Increasing fluoroquinolone resistance in salmonella serotypes in Finland during 1995-1997

Escherichia coli survival in response to ciprofloxacin antibiotic stress correlates with increased nucleoid length and effective misfolded protein management

The evolution of antibiotic resistance is a fundamental problem in disease management but is rarely quantified on a single-cell level owing to challenges associated with capturing the spatial and temporal variation across a population. To evaluate cell biological phenotypic responses, we tracked the single-cell dynamics of filamentous bacteria through time in response to ciprofloxacin antibiotic stress. We measured the degree of phenotypic variation in nucleoid length and the accumulation of protein damage under ciprofloxacin antibiotic and quantified the impact on bacterial survival. Increased survival was correlated with increased nucleoid length and the variation in this response was inversely correlated with antibiotic concentration. Survival time was also increased through clearance of misfolded proteins, an unexpected mechanism of stress relief deployed by the filamentous bacteria. Our results reveal a diverse range of survival tactics employed by bacteria in response to ciprofloxacin and suggest potential evolutionary routes to resistance.

Repeated exposure of nosocomial pathogens to silver does not select for silver resistance but does impact ciprofloxacin susceptibility

The rise of antimicrobial resistant bacteria coupled with a void in antibiotic development marks Antimicrobial Resistance as one of the biggest current threats to modern medicine. Antimicrobial metals are being developed and used as alternative anti-infectives, however, the existence of known resistance mechanisms and limited data regarding bacterial responses to long-term metal exposure are barriers to widespread implementation. In this study, a panel of reference and clinical strains of major nosocomial pathogens were subjected to serial dosage cycles of silver and ciprofloxacin. Populations exposed to silver initially showed no change in sensitivity, however, increasingly susceptibility was observed after the 25th cycle. A control experiment with ciprofloxacin revealed a selection for resistance over time, with silver treated bacteria showing faster adaptation. Morphological analysis revealed filamentation in Gram negative species suggesting membrane perturbation, while sequencing of isolated strains identified mutations in numerous genes. These included those encoding for efflux systems, chemosensory systems, stress responses, biofilm formation and respiratory chain processes, although no consistent locus was identified that correlated with silver sensitivity. These results suggest that de novo silver resistance is hard to select in a range of nosocomial pathogens, although silver exposure may detrimentally impact sensitivity to antibiotics in the long term. STATEMENT OF SIGNIFICANCE: The adaptability of microbial life continuously calls for the development of novel antibiotic molecules, however, the cost and risk associated with their discovery have led to a drying up in the pipeline, causing antimicrobial resistance (AMR) to be a major threat to healthcare. From all available strategies, antimicrobial metals and, more specifically, silver showcase large bactericidal spectrum and limited toxic effect which coupled with a large range of processes available for their delivery made these materials as a clear candidate to tackle AMR. Previous reports have shown the ability of this metal to enact a synergistic effect with other antimicrobial therapies, nevertheless, the discovery of Ag resistance mechanisms since the early 70s and limited knowledge on the long term influence of silver on AMR poses a threat to their applicability. The present study provides quantitative data on the influence of silver based therapies on AMR development for a panel of reference and clinical strains of major nosocomial pathogens, revealing that prolonged silver exposure may detrimentally impact sensitivity to antibiotics.

Antibiotic resistance and drug modification: Synthesis, characterization and bioactivity of newly modified potent ciprofloxacin derivatives

