The importance of integrons for development and propagation of resistance in Shigella: the case of Latin America

Abstract In Latin America, the disease burden of shigellosis is found to coexist with the rapid and rampant spread of resistance to commonly used antibiotics. The molecular basis of antibiotic resistance lies within genetic elements such as plasmids, transposons, integrons, genomic islands, etc., which are found in the bacterial genome. Integrons are known to acquire, exchange, and express genes within gene cassettes and it is hypothesized that they play a significant role in the transmission of multidrug resistance genes in several Gram-negative bacteria including Shigella. A few studies have described antibiotic resistance genes and integrons among multidrug resistant Shigella isolates found in Latin America. For example, in Brazil, Bolivia, Chile, Costa Rica and Peru, class 1 and class 2 integrons have been detected among multidrug resistant strains of Shigella; this phenomenon is more frequently observed in S. flexneri isolates that are resistant to trimethoprim, sulfamethoxazole, streptomycin, ampicillin, chloramphenicol, and tetracycline. The gene cassette sul2, which is frequently detected in Shigella strains resistant to the sulfonamides, suggests that the sulfonamide-resistant phenotype can be explained by the presence of the sul2 genes independent of the integron class detected. It is to be noted that sul3 was negative in all isolates analyzed in these studies.The high frequency of sulfonamide (as encoded by sul2) and trimethoprim resistance is likely to be a result of the recurrent use of trimethoprim sulfamethoxazole as a popular regimen for the treatment of shigellosis. The observed resistance profiles of Shigella strains confirm that ampicillin and trimethoprim-sulfamethoxazole are ineffective as therapeutic options. In-depth information regarding antibiotic resistance mechanism in this pathogen is needed in order to develop suitable intervention strategies. There is a pressing need for regional and local antimicrobial resistance profiling of Shigella to be included as a part of the public health strategy.

CTX-M extended-spectrum ß-lactamase-producing Klebsiella spp, Salmonella spp, Shigella spp and Escherichia coli isolates in Iranian hospitals

Abstract This study was conducted in Iran in order to assess the distribution of CTX-M type ESBLs producing Enterobacteriaceae. From January 2012 to December 2013, totally 198 E. coli, 139 Klebsiella spp, 54 Salmonella spp and 52 Shigella spp from seven hospitals of six provinces in Iran were screened for resistance to extended-spectrum cephalosporins. After identification and susceptibility testing, isolates presenting multiple-drug resistance (MDR) were evaluated for ESBL production by the disk combination method and by Etest using (cefotaxime and cefotaxime plus clavulanic acid). All isolates were also screened for bla CTX-M using conventional PCR. A total of 42.92%, 33.81%, 14.81% and 7.69% of the E. coli, Klebsiella spp, Salmonella spp and Shigella spp isolates were MDR, respectively. The presence of CTX-M enzyme among ESBL-producing isolates was 85.18%, 77.7%, 50%, and 66.7%, in E. coli, Klebsiella spp, Salmonella spp and Shigella spp respectively. The overall presence of CTX-M genes in Enterobacteriaceae was 15.4% and among the resistant isolates was 47.6%. This study indicated that resistance to β-lactams mediated by CTX-M enzymes in Iran had similar pattern as in other parts of the world. In order to control the spread of resistance, comprehensive studies and programs are needed.

Enhanced resistance to fluoroquinolones in laboratory-grown mutants & clinical isolates of Shigella due to synergism between efflux pump expression & mutations in quinolone resistance determining region.

Background & objectives: There is a worldwide emergence of fluoroquinolone resistance in Shigella species. To understand the molecular mechanisms associated with fluoroquinolone resistance, naturally occurring fluoroquinolone-resistant strains and laboratory-induced spontaneous mutants of Shigella spp. were used and the relative contributions of acrAB-tolC efflux pumps, gyrase and topoisomerase target gene mutations towards fluoroquinolone resistance were determined. Methods: Eight Shigella flexneri and six S. dysenteriae clinical isolates were studied. Three consecutive mutants resistant to ciprofloxacin for S. flexneri SFM1 (≥0.25 μg/ml), SFM2 (≥4 μg/ml) and SFM3 (≥32 μg/ml) were selected in 15 steps from susceptible isolates by serial exposure to increasing concentrations of nalidixic acid and ciprofloxacin. Similarly, two mutants for S. dysenteriae SDM1 (≥0.25 μg/ml) and SDM2 (≥4 μg/ml) were selected in eight steps. After PCR amplification sequence analyses of gyrase and topoisomerase target genes were performed. Expression of efflux genes acrA, acrB, acrR and tolC was measured using real-time PCR. Results: Mutations were observed in gyrA Ser83→Leu, Asp87→Asn/Gly, Val196→Ala and in parC Phe93→Val, Ser80→Ile, Asp101→Glu and Asp110→Glu. Overall, acrA and acrB overexpression was associated with fluoroquinolone resistance (p<0.05); while tolC and acrR expression levels did not. Interpretation & conclusions: Fluoroquinolone resistance in Shigella spp. is the end product of either a single or a combination of mutations in QRDRs and/ or efflux activity. Novel polymorphisms were observed at Val196→Ala in gyrA in clinical isolates and Phe93→Val, Asp101→Glu, Asp110→Glu and in parC in majority of laboratory-grown mutants.

