Genetical relationship between R plasmids derived from Salmonella and Escherichia coli obtained from a pig farm, and its epidemiological significance.

A total of 475 Salmonella strains belonging to 5 serovars, isolated from a pig farm which had been heavily contaminated with Salmonella for the past 2 years were tested for antibiotic susceptibility and detection of R plasmids. Thirty-three Escherichia coli isolates from the same farm were also examined in a similar way. Out of 475 strains 348 (73.2%) were resistant to one or more antibiotics such as tetracycline (Tc), streptomycin (Sm), sulfadimethoxine (Su), chloramphenicol (Cm) and kanamycin (Km), and 247 (85.2%) out of 290 strains belonging to 3 serovars examined harboured conjugative R plasmids. There was no change in the pattern of drug resistance during this survey nor any variation in the pattern of resistance of R plasmids, whatever the serovar. The antibiogram pattern Tc Sm Su, mainly S. typhimurium, was common among Salmonella strains. Among the transferred resistance patterns, the thermosensitive R plasmids conferring the Tc marker detected in this study were Fi-, and belonged to incompatibility group H1, whereas the R plasmids conferring Sm Su resistances which coexisted in the same host were Fi+, and compatible with the reference R plasmids tested. The I alpha plasmid conferring Cm resistance alone was isolated from S. anatum and the FII plasmid conferring Sm Km resistances was also isolated from S. typhimurium. In contrast, the 33 E. coli strains examined were resistant to three or five antibiotics and most of the resistance markers were located on conjugative R plasmids. I alpha plasmids conferring Cm resistance alone or FII plasmids conferring Cm or Km markers were common in the E. coli strains. H1 and H2 plasmids conferring multiple resistance markers were also found in them. The genetic properties of R plasmids derived from Salmonella or E. coli strains are compared, and the potential spread of R plasmids between strains of Salmonella and E. coli is discussed.     

Genetical relationship between R plasmids derived from Salmonella and Escherichia coli obtained from a pig farm, and its epidemiological significance

A total of 475 Salmonella strains belonging to 5 serovars, isolated from a pig farm which had been heavily contaminated with Salmonella for the past 2 years were tested for antibiotic susceptibility and detection of R plasmids. Thirty-three Escherichia coli isolates from the same farm were also examined in a similar way. Out of 475 strains 348 (73.2%) were resistant to one or more antibiotics such as tetracycline (Tc), streptomycin (Sm), sulfadimethoxine (Su), chloramphenicol (Cm) and kanamycin (Km), and 247 (85.2%) out of 290 strains belonging to 3 serovars examined harboured conjugative R plasmids. There was no change in the pattern of drug resistance during this survey nor any variation in the pattern of resistance of R plasmids, whatever the serovar. The antibiogram pattern Tc Sm Su, mainly S. typhimurium, was common among Salmonella strains. Among the transferred resistance patterns, the thermosensitive R plasmids conferring the Tc marker detected in this study were Fi-, and belonged to incompatibility group H1, whereas the R plasmids conferring Sm Su resistances which coexisted in the same host were Fi+, and compatible with the reference R plasmids tested. The I alpha plasmid conferring Cm resistance alone was isolated from S. anatum and the FII plasmid conferring Sm Km resistances was also isolated from S. typhimurium. In contrast, the 33 E. coli strains examined were resistant to three or five antibiotics and most of the resistance markers were located on conjugative R plasmids. I alpha plasmids conferring Cm resistance alone or FII plasmids conferring Cm or Km markers were common in the E. coli strains. H1 and H2 plasmids conferring multiple resistance markers were also found in them. The genetic properties of R plasmids derived from Salmonella or E. coli strains are compared, and the potential spread of R plasmids between strains of Salmonella and E. coli is discussed.     

Change of drug resistance patterns and genetic properties of R plasmids in Salmonella typhimurium of bovine origin isolated from 1970 to 1979 in northern Japan.