Development of new derivatives of commercial antibiotics using different organic reagents and testing these derivatives against different microorganisms are the main goals of this article. Thus, the antibiotic ciprofloxacin, CF, was acylated via reaction with ethyl cyanoacetate and ethyl acetoacetate in basic medium to give the cyanoacetylpiprazinyl dihydroquinoline derivative 3, and oxobutanoylpiprazinyl dihydroquinoline derivative 5, respectively. On the other hand, N-alkylated derivatives 8-10, were prepared through the reaction of CF with chloroacetonitrile, chloroacetyl acetone and chloroacetone in the presence of carbonate salt. In basic medium, both 3 and 10 were coupled with benzenediazonium chloride to afford hydrazono derivatives, which were then cyclized to give 4-(dihydropyridazinecarbonyl)piperazinyl-1,4-dihydroquinoline. Furthermore, compounds 3 and 10 were reacted with benylidenemalononitrile to produce 4H-pyan and pyrido[1,2-a]pyrazine derivatives, respectively. Both 3 and 10 were reacted with DMFDMA to give enaminone derivatives. These enaminones were cyclized to aminopyrimidine derivatives by reacting with urea or thiourea. X-ray, elemental analysis and spectral data were used to illustrate and confirm the structures of the isolated compounds. The bioactivities of the novel compounds were investigated against different gram-positive and gram-negative bacteria. In addition, these novel antibiotic derivatives were tested against ciprofloxacin-resistant bacteria isolated from patients aged 65-74 years. This study reveals that most of the modified drugs show high to moderate antibacterial activity. Additionally, these drugs show good effects against ciprofloxacin-resistant bacteria.

Interplay of the Quality of Ciprofloxacin and Antibiotic Resistance in Developing Countries

Ciprofloxacin, a second generation broad spectrum fluoroquinolone, is active against both Gram-positive and Gram-negative bacteria. Ciprofloxacin has a high oral bioavailability and a large volume of distribution. It is used for the treatment of a wide range of infections including urinary tract infections caused by susceptible bacteria. However, the availability and use of substandard and spurious quality of oral ciprofloxacin formulations in the developing countries has been thought to have contributed toward increased risk of treatment failure and bacterial resistance. Therefore, quality control and bioequivalence studies of the commercially available oral ciprofloxacin formulations should be monitored. Appropriate actions should be taken against offending manufacturers in order to prevent the sale of substandard and spurious quality of ciprofloxacin formulations.

Antimicrobial resistance among Salmonella and Shigella isolates in five Canadian provinces (1997 to 2000)

OBJECTIVE

To describe rates of antimicrobial resistance (AMR) among Salmonella and Shigella isolates reported in five Canadian provinces, focusing on clinically important antimicrobials.

METHODS

The authors retrospectively investigated AMR rates among 6219 Salmonella and 1673 Shigella isolates submitted to provincial public health laboratories in Alberta, Newfoundland and Labrador, Ontario, Prince Edward Island and Saskatchewan from 1997 to 2000; these isolates were estimated to represent 41% of Salmonella cases and 72% of Shigella cases reported by the study provinces.

RESULTS

Among Salmonella isolates, 27% (1704 of 6215) were resistant to ampicillin, 2.2% (135 of 6122) to trimethoprim/ sulfamethoxazole, 1.5% (14 of 938) to nalidixic acid, 1.2% (one of 84) to lomafloxacin and 0.08% (five of 6163) to ciprofloxacin. Among Shigella isolates, 70% (1144 of 1643) were resistant to trimethoprim/sulfamethoxazole, 65% (1079 of 1672) to ampicillin, 3.1% (eight of 262) to nalidixic acid, 0.49% (eight of 1636) to ciprofloxacin, 0.14% (one of 700) to ceftriaxone and 0.08% (one of 1292) to ceftazidime.

CONCLUSIONS

Higher rates of resistance to clinically important antimicrobials (including ciprofloxacin) were observed among both Salmonella and Shigella isolates than has previously been reported. Current Canadian data on rates of AMR for these pathogens are required.

