Validity of nalidixic acid screening in fluoroquinolone-resistant typhoid salmonellae.
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To validate the screening of low-level fluoroquinolone resistance in typhoid salmonellae by using nalidixic acid (30 mg) disk providing an acceptable zone of inhibition.Quasi-experimental study.The Department of Microbiology, Armed Forces Institute of Pathology, Rawalpindi, Pakistan from July 2002 to June 2003.Antimicrobial susceptibility of 225 clinical isolates of S. typhi (n=126) and S. paratyphi A (n=99) against nalidixic acid and ciprofloxacin was determined by the modified Kirby-Bauer disk diffusion and agar dilution techniques of NCCLS. The relationship between the zone sizes and the MICs of the two quinolones was plotted in the form of scattergrams and nalidixic acid MICs and zone of inhibition sizes were correlated with those of ciprofloxacin by regression analysis.One hundred and ninety-five isolates were nalidixic acid-susceptible (MIC <16 microg/mL) and approximately 30 were nalidixic acid-resistant (MIC >32 microg/mL). All the nalidixic acid-susceptible isolates had ciprofloxacin MIC of <0.064 microg/mL. Among the nalidixic acid-resistant isolates approximately 20 had ciprofloxacin MIC > or =0.125 microg/mL and approximately 10 had ciprofloxacin MIC < or =0.03-0.064 microg/mL. The diameter of inhibition zone around a 30 mg nalidixic acid disk of nalidixic acid-resistant isolates was < or =13 mm (range 6-16 mm, mean 10.3 mm + SD 3.5 mm), while among nalidixic acid-susceptible isolates it ranged from 14 to 30 mm (mean 23.8 mm + SD 2.2 mm). The diameter of inhibition zone around a 5mg ciprofloxacin disk of nalidixic acid-resistant isolates ranged from 26 to 35 mm (mean 29.8 mm + SD 3.1 mm), while in nalidixic acid-susceptible isolates it ranged from 32 to 42 mm (mean 36.6 mm + SD 1.9 mm). With ciprofloxacin MIC > or =0.125 microg/mL taken as a breakpoint, a zone of Keywords:
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Objective To investigate the antimicrobial resistance among the Salmonella strains isolated from Shenzhen People's Hospital.Methods The minimal inhibitory concentrations (MICs) of antibacterial agents were determined by agar dilution method against 95 strains of Salmonella. WHONET 5.3 software was used to analyze the data.Results S. typhi and S. paratyphi A remained highly susceptible to ampicillin,chloramphenicol and trimethoprim-sulfamethoxazole. About 96%-100% and 97%-100% of the strains were susceptible respectively. Multidrug-resistant isolate was not found. About 52% (13/25) of S. typhi isolates and 94% (62/66) of S. paratyphi A isolates were resistant to nalidixic acid,respectively. The prevalence of S. typhi and S. paratyphi A with decreased susceptibility to ciprofloxacin (MIC=0.125-1 mg/L) was 24% (6/25) and 92.4% (61/66),respectively. One strain of S. paratyphi B and one strain of S. typhimurium showed high resistance to ciprofloxacin (MIC≥16 mg/L),and resistance to ampicillin,chloramphenicol and trimethoprim-sulfamethoxazole too.Conclusions The S. typhi and S. paratyphi A with decreased susceptibility to ciprofloxacin were prevalent in our hospital. Ciprofloxacin-resistant S. paratyphi B and S. typhimurium were identified.
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Increasing number of patients suffering from enteric fever are being diagnosed in and around Bastar District of Chhattisgarh in last 5 years.Over 500 samples from febrile patients were cultured during May 2012 to January 2013 in a tertiary care hospital in Jagdalpur, Chhattisgarh.The aim of this study was to evaluate the ciprofloxacin and other antibiotics susceptibility patterns of Salmonella spp from blood samples of suspected enteric fever patients.Antimicrobial susceptibility tests were performed against commonly used antimicrobials by disc diffusion method and Minimum Inhibitory Concentration (MIC) of ciprofloxacin was determined by agar dilution method.Altogether 62 Salmonella Typhi and 21 Salmonella Paratyphi A were isolated from blood samples.All isolates were sensitive to ceftriaxone and ofloxacin whereas 9 isolates were resistant to ciprofloxacin.Nalidixic acid resistant isolates were significantly associated with raised MIC values for ciprofloxacin, suggesting that resistance to nalidixic acid is a reliable indicator of decreased ciprofloxacin susceptibility where disc diffusion test showed susceptible.
