Characterization of resistance plasmids and carried phages in an epidemic clone of multi-resistant Salmonella typhimurium in India.

Hospital outbreaks of severe gastroenteritis caused by multi-resistant Salmonella typhimurium have occurred in a number of cities throughout India since 1977. The strains involved belong to phage types 66 or 122, or are untypable; the latter are derived from types 66 or 122 by acquisition of one or more of a number of temperate bacteriophages. Types 66 and 122 are closely related and react with the same phages of the S. typhimurium typing scheme. A plasmid belonging to compatibility group F1me encoding resistance to ampicillin, chloramphenicol, kanamycin, streptomycin, sulphonamides, spectinomycin, tetracyclines, gentamicin and trimethoprim (R-type ACKSSuSpTGTm) is present in all of the multi-resistant strains. Several other plasmids have been identified including an SSu resistance determinant, a group I2 transfer factor and an R factor coding for resistance to kanamycin, streptomycin and sulphonamides which is compatible with plasmids of all the standard compatibility groups. These plasmids are only present in a proportion of the strains examined. Examination of strains from other sources has identified a paediatric hospital outbreak in Saudi Arabia and a number of sporadic infections in Great Britain which have been caused by the same organisms. These studies show that, despite differences in phage type and plasmid content, this group of strains belongs to a single clone which has become widespread in India with some extension to other countries.     

Instability of multiple drug resistance plasmids in Salmonella typhimurium isolated from poultry

Plasmids in five strains of Salmonella typhimurium resistant to ampicillin, chloramphenicol, gentamicin, neomycin/kanamycin, streptomycin, sulphonamides, tetracyclines and trimethoprim (ACGKSSuTTm), CGKSSuTTm, ACSSuT or CSSuT which had been isolated from poultry in the first 3 months of 1989 have been characterized and compared with plasmids in two strains of R-types ACGKSSuTTm and ASSuTTm isolated from two patients later in the year. With the exception of the human isolate of R-type ASSuTTm, all strains carried two non-conjugative plasmids, one coding for SSu and belonging to incompatibility group Q, and a second coding for multiple resistance and belonging to the FIme incompatibility group. The human isolate of R-type ASSuTTm did not carry the IncQ SSu plasmid but like the poultry isolates, carried a non-conjugative FIme plasmid. Restriction endonuclease digestion with the enzymes EcoR I, Pst I and Hind III demonstrated that the FIme plasmids from strains of different R-types showed a high degree of homology but exhibited numerous fragment size polymorphisms. The restriction digest fingerprint of plasmids in the human isolate of R-type ACGKSSuTTm was indistinguishable from a poultry isolate of the same R-type. Analysis of segregants of one of the poultry isolates of R-type ACGKSSuTTm demonstrated that resistance determinants could be rapidly lost from the FIme plasmid to give rise to a number of R-types and fingerprint patterns. Loss of tetracycline resistance from this plasmid appeared to be correlated with the integration of other plasmid-mediated resistances into the bacterial chromosome. Evidence is presented for the rapid loss of antimicrobial resistance determinants from a multiple resistance plasmid of the FIme incompatibility group in response to withdrawal of antibiotic selective pressure.     

Emerging antibiotic resistance in Salmonella typhimurium in Norway

The antimicrobial resistance of 809 Salmonella Typhimurium isolates collected from humans in Norway between 1975 and 1998 was studied. The material was subdivided into domestic and foreign isolates according to whether the patient had recently travelled abroad or not. In imported isolates the largest increase in resistance was in 1996 when 35% of the isolates were multi-resistant. The first multi-resistant isolate acquired in Norway appeared in 1994, but already in 1998 23% of the isolates domestically acquired were multi-resistant, and a majority were S. Typhimurium DT104. We found no ciprofloxacin resistance in domestically acquired isolates. Amplified fragment length polymorphism analysis was performed on selected multi-resistant isolates. The method discriminated well between different multi-resistant isolates, but not between DT104 isolates. Resistant and multi-resistant S. Typhimurium were until 1998 essentially recovered from patients who had travelled abroad, but multi-resistant isolates, mainly DT104, are now also being transmitted within the country.     

