Increase of trimethoprim resistance among Shigella species, 1975-1988: analysis of resistance mechanisms

Phytochemical constituents of Inula britannica as potential inhibitors of dihydrofolate reductase: A strategic approach against shigellosis

Shigella dysenteriae type 1 is considered as an epidemic in different developing countries, which is responsible for the most severe form of bacterial dysentery. It habitually can develop to the most severe form of dysentery with deadly complications. Development of drugs against this disease is still ongoing. Therefore, we used in silico studies to screen the Inula britannica phytocompounds that are used in traditional Chinese and Kampo Medicines and have activities against different diseases. Spinacetin, eupatin, chrysoeriol and diosmetin were successfully passed through the docking-based screening and absorption, distribution, metabolism, excretion and toxicity (ADMET) filtration. The estimated docking affinities of eupatin, diosmetin, chrysoeriol and spinacetin with Dihydrofolate reductase type 1 (DHFR-1), were -6.5, -6.5, -6.3 and -6.1 kcal/mol, respectively. Which were selected for further investigations based on their favorable ADME/Tox characteristics. Then, the 100 ns molecular dynamics (MD) simulations of apo DHFR, spinacetin-DHFR, eupatin-DHFR, chrysoeriol-DHFR and diosmetin-DHFR complexes were carried out. The RMSD fluctuations of the spinacetin, eupatin, chrysoeriol and diosmetin inside the binding site were explored. Subsequently, the effect of binding Spinacetin, eupatin, chrysoeriol and diosmetin upon the dynamic stability of protein was assessed. Additionally, Principal Component Analysis (PCA) and Hydrogen bond analysis was performed for the apo protein and the protein ligand complexes. The results revealed that chrysoeriol and eupatin has good inhibitory effects against DHFR-1 as treatment for Shigella dysenteriae type when compared to other compounds under study. Hence this study implies that eupatin and chrysoeriol are a significantly potential drug like molecule for the treatment of Shigellosis and must undergo validation through in vivo and in vitro experiments.Communicated by Ramaswamy H. Sarma.

Efficacy and potential of phage therapy against multidrug resistant Shigella spp

Shigella-infected bacillary dysentery or commonly known as Shigellosis is a leading cause of morbidity and mortality worldwide. The gradual emergence of multidrug resistant Shigella spp. has triggered the search for alternatives to conventional antibiotics. Phage therapy could be one such suitable alternative, given its proven long term safety profile as well as the rapid expansion of phage therapy research. To be successful, phage therapy will need an adequate regulatory framework, effective strategies, the proper selection of appropriate phages, early solutions to overcome phage therapy limitations, the implementation of safety protocols, and finally improved public awareness. To achieve all these criteria and successfully apply phage therapy against multidrug resistant shigellosis, a comprehensive study is required. In fact, a variety of phage-based approaches and products including single phages, phage cocktails, mutated phages, genetically engineered phages, and combinations of phages with antibiotics have already been carried out to test the applications of phage therapy against multidrug resistant Shigella. This review provides a broad survey of phage treatments from past to present, focusing on the history, applications, limitations and effective solutions related to, as well as the prospects for, the use of phage therapy against multidrug resistant Shigella spp. and other multidrug resistant bacterial pathogens.

Destination specific risks of acquisition of notifiable food- and waterborne infections or sexually transmitted infections among Finnish international travellers, 1995-2015

BACKGROUND

Overnight international travels made by Finns more than doubled during 1995-2015. To estimate risks and observe trends of travel-related notifiable sexually transmitted and food- and water-borne infections (STIs and FWIs) among travellers, we analysed national reports of gonorrhoea, syphilis, hepatitis A, shigellosis, campylobacteriosis and salmonellosis cases and related them to travel statistics.

METHOD

Cases notified as travel-related to the Finnish infectious diseases register were used as numerators and overnight stays of Statistics Finland surveys as denominator. We calculated overall risks (per 100,000 travellers) and assessed trends (using regression model) in various geographic regions.