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Ciprofloxacin replaced chloramphenicol (C), the best choice of antibiotic in the treatment of enteric fever, when C-resistant enteric fever emerged and caused outbreaks in different parts of the world. C-sensitive S. enterica serovar Typhi emerged again due to withdrawal of the antibiotic pressure.To assess the in vitro efficacy of C against Salmonella enterica serovar Typhi isolates (1991-2003).A total of 464 blood culture isolates of S. enterica serovar Typhi were subjected to C susceptibility by disc diffusion and agar dilution methods using Mueller-Hinton agar. The antibiotic susceptibility of S. enterica serovar Typhi isolates obtained in the year 2002 and 2003 was determined using ampicillin, cotrimoxazole, ciprofloxacin, nalidixic acid, ceftriaxone and cefotaxime, in addition to C. Escherichia coli strain ATCC 25922 was used as the control. Changes in C sensitivity of the isolates were analyzed using chi2 test with Yates correction.All the isolates of 1991 were C-resistant with minimum inhibitory concentration values (MICs) of 2000-5000 mg/ml. In the following years decrease in frequency of C resistance was noticed: 1992 (50%), 1993 (32%), 1994 (27%) and 1995 (05%). The isolates of 1996-99 and 2001 were 100% C-sensitive. In 2000, sensitivity was also high (79%). The strains isolated in the year 2002 and 2003, showing reduced susceptibility of ciprofloxacin, were nalidixic acid resistant, but sensitive to the third-generation cephalosporins (ceftriaxone and cefotaxime). The MICs for C-sensitive isolates (1991-2003) ranged 0.1-5 mg/ml. Results suggest the necessity for re-evaluation of C therapy in typhoid fever.
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To validate the screening of low-level fluoroquinolone resistance in typhoid salmonellae by using nalidixic acid (30 mg) disk providing an acceptable zone of inhibition.Quasi-experimental study.The Department of Microbiology, Armed Forces Institute of Pathology, Rawalpindi, Pakistan from July 2002 to June 2003.Antimicrobial susceptibility of 225 clinical isolates of S. typhi (n=126) and S. paratyphi A (n=99) against nalidixic acid and ciprofloxacin was determined by the modified Kirby-Bauer disk diffusion and agar dilution techniques of NCCLS. The relationship between the zone sizes and the MICs of the two quinolones was plotted in the form of scattergrams and nalidixic acid MICs and zone of inhibition sizes were correlated with those of ciprofloxacin by regression analysis.One hundred and ninety-five isolates were nalidixic acid-susceptible (MIC <16 microg/mL) and approximately 30 were nalidixic acid-resistant (MIC >32 microg/mL). All the nalidixic acid-susceptible isolates had ciprofloxacin MIC of <0.064 microg/mL. Among the nalidixic acid-resistant isolates approximately 20 had ciprofloxacin MIC > or =0.125 microg/mL and approximately 10 had ciprofloxacin MIC < or =0.03-0.064 microg/mL. The diameter of inhibition zone around a 30 mg nalidixic acid disk of nalidixic acid-resistant isolates was < or =13 mm (range 6-16 mm, mean 10.3 mm + SD 3.5 mm), while among nalidixic acid-susceptible isolates it ranged from 14 to 30 mm (mean 23.8 mm + SD 2.2 mm). The diameter of inhibition zone around a 5mg ciprofloxacin disk of nalidixic acid-resistant isolates ranged from 26 to 35 mm (mean 29.8 mm + SD 3.1 mm), while in nalidixic acid-susceptible isolates it ranged from 32 to 42 mm (mean 36.6 mm + SD 1.9 mm). With ciprofloxacin MIC > or =0.125 microg/mL taken as a breakpoint, a zone of
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Background: Fluoroquinolones are the drugs extensively employed for the treatment of Salmonella infections. Over the couple of decades that have elapsed since the introduction of fluoroquinolones, resistance to these agents by Enterobacteriaceae family members has become common and widespread. Although fluoroquinolone resistance is mediated by genomic DNA (deoxyribonucleic acid) as well as plasmid DNA, the plasmid-mediated quinolone resistance (PMQR) facilitates higher level resistance by interacting with genomic mechanism and is capable of horizontal spread. Materials and Methods: During a period of 1-year, 63 typhoidal Salmonellae were isolated from 14,050 blood cultures and one parietal wall abscess. 36 (56.25%) were Salmonella Typhi and 27 (42%) were Salmonella Paratyphi A. They were all screened for resistance by the disc diffusion method and their minimum inhibitory concentrations were determined using agar dilution, broth dilution and E-strip method. Ciprofloxacin resistant isolates were screened for PMQR determinants by polymerase chain reaction assay. Results: All the 63 isolates were resistant to nalidixic acid. Among the 36 S. Typhi isolates 20 were resistant to ciprofloxacin, of which 14 carried the plasmid gene qnrB and one carried the aac(6')-Ib-cr gene. qnrA and qnrS genes were not detected. Ciprofloxacin resistance was not seen in any of the S. Paratyphi A isolates. Conclusion: The antibiotic sensitivity pattern of typhoidal Salmonellae shows an increasing trend of PMQR. The allele B of qnr gene was found to be the predominant cause of PMQR in this study.