Antioxidant, antimicrobial, toxicity and analgesic properties of ethanol extract of Solena amplexicaulis root

BACKGROUND: This study was subjected to investigate different pharmacological properties of ethanol extract ofSolena amplexicaulis root. RESULTS: The extract contains flavonoid, alkaloid, saponin and steroid compounds. The extract exhibited excellent antioxidant activity in DPPH radical scavenging activity. The extract also showed potent activity in brine shrimp lethality bioassay. The LC50 value was found to 44.677 µg/ml. The extract showed better anti-bacterial activity against gram-negative bacteria. In antifungal assay, the maximum 79.31% of anti-mycotic activity was observed against Aspergillus ochraceus while minimum 44.2% against Rhizopus oryzae. MIC value ranged between 1500 - 3000 µg/ml. The extract was found moderately toxic with a 24-hr LD50 value of 81.47 mg/kg in Swiss albino mice. The degree of inhibition by the ethanolic extract of the root was found less than that of standard analgesic drug diclofenac sodium. The extract also showed moderate anti-inflammatory and antinociceptive activity and anti-diabetic property. Reducing power of the extract was comparable with standard ascorbic acid. Moderate in vitro thrombolytic activity, lipid peroxidation inhibition property, metal chelating ability and stress-protective activity was also observed. CONCLUSION: Ethanol extract of Solena amplexicaulis root can be valuable for treatment of different diseases.

Shigella in Brazilian children with acute diarrhoea: prevalence, antimicrobial resistance and virulence genes

Diarrhoeal disease is still considered a major cause of morbidity and mortality among children. Among diarrhoeagenic agents, Shigella should be highlighted due to its prevalence and the severity of the associated disease. Here, we assessed Shigella prevalence, drug susceptibility and virulence factors. Faeces from 157 children with diarrhoea who sought treatment at the Children's Hospital João Paulo II, a reference children´s hospital in Belo Horizonte, state of Minas Gerais, Brazil, were cultured and drug susceptibility of the Shigella isolates was determined by the disk diffusion technique. Shigella virulence markers were identified by polymerase chain reaction. The bacterium was recovered from 10.8% of the children (88.2% Shigella sonnei). The ipaH, iuc, sen and ial genes were detected in strains isolated from all shigellosis patients; set1A was only detected in Shigella flexneri. Additionally, patients were infected by Shigella strains of different ial, sat, sen and set1A genotypes. Compared to previous studies, we observed a marked shift in the distribution of species from S. flexneri to S. sonnei and high rates of trimethoprim/sulfamethoxazole resistance.

Surveillance of Antimicrobial Susceptibility Patterns among Shigella Species Isolated in China during the 7-Year Period of 2005-2011

BACKGROUND: Shigella is a frequent cause of bacterial dysentery in the developing world. Treatment with antibiotics is recommended for shigellosis, but the options are limited due to globally emerging resistance. This study was conducted to determine the frequency and pattern of antimicrobial susceptibility of Shigella in China. METHODS: We studied the antimicrobial resistance profiles of 308 Shigella spp. strains (260 S. flexneri, 40 S. sonnei, 5 S. boydii, and 3 S. dysenteriae) isolated from fecal samples of patients (age, from 3 months to 92 yr) presenting with diarrhea in different districts of Anhui, China. The antimicrobial resistance of strains was determined by the agar dilution method according to the CSLI guidelines. RESULTS: The most common serogroup in the Shigella isolates was S. flexneri (n=260, 84.4%), followed by S. sonnei (n=40, 13.0%). The highest resistance rate was found for nalidixic acid (96.4%), followed by ampicillin (93.2%), tetracycline (90.9%), and trimethoprim/sulfamethoxazole (80.8%). Among the isolates tested, 280 (91.0%) were multidrug resistant (resistant to > or =2 agents). The most common resistance pattern was the combination of ampicillin, tetracycline, and trimethoprim/sulfamethoxazole (70.8%). Resistance to ampicillin and tetracycline were more common among S. flexneri than among S. sonnei isolates. CONCLUSIONS: S. flexneri is predominant in Anhui, China, and its higher antimicrobial resistance rate compared with that of S. sonnei is a cause for concern. Continuous monitoring of resistance patterns is necessary to control the spread of resistance in Shigella. The recommendations for antimicrobial treatment must be updated regularly based on surveillance results.