RESULTS

Of all travel-related cases during 1995-2015, 2304 were STIs and 70,929 FWIs. During 2012-2015, Asia-Oceania showed highest risk estimates for gonorrhoea (11.0; 95%CI, 9.5-13), syphilis (1.4; 0.93-2.1), salmonellosis (157; 151-164), and campylobacteriosis (135; 129-141), and Africa for hepatitis A (4.5; 2.5-7.9), and shigellosis (35; 28-43). When evaluating at country level, the highest risks of infections was found in Thailand, except for hepatitis A ranking Hungary the first. During 2000-2011, significantly decreasing trends occurred for most FWIs particularly in the European regions and for STIs in Russia-Baltics.

CONCLUSIONS

Our findings can be used in targeting pre-travel advice, which should also cover those visiting Thailand or European hepatitis A risk areas.

Regional dissemination of a trimethoprim-resistance gene cassette via a successful transposable element

Background

Antimicrobial resistance is a growing international problem. We observed a 50% increase in the prevalence of trimethoprim resistance among fecal Escherichia coli from healthy Nigerian students between 1998 and 2005, a trend to increase that continued in 2009.

Methods and Findings

A PCR-based screen revealed that 131 (43.1%) of isolates obtained in Nigeria in 2005 and 2009 carried integron-borne dfrA cassettes. In the case of 67 (51.1%) of these isolates, the cassette was a class 1-integron-borne dfrA7 gene, which has been reported at high prevalence from E. coli isolates from other parts of Africa. Complete sequencing of a 27 Kb dfrA7-bearing plasmid from one isolate located the dfrA7 gene within a Tn21-type transposon. The transposon also contained an IS26-derived bla/sul/str element, encoding resistance to β-lactams, sulphonamides and streptomycin, and mercury resistance genes. Although the plasmid backbone was only found in 12 (5.8%) of trimethoprim-resistant isolates, dfrA7 and other transposon-borne genes were detected in 14 (16.3%) and 32 (26.3%) of trimethoprim resistant isolates collected in Nigeria in 2005 and 2009, respectively. Additionally, 37 (19.3%) of trimethoprim-resistant E. coli isolates collected between 2006 and 2008 from Ghana were positive for the dfrA7 and a transposon marker, but only 4 (2.1%) harbored the plasmid backbone.

Conclusions

Our data point to transposition as a principal mechanism for disseminating dfrA7 among E. coli from Nigeria and Ghana. On-going intensive use of the affordable broad-spectrum antibacterials is likely to promote selective success of a highly prevalent transposable element in West Africa.

Emerging resistance to newer antimicrobial agents among Shigella isolated from Finnish foreign travellers

In Finland, most cases of shigellosis are related to travel abroad. Antimicrobial drug resistance of 1814 Shigella strains isolated from Finnish patients during 1990-2005 was studied using discs of 12 antimicrobial agents. Since 2000, the E-test has been performed to determine ciprofloxacin minimum inhibitory concentrations of nalidixic acid-resistant isolates. The proportion of multi-resistant strains (resistant to >or =4 antimicrobials) was highest among isolates from China and India, but is increasing significantly in other parts of Asia. Resistance to nalidixic acid has become common among the strains from the Far East, and the first isolates also resistant to ciprofloxacin were detected during 2004-2005. All the ciprofloxacin-resistant isolates belonged to the S. flexneri 2a serotype. All the nalidixic acid-resistant S. flexneri strains had reduced susceptibility to ciprofloxacin, whereas 23% of the nalidixic acid-resistant S. sonnei strains were still completely susceptible to ciprofloxacin.