A total of 321 Salmonella typhimurium strains of bovine origin obtained in northern Japan during the period 1970-1979 were tested for drug resistance and detection of conjugative R plasmids. Three hundred and eighteen (99.1%) of these strains were resistant to one or more drugs. The isolation frequently of multiply drug-resistant strains tended to increase year by year. Two hundred and thirty-seven (74.5%) of these resistant strains carried conjugative R plasmids. A total of 308 R plasmids including 174 (56.5%) thermosensitive (ts) R plasmids were derived from the 237 drug-resistant strains, indicating that 71 (30.0%) strains have two different conjugative R plasmids in a single host cell. Of the 308 R plasmids examined for fertility inhibition (fi), 167 ts and 131 non-ts R plasmids were fi-. Of the 60 ts r plasmids examined for incompatibility, 50 were classified into H1 group and 10 into H2 group. Of the 52 non-ts R plasmids examined, 35 were classified into the I alpha-group and the remaining plasmids were untypable in our tests. Mercury resistance marker was found in about 20% of H1 R plasmids coding for multiresistance, and all of H2 R plasmids coded for resistance to tellurite. The clonal distribution of an S. typhimurium strain which carried an H1 R plasmid coding for resistance to six drugs and mercury was recognized in 1978 and 1979.     

Shigella species from Addis Ababa: frequency of isolation and in vitro drug sensitivity.

One hundred and five shigella isolates from Addis Ababa were studied to determine serogroup frequency and in vitro antibacterial drug sensitivity. About 70% of the isolates were Shigella flexneri followed by Sh. dysenteriae (15%), Sh. boydii (10%) and Sh. sonnei (5%). All or most of the strains were susceptible to cephalothin, gentamicin, kanamycin, polymyxin B and trimethoprim-sulphamethoxazole. Frequencies of susceptibility to ampicillin, carbenicillin and chloramphenicol were, respectively, 79, 80 and 75%. Only 37, 23 and 58% were susceptible to streptomycin, sulphadiazine and tetracycline, respectively. Resistance to one or more drugs was detected in 85% while 72% were multiply resistant. There were 24 different resistance patterns, varying from resistance to one drug to resistance to seven drugs. The findings have been compared with reports from other countries. This study and several others cited support the view that trimethoprim-sulphamethoxazole is the best alternative drug for treatment of shigellosis particularly in regions with multiple drug-resistant strains.     

儿童细菌性痢疾36例多重耐药的分析

目的 进一步了解儿童多重耐药志贺菌感染的菌群分布及药敏情况。方法 对杭州市儿童医院2011年4月至2013年6月就诊的14周岁以下患儿多重耐药志贺菌感染的菌群及药敏结果进行统计分析。结果 在培养出多重耐药志贺菌的36名患儿中,男童23名,女童13名,男女比例为1．77：1,年龄分布10个月至9岁,平均年龄3．14±1．23岁。在收集到的36株多重耐药志贺菌中,有27株分离于0～5岁患儿粪便,占75．0％;9株分离于6～10岁患儿粪便,占25．0％。药敏结果显示,氨苄西林、庆大霉素以及头孢唑林的耐药率最高达100．0％。收集的36株志贺菌全部多重耐药,均对头孢唑林、氨苄西林、庆大霉素耐药;四重耐药只有福氏志贺菌4株,宋内志贺菌1株,共占13．9％（5／36）,其余31株均为四重以上耐药,占86．1％（31／36）。结论 本地区儿童疑为多重耐药志贺菌感染时,宜首选呋喃妥因、头孢他啶、头孢哌酮／舒巴坦、哌拉西林／他唑巴坦等抗菌素。     

High and low level tetracycline resistance in Shigella sonnei.

The results presented in this paper confirm the existence of two types of tetracycline resistance in Shigella sonnei. One group of strains had a high level of resistance to tetracycline and oxytetracyline, with a variable level of minocycline resistance. The second group had a lower level of tetracycline resistance and were sensitive to minocycline. After conjugation with E. coli K12 the selected E. coli transconjugants had the same levels of resistance as the parent Sh. sonnei strain, with one exception. Sh. sonnei 87 was resistant to a high level of tetracycline, but was able to transfer only low level resistance. It is suggested that Sh. sonnei 87 carriers two plasmids: pSU1, a conjugative plasmid conferring a low level of tetracycline resistance, and pSU2, a non-conjugative plasmid which confers a high level of resistance to tetracycline.     

Plasmid-determined antibiotic resistance in Shigella flexneri isolated in England and Wales between 1974 and 1978.