Antimicrobial resistance in Shigella - rapid increase & widening of spectrum in Andaman Islands, India.

Background & objectives: Shigellosis is known to be a major cause of acute childhood diarrhoea in Andaman & Nicobar Islands, India. Rapid emergence of antibiotic resistance warrants continuous monitoring of sensitivity pattern of bacterial isolates. We report here the salient findings of an ongoing study on shigellosis in Andaman Islands, India, with regards to change in drug resistance pattern during the past one decade. Method: During 2006-2009, stools samples from 412 paediatric diarrhoea patients were collected and processed for isolation and identification of Shigella spp. Susceptibility to 22 antimicrobial drugs was tested and MICs were determined for 3rd generation cephalosporins, quinolones, amoxicillin-clavulanic acid combination and gentamicin. Drug susceptibility pattern of these isolates were compared with that of 33 isolates obtained during 2000-2002. Results: Shigella isolates were recovered from 50 of 412 stool samples processed. Resistance to ampicillin, nalidixic acid, tetracycline and ciprofloxacin was observed in 100, 96, 94 and 82 per cent of the isolates, respectively. The frequency of resistance to these drugs was significantly (P<0.001) higher than that observed during 2000-2002. Resistance to seven drugs was observed in 2000-2002, whereas resistance to 21 drugs was seen during 2006-2009. The number of drug resistance pattern increased from 13 in 2000-2002 to 43 in 2006-2009. Resistance to newer generation fluoroquinolones, 3rd generation cephalosporins and augmentin, which was not observed during 2000-2002, appeared during 2006-2009. Interpretation & conclusions: The frequency of resistance among Shigella isolates has increased substantially between 2000-2002 and 2006-2009 and the spectrum of resistance has widened. At present, the option for antimicrobial therapy in shigellosis in Andaman is limited to a small number of drugs. Continuous local monitoring of resistance patterns is necessary for the appropriate selection of empirical antimicrobial therapy.

Antimicrobial Resistance of Shigella spp. isolated in the State of Pará, Brazil / Resistência Antimicrobiana de Shigella spp. isoladas no Estado do Pará

INTRODUCTION: Shigella spp. are Gram-negative, nonsporulating, rod-shaped bacteria that belong to the family Enterobacteriaceae and are responsible for shigellosis or bacillary dysentery, an important cause of worldwide morbidity and mortality. METHODS: We studied the antibiotic resistance profiles of 122 Shigella spp. strains (81 S. flexneri, 41 S. sonnei, 1 S. boydii) isolated from patients (female and male from 0 to 80 years of age) presenting diarrhea in different districts of the State of Pará, in the North of Brazil. The antibiotic resistance of the strains, isolated from human fecal samples, was determined by the diffusion disk method and by using the VITEK-2 system. RESULTS: The highest resistance rate found was the resistance rate to tetracycline (93.8 percent), followed by the resistance rate to chloramphenicol (63.9 percent) and to trimethoprim/sulfamethoxazole (63.1 percent). Resistance to at least three drugs was more common among S. flexneri than S. sonnei (39.5 percent vs. 10 percent). Six (4.9 percent) strains were susceptible to all the antibiotics tested. All strains were susceptible to cefotaxime, ceftazidime, ciprofloxacin, nalidixic acid and nitrofurantoin. CONCLUSIONS: High rates of multidrug resistance in Shigella spp. are a serious public health concern in Brazil. It is extremely important to continuously monitor the antimicrobial resistances of Shigella spp. for effective therapy and control measures against shigellosis.