[Shigellosis or bacillary dysentery]

Shigellosis, commonly known as bacillary dysentery, is an enterobacterial disease caused by the Shigella genus, which now belongs to the Escherichia tribe, because of their genetic and phenotypic similarities. S. sonnei, flexneri, boydii and dysenteriae differ in their epidemiologic and pathogenic characteristics. S. sonnei is predominant in industrialized countries and causes the mildest disease. S. dysentery is especially dangerous because it occurs in outbreaks, sometimes in catastrophic situations, and has a high mortality rate. Shigellosis typically causes watery diarrhea followed by dysentery. It may be associated with a variety of mild to severe or even life-threatening complications. Shigellosis is a significant public health problem in developing countries where it remains a major cause of diarrhea-related morbidity and mortality, especially among children. Annual cases worldwide are estimated at 160 million. Shigellosis is a highly contagious disease of poor and crowded communities, with fecal-oral (hand-to-mouth) transmission, and an extremely low minimum infectious dose. Multidrug resistance is a serious problem. Ciprofloxacin is the first-line antibiotic, recommended for 3 days. Prevention and control should include personal hygiene, hand washing, sanitation, and water supply. No vaccine is available, but several candidates are currently being evaluated.

High prevalence of antimicrobial resistance among Shigella isolates in the United States tested by the National Antimicrobial Resistance Monitoring System from 1999 to 2002

Shigella spp. infect approximately 450,000 persons annually in the United States, resulting in over 6,000 hospitalizations. Since 1999, the National Antimicrobial Resistance Monitoring System (NARMS) for Enteric Bacteria has tested every 10th Shigella isolate from 16 state or local public health laboratories for susceptibility to 15 antimicrobial agents. From 1999 to 2002, NARMS tested 1,604 isolates. Among 1,598 isolates identified to species level, 1,278 (80%) were Shigella sonnei, 295 (18%) were Shigella flexneri, 18 (1%) were Shigella boydii, and 7 (0.4%) were Shigella dysenteriae. Overall, 1,251 (78%) were resistant to ampicillin and 744 (46%) were resistant to trimethoprim-sulfamethoxazole (TMP-SMX). Prevalence of TMP-SMX- or ampicillin- and TMP-SMX-resistant Shigella sonnei isolates varied by geographic region, with lower rates in the South and Midwest regions (TMP-SMX resistance, 27% and 30%, respectively; ampicillin and TMP-SMX resistance, 25% and 22%, respectively) and higher rates in the East and West regions (TMP-SMX resistance, 66% and 80%, respectively; ampicillin and TMP-SMX resistance, 54% and 65%, respectively). Nineteen isolates (1%) were resistant to nalidixic acid (1% of S. sonnei and 2% of S. flexneri isolates); 12 (63%) of these isolates had decreased susceptibility to ciprofloxacin. One S. flexneri isolate was resistant to ciprofloxacin. All isolates were susceptible to ceftriaxone. Since 1986, resistance to ampicillin and TMP-SMX has dramatically increased. Shigella isolates in the United States remain susceptible to ciprofloxacin and ceftriaxone.

Community-based safety, immunogenicity, and transmissibility study of the Shigella sonnei WRSS1 vaccine in Israeli volunteers

We describe the first community-based evaluation of Shigella sonnei strain WRSS1, a live, oral candidate vaccine attenuated by a 212-bp deletion in the virG (or icsA) plasmid virulence gene. Three single-dose regimens of WRSS1 (5 x 10(3) CFU, 2 x 10(4) CFU, and 4 x 10(5) CFU) were tested with cohorts of 15 adult volunteers. The vaccine was generally well tolerated at the 10(3)- and 10(4)-CFU doses. There were no fevers and there was one report of moderate diarrhea in 30 vaccinees; five additional vaccinees reported mild diarrhea. At the 10(5)-CFU dose, there were two reports of low-grade fevers and four reports of moderate diarrhea. The geometric means for immunoglobulin A (IgA) antibody-secreting cells (ASC) against lipopolysaccharide (LPS) were 30, 75, and 193 ASC per 10(6) peripheral blood mononuclear cells (PBMC) for the 10(3)-, 10(4)-, and 10(5)-CFU doses, respectively. The IgG means were 40, 46, and 135 ASC per 10(6) PBMC, respectively. The 10(4)-CFU dose of WRSS1 gave the best balance of safety and immunogenicity, since all vaccinees had a significant IgA ASC response and 73% had a response of more than 50 ASC. The anti-LPS seroconversion rate (threefold) for IgA was 60% and the IgG rate was 27% for the 10(4)-CFU cohort. Each vaccinee and a cohabitating household contact delivered daily perianal stool swabs for bacteriological culture. WRSS1 colonized vaccinees for a median of 5 days, and one individual excreted WRSS1 intermittently for 23 days. None of the 45 household contacts were colonized with WRSS1 after a cumulative 192 days of cohabitation with colonized vaccinees, suggesting that adventitious vaccine spread was not common in the community setting.

