healthy and hospitalized humans, suggesting that pathogens in the environment might originate both from humans and from animals.     

A case of shigellosis caused by Shigella dysenteriae type 1 and Shigella flexneri type 5B

Shigella dysenteriae type 1 and Shigella flexneri type 5b strains were isolated as causative agents of bacterial dysentery in a patient having visited South-East Asia. Both strains are a rare finding for Bulgaria. S. dysenteriae 1 strains have not been isolated since 1962, and there were only single isolates of S. flexneri 5b. The strains were of the same antibiotic resistance patterns. Conjugation experiments showed that resistance is determined by transferrable R-plasmids having identical characteristics. It is assumed that in the patient's gut transfer of an R-plasmid occurs from E. coli of the normal flora to the pathogenic shigellae.     

Worldwide distribution of the conjugative Clostridium perfringens tetracycline resistance plasmid, pCW3

The aim of this study was to test the hypothesis that all conjugative R-plasmids of Clostridium perfringens are closely related to the previously characterized tetracycline resistance plasmid, pCW3. Fourteen conjugative R-plasmids derived from 11 C. perfringens strains isolated in Australia, the United States, France, Belgium, and Japan were analyzed. Eleven of the plasmids encoded tetracycline resistance while three carried both tetracycline and chloramphenicol resistance. Each of these plasmids was compared, by restriction analysis, to the reference plasmid, pCW3. Seven of the tetracycline resistance plasmids had EcoRI, XbaI, and ClaI restriction profiles that were identical to those of the corresponding pCW3 digests. The seven remaining R-plasmids were different from pCW3. Comparison of partial restriction maps of these plasmids with a complete map of pCW3 indicated that they contained at least 17 kb of DNA that also was present in pCW3. Hybridization analysis confirmed that these plasmids shared substantial homology with pCW3. The three tetracycline and chloramphenicol resistance plasmids frequently lost a 6-kb chloramphenicol resistance segment during conjugation. Cloning experiments showed that the chloramphenicol resistance determinant was expressed in Escherichia coli and that the chloramphenicol resistance gene of one of these plasmids, pIP401, was contained within a 1.5-kb region of the 6-kb deletion segment. Hybridization analysis indicated that the deletion segment of pIP401 was related to those of the other two chloramphenicol resistance plasmids. During the course of this study, conjugative R-plasmids which appear to be identical to pCW3 or closely related to pCW3 were identified from C. perfringens strains from human, animal and environmental sources in five countries. It is concluded that C. perfringens strains in humans and animals throughout the world have overlapping gene pools and that all the conjugative C. perfringens R-plasmids examined probably evolved from a pCW3-like element.     

Significance of the antibiotic resistance of the causative agents of salmonellosis in its epidemiology and the procedure for controlling the infection

Antibiotic resistance of a wide set of strains (1501) of different serovars (69) was studied and the nature of the resistance was determined. Virulent bacteriophages designed with regard to the biological properties of the isolates were considered as possible agents for the control of antibiotic-resistant microorganisms. It was shown that multiple resistance to antibacterial drugs was mainly characteristic of the serovar of S. typhimurium. In Gorky and its region, strains carrying R plasmids determining the resistance to tetracycline and chloramphenicol with a molecular weight of 58-64 Md predominated. The antibiotic-resistant strains were dangerous from the epidemiological point of view. The use of the bacteriophages is advisable for the treatment of patients, sanation of bacterial carriers or decontamination of disease sources and prophylactic phaging with regard to the epidemiological indications for preventing group diseases.     

Plasmid profiles of Neisseria gonorrhoeae in Peninsular Malaysia

The plasmid profiles of 160 strains of Neisseria gonorrhoeae isolated in Peninsular Malaysia, comprising 80 penicillinase-producing (PPNG) and 80 non-penicillinase-producing (non-PPNG) isolates, were determined. The 80 PPNG isolates were divided into two plasmid groups. All of them harbored two common plasmid species, a 4.4 megadalton (Md) R plasmid previously associated with beta-lactamase production in PPNG strains from the Far East and a 2.6 Md multicopy plasmid of unknown function. In addition to these two plasmids, 60 (75%) PPNG isolates also carried a large 24.5 Md conjugative plasmid. In contrast, the 80 non-PPNG strains were divided into three plasmid groups. All of them possessed the 2.6 Md cryptic plasmid, and 35 (44%) isolates also harbored the 24.5 Md transfer plasmid. Besides these two plasmids, one non-PPNG isolate carried an additional 7.8 Md cryptic plasmid.