INTRODUÇÃO: Shigella spp. são bactérias Gram-negativas, não esporuladas, em forma de bastonete, pertencentes a família Enterobacteriaceae responsáveis pela shigelose ou disenteria bacilar, uma importante causa de mortalidade e morbidade mundial. MÉTODOS: Foi estudado o perfil de resistência a antimicrobianos de 122 amostras de Shigella spp. (81 S. flexneri, 41 sonnei, 1 S. boydii) isoladas de pacientes (sexo feminino e masculino com faixa etária de 0 a 80 anos) com distúrbios gastrointestinais em diferentes municípios no Estado do Pará, Brasil. A resistência antimicrobiana das amostras isoladas de coprocultura, foi determinada pelo método de difusão em disco e pelo sistema Vitek II. RESULTADOS: A maior resistência foi observada em relação à tetraciclina (93,8 por cento), seguida de cloranfenicol (63,9 por cento), e trimetoprimsulfametoxazol (63,1 por cento). Multirresistência a pelo menos três antimicrobianos foi mais comum em S. flexneri comparada a S. sonnei (39,5 por cento vs. 10 por cento). Seis (4,9 por cento) amostras foram sensíveis a todos antimicrobianos testados. Todas as amostras apresentaram sensibilidade a cefotaxima, ceftazidima, ciprofloxacina, ácido nalidixico e nitrofurantoína. CONCLUSÕES: As altas taxas de multirresistência de Shigella spp. são um sério problema de saúde pública no Brasil. Sendo assim, torna-se extremamente importante um monitoramento contínuo da resistência antimicrobiana de Shigella spp. para uma terapia efetiva e medidas de controle contra shigelose.

Frequency and antimicrobial susceptibility of Shigella species isolated in Children Medical Center Hospital, Tehran, Iran, 2001-2006

Appropriate antimicrobial treatment of shigellosis depends on identifying its changing resistance pattern over time. We evaluated 15,255 stool culture submitted from July 2001 to June 2006 to the Laboratory of Children Medical Center Hospital. Specimen culture, bacterial identification, and disk diffusion susceptibility testing were performed according to National Committee for Clinical Laboratory Standards guidelines. From 15,255 stool samples, 682 (4.5 percent) were positive for Shigella species. The most common species of Shigella were S. flexneri (48 percent) and S. sonnei (45 percent); other results were S. dysenteriae (5 percent) and S. boydii (2 percent). The rate of Sensitivity to ceftriaxone (95 percent), ceftizoxime (94 percent), and nalidixic acid (84 percent) were among our isolates. Resistance to co-trimoxazole and ampicillin was 87 percent and 86 percent, respectively. S. flexneri was more multiresistant than other species (47.9 percent). Our isolates are overall most sensitive to ceftriaxone, ceftazidime, and nalidixic acid (> 84 percent). They were most resistant to co-trimoxazole and ampicillin (> 86 percent). Because resistance varies according to specific location, continuous local monitoring of resistance patterns is necessary for the appropriate selection of empirical antimicrobial therapy.

Plasmid-Encoded Multidrug Resistance: A Case study of Salmonella and Shigella from enteric diarrhea sources among humans

Salmonellosis and shigellosis are signifcant and persistent causes of diarrheal diseases among humans in developing countries. With that in mind, the current study investigates the occurrence of plasmid-encoded multidrug resistances in Salmonella and Shigella from diarrheal cases among humans. The isolates were characterized by serotyping, antimicrobial-susceptibility testing, transfer experiments and curing. The extended spectrum β-lactamase (ESBL) was detected by the double disc diffusion synergy test (DDST). A signifcant number of the plasmid-encoded multidrug resistant (PEMDR) Salmonella and Shigella isolates were found to harbour transferable plasmid genes resistant to antibiotics like ampicillin, chloramphenicol, trimethoprim-sulfamethoxazole, ceftriaxone, cefuroxime and to a lesser extent to ciprofoxacin and ofoxacin. The conjugative R-plasmids-encoded extended-spectrum β-lactamase also showed resistances to cephalosporins (ceftriaxone and cefuroxime) and ampicillin. Curing experiments showed chromosomal resistances to varied antibiotics. The fndings confrmed the presence of PEMDR in Salmonella and Shigella strains as a suitable adaptation to a changing antibiotic environment. The results therefore suggest the limited use of the commonly prescribed/or third generation cephalosporins as an empirical treatment of multidrug resistant Salmonella and Shigella because this may affect therapeutic outcomes.