The epidemiology of travel-associated shigellosis—regional risks, seasonality and serogroups

OBJECTIVES

To give a detailed risk estimate of contracting travel-associated shigellosis in various regions of the world.

METHODS

Data on notifications of travel-associated shigellosis in Sweden 1997-2003 were compared with information on recent travel abroad from a comprehensive database based on telephone interviews with more than 160,000 Swedish travellers.

RESULTS

From the national notification database 2678 patients with travel-associated shigellosis were retrieved. The highest risk of being notified with shigellosis was seen in returning travellers from India and neighbouring countries (318/100,000 travellers), East Africa (219/100,000), West Africa (120/100,000), and North Africa (76/100,000). Data on serogroup was available for 2529 isolates. Shigella sonnei was the most common serogroup (67%), followed by Shigella flexneri (26%), Shigella boydii (5%), and Shigella dysenteriae (3%). A higher risk was seen in children below the age of six, compared to older children and adults and in women compared to men. A distinct seasonal pattern was noted with the highest risk of shigellosis in July-October and the lowest in May.

CONCLUSIONS

Denominator based data on reported travel-associated infections are well suited to give risk estimates per region of infection, that could be used to target high-risk groups for pre-travel advice.

[Intercontinental spread of a trimethoprim-resistant strain of Shigella flexneri]

INTRODUCTION

In this study we characterize a trimethoprim-resistant strain of Shigella flexneri recovered from stool samples of an international traveler after a trip to Kenya, and analyze its epidemiological relationship with a set of strains having similar characteristics from Tanzania.

METHODS

Clonal relationships were studied by three techniques - plasmid profile, repetitive-element (REP)-PCR and pulse-field gel electrophoresis (PFGE). The presence of type 1 integrons was studied by PCR and sequencing. The location and transferability of the detected integron was analyzed by conjugation and PCR.

RESULTS

The epidemiological studies showed that all six strains studied belonged to the same clone. Furthermore, all of them carried the same gene encoding for trimethoprim resistance (dfrA7), which was located in an integron within a chromosome.

CONCLUSION

Continuous epidemiological surveillance is required to control the spread of pathogenic microorganisms and the dissemination of resistance-encoding genes among geographical areas.

Epidemic strains of Shigella sonnei biotype g carrying integrons

Class 2 integrons (Tn7) were found in all randomly selected epidemic (n = 27) and preepidemic (n = 13) strains of multiresistant Shigella sonnei biotype g. A class 1 integron was also found in two epidemic strains. Gene cassettes within these integrons account for resistance to commonly used therapeutic agents.

Comparative antibiotic resistance of diarrheal pathogens from Vietnam and Thailand, 1996-1999

Antimicrobial resistance rates for shigella, campylobacter, nontyphoidal salmonella, and enterotoxigenic Escherichia coli were compared for Vietnam and Thailand from 1996 to 1999. Resistance to trimethoprim-sulfamethoxazole, ampicillin, chloramphenicol, and tetracycline was common. Quinolone resistance remains low in both countries, except among campylobacter and salmonella organisms in Thailand. Nalidixic acid resistance among salmonellae has more than doubled since 1995 (to 21%) in Thailand but is not yet documented in Vietnam. Resistance to quinolones correlated with resistance to azithromycin in both campylobacter and salmonella in Thailand. This report describes the first identification of this correlation and its epidemiologic importance among clinical isolates. These data illustrate the growing magnitude of antibiotic resistance and important differences between countries in Southeast Asia.