Genotype, serotype, and antibiotic resistance of sorbitol-negative Escherichia coli isolates from feedlot cattle

Rectal fecal samples from 80 steers receiving Rumensin, Revalor-S, and Liquamycin alone or in combination for growth promotion and disease prevention were examined for the presence of non-O157:H7 Shiga toxin-producing Escherichia coli. All isolates were identified with the API 20E test, virulence genes were detected with a PCR assay, and antibiotic susceptibilities were determined with the Sensititre system. Of the 153 E. coli isolates recovered 126 (82.3%) were sorbitol negative. Isolates were classified into 14 biochemical E. coli groups; 51.6% were negative for arginine dihydrolase, ornithine decarboxylase, sorbitol, and saccharose reactions but positive for lysine decarboxylase, indole production, and rhamnose reactions. Twenty-one O:H serotypes were detected in the 153 E. coli isolates. The most frequent serotypes were O2:H42 (49.7% of isolates), O49:NM (13.7%), O?:H25 (9.2%), and O10:NM (7.2%). One isolate of E. coli O172:H25 and one of E. coli O157: H39 were found. The stx1 gene was found in the two E. coli O98:H25 isolates. The eaeA and e-hlyA genes were detected in 21, 14, and 10 isolates of serotypes O49:NM, O?:H25, and O10:NM, respectively, and in each isolate of serotype O156:H25 and O172:H25. Four E. coli O132:H18 isolates were multiresistant to ampicillin, chloramphenicol, kanamycin, streptomycin, and sulfisoxazole. Tetracycline resistance due to the tet(B) gene was observed in 74 of the 76 E. coli O2:H42 isolates. Except for one isolate, all tetracycline-resistant isolates were negative for the virulence genes eaeA and e-hlyA or stx1. Pulsed-field gel electrophoresis typing revealed that the tetracycline-resistant serotypes were genetically diverse. Our data illustrate that cattle are a potential source of some atypical antibiotic-resistant E. coli isolates that harbor virulence genes.

Antimicrobial resistance in Salmonella enterica serovar Typhimurium from human and animal sources in Italy

Salmonella Typhimurium strains isolated in Italy in the period 2002-2004 from human and animal sources were examined for their antimicrobial susceptibility. Resistance to tetracycline (T, 73.6%), sulfonamides (Su, 73.3%), ampicillin (A, 67.6%), streptomycin (S, 65.4%) and chloramphenicol (C, 32.3%) were frequently observed. Resistance to ciprofloxacin was only observed in a swine strain, but most human strains resistant to nalidixic acid showed reduced susceptibility to that drug (MIC > or = 0.125 mg/l). Overall, 64% of the strains were resistant to four or more drugs. The most common resistance profiles were ACSSuT, prevalent in strains belonging phage type DT104 and ASSuT, prevalently associated with strains unable to be typed.

Impact of feed supplementation with antimicrobial agents on growth performance of broiler chickens, Clostridium perfringens and enterococcus counts, and antibiotic resistance phenotypes and distribution of antimicrobial resistance determinants in Escherichia coli isolates

The effects of feed supplementation with the approved antimicrobial agents bambermycin, penicillin, salinomycin, and bacitracin or a combination of salinomycin plus bacitracin were evaluated for the incidence and distribution of antibiotic resistance in 197 commensal Escherichia coli isolates from broiler chickens over 35 days. All isolates showed some degree of multiple antibiotic resistance. Resistance to tetracycline (68.5%), amoxicillin (61.4%), ceftiofur (51.3%), spectinomycin (47.2%), and sulfonamides (42%) was most frequent. The levels of resistance to streptomycin, chloramphenicol, and gentamicin were 33.5, 35.5, and 25.3%, respectively. The overall resistance levels decreased from day 7 to day 35 (P < 0.001). Comparing treatments, the levels of resistance to ceftiofur, spectinomycin, and gentamicin (except for resistance to bacitracin treatment) were significantly higher in isolates from chickens receiving feed supplemented with salinomycin than from the other feeds (P < 0.001). Using a DNA microarray analysis capable of detecting commonly found antimicrobial resistance genes, we characterized 104 tetracycline-resistant E. coli isolates from 7- to 28-day-old chickens fed different growth promoters. Results showed a decrease in the incidence of isolates harboring tet(B), bla(TEM), sulI, and aadA and class 1 integron from days 7 to 35 (P < 0.01). Of the 84 tetracycline-ceftiofur-resistant E. coli isolates, 76 (90.5%) were positive for bla(CMY-2). The proportions of isolates positive for sulI, aadA, and integron class 1 were significantly higher in salinomycin-treated chickens than in the control or other treatment groups (P < 0.05). These data demonstrate that multiantibiotic-resistant E. coli isolates can be found in broiler chickens regardless of the antimicrobial growth promoters used. However, the phenotype and the distribution of resistance determinants in E. coli can be modulated by feed supplementation with some of the antimicrobial agents used in broiler chicken production.