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Background Disc diffusion technique is the routine susceptibility testing procedure for isolates of enteric fever, the most common clinical diagnosis among febrile patients in Nepal. Objective To evaluated the current fluoroquinolones (FQs) susceptibility criteria and nalidixic acid screening test in Salmonella enterica serovar Typhi and Paratyphi A. Methods S. Typhi and Paratyphi A strains isolated from 443 suspected enteric fever patients visiting National Public Health Laboratory (NPHL) during April through October 2008 were analyzed. All isolates were confirmed by standard microbiological procedures including serotyping. Antibiotic susceptibility testing was performed by using Kirby Bauer disc diffusion method and Clinical and Laboratory Standards Institute (CLSI) approved interpretive criteria. Agar dilution method was used to determine Minimum Inhibitory Concentration (MIC) of ciprofloxacin, ofloxacin and nalidixic acid. Result Out of 41 Salmonella isolates, 80.49% were nalidixic acid resistant, with S. Paratyphi A showing higher resistance rate (88.23%) compared to S. Typhi (75%). The difference in both MIC and zone diameter in nalidixic acid susceptible and nalidixic acid resistant isolates was found to be significant (P < 0.001) and decreased susceptibility to FQs was strongly correlated (sensitivity and specificity of 100%) with resistance to nalidixic acid. Regression analysis of MIC against zone diameter based on the current CLSI recommended guidelines suggests that accommodation of current susceptible and resistant MIC requires increase in the zone diameter of ciprofloxacin and ofloxacin. Conclusion Before using these drugs for management of enteric fever, appropriate identification of Salmonella isolates with reduced susceptibility to FQs is essential to limit the possible treatment failure and development of highly resistant strains. The current FQs susceptibility break point criteria for Salmonella need re-evaluation. KATHMANDU UNIVERSITY MEDICAL JOURNAL VOL.10 | NO. 1 | ISSUE 37 | JAN - MAR 2012 | 24-29DOI: http://dx.doi.org/10.3126/kumj.v10i1.6909
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The minimal inhibitory concentrations (MICs) of twelve 4-quinolone antimicrobials were determined for 100 isolates of Haemophilus influenzae (including 30 beta-lactamase producing strains) and 100 isolates of Streptococcus pneumoniae. MICs were determined using an agar dilution technique in Mueller-Hinton agar supplemented with 10% lysed horse blood. The inoculum used was approximately 10(4) colony-forming units, contained in 10 microliters of Mueller-Hinton broth, which was applied to the agar plates using a multipoint inoculator. Following inoculation, plates were incubated at 37 degrees C for 18 h in an atmosphere enriched to 10% carbon dioxide. The MIC of each antimicrobial for each isolate examined was determined as the lowest concentration of the antimicrobial which completely inhibited growth of the inoculum. The minimum concentrations required to inhibit the growth of 50% (MIC50) and 90% (MIC90) of the organisms examined were also determined. The more recently synthesised 4-quinolones showed considerably greater activity than nalidixic acid and pipemidic acid against clinical isolates of Haemophilus influenzae and Streptococcus pneumoniae. There was no apparent difference between the MICs observed for beta-lactamase producing and non-beta-lactamase producing strains of Haemophilus influenzae. Ciprofloxacin was the most active 4-quinolone examined (MIC90 for Haemophilus influenzae 0.008 microgram/ml; Streptococcus pneumoniae 2 micrograms/ml). Clinical studies on a possible role for some of the more recently synthesised 4-quinolones in the management of patients with respiratory infection are indicated.