Multiresistant Shigella species isolated from pediatric patients with acute diarrheal disease

A total of 57 strains of Shigella (36 S sonnei, 21 S flexneri), isolated from children with acute diarrheal disease who presented for treatment at the Andes University Hospital, Merida, Venezuela, from June 1993 to June 1995, were tested for their susceptibility to trimethoprim, sulfamethoxazole, ampicillin, cefamandole, ceftriaxone, streptomycin, fleroxacin, and nalidixic acid, by the agar dilution method. Twenty-seven strains (75%) of S sonnei and eight strains of S flexneri (38.1%) isolates showed high-level resistance to trimethoprim (MIC90 > 1024 microg/mL), which was also associated with other resistance patterns. The most common resistant phenotype associated with trimethoprim-resistance among S sonnei isolates was sulfamethoxazole-streptomycin (63%); among S flexneri isolates, it was sulfamethoxazole-ampicillin-streptomycin (87.5%). Individual resistance was only observed for ampicillin, mainly in four isolates of S flexneri, and in one isolate of S sonnei. Most Shigella strains were resistant to three or more antimicrobial agents. These results confirmed that multiresistant strains of Shigella are present in Merida, and emphasize the importance to maintain these under surveillance in order to assess local susceptibility patterns and empiric therapy.

High frequency of strains multiply resistant to ampicillin, trimethoprim-sulfamethoxazole, streptomycin, chloramphenicol, and tetracycline isolated from patients with shigellosis in northeastern Brazil during the period 1988 to 1993

The occurrence and antimicrobial resistance pattern of Shigella isolates obtained from persons in community and hospital-based studies of diarrhea and matched controls in northeastern Brazil were studied. The isolation rate of Shigella spp. from patients with diarrhea during 1988 to 1993 varied from 4.5% (26 of 575) for the urban community of Gonçalves Dias to 6.7% (12 of 179) and 5.9% (7 of 119) for Hospital Infantil and Hospital Universitário, respectively. Of the 55 Shigella isolates (45 from patients with diarrhea, 8 from controls, and 2 undetermined) 73% (40 of 55) were Shigella flexneri, 16% (9 of 55) were S. sonnei, 7% (4 of 55) were S. boydii, and 4% (2 of 55) were S. dysenteriae. Of 39 S. flexneri strains, over half were resistant to ampicillin, trimethoprim-sulfamethoxazole, or both. Over 64% were resistant to streptomycin, chloramphenicol, and tetracycline. Overall, 82% of all S. flexneri isolates were resistant to four or more antimicrobial agents tested. As elsewhere, in the northeast of Brazil, ampicillin and trimethoprim-sulfamethoxazole are no longer reliable for treatment of S. flexneri infection. Most Shigella strains were resistant to four or more antimicrobial agents. Nalidixic acid was still useful for treatment of infections due to S. flexneri.

Trimethoprim resistant dihydrofolate reductases in normal faecal flora isolated in India

A high incidence of resistance to trimethoprim has been shown in the normal faecal flora in a population in south India. The dihydrofolate reductase (dhfr) genes mediating transferable resistance to trimethoprim have been identified. Unusually, in this study, the dhfrV was shown to be the predominant resistance gene (dhfrV 50% of transconjugants, dhfrIa 30%), the dhfrIb was also detected being distinguished from the dhfrV by an oligo-probe. However, when non-transferable resistance was considered, the dhfrIa was the most prevalent of the dhfrs identified. All those plasmids harbouring the dhfrIa were shown to possess Tn7. All the plasmids that probed positive for the dhfrV and the dhfrIb were shown to be associated with the integrase of the Tn21-like transposons, but 8 of the dhfrV genes were not associated with the Tn21 resolvase. The dhfrIV was shown to be present in all seven plasmids that produced low level trimethoprim-resistance. The dhfrV, first characterized in Sri Lanka, would seem to have a local distribution in this region of Asia but is distinguishable from the dhfrIb only by the use of an oligo-probe.