Trends in antimicrobial resistance phenotypes in non-typhoid Salmonellae from human and poultry origins in France

A total of 1873 strains from human origin and 4283 strains from non-human origin of Salmonella enterica serotypes Typhimurium, Enteritidis, Heidelberg, Hadar and Virchow, collected over three years 1993, 1997 and 2000, were examined in order to determine the rate of antimicrobial resistance to 12 antimicrobial drugs. The objective of the study was to describe and to compare the evolution of the main resistance types in human and non-human isolates, focusing on the poultry sector. The evolution and the rates of antimicrobial resistances for the five serotypes, with the exception of Virchow, were almost comparable in strains isolated from human and non-human sources over the period studied. The most striking result concerning single resistance was the spectacular increase of the resistance frequency to nalidixic acid for the strains belonging to serotypes Hadar and Virchow, especially in the poultry food sector (14% in 1993 vs. 72% in 2000 for Salmonella Virchow, 4% in 1993 vs. 70% in 2000 for Salmonella Hadar) and also in human isolates (24% in 1997 vs. 48% in 2000 for S. Virchow, 31% in 1997 vs. 78% in 2000 for S. Hadar). In addition to the classical resistance to ampicillin, streptomycin, sulphonamide, chloramphenicol and tetracycline (ASSuCT resistance type), which stabilized between 1997 and 2000, the emergence of a new resistance type was observed.

Reduction in fluoroquinolone susceptibility among non-typhoidal strains of Salmonella enterica isolated from Finnish patients

OBJECTIVES

The proportion of Salmonella isolates with reduced susceptibility to fluoroquinolones has increased during recent years in many countries, especially in South-east Asia. The present study was performed to evaluate the incidence of and changes in quinolone resistance in Salmonella isolates of either foreign or domestic origin in Finland.

METHODS

A total of 1004 Salmonella isolates collected from Finnish patients between 2000 and 2004 were analysed for ciprofloxacin susceptibility. Of these isolates, 504 were of domestic origin and 500 were of foreign origin, collected from travellers to 43 different countries. The Salmonella collection consisted of 89 different serotypes. All isolates belonged to non-typhoidal Salmonella enterica.

RESULTS

Of all isolates, 3 (0.3%) were ciprofloxacin-resistant (MIC > or = 4 mg/L) and 214 (21.3%) exhibited reduced susceptibility to ciprofloxacin (MIC > or = 0.125-2 mg/L). The annual proportion of reduced susceptibility varied between 3 and 15% among the domestic Salmonella isolates (P = 0.123). Between 2000 and 2004, the annual proportion of reduced susceptibility increased significantly (from 23 to 39%; P = 0.001) among all foreign isolates as well as among those from Spain alone (from 4 to 73%; P < 0.001). Among the isolates from Thailand, reduced ciprofloxacin susceptibility remained at a constantly high level (52-66%) throughout the study.

CONCLUSIONS

Our results show that reduced fluoroquinolone susceptibility in S. enterica is not restricted to South-east Asia alone but continues to grow rapidly in many parts of the world including countries of the European Union.

New quinolone resistance phenomenon in Salmonella enterica: nalidixic acid-susceptible isolates with reduced fluoroquinolone susceptibility

We describe the emergence of a new quinolone resistance pattern in Salmonella enterica isolates from Southeast Asia. These isolates are susceptible to nalidixic acid but exhibit reduced susceptibility to ciprofloxacin. The increase of such strains may threaten the value of the nalidixic acid disk test to screen for reduced fluoroquinolone susceptibility in salmonellas.

