The role of mechanically purified city sewers in the spread of antibiotic-resistant bacteria of the Enterobacteriaceae family

The aim of this study was to evaluate a degree of contribution of mechanically cleansed municipal sewage in a spread in on environment of bacteria of Enterobacteriaceae family with special regard to antibiotic resistant strains. High number of bacteria of Enterobacteriaceae family was found in 1 ml of sewage and the number of antibiotic-resistant bacteria was 0.5-50 X 10(3)/ml. Among the strains tested the resistance to more than one antibiotics was encountered. 78.3% of strains transferred antibiotic resistance to E. coli recipient strain, what indicate a participation of potentially pathogenic bacteria from Enterobacteriaceae family in a spread of antibiotic resistance in a environment.     

Trends in the development of the epidemic process in salmonellosis caused by Salmonella typhimurium and Salmonella enteritidis

The dynamics and structure of the epidemic process of Salmonella infections among the population of Perm in 1983-1988 was studied and the results of evaluation of antibiotic resistance of the dominating Salmonella species analyzed. The study revealed that a decrease in salmonellosis morbidity caused by S. typhimurium was associated with a limited circulation of anthroponotic (antibiotic-resistant) variants of Salmonellae and a relative increase in the proportion of zoonotic (antibiotic-sensitive) strains. At the period of elevated morbidity this Salmonella infection affected mainly young children in cold months, whereas in recent years seasonal morbidity rises shifted to spring-summer and summer-autumn months, affecting older age groups of the population. The study also revealed that a rise in salmonellosis morbidity caused by S. enteritidis was due to increased circulation of zoonotic variants of Salmonellae. Changes in the epidemiological situation necessitate correction of the system of epidemiological surveillance on Salmonella infections with the emphasis on sanitation measures in stock-breeding farms with unfavorable epidemiological situation.     

The use of bacteriophages in eliminating polyresistant strains ofStaphylococcus aureus andStreptococcus agalactiae

Temperate bacteriophages were induced in and released from isolates of Staphylococcus aureus and Streptococcus agalactiae using mitomycin C. Various specific indicator cultures were tested for providing clear plaques after phage infection. Specific lytic mixture of bacteriophages was prepared using the induced, modified and laboratory variants of phages. Under laboratory conditions, the mixture eliminated all isolates from the tested collection of microorganisms. The restriction barrier of some bacterial isolates to bacteriophage infection was overcome either by UV irradiation or in vitro modification of bacteriophage DNA with specific methyltransferases. Conjugative R plasmids, capable of replication in G+ and G- bacteria, were detected and isolated from S. aureus and S. agalactiae antibiotic-resistant strains.     

Antibiotic resistance of Lactobacillus strains]

One hundred and thirty six Lactobacillus strains isolated from poultry and 23 Lactobacillus strains isolated from long-living persons were tested for their antibiotic sensitivity. Occurrence of some type determinants of resistance to aminoglycoside antibiotics and tetracyclines in the Lactobacillus strains resistant to these antibiotics was studied. The majority of the strains from the both collections were resistant to aminoglycosides (73 and 79 per cent, respectively). The isolates from the poultry were characterized by multiple resistance. The isolates from the long-living persons were most frequently resistant to one of two antibiotics. All the tested Lactobacillus strains isolated from the long-living persons were sensitive to tetracyclines. The species composition of the isolates was different. The antibiotic-resistant strains were detected in all the species involved in the study. By hybridization of Lactobacillus colonies with the probes containing various genes of the resistance it was shown that in 14 per cent of the antibiotic-resistant strains belonging to Lactobacillus the antibiotic resistance was controlled by the genes homologous to resistance genes widely distributed in gramnegative organisms. This indicated a possible wide exchange and heterologous expression of the antibiotic resistance determinants between microorganisms of various taxonomic groups.     

Transferable sodium arsenate resistance in enterobacteriaceae

The sodium arsenate and antibiotic resistance of a total of 750 strains of Enterobacteriaceae andPseudomonas aeruginosa isolated from hospital patients was determined. Resistance to sodium arsenate (minimal inhibitory concentration ≥25 mg/ml) was found in 61.4% of the isolates and was present both in antibiotic-susceptible and antibiotic-resistant strains. Ten enterobacterial isolates (3 sodium arsenate-resistant, antibiotic-susceptible strains and 7 sodium arsenate-resistant, antibiotic-resistant strains) could transfer sodium arsenate resistance to susceptible isolates and toEscherichia coli K-12 by conjugation. From sodium arsenate-and antibioticresistant strains, sodium arsenate and antibiotic resistances were transferred en bloc. Sodium arsenate resistance of antibiotic-susceptible strains was not self-transmissible, and transfer occurred only after R-plasmid mobilization.     