A randomized, double-blind study comparing cefixime and trimethoprim-sulfamethoxazole in the treatment of childhood shigellosis

We compared the clinical and bacteriologic response of 5-day treatment with cefixime, 8 mg/kg per day, with the response to trimethoprim-sulfamethoxazole (TMP-SMX), 10-50 mg/kg per day, the currently recommended therapy. Of the assessable children with acute, culture-proven shigellosis, 38 received cefixime and 39 received TMP-SMX. Pretreatment data on the two study groups were similar. In the first group, all isolates were susceptible to cefixime; in the TMP-SMX group, 32 isolates were resistant and 7 were susceptible to TMP-SMX. Clinical response (day 5) showed cure, improvement, and failure in 89%, 8%, and 3%, respectively, of the cefixime group, and in 25%, 44%, and 31%, respectively, of the TMP-SMX-resistant group (p < 0.001). Bacteriologic cure (day 3) occurred in 78% and 23% of the cefixime and TMP-SMX-resistant groups, respectively (p < 0.001). Clinical or bacteriologic relapse (day 12) was infrequent in both groups. The response to treatment of the cefixime and the TMP-SMX-susceptible groups was similar. No significant side effects were noted. We conclude that cefixime is superior to TMP-SMX in the treatment of suspected shigellosis in areas with a high rate of resistance to TMP-SMX.

A novel dihydrofolate reductase cassette inserted in an integron borne on a Tn21-like element

In this study, a 498-bp dhfrXII gene coding for trimethoprim resistance was found inserted in a cassette-like manner in the recombinationally active locus, the integron, borne on a transposon Tn21-like element. The dhfrXII cassette is distinct from those cassettes earlier observed in integrons and was found here upstream of two similarly inserted cassettes. The second one carried the new unidentified orfF, which is 85% identical to the orfD cassette in R46. The third cassette contained the aadA2 gene mediating spectinomycin resistance. The plasmid carrying this Tn21-like element was originally isolated from a trimethoprim-resistant urinary tract pathogen, Escherichia coli, from Turku City Hospital, Turku, Finland. By colony hybridization and polymerase chain reaction, this group of three cassettes, including dhfrXII, was detected in four additional E. coli strains of similar origin and in four Shigella strains isolated in Finland but originating from Asia. The dihydrofolate reductase produced from dhfrXII showed an unusual drug resistance in that 50% of the enzymatic activity remained at a trimethoprim concentration of 1 mM.

Quinolones in the treatment of acute bacterial diarrhoeal diseases

Acute bacterial diarrhoea is still an important disease, especially in developing countries. Resistance to antibiotics among enteric pathogens is relatively common in many parts of the world. The quinolones are active in vitro against these organisms, and achieve high stool concentrations. Because of these features, quinolones have been used in the treatment of acute diarrhoeal diseases caused by various bacteria. They appear to be effective in the therapy of shigellosis and travellers' diarrhoea, as well as in the prevention of diarrhoeal disease in travellers. However, their role in the treatment of salmonella gastroenteritis has not been established yet.

High level resistance to trimethoprim, cotrimoxazole and other antimicrobial agents among clinical isolates of Shigella species in Ontario, Canada--an update

A total of 598 isolates of Shigella species (24 S. dysenteriae, 254 S. flexneri, 30 S. boydii, 290 S. sonnei) submitted to the Ontario Public Health Laboratories in 1990 were tested for their susceptibility to 14 antimicrobial agents by the agar dilution method. Overall 79.6% of isolates were resistant to one or more antimicrobial agents and 52.0% were resistant to four or more. Trimethoprim resistance ranged from 26.7% among isolates of S. boydii to 39.4% among S. flexneri strains. The majority of the 224 TMP resistant isolates (88.8%) demonstrated high level resistance (MIC > 1000 mg/l) to trimethoprim. Resistance to cotrimoxazole increased from 3% in 1978 to between 26.7 and 37.6% in 1990. MICs for 90% of isolates (MIC90s) for ampicillin, ticarcillin and piperacillin were 128 to > 256 mg/l, > 256 for tetracycline and chloramphenicol, and > 2.0/38.0 for cotrimoxazole. These results from the Canadian Province of Ontario emphasize the need for prudent use of antimicrobial agents in the treatment of shigellosis.