Increasing incidence of quinolone resistance in human non-typhoid Salmonella enterica isolates in Korea and mechanisms involved in quinolone resistance

OBJECTIVES

We investigated the trends of nalidixic acid resistance in human non-typhoid Salmonella enterica in a Korean population, and examined some possible mechanisms involved in this resistance.

METHODS

A total of 261 clinical strains were tested. For all strains, the MICs of nalidixic acid were determined. Nalidixic acid-resistant strains underwent further analysis, including determination of MICs of other antibiotics, mutation analysis within the topoisomerase genes, organic solvent tolerance test, western blotting for AcrA, marOR mutation analysis, ciprofloxacin accumulation test, and PCR for the qnr gene. The clonal relationships of Salmonella strains were examined by random amplified polymorphic DNA analysis.

RESULTS

The incidence of nalidixic acid resistance increased from 1.8% in 1995-96 to 21.8% in 2000-02. The resistance rate was higher in S. enterica serotype Enteritidis (21.6%) than in serotype Typhimurium (12.1%). The nalidixic acid resistance rates in Salmonella Enteritidis varied according to the phage type (PT) and Salmonella Enteritidis PT 1 was most commonly associated with resistance to nalidixic acid. Several cases of clonal spread, especially by Salmonella Enteritidis PT 1, were identified. Of the 46 nalidixic acid-resistant strains, 43 had single mutations in the gyrA gene. Four strains were organic solvent-tolerant and were associated with decreased ciprofloxacin accumulation; three of these showed increased expression of AcrA and had novel mutations in marOR (84L). The qnr gene was not identified.

CONCLUSIONS

Recently, the rate of nalidixic acid resistance in Korean clinical Salmonella strains markedly increased and it was partly due to the clonal spread of Salmonella Enteritidis, especially PT 1. The main mechanism of nalidixic acid resistance was a mutation in the gyrA region.

In vitro activities of 11 fluoroquinolones against 816 non-typhoidal strains of Salmonella enterica isolated from Finnish patients with special reference to reduced ciprofloxacin susceptibility

Background

The number of Salmonella strains with reduced susceptibility to fluoroquinolones has increased during recent years in many countries, threatening the value of this antimicrobial group in the treatment of severe salmonella infections.

Methods

We analyzed the in vitro activities of ciprofloxacin and 10 additional fluoroquinolones against 816 Salmonella strains collected from Finnish patients between 1995 and 2003. Special attention was focused on the efficacy of newer fluoroquinolones against the Salmonella strains with reduced ciprofloxacin susceptibility.

Results

The isolates represented 119 different serotypes. Of all 816 Salmonella strains, 3 (0.4%) were resistant to ciprofloxacin (MIC ≥ 4 μg/ml), 232 (28.4%) showed reduced susceptibility to ciprofloxacin (MIC ≥ 0.125 – 2 μg/ml), and 581 (71.2%) were ciprofloxacin-susceptible. The MIC₅₀ and MIC₉₀ values of ciprofloxacin for these strains were 0.032 and 0.25 μg/ml, respectively, being lower than those of the other fluoroquinolone compounds presently on market in Finland (ofloxacin, norfloxacin, levofloxacin, and moxifloxacin). For two newer quinolones, clinafloxacin and sitafloxacin, the MIC₅₀ and MIC₉₀ values were lowest, both 0.016 and 0.064 μg/ml, respectively. Moreover, clinafloxacin and sitafloxacin exhibited the lowest MIC₅₀ and MIC₉₀ values, 0.064 and 0.125 μg/ml, against the 235 Salmonella strains with reduced susceptibility and strains fully resistant to ciprofloxacin.

Conclusion

Among the registered fluoroquinolones in Finland, ciprofloxacin still appears to be the most effective drug for the treatment salmonella infections. Among the newer preparations, both clinafloxacin and sitafloxacin are promising based on in vitro studies, especially for strains showing reduced ciprofloxacin susceptibility. Their efficacy, however, has not been demonstrated in clinical investigations.