Comparative in vitro activity of tigecycline and other antimicrobial agents against Shigella species from Kuwait and the United Arab of Emirates

Shigella species isolated from stool samples of symptomatic patients of all age groups at the Mubarak Al Kabir Hospital and Infectious Diseases Hospital, Kuwait and Tawam Hospital, UAE during a 2-year period were investigated for their susceptibility to tigecycline and several other antibiotics by determining the minimum inhibitory concentrations [MICs] using the E test method. A total of 100 and 42 strains were collected from UAE and Kuwait, respectively. The extent of drug resistance in the Shigella spp. isolates from these two countries was analyzed by criteria recommended by the Clinical and Laboratory Standards Institute [CLSI]. Amikacin, cefotaxime, cefuroxime, ciprofloxacin, imipenem, meropenem, piperacillin-tazobactam and tigecycline had excellent activities against all isolates from UAE and Kuwait with MIC[90s] of 12, 0.094, 4, 0.012, 0.25, 0.032, 3 and 0.25micro g/ml and 4, 1, 4, 0.125, 0.38, 0.19, 3 and 0.25 micro g/ml, respectively. Half of all isolates from both countries were resistant to ampicillin. None of the isolates in Kuwait was resistant to amoxicillin-clavulanic acid compared with 22% in UAE. Resistance to chloramphenicol was recorded in 50 and 36% of the isolates in Kuwait and UAE, respectively. The percentages of non-susceptibility to trimethoprim-sulfamethoxazole and tetracycline were very high in Kuwait and UAE [76% vs. 92% and 76% vs. 98%, respectively]. Notably, one isolate, S. flexneri, from UAE had reduced susceptibility to ciprofloxacin [MIC, 0.25 micro g/ml]. Four [2.8%] of the isolates were ESBL producers by the E test ESBL method but could not be confirmed by PCR using primers for bla[tem], BLA [SHV] and- bla[tem]. In conclusion, Shigella spp. isolated from symptomatic patients in Kuwait and the UAE demonstrated high

Trends in antimicrobial resistance of fecal Shigella and Salmonella isolates in Tehran, Iran.

CONTEXT: The resistance of bacteria to commonly prescribed antibiotics is increasing both in developing as well as developed countries. Resistance has emerged even to newer, more potent antimicrobial agents. The present study was therefore undertaken to report resistance rates to antimicrobial agents in 2487 stool culture isolates in a tertiary care hospital between 1996 and 2000 and 2001 and 2005. MATERIALS AND METHODS: During 1996 to 2005, 31776 fecal samples were collected from all patients having diarrhea aged> 1 month to 14 years old. Microbiology records were reviewed and information on each isolate regarding its antimicrobial susceptibility profile was collected and recorded. STATISTICAL ANALYSIS USED: The statistical analysis was performed using SPSS, Version 11.5 software. RESULTS: Of the positive fecal cultures, 1329 (53.43%) of the isolates were Shigella spp and 700 (28.14%) of the isolates were Salmonella spp. Resistance to antimicrobial agents increased among most of the pathogens between 2001 and 2005. An increase in the rate of resistance was observed in Shigella spp for kanamycin (from 11 to 37%) and ceftazidime (from 1 to 9.9%) and among Salmonella spp. for nalidixic acid (from 9.2 to 42.3%) and ceftazidime (from 3 to 23.4%). CONCLUSIONS: Routine surveillance of antimicrobial susceptibilities to all classes of clinically used agents is necessary to detect resistance trends in different parts of world, detecting the emergence of new resistance mechanisms that guide infection control measures and public health guidelines; such trends may help in identifying outbreaks of resistant organisms. Such a check seems to be the best way to find appropriate antibiotic regimens.

Bacterial etiology and antimicrobials susceptibility of diarrhea among displaced communities during 2006-2008