The majority of Shigella flexneri strains isolated in England and Wales are from infections contracted abroad. Most of these strains are drug-resistant, over 75% being resistant to streptomycin and sulphonamides, sulphonamides alone or streptomycin, sulphonamides and tetracyclines. A selection of resistant strains was tested for resistance transfer and the plasmids identified were characterized by compatibility grouping. Streptomycin and sulphonamide resistance was usually determined by a non-autotransferring plasmid which may be mobilized by standard transfer factors, or by the plasmid which conferred tetracycline resistance where this was present. The remaining resistant strains were predominantly resistant to four or more drugs. These strains carried autotransferring plasmids of a variety of compatibility groups, of which groups B, I1 and FII were the most common.     

Shifting serotypes,plasmid profile analysis and antimicrobial resistance pattern of shigellae strains isolated from Kolkata,India during 1995-2000

One hundred and sixty-six shigellae strains, isolated from stool samples of paediatric patients (< 5 years old) at a Childrens' Hospital in Kolkata, India during the period of 1995-2000 were examined for serotyping, drug resistance pattern and plasmid profiles. Sh. flexneri (58 %) was found to be commonest isolate of total shigellae, followed by Sh. sonnei (28 %), Sh. boydii (9%) and Sh. dysenteriae (5%). This profile of species was in sharp contrast to the picture obtained before 1995, when Sh. dysenteriae 1 predominated over Sh. flexneri. In Sh. flexneri strains, Sh. flexneri 2a (35%) was the most prevalent serotype, following Sh. flexneri 3a (31%), Sh. flexneri 6 (14%), Sh. flexneri 2b (11%) and Sh. flexneri 4 (9%). Resistance patterns of the strains to 12 commonly used antimicrobial agents and minimum inhibitory concentrations (MICs) of the antibiotics were also tested. All strains were found uniformly susceptible to norfloxacin, but more than 90% strains were resistant to tetracycline, co-trimoxazole and 67% strains were resistant to ampicillin. Resistance to amoxicillin, chloramphenicol and nalidixic acid was found in 55% (range 45-74%), 46% (range 40-60%) and 29% (range 15-40%) strains respectively. Overall, shigellae strains showed statistically significant increase in resistance against tetracycline, nalidixic acid and furazolidone (P < 0.05) over the years of this study. This indicates decreased efficacy of furazolidone, cotrimoxazole and nalidixic acid for the empirical treatment of shigellosis in Kolkata. Although a few strains showed intermediate susceptibility to ciprofloxacin (4%) and cefotaxime (10%) by disk diffusion test, but the MICs of those antibiotics were within the normal limits. Almost 57% of the strains were resistant to four or more drugs with high MICs of the antibiotics. Plasmid profile analysis revealed presence of large plasmid of 220 kb in majority of the strains except in Sh. sonnei and a correlation between presence of smaller plasmids and shigellae serotypes. Hence this study reports epidemiological change of shigellae species in Kolkata, India with regard to serotypes and antibiotic resistance patterns.     

Plasmid characterization of drug-resistant Shigella dysenteriae 1 from an epidemic in Central Africa

A widespread epidemic of severe dysentery in Zaire and neighbouring Central African countries was caused by a multiply drug-resistant strain of Shigella dysenteriae 1. Early isolations were resistant to ampicillin, chloramphenicol, streptomycin, sulphonamides and tetracyclines (R-type = ACSSuT). Later in the epidemic strains resistant to trimethoprim (Tm) became prevalent and a few strains resistant to kanamycin (K) or nalidixic acid were also isolated. All resistances except nalidixic acid were encoded by plasmids of incompatibility groups X (ACT) or I1 (ACSSuTTm) and the epidemic strain also carried an SSu plasmid and a number of cryptic plasmids. The Inc X plasmid from this epidemic is the same as that in Sh. dysenteriae 1 strains isolated in Somalia in 1976 whereas the epidemic strains from the Shiga outbreaks in Central America, 1969 to 1971, and Sri Lanka, 1979, carried plasmids of group B. This epidemic demonstrates that when a multiresistant strain includes resistance to trimethoprim, nalidixic acid is a suitable alternative therapeutic agent.     

Plasmid characterization of drug-resistant Shigella dysenteriae 1 from an epidemic in Central Africa.