Association of qacE and qacEDelta1 with multiple resistance to antibiotics and antiseptics in clinical isolates of Gram-negative bacteria

Clinical isolates of Enterobacter cloacae, Citrobacter freundii, Pseudomonas aeruginosa, and Stenotrophomonas maltophilia were tested for resistance to antibiotics and to the antiseptics benzalkonium chloride and cetyltrimethylammonium bromide. Furthermore, they were examined for the presence of the resistance genes qacE and qacEDelta1. qacEDelta1 was detected by PCR in 10% of all (n=103) and in 81% of multiply antibiotic-resistant strains (n=15). qacE was found in only one of 37 P. aeruginosa strains. The minimum inhibitory concentrations of benzalkonium chloride, cetyltrimethylammonium bromide, and ethidium bromide were not significantly different for qacEDelta1/qacE-positive or -negative strains. Our data indicate that multiply antibiotic-resistant Gram-negative bacteria are not necessarily more resistant to quaternary ammonium compounds than antibiotic-sensitive strains even though qacE or qacEDelta1 is present.     

Study of Erwinia carotovora phage resistance with the use of temperate bacteriophage ZF40

The causes of the unique phage resistance of the pectinolytic phytopathogenic strains of Erwinia carotovora were studied with the use of temperate bacteriophage ZF40. It was shown that, in these bacteria, the bacteriophage-cell interaction can be substantially blocked at the adsorption level. An adequate indicator for studying the temperate bacteriophages of erwinias was developed on the basis of mutants resistant to macromolecular bacteriocins. Various restriction-modification systems, which influence cell resistance to bacteriophages, were revealed for the first time in E. carotovora. The phage resistance was shown to be determined by the wide occurrence of homoimmune temperate viruses in pectinolytic erwinias.     

A formal scheme of adsorptional receptors in <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> and possibilities for its practical implementation

In recent years, a revival of interest to study of bacteriophages has been observed. Bacteriophages and phage-coded products can be used instead of antibiotics in the treatment of some human and animal infections caused by antibiotic-resistant bacterial strains. Bacteriophages may serve as an excellent method for monitoring anthropogenic changes in bacterial communities, which are connected with the contamination by industrial sewages or infection of water reservoirs with pathogenic bacteria. Technical applicability of bacteriophages may be successful for combating bacterial biofilms, for example, in pipelines. And finally, comparative basic and systemic genomic studies of bacteriophages belonging to various bacterial species are conclusive in understanding and assessing their role in the joint evolution (coevolution) with host bacteria; particularly, this research is important for elucidating mechanisms of phage participation in the horizontal exchange of genetic modules. Possibly, these studies may be useful for the prediction of not only the direction of coevolution of certain bacterial species and their phages but also the time of new pathogenic bacteria origination.     

Antibiotic resistance of gram-negative enteric bacteria from pigs in three herds with different histories of antibiotic exposure

The antibiotic resistance patterns of gram-negative fecal bacteria from pigs in three herds with different histories of antibiotic exposure were examined. In general, smaller proportions of antibiotic-resistant or multiply resistant fecal isolates (P less than 0.05) were obtained from pigs in a herd not exposed to antimicrobial agents for 154 months than from pigs in a herd continuously exposed to antimicrobial agents at subtherapeutic doses or from pigs in a herd exposed only to therapeutic doses of antimicrobial agents. The proportions of antibiotic-resistant and multiply resistant strains were greater among isolates from pigs in the therapeutic herd than in the non-antibiotic-exposed herd (P less than 0.05). The proportion of antibiotic-resistant isolates in the non-lactose-fermenting population was greater than that in the lactose-fermenting population, regardless of herd. The results suggest that any form of antimicrobial exposure will increase the prevalence of antimicrobial resistance and multiple resistance of fecal bacteria.     

Antibiotic resistance of gram-negative enteric bacteria from pigs in three herds with different histories of antibiotic exposure.

The antibiotic resistance patterns of gram-negative fecal bacteria from pigs in three herds with different histories of antibiotic exposure were examined. In general, smaller proportions of antibiotic-resistant or multiply resistant fecal isolates (P less than 0.05) were obtained from pigs in a herd not exposed to antimicrobial agents for 154 months than from pigs in a herd continuously exposed to antimicrobial agents at subtherapeutic doses or from pigs in a herd exposed only to therapeutic doses of antimicrobial agents. The proportions of antibiotic-resistant and multiply resistant strains were greater among isolates from pigs in the therapeutic herd than in the non-antibiotic-exposed herd (P less than 0.05). The proportion of antibiotic-resistant isolates in the non-lactose-fermenting population was greater than that in the lactose-fermenting population, regardless of herd. The results suggest that any form of antimicrobial exposure will increase the prevalence of antimicrobial resistance and multiple resistance of fecal bacteria.     