The aim of the study was to isolate and identify the common bacteria causing acute diarrhea among displaced persons and assess antimicrobial sensitivity of bacterial isolates. Mandella [South Khartoum] and Wad Elbashir [West Omdurman] Displaced Camps, Health Centers. Descriptive Cross Sectional Study. Four hundred and twenty patients, age group ranging from 3 months to 55 years suffering from diarrhea and attending the health centers were included in the study. Stool specimens or rectal swabs were collected and investigated for enteropathogenic bacteria. Personal characteristic data were collected using direct interviewing questionnaire. The study was conducted from April 2006 to September 2007. Ethical clearance was obtained from Sudan Ministry of health, Research Ethical Committee. Bacterial pathogens were detected in 110 [26.2%] of the patients. Children under 5 years were mostly affected, 178 [42.4%], followed by children over 5 years [5-14 years], 142 [33.8%], and then adults [more than 14] 100 [23.8%]. Different pathogens were isolated, however Shigeila spp were frequently isolated [41.8%]. Most isolates were sensitive to Cefuroxime, followed by Ciprofloxacin and Gentamicin. Most patients depend on donkey cart as water source 222 [52.9%], 120 [28.6%] patients getting their water directly from water pump and 70 [16.7%] patients are using storage tanks as a water supply. Two hundred and thirty [54.8%] patients are consuming untreated drinking water. At the same time 76.1% of patients under study have no disposal latrines. Most cases of bacterial diarrhea in displaced camps are caused by Shigella spp, especially among adults, and children over 5 years; in children under 5 years the main culprit was Campylobacter jejuni. High degree of resistance to antimicrobials was observed against several antimicrobials: Amoxicillin, Erythromycin, and Co-Trimoxazole, but low resistance to Cefuroxime. Most patients consume water from donkey cart, drink untreated water, had no latrines, and live in a poor environmental condition; all of them are risk factors for acquiring diarrhea

Epidemiología clínica y molecular de las infecciones por Shigella spp en niños de la Región Metropolitana durante el verano 2004-2005 / Shigella spp Infections In children living In the Metropolitan RegionChile, during summer of 2004-2005

Background: Shigella spp is a frequent cause of diarrhea in children. Antimicrobials decrease the duration of diarrhea and pathogen excretion. However, the increasing resistance limits their therapeutic value. Aim: To study Shigella serotype distribution in the Metropolitan Region in Chile, and its relationship with severity of disease, antimicrobial resistance pattern and clonality. Material and methods: During summer 2004-2005, stool samples from children with diarrhea were collected in Cary Blair transpon medium and cultured. Shigella isolates were serotyped using monoclonal and polyclonal commercial antibodies. In vitro activity of ampicillin, amoxicillin/clavulanic acid, chloramphenicol, cotrimoxazol, nalidixic acid, ciprofloxacin, ceftriaxone and azythromycin was determined by minimal inhibitory concentration (MIC). Clonality was studied by pulsed-field gel electrophoresis (PFGE) using Xbal as restriction enzyme. Results: One hundred thirty nine Shigella strains were isolated (77 S sonnei and 62 S flexneri). S sonnei and S flexneri 2a serotypes were responsible for 95 percent of episodes. Children aged 2-4 years, showed a greater incidence of Shigella infections and 77 percent of episodes were treated on an ambulatory basis. High resistance levels were observed for ampicillin, cotrimoxazole, amoxicillin-clavulanic acid and chloramphenicol (67 percent, 60 percent, 56 percent and 45 percent, respectively). We found 11 resistance patterns and 61,2 percent of strains were multiresistant. There were multiple clones without a strict relationship with resistance patterns. Conclusions: Shigella infections in Metropolitan Region in Chile are associated to a restricted number of serotypes, representing a clonal expansion associated to different antimicrobial resistant patterns.

Changing patterns of antimicrobial susceptibility of Shigella serotypes isolated from children with acute diarrhea in Manipal, South India, a 5 year study.

This study was carried out to determine the current pattern of Shigella serogroups and their antimicrobial resistance in children with acute gastroenteritis in Manipal, South India. A total of 1,200 stool samples were collected from April 2001 to May 2006 in children suffering from acute gastroenteritis attending the out-patient department of pediatrics at Kasturba Hospital, Manipal, South India. These samples were cultured for enteric pathogens. The isolates were confirmed to be Shigella by biochemical reactions and slide agglutination tests using specific antisera. Antimicrobial susceptibility was performed using an agar diffusion technique method following the National Committee for Clinical Laboratory Standard guidelines. Of 1,200 stool samples, 68 (5.6%) were positive for Shigella spp, 31 (45%) were Shigella flexneri followed by S. sonnei in 20 (31%), S. boydii in 10 (15%), and S. dysenteriae in 6 (8%). Of the 68 isolates, 58 (85.7%) showed resistance to various drugs and 47 (70%) were resistant to two or more drugs. Resistance to trimethoprim-sulfmethoxazole, tetracycline, nalidixic acid and ampicillin was observed in this study. All the strains were resistant to nalidixic acid (100%) but sensitive to cefotaxime and ceftriaxone.