A widespread epidemic of severe dysentery in Zaire and neighbouring Central African countries was caused by a multiply drug-resistant strain of Shigella dysenteriae 1. Early isolations were resistant to ampicillin, chloramphenicol, streptomycin, sulphonamides and tetracyclines (R-type = ACSSuT). Later in the epidemic strains resistant to trimethoprim (Tm) became prevalent and a few strains resistant to kanamycin (K) or nalidixic acid were also isolated. All resistances except nalidixic acid were encoded by plasmids of incompatibility groups X (ACT) or I1 (ACSSuTTm) and the epidemic strain also carried an SSu plasmid and a number of cryptic plasmids. The Inc X plasmid from this epidemic is the same as that in Sh. dysenteriae 1 strains isolated in Somalia in 1976 whereas the epidemic strains from the Shiga outbreaks in Central America, 1969 to 1971, and Sri Lanka, 1979, carried plasmids of group B. This epidemic demonstrates that when a multiresistant strain includes resistance to trimethoprim, nalidixic acid is a suitable alternative therapeutic agent.     

Shigellosis in the south-western Cape of Good Hope 1968-85

During the period 1968-85 shigella organisms were isolated from stool specimens of 1562 patients attending Tygerberg Hospital, situated in the south-western province of the Cape of Good Hope of the Republic of South Africa. Shigella flexneri (72% of patients) was the commonest subgroup identified. Sh. sonnei was the second-commonest isolate (20%), with smaller numbers of Sh. boydii (5%) and Sh. dysenteriae (3%). Sh. dysenteriae has not been isolated since 1979. In 1985 30% of isolates were resistant to ampicillin and 52% to trimethoprim-sulphamethoxazole. During this period 12 cases of shigellaemia were seen, 11 in young infants less than 13 months of age who were malnourished in 6 cases. The single adult had had a previous gastrectomy and splenectomy.     

Resistance to chloramphenicol and ampicillin Salmonella johannesburg in Hong Kong: observations over a five-year period 1973-1977.

Salmonella johannesburg has been prevalent in Hong Kong since 1973 and most strains were resistant to a multiplicity of antibiotics. The susceptibility of S. johannesburg strains isolated in a 5-year period from 1973 to 1977 to eight antimicrobial drugs including ampicillin (A), streptomycin (S), tetracycline (T), chloramphenicol (C), Kanamycin (K), sulphadiazine (Su), trimethoprim (Tm) and gentamicin (G) was tested by the agar dilution method. The proportion of strains resistant to chloramphenicol and ampicillin increased steadily during the 5-year period while those resistant to tetracycline decreased dramatically. This change was associated with an alteration of predominant patterns of antibiotic resistance: strains with the resistance pattern A.S.T.C.K.Su predominated in years 1973, 1974 and 1975 while those with the resistance pattern A.S.C.K.Su predominated in years 1976 and 1977. Analysis of the resistance patterns of S. johannesburg strains isolated from the same cases showed that the resistance pattern A.S.C.K.Su was more stable, and changed less frequently to other patterns of resistance than strains with the resistance pattern A.S.T.C.K.Su. In donor salmonella strains with the A.S.T.C.K.Su resistance pattern, transmissible factors carrying resistance to A.S.T.C.K.Su in toto, to A.S.T.C.Su,A.T.C.K.Su and to A or T alone were demonstrated. In donor salmonella strains with the A.S.C.K.Su resistance pattern, transmissible factors carrying resistance to A.S.C.K.Su in toto and to A.S.K.Su were detected. The significance of the carriage of such transmissible resistance factors by this Salmonella is briefly discussed.     

嘉定区2004年志贺氏菌的分布特征及耐药性研究

目的：了解本地区志贺氏菌的分布情况和耐药水平。方法：收集本地区肠道门诊腹泻患者的肛拭标本，进行志贺氏菌的分离鉴定，并对所分离到的菌株用K-B法进行药物敏感试验。结果：从2626份肛拭中检出237株志贺氏菌，检出率为9．03％，其中B群占95．78％，为优势菌群。本地区出现了一种新的志贺氏菌血清型F4c占28．69％，是引起本地区菌痢的优势菌型。志贺氏菌对复方新诺明、氯霉素、氨苄青霉素的耐药性较高，分别为92．41％、89．45％、88．61％，对2种及2种以上药物耐药的占92．83％，主要耐药谱为CMP-SXT-AMP。结论：本地区志贺氏菌的检出率和耐药性较高，存在明显的季节性分布，优势菌型出现了变迁，应加强对菌痢的长期监测。     