Transferable high-level trimethoprim resistance among isolates of Escherichia coli from urinary tract infections in Ontario, Canada

Of 1171 isolates of Escherichia coli isolated from urine samples at the Public Health Laboratory, Toronto, Ontario, Canada, between May 1990 and December 1991, 120 (10.3%) were resistant to trimethoprim (TMP), cotrimoxazole (TMP/SMX), sulfamethoxazole (SMX) and other antimicrobial agents; 110 of the 120 isolates (91.7%) were resistant to four or more agents. The majority of resistant isolates (91.7%) exhibited high-level resistance (MIC > 1000 mg/L) to TMP. The MIC of TMP/SMX for all 120 isolates was > 2.0/38.0 mg/L and for SMX > 1024 mg/L. High-level resistances were also present among the beta-lactam antimicrobials with MICs ranging from 16- > 256 mg/L. Forty-three of 120 TMP-resistant (35.8%) isolates conjugally transferred TMP-resistance to E. coli K-12. Co-transfer of several other resistances was observed. SMX cotransferred from 86% of the 43 donors and beta-lactams together with SMX cotransferred from 70%. Nalidixic acid resistance was present among 22 (18.3%) of the 120 resistant isolates, however, nalidixic acid resistance was not transferred to E. coli K-12.

Molecular epidemiology of trimethoprim-resistant Shigella boydii serotype 2 strains from Bulgaria

In 1990 an increased number of strains of Shigella boydii serotype 2 were isolated from different regions of Bulgaria. Strains were reported as sporadic, although they showed identical phenotypic characteristics, including resistance to ampicillin, carbenicillin, streptomycin, sulfonamide, tetracycline, ticarcillin, and trimethoprim. The objective of this study was to determine the genetic relatedness of the strains and the mechanism of their antimicrobial resistance. Plasmid fingerprinting showed an identical pattern for 23 of 25 of the selected strains. All 25 strains tested transferred their resistances en bloc to an Escherichia coli recipient. Transconjugants contained a 112-kb R plasmid which carried all the resistance genes, including that conferring type I dihydrofolate reductase-mediated trimethoprim resistance (MIC greater than 2,000 micrograms/ml). Riboprobe analysis showed identical restriction length fragment polymorphisms, suggesting a highly conserved genome. All findings indicate that strains of S. boydii serotype 2 isolated in 1990 from different regions of Bulgaria were highly related genetically and can be considered representatives of a single bacterial clone. The presence of an R plasmid and selection pressure because of the usage of antimicrobial agents, particularly trimethoprim, have likely facilitated the spread of the clone throughout the country.

The relative importance of Shigella in the aetiology of childhood gastroenteritis in Saudi Arabia

The role of shigella infection in childhood gastroenteritis was studied over a 2-year period. Shigella species were found in the faecal specimens of 70 (1%) of 7369 children with gastroenteritis, but in only 1 (0.1%) of 1130 controls. S. flexneri was the commonest isolate (51%), followed by S. sonnei (37%). Most shigella species were isolated during the winter. The prevalence of shigellosis was highest for children 1-5 years of age but equal for both sexes. Fever, abdominal cramps, vomiting, and bloody diarrhoea were the predominant clinical features. Of the shigella isolates, 73% were resistant to cotrimoxazole, 43% to ampicillin, and 41% to chloramphenicol. One-third of isolates were resistant to greater than or equal to 3 antibiotics. All isolates were susceptible to nalidixic acid. The illness was mild and self-limiting and most patients recovered without antimicrobial therapy.