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A panel of 203 staphylococci, Enterobacteriaceae, Pseudomonas aeruginosa, and miscellaneous nonfermentative gram-negative bacilli were chosen for their various susceptibilities to ciprofloxacin. On the basis of agar dilution susceptibilities, each of the four taxonomic groups was divided into ciprofloxacin-susceptible, moderately resistant, and highly resistant subgroups, and each subgroup was then further analyzed for its susceptibility to the fluoroquinolones CI-960, CI-990, sparfloxacin, and ofloxacin. Although the MICs of each quinolone increased as ciprofloxacin resistance increased, the potency of CI-960 appeared to increase relative to the potencies of the other quinolones. Similarly, the MICs of sparfloxacin and ofloxacin appeared to be less affected by ciprofloxacin resistance than were the MICs of ciprofloxacin or CI-990. Single-step mutants of representative clinical isolates with different levels of ciprofloxacin resistance were selected to determine whether the study quinolones differed in their propensity to select resistant mutants and whether the presence of preexisting ciprofloxacin resistance influenced the subsequent development of resistance. Each of the five fluoroquinolones and nalidixic acid selected mutants that exhibited generally modest decreases in quinolone susceptibility (4- to 16-fold). However, CI-960 inhibited significantly more mutants (80%) than did the other quinolones (39 to 59%) at a concentration of 1 microgram/ml. The presence of preexisting ciprofloxacin resistance appeared to be associated with higher mutational frequencies in coagulase-negative staphylococci exposed to each of the fluoroquinolones and in Serratia marcescens exposed to nalidixic acid. Preexisting ciprofloxacin resistance did not influence the development of resistance in the strains of Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, or Pseudomonas aeruginosa that were studied. The results of this study suggest that quinolones are not affected equally by all resistance mechanisms, and although each one can select mutants, some quinolones may be active against these mutants at clinically achievable concentrations.
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Background: Increasing resistance of Pseudomonas aeruginosa to ciprofloxacin in ICU/burn units has created a problem in the treatment of infections caused by this microorganism. Methods: Fifty P. aeruginosa strains were isolated from burn patients hospitalized in the Kerman Hospital during May 1999-April 2000 and were tested for in-vitro sensitivity to different antibiotics by disc diffusion breakpoint assay. The isolates were subjected to minimum inhibitory concentration (MIC) test by agar dilution method. Existence of the plasmids was also investigated in the isolates. Results: Thirty-four patients infected with ciprofloxacin strains showed MIC of 8 m g/ml [p<0.001]. Sixteen patients were infected with sensitive strains exhibiting MIC range of 0.0125-0.125 ± 0.033 m g/ml. The isolates were also also resistant to other antibiotics [p<0.001]. Plasmid isolation and agarose gel electrophoresis (0.7%) revealed three plasmid bands in strains 8 and 16, and one band in strain 35. Conclusion: The emergence of ciprofloxacin resistance of P. aeruginosa in burn patients is alarming since this antibiotic has only recently been introduced onto the market in Iran. One important observation was that some isolates exhibited cross resistance to other antibiotics. Furthermore, some strains were carriers of plasmids which might have acted as the potential source of acquired resistance in the hospital setting.
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The antibiotic susceptibility pattern of Vibrio cholerae O139, Bengal, an emerging intestinal pathogen has been determined by the Kirby Bauer technique and the MIC values of some antibiotics against these strains by agar dilution technique. All the strains were susceptible to tetracycline, norfloxacin, ciprofloxacin and a majority was susceptible to gentamicin (95.7%) and nalidixic acid (82.9%). Only 51% were susceptible to cefotaxime and most strains were resistant to furazolidone (95.7%), ampicillin (87.3%) and co-trimoxazole (91.5%). The study shows the importance of judicious use of antibiotics in cholera cases and the need for monitoring the susceptibility status of these strains particularly because of their ability to cause extra-intestinal infections like septicaemia.
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