武汉市2006～2007年细菌性痢疾监测及耐药性分析

目的了解武汉市细菌性痢疾的病原菌志贺氏菌型分布及其药物敏感状况,为细菌性痢疾临床治疗和预防控制提供依据。方法按《全国细菌性痢疾监测方案》的要求进行监测、采样并系统检测。结果临床初步诊断为细菌性痢疾标本539份,经复核鉴定为志贺氏菌的有17株,检出率为3．2％。其中宋内氏菌15株。福氏志贺氏菌2株,分别占检出菌株数的88．2％和11．8％。药敏试验显示17株志贺氏菌敏感药物为阿莫西林（100％）、环丙沙星（100％）,全部耐药的有利福平（100％）,且有5株菌出现了3种或3种以上的多重耐药现象。结论2006～2007年武汉市细菌性痢疾病原菌以宋内氏志贺氏菌为主,其次为福氏志贺氏菌,并对目前常用的抗生素表现一定的耐药性,应引起重视。     

Plasmid profiles of drug resistant Shigella boydii types 1-5, 8, 10, 12-14 from Ethiopia (1974-85).

Plasmid profile analysis by agarose gel electrophoresis was performed on 42 drug resistant strains of Shigella boydii serotypes 1-5, 8, 10, 12-14, collected between 1974 and 1985 from endemic cases of shigellosis in Ethiopia, and their Escherichia coli K12 transconjugants. Resistance factors (R factors) were further characterized by incompatibility testing. Patterns of small plasmids, less than 15 kb, were similar within each of the individual S. boydii serotypes. Plasmids of about 3.3-3.7 kb were found in all strains of serotypes 2 and 4. Plasmids of about 4.3-4.6 kb were found in about 86% of strains. Serotypes 1, 2 and 3 were characterized by plasmids of about 5.6-5.7 kb. The 6.4-6.7 kb plasmid was found consistently in serotypes 1, 2, 3, 5, 8, 12 and 13 which were resistant to SSu or had an SSu resistance component in their phenotypes. Large plasmids (155-186 kb) were found in most S. boydii strains. Conjugative drug resistance plasmids, most often coding for three or less drugs, were found in about 26% of drug resistant strains. R-factors, coding for AT resistance (in types 2 and 8), and ASSuT resistance (in type 4), were compatible with all reference plasmids tested. Plasmids belonging to incompatibility groups X and N were found in serotypes 5 and 10, respectively.     

Dissemination of gentamicin-resistant plasmids among strains of Enterobacteriaceae

The frequency of gentamicin-resistance among strains of many species of Enterobacteriaceae isolated from in-patients in our hospital has increased considerably since 1979. To clarify the reason for this increase, we tried to detect R-plasmids conferring gentamicin-resistance in all of the isolates in 1981 and found that most of them had conjugative R-plasmids. For epidemiological purposes we classified these into types I to X and 'others' by the following criteria: the nature of the resistances conferred; their incompatibility group; their molecular weight and the pattern of the DNA fragments after digestion with restriction endonucleasis. In the urology department, type-I plasmids conferring resistance to gentamicin, kanamycin, tobramycin and amikacin, and type-II plasmids conferring resistance to gentamicin, kanamycin and tobramycin were detected in the isolates belonging respectively to six species and twelve biotypes, and four species and six biotypes. In the second surgery ward, isolates belonging to six species and twelve biotypes were found to have type-III plasmids conferring resistance to gentamicin, kanamycin, tobramycin and chloramphenicol. Our investigation shows that not only antibiotic-resistant strains but also R-plasmids may be disseminated in hospitals.     