Increasing spectrum in antimicrobial resistance of Shigella isolates in Bangladesh: resistance to azithromycin and ceftriaxone and decreased susceptibility to ciprofloxacin.

Antimicrobial resistance of Shigella isolates in Bangladesh, during 2001-2002, was studied and compared with that of 1991-1992 to identify the changes in resistance patterns and trends. A significant increase in resistance to trimethoprim-sulphamethoxazole (from 52% to 72%, p < 0.01) and nalidixic acid (from 19% to 51%, p < 0.01) was detected. High, but unchanged, resistance to tetracycline, ampicillin, and chloramphenicol, low resistance to mecillinam (resistance 3%, intermediate 3%), and to emergence of resistance to azithromycin (resistance 16%, intermediate 62%) and ceftriaxone/cefixime (2%) were detected in 2001-2002. Of 266 recent isolates, 63% were resistant to > or =3 anti-Shigella drugs (multidrug-resistant [MDR]) compared to 52% of 369 strains (p < 0.007) in 1991-1992. Of 154 isolates tested by E-test in 2001-2002, 71% were nalidixic acid-resistant (minimum inhibitory concentration [MIC] > or =32 microg/mL) and had 10-fold higher MIC90 (0.25 microg/mL) to ciprofloxacin than that of nalidixic acid-susceptible strains exhibiting decreased ciprofloxacin susceptibility, which were detected as ciprofloxacin-susceptible and nalidixic acid-resistant by the disc-diffusion method. These strains were frequently associated with MDR traits. High modal MICs were observed to azithromycin (MIC 6 microg/mL) and nalidixic acid (MIC 128 micdrog/mL) and low to ceftriaxone (MIC 0.023 microg/mL). Conjugative R-plasmids-encoded extended-spectrum beta-lactamase was responsible for resistance to ceftriaxone/cefixime. The growing antimicrobial resistance of Shigella is worrying and mandates monitoring of resistance. Pivmecillinam or ciprofloxacin might be considered for treating shigellosis with caution.

Shigella isolates of Nepal: changes in the incidence of shigella subgroups and trends of antimicrobial susceptibility pattern.

OBJECTIVES: Shigellosis is an important cause of bloody diarrhoea in all age groups, especially in children. A retrospective study was done to analyse the pattern of shigella isolates and the antimicrobial susceptibility trend of these shigella isolated at different hospitals of Nepal from Jan, 2003- Dec, 2005. MATERIALS AND METHODS: A total of 118 Shigella species isolated at nine different hospital laboratories of Nepal were reported to National Public Health Laboratory during January, 2003- December 2005 .The isolates were tested for the confirmation of identification and antimicrobial susceptibility pattern by standard bacteriological techniques. RESULTS: Of the 118 Shigella isolates reported, Shigella flexneri 51 (43.22%) was the predominant of the four species followed by Shigella dysenteriae 49(41.52 %) , Shigella boydii (7.62%) and Shigella sonnei (7.62%).But the yearly distribution of the Shigella isolates in 2003 and 2004 showed that Shigella dysenteriae was the most common of the four species. In 2005, a shift in the species was noted as Sh flexneri replaced Sh dysenteriae and became the most prevalent species. The percentage of Shigella dysenteriae type-1 among all Shigella dysenteriae were 66.66 % in 2003, 44.44 % in 2004 and 60 % in 2005. Individual or multiple resistances to Ampicillin, Nalidixic acid, and/or Cotrimoxazole was seen in all the four species of Shigella. 33% of the total Shigella isolates reported were multi drug resistant (showing resistance to 3 or more antibiotics at a time). Shigella dysenteriae type-1(Sd 1) isolates resistant to ciprofloxacin were also encountered in the present study .Of the total 25 Shigella dysenteriae type 1 isolates reported, 18(72%) were ciprofloxacin resistant . All the Shigella isolates were however sensitive to Ceftriaxone and Azithromycin. CONCLUSION: Distribution of different species of Shigella and their antibiotic susceptibility profile may vary from one geographical location to another and may also change with time. Systematic monitoring of the species and serotypes of Shigellae and their antimicrobial susceptibility can help to guide therapy and reveal periodic epidemics due to Sd 1, which may have acquired resistance to antibiotics that have previously been effective. Key words: Dysentery, Shigella, Shigella dysenteriae type-1, Antimicrobial resistance.