Chromosomally integrated conjugative plasmids are common in antibiotic-resistant Haemophilus influenzae.

Twenty-three highly antibiotic-resistant strains of Haemophilus influenzae and two of Haemophilus parainfluenzae without detectable large plasmids were examined for conjugative transfer of their resistance to H. influenzae strain Rd or to other strains. Very inefficient transfer was observed for 18 H. influenzae strains and 1 H. parainfluenzae strain. All H. influenzae transcipients carried a large plasmid, and they were in turn efficient donors of their resistances in standard conjugation crosses with isogenic recipients. This was not seen for the H. parainfluenzae transcipients. It is concluded that most of the original antibiotic-resistant cultures carried an integrated conjugative R plasmid which had been excised in a few cells in each population. It was these cells which transferred resistance in the primary crosses.     

Specific Distribution of R Factors in Serratia marcescens Strains Isolated from Hospital Infections

Serratia marcescens strains from three hospitals in the city of New York were tested for antibiotic susceptibility patterns and the presence of transmissible antibiotic resistance factors. There appears to be a pattern characteristic for each hospital with regard to the sensitivity to nalidixic acid, tetracycline, chloramphenicol, and sulfonamides, whereas the resistance to ampicillin, cephalothin, and streptomycin is similar in the strains isolated from all three hospitals. In one hospital, a single type of R factor was found which transfers resistance to streptomycin, kanamycin, ampicillin, and sulfonamides, whereas strains isolated from a second hospital transfer only ampicillin resistance. No R factors could be detected in multiply resistant Serratia strains isolated in a third hospital. The presence of a single type of R factor probably reflects the relative ecological isolation of S. marcescens and could be useful for epidemiological studies of hospital infections with Serratia.     

Isolation and characterization of bacteriophages for avian pathogenic E. coli strains

Aims:  To isolate and characterize bacteriophages, and to evaluate its lytic performance against avian pathogenic Escherichia coli (APEC) strains with high patterns of antibiotic resistance, in order to select phages for a therapeutic product to treat colibacillosis in chickens.
Methods and Results:  Bacteriophages were isolated from poultry sewage and tested against 148 O-serotyped APEC strains. The morphological characterization of the bacteriophages was made by transmission electronic microscopy (TEM) observations and the genetic comparison between bacteriophages DNA was performed by restriction fragment length polymorphism (RFLP) patterns. Results showed that 70·5% of the tested E. coli strains were sensitive to a combination of three of the five isolated phages, that seemed to be virulent and taxonomically belong to the Caudovirales order. Two of them look like 16–19, T4-like phages ( Myoviridae ) and the third is a T1-like phage and belongs to Syphoviridae family. All of them are genetically different.
Conclusions:  It was possible to obtain a combination of three different lytic bacteriophages with broad lytic spectra against the most prevalent O-serotypes of APEC.
Significance and Impact of the Study:  Data reported in this study, presents an in vitro well studied phage product to be used as antimicrobial agent to treat colibacillosis in poultry industry.     

临床分离4544株革兰阴性杆菌的耐药分布与变迁

目的了解玉溪市革兰阴性杆菌的耐药分布与变迁,为临床用药提供依据。方法对玉溪市人民医院1999—2004年临床各科送检的各类标本中培养分离出的4544株革兰阴性杆菌作回顾性分析。结果9种（属）细菌对25种药物的药敏结果耐药率〉50％者72种次（40．9％）,〈20％者44种次（25．0％）。总的耐药情况为不动杆菌和阴沟肠杆菌最高,铜绿假单胞菌和大肠埃希菌次之,甲型副伤寒沙门菌和福氏志贺菌最低。亚胺培南对多种细菌有较高的敏感覆盖率。有4种细菌对10种抗菌药物耐药率的上升具有临床意义（P〈0.01或P〈0．05）,其中以甲型副伤寒沙门菌对氟喹诺酮类上升最为显著。结论临床分离革兰阴性杆菌的耐药形势十分严峻,应定期监测区域内细菌的耐药变化．指导临床合坪用药。     

限制和修饰系统LlaBIII在构建抗噬菌体菌株中的作用

限制和修饰 (ｒｅｓｔｒｉｃｔｉｏｎａｎｄｍｏｄｉｆｉｃａｔｉｏｎ ,Ｒ Ｍ)系统是指由限制性内切酶和甲基化酶组成的单亚基或多亚基复合酶系统 ,两者通常成对出现 ,具有相同的ＤＮＡ识别位点 ,其作用相反。Ｒ Ｍ系统在原核生物中普遍存在 ,在保护细胞免遭外源病毒侵害方面具有重要作用[1] 。作为发酵剂的乳酸乳球菌在乳制品发酵中具有重要作用 ,但这类菌株极易遭受噬菌体感染 ,导致菌株产酸力降低 ,甚至发酵失败 ,造成严重的经济损失。所以在乳制品发酵过程中防止噬菌体感染就成为十分重要的问题。通过自然筛选或诱变处理等手段筛选噬菌…     