鼠伤寒沙门菌耐药株拓扑异构酶基因突变分析

目的　探讨鼠伤寒沙门菌对氟喹诺酮类药物的耐药性与拓扑异构酶基因突变之间的关系。方法　三株鼠伤寒沙门菌分离株X2 ,X7,X11对氟喹诺酮类药物环丙沙星的MIC分别为 32、0 38和 0 0 2 3μg ml,X2为耐药株。利用聚合酶链反应 (PCR)对其拓扑异构酶四个耐药基因gyrA ,gyrB ,parC ,和parE进行扩增和序列分析。结果　发现分离株X2的gyrA基因同时在 2 4 8、2 5 9位点发生点突变 (Ser83→Phe ,Asp87→Asn)。分离株X7gyrA基因在 2 4 8位点发生点突变 (Ser83→Tyr)。分离株X11的gyrA基因没有发生突变。X2parC基因QRDR在 2 38位点发生点突变 (Ser80→Arg)。而分离株X7、X11的parC基因没有发生突变。三株鼠伤寒沙门菌分离株的gyrB和parE基因都没有发现突变。结论　gyrA和parC上同时发生突变会导致鼠伤寒沙门菌对环丙沙星的高耐药性     

Porin content modifies resistance of Salmonella typhimurium to phagocytosis

Mutants of Salmonella typhimurium, which contain different quantities of outer membrane proteins, show different susceptibility to phagocytosis. We correlate susceptibility to phagocytosis with molecular surface characteristics which are responsible for invasiveness and virulence of bacteria.     

AcrAB-TolC电泵系统介导的鼠伤寒沙门菌多重耐药机理研究

目的探讨AcrAB-TolC电泵系统在鼠伤寒沙门菌产生多重耐药中的作用。方法利用基因敲除技术,敲除多重耐药鼠伤寒沙门菌野生株X2的acrAB基因和tolC基因,获得两个突变株△tolCX2和△acrABX2。通过基因敲除前后细菌耐药水平的改变,验证AcrAB-TolC系统在鼠伤寒沙门菌产生多重耐药中的作用。结果△tolCX2和△acrABX2对万古霉素耐药,对丁胺卡那霉素、头孢曲松敏感,与野生株X2一致;但对11种抗生素由耐药变为敏感。结论AcrAB-TolC系统与鼠伤寒沙门菌多重耐药的产生有关。     

Bavaroise and an epidemic of Salmonella enteritidis

In the literature an association is made between the increasing prevalence of Salmonella enteritidis in poultry products and in the isolates of patients with gastroenteritis, without sufficient evidence of a causal relationship between the increasing prevalences. A microbiological and epidemiological analysis of a food poisoning incident among 239 visitors of a restaurant by way of food specific attack rates and food specific infection rates revealed an epidemic of 70 cases of S. enteritidis enteritis. The analysis supports the causal relationship with the consumption of an infected, unhygienically prepared egg product, in this case bavaroise.     

Malaria epidemic and drug resistance, Djibouti

Analysis of Plasmodium falciparum isolates collected before, during, and after a 1999 malaria epidemic in Djibouti shows that, despite a high prevalence of resistance to chloroquine, the epidemic cannot be attributed to a sudden increase in drug resistance of local parasite populations.     

Clonal distribution of resistance plasmid-carrying Salmonella typhimurium, mainly in the Middle East

Strains of Salmonella typhimurium of predominantly Middle Eastern origin, but distributed from England to India, were found to carry at least three types of resistance plasmid. The most important was initially identified as an F_I plasmid by compatibility tests, but differs from the F factor on the one hand and the F_I factors R162 and ColV on the other. The three groups of F_I plasmids can be distinguished by their compatibility reactions with the MP10 plasmid of S. typhimurium (Smith, Humphreys, Grindley, Grindley & Anderson, 1973) and group H₁ factors: the F factor is unilaterally incompatible with group H₁ (Smith, Grindley, Humphreys & Anderson, 1973; Anderson, 1975b); the F_I factors are compatible with MP10 and group H₁; and F_Ime factors are incompatible with MP10 but compatible with H₁. The majority of S. typhimurium cultures belonged to phage type 208; most of those that did not, belonged to types related to 208. Only a minority of their F_Ime plasmids were autotransferring. The remainder were mobilizable by F-like plasmids, and by group H₁ and H₂ factors, but not by the fi^- I₁ factor Δ, or by plasmids of the I₂, B, P, W, N and com 7 groups. The compatibility reactions of the autotransferring F_Ime plasmids were identical with those of the non-transferring members of the group, and both were large, single-copy plasmids.     