Multiresistant Shigella species from African AIDS patients: antibacterial resistance patterns and application of the E-test for determination of minimum inhibitory concentration

The antibacterial resistance pattern and minimum inhibitory concentrations (MIC) of 25 Shigella flexneri, 5 S. boydii, 8 S. sonnei, and 3 strains of S. dysenteriae type 2 isolated from Kenyan prostitutes with bacillary dysentery and AIDS were determined, and the applicability of the E-test for MIC determination evaluated. All strains were resistant to > or = 3 of 9 different antibacterial agents tested. All strains were resistant to tetracycline and erythromycin, 95% to trimethoprim/sulfonamide, 93% to streptomycin, 54% to ampicillin, 39% to chloramphenicol, 2% to nalidixic acid and none to gentamicin and ciprofloxacin. Six different resistance patterns were observed. The most common pattern was resistance to tetracycline, erythromycin, trimethoprim/sulfa and streptomycin (39%). The E-test was shown to be well-suited for susceptibility testing of multiresistant Shigella spp.; the reproducibility was excellent and the correlation with the microtiter dilution method and the disk diffusion method were 98% in both instances. The MIC measured with E-test and the microdilution method were within +/- 1 dilution step for 94.4% of the combinations tested.

Appearance of a new trimethoprim resistance gene, dhfrIX, in Escherichia coli from swine

A new gene, dhfrIX, coding for a trimethoprim-resistant dihydrofolate reductase (DHFR), was found in porcine isolates of Escherichia coli. The new enzyme, DHFR IX, containing 178 amino acids, showed an amino acid similarity of about 26% with DHFR I and the chromosomal DHFR of E. coli K-12. The dhfrIX gene was observed to occur on two distinctly different transferable plasmids, although a fragment of about 2.9 kb, including dhfrIX, had an identical restriction enzyme digestion map in each case. The new plasmid-borne dhfrIX gene mediates resistance to a drug level of only about 250 micrograms/ml, as compared with more than 1,000 micrograms/ml for the more frequently encountered dhfrI gene. The new plasmid-borne trimethoprim resistance gene could have been selected and spread as a consequence of the extensive use of trimethoprim in veterinary practice in Sweden. It will be important to try to follow its possible occurrence in human pathogens as well.

Analysis of genetic localization of the type I trimethoprim resistance gene from Escherichia coli isolated in Finland

Among a collection of clinical Escherichia coli isolates, the type I dihydrofolate reductase (DHFR) mediating trimethoprim resistance was generally observed to be chromosomally determined. Only a minority of isolates carried the type I DHFR gene simultaneously on a plasmid. The majority of E. coli isolates studied also hybridized with a probe specific for the transposition gene tnsC of transposon Tn7; and in most of these isolates, Tn7 was found to be inserted into a preferred site in the E. coli chromosome. A minority of isolates that harbored the type I DHFR gene in the chromosome lacked a complete Tn7. Some of these harbored the type I DHFR gene inserted in a structure similar to that containing the gene for streptomycin resistance in Tn21. In the other isolates that were negative for a complete Tn7, the sequences upstream of the type I DHFR gene were demonstrated to be homologous to those flanking the type I DHFR gene in Tn7. This could indicate that the antibiotic resistance region of Tn7 may occur independently of this transposon. In two isolates, no sequences resembling Tn7 or Tn21 were found adjacent to the type I DHFR gene.

Trimethoprim resistance in Escherichia coli isolates from a geriatric unit

The frequency of trimethoprim resistance among Escherichia coli isolates from urine samples collected at Turku City Hospital, Turku, Finland, remained at 40% during 1984 to 1988. The proportion of highly resistant (MIC, greater than or equal to 1,024 micrograms/ml) isolates increased, however, and most of these harbored the type I dihydrofolate reductase gene. Only a few isolates possessed type II or VII genes.