Bacteriophage selection against a plasmid-encoded sex apparatus leads to the loss of antibiotic-resistance plasmids

Antibiotic-resistance genes are often carried by conjugative plasmids, which spread within and between bacterial species. It has long been recognized that some viruses of bacteria (bacteriophage; phage) have evolved to infect and kill plasmid-harbouring cells. This raises a question: can phages cause the loss of plasmid-associated antibiotic resistance by selecting for plasmid-free bacteria, or can bacteria or plasmids evolve resistance to phages in other ways? Here, we show that multiple antibiotic-resistance genes containing plasmids are stably maintained in both Escherichia coli and Salmonella enterica in the absence of phages, while plasmid-dependent phage PRD1 causes a dramatic reduction in the frequency of antibiotic-resistant bacteria. The loss of antibiotic resistance in cells initially harbouring RP4 plasmid was shown to result from evolution of phage resistance where bacterial cells expelled their plasmid (and hence the suitable receptor for phages). Phages also selected for a low frequency of plasmid-containing, phage-resistant bacteria, presumably as a result of modification of the plasmid-encoded receptor. However, these double-resistant mutants had a growth cost compared with phage-resistant but antibiotic-susceptible mutants and were unable to conjugate. These results suggest that bacteriophages could play a significant role in restricting the spread of plasmid-encoded antibiotic resistance.     

Effect of the pC194 plasmid on the development of Bacillus thuringiensis phages

Bacillus thuringiensis var. galleriae strains were transformed by plasmid pC194, coding for chloramphenicol resistance (CmR). Efficiency of plating and the yields of bacteriophages Tg13 and Tg27 maturating in CmR transformant cells were decreased for 2-3 orders as compared with the ones in parental strains. The CmR transformants are characterized by the increased level of spontaneous induction of bacteriophage Tg22.     

A Study of Erwinia carotovora Phage Resistance with the Use of Temperate Bacteriophage ZF40

The causes of the unique phage resistance of the pectinolytic phytopathogenic strains of Erwinia carotovora were studied with the use of temperate bacteriophage ZF40. It was shown that, in these bacteria, the bacteriophage–cell interaction can be substantially blocked at the adsorption level. An adequate indicator for studying the temperate bacteriophages of erwinias was developed on the basis of mutants resistant to macromolecular bacteriocins. Various restriction–modification systems, which influence cell resistance to bacteriophages, were revealed for the first time in E. carotovora. The phage resistance was shown to be determined by the wide occurrence of homoimmune temperate viruses in pectinolytic erwinias.     

Transferable tetracycline resistance in Clostridium perfringens strains of porcine origin

These studies represent the first systematic survey of the incidence of conjugative antibiotic resistance in Clostridium perfringens. Ninety-two antibiotic-resistant porcine strains were examined to see if they could donate their antibiotic-resistance determinants to sensitive recipient strains. Fifteen of the 89 tetracycline-resistant strains transferred their tetracycline resistance in mixed-plate mating experiments but no transfer of macrolide-lincosamide resistance was detected. The efficiencies of transfer of tetracycline resistance varied from 1.3 X 10(-3) to 1.9 X 10(-6) transconjugants per donor cell. Significantly higher transfer efficiencies were observed when both the donor and recipient strains were derivatives of strain CW 362. These values ranged from 3.7 X 10(-1) to 4.6 X 10(-2) transconjugants per donor cell. This high frequency transfer system should prove invaluable for further genetic studies on this microorganism.     

Mode of the rational use of Pseudomonas aeruginosa bacteriophages in therapeutic and epidemic control practice

Ecological aspects of the circulation of P. aeruginosa and P. aeruginosa bacteriophages under hospital conditions were under study. The statement concerning the formation of triple parasitic systems was put forward. The influence of these systems on the formation of phage and antibiotic resistance in P. aeruginosa hospital strains was studied. Spontaneous circulation of faintly virulent phages taking part in the formation of triple parasitic systems was shown not to ensure the elimination of P. aeruginosa hospital strains in clinics. Construction of highly virulent phages adapted to local P. aeruginosa strains was the only way of ensuring the protection of patients. Theoretical and practical approaches to the use of highly active bacteriophages for controlling P. aeruginosa infection were substantiated. The realization of these approaches resulted in achieving not only a clinical, but also essential epidemic control effect in cases of purulent septic infections caused by P. aeruginosa (a decreased frequentcy of hospital infections from 40.8% to 8.93%).