Behavior of drug resistant fecal coliforms and R plasmids in a wastewater treatment plant

Fecal coliforms were isolated from the inlet, the primary sedimentation tank, the activated sludge digestion tank, the final settling tank, the outlet and the return activated sludge drain at the municipal wastewater plant in Ube City, and examined for drug resistance and presence of R plasmids. Drug concentrations employed to distinguish resistant isolates from sensitive isolates were 25 micrograms/ml for tetracycline, kanamycin, chloramphenicol and streptomycin, 50 micrograms/ml for ampicillin, nalidixic acid and rifampicin, and 200 micrograms/ml for sulfisoxazole, respectively. Of a total of 900 isolates, 45.7% were drug resistant and 51.1% of them carried R plasmids. The further along that wastewater had progressed through the treatment process the greater the tendency was for appearance of the multiresistant isolates. These isolates also were shown to simultaneously carry transferable R plasmids. Observed resistant patterns of R plasmids were mainly multiple and encoded to resistance to tetracycline, chloramphenicol, streptomycin and sulfisoxazole. It became clear that multiplication of R plasmids took place in the activated sludge digestion tank. This study show that drug resistance transfer mediated by these R plasmids may occur in actual wastewater treatment plants.     

Molecular characterization of trimethoprim resistance in salmonellas isolated in Sicily, 1985–1988

The occurrence of trimethoprim (Tp) resistance in salmonellas isolated from humans and water samples in Sicily between 1985 and 1988 has been investigated and the Tp resistance mechanisms have been further characterized on the basis of hybridization with probes for the dihydrofolate reductase (DHFR) genes types I, II, IV and V. Of 765 strains examined, high level (>1000 mg/1) resistance to Tp was identified in 23 strains (3%). In 22 of these strains, such resistance was associated with resistance to sulphonamides. Six serovars with Tp-resistant strains were identified,Salmonella typhimurium (14 strains),S. enteritidis (2),S. agona (2),S. mbandaka (2),S. virchow (2),S. Indiana (1). In all strains with high level Tp resistance, resistance to this antimicrobial was plasmid-encoded, in most strains by plasmids with MWs ranging from 70–100 MDa. On the basis of restriction endonuclease analysis, four different categories of Tp resistance plasmids were identified in Tp-resistant strains ofS. typhimurium. Hybridization with the DHFR I probe was observed in three strains of Tp-resistantS. typhimurium and two strains of Tp-resistantS. enteritidis; in contrast, in none of the strains tested was there any detectable hybridization with the probes for DHFR types II, IV and V. It is concluded that the DHFR type I resistance mechanism, common in Tp-resistant enterobacteria in many European countries, is relatively uncommon in Tp-resistant salmonellas isolated in Sicily. Furthermore, the DHFR V resistance mechanism, previously identified in strains ofShigella sonnei isolated in Sicily and associated with travellers from Sri Lanka, has not yet appeared in salmonellas in Sicily.     

1992～2005年玛纳斯县志贺菌菌群分布及耐药性分析

[目的]探讨玛纳斯县细菌性痢疾病原菌志贺菌的菌群、菌型分布及耐药状况，以制定科学有效的防治对策。[方法]对1992～2005年玛纳斯县检出的149株志贺菌有关资料进行分析。[结果]149株志贺菌中，福氏（B群）占69．80％，痢疾志贺菌（A群）占13．42％，宋内氏（D群）占12．75％，鲍氏（C群）占4．03％，B／D为5．47，不同时期分离的菌均以B群为主，A群次之，D群和C群分列第3、4位；B群2a、1b分别占36．91％、8．72％，Al型和宋内氏菌分别占11．41％、12．75％。检测87株菌，对氨苄青霉素、四环素、复方新诺明、利福平、氯霉素、庆大霉素、氟哌酸、头孢呋辛、痢特灵的耐药率分别为95．40％、98．85％、95．40％、97．70％、60．92％、16．09％、26．44％、10．34％、14．94％。[结论]玛纳斯县志贺氏菌的主要流行菌为B群（以2a为主），菌株对常用抗菌药物的耐药性较严重。     

118株志贺菌的流行病学调查及药物敏感临床分析

目的了解深圳市龙岗区引发痢疾的志贺菌优势菌型及其药物敏感状况,为痢疾临床治疗和预防控制提供依据。方法采用血清凝集试验、菌种VITEK-32鉴定仪系统生化鉴定和K-B法对从腹泻病人分离的志贺菌进行流行病学分析和药物敏感试验。结果复方新诺明耐药率为92.37%,氨苄西林耐药率为85.59%。头孢噻吩、头孢噻肟、头孢唑啉、环丙沙星均敏感,耐药率均在10.00%以下。结论地区志贺菌感染的优势菌型为福氏2a型。药物头孢噻吩、头孢噻肟、头孢唑啉、氟哌酸可作为目前临床治疗痢疾的常用药物。