Transmissible mupirocin resistance in Staphylococcus aureus

The spread of two strains of Staphylococcus aureus with high level resistance to mupirocin is described. The resistance proved to be easily transferred to other S. aureus strains by filter mating experiments and on the skin of mice. No plasmid band corresponding to the resistance could be demonstrated by agarose gel electrophoresis or by caesium chloride gradient centrifugation but cleavage of 'chromosomal' DNA from resistant recipients showed bright bands of DNA absent from sensitive controls.     

Reduction in faecal excretion of Salmonella typhimurium strain F98 in chickens vaccinated with live and killed S. typhimurium organisms

Chickens given orally at 4 days of age a smooth spectinomycin resistant mutant (Spcr) of Salmonella typhimurium strain F98 excreted the organism in their faeces for approximately 4 weeks. Following oral administration of a nalidixic acid resistant (Nalr) mutant of the same strain 4 weeks later when the chickens had virtually cleared themselves of the first infection, these chickens excreted far fewer salmonella organisms and for a shorter time than did a previously uninfected control group of chickens which were infected at the same time with the Nalr mutant. Chickens inoculated intramuscularly at 4 days developed a similar immunity to challenge and also excreted the immunizing strain in their faeces. In contrast intramuscular inoculation or incorporation into the food of formalin-killed S. typhimurium organisms had little lasting effect on the faecal excretion of the challenge strain. Two attenuated mutants of strain F98 Nalr were produced: one was a rough strain produced by lytic bacteriophage and the other was an aro A auxotrophic mutant which had been cured of the 85 kilobase-pair virulence-associated plasmid. These mutants were avirulent for chickens, mice, calves and man and when ingested by human volunteers did not persist in the faeces. When inoculated intramuscularly into chickens they produced an early reduction in faecal excretion of the challenge strain (Spcr) which was not maintained. Oral administration of both strains produced reductions in faecal excretion of the challenge strain. This was much more noticeable with the rough strain which was itself excreted for a much longer period than the parent strain.     

Phagocytosis and resistance to Salmonella typhimurium infection in mice fed with lipidic diet

The peritoneal macrophages from mice on a lipidic diet have shown an increase of surface hydrophobicity of cytoplasmatic membrane. This fact is correlated with a decrease of the phagocytic index and with an impairment of Salmonella typhimurium.[/p]Corresponding author.     

A study of drug resistance among Salmonella typhi and Salmonella paratyphi A in an endemic area, 1977–1979

Tests for antibiotic resistance were carried out on 198 strains of Salmonella typhi and S. paratyphi A isolated from cases of enteric fevers. Their minimal inhibitory concentrations for streptomycin, chloramphenicol, ampicillin, furazolidine and co-trimoxazole were estimated by plate dilution technique. Four strains of S. typhi and one strain of S. paratyphi A were found to show multiple resistance with a set pattern of resistance to chloramphenicol, streptomycin, sulphonamide, tetracycline and spectinomycin. All the five strains carried R-factors. Three of the resistant S. typhi belonged to Phage type ‘O’ and one was in Phage type ‘A’. The single resistant S. paratyphi A belonged to Phage type ‘2’.     

中山市科瓦利斯沙门氏菌耐药特征及分子分型研究

目的 分析中山市科瓦利斯沙门氏菌的耐药特征及分子分型情况,了解该血清型沙门氏菌的流行趋势,为本地区食源性疾病防控工作的开展提供可靠依据.方法 参照GB4789.4-2016《食品安全国家标准食品微生物学检验沙门氏菌检验》对样本进行分离培养、生化及血清学鉴定;采用最小抑菌浓度(MIC)法进行14种抗菌药物敏感试验;运用P...