Trends in nalidixic acid resistance in nontyphoidal Salmonella isolated from 1999 to 2002: decreased susceptibility to 6 fluoroquinolones

We determined the resistance to nalidixic acid and 6 fluoroquinolones of 771 nontyphoidal Salmonella strains isolated from humans between 1999 and 2002. A total of 22 different serotypes were identified among the Salmonella isolates, the most common being Salmonella Enteritidis (79%) and Salmonella Derby (8%). Resistance to nalidixic acid increased from 38% in 1999 to 43% in 2002. This resistance was not homogeneous among the different serotypes, with the highest percentage of resistant isolates belonging to Salmonella Hadar (79%) followed by Salmonella Enteritidis (46%). Reduced ciprofloxacin susceptibility (minimal inhibitory concentrations [MICs] from 0.12 to 0.5 microg/mL) was observed in 300 (39%) Salmonella. In our study, the nalidixic acid-resistant strains had an MIC90 at least 4-fold higher than the susceptible ones for all the fluoroquinolones tested, thus showing that resistance to nalidixic acid is an indicator of low-level resistance to all fluoroquinolones.

Antimicrobial resistance in Salmonella enteritidis strains isolated from broiler carcasses, food, human and poultry-related samples

Antimicrobial resistance was investigated in 91 Salmonella enteritidis isolates from broiler carcasses, food, human and poultry-related samples originated from South of Brazil. A great proportion of resistant strains was found, 90.1% showing resistance to at least one antimicrobial drug. There was a high resistance to sulfonamides (75.8%) and nitrofurantoin (52.8%). Lower levels of resistance were found for tetracycline (15.4%), streptomycin (7.7%), nalidixic acid (7.7%), gentamicin (5.5%), norfloxacin (3.3%), trimethoprim (3.3%), cefalotin (2.2%), ampicillin (1.1%), and chloramphenicol (1.1%). Resistance to ciprofloxacin was not detected. A total of 51.6% of S. enteritidis strains were multiresistant (resistance to two or more antimicrobial agents) and 18 resistance patterns were found. The highest resistance was found in strains isolated from poultry-related samples, where all strains were resistant to at least one antimicrobial agent. No predominant resistance pattern was related to phage type in our isolates. The high number of antimicrobial resistant S. enteritidis found in Southern Brazil indicates the need for the prudent drugs uses to diminish the development and spread of antimicrobial resistance.

Increasing prevalence of quinolone resistance in human nontyphoid Salmonella enterica isolates obtained in Spain from 1981 to 2003

From January 1981 to December 2003, susceptibility to nalidixic acid was tested in 10,504 nontyphoid Salmonella enterica isolates from patients with acute enteric disease in Gipuzkoa, Spain. The prevalence of nalidixic acid resistance steadily increased from less than 0.5% before 1991 to 38.5% in 2003, mainly due to the increase in resistance among isolates of the most prevalent serovar, S. enterica serovar Enteritidis. For nalidixic acid-resistant isolates, the ciprofloxacin MIC was eightfold higher than that for susceptible isolates, and the nalidixic acid-resistant isolates contained a single point mutation in the gyrA gene (at codons for Ser83 or Asp87). The same mutations were found in a sample of nalidixic acid-resistant nontyphoid Salmonella strains isolated between 1999 and 2003 from retail food for human consumption. In 2003, we identified five S. enterica serovar Typhimurium clinical isolates with high-level fluoroquinolone resistance (ciprofloxacin MIC, 16 microg/ml) with two point mutations in the gyrA gene (coding for Ser83-->Phe and Asp87-->Asn) and one point mutation in the parC gene (coding for Ser80-->Arg). Strict sanitary controls are needed to avoid the spread of ciprofloxacin-resistant serovar Typhimurium isolates, and a more efficient veterinary policy must be adopted to decrease the large burden of Salmonella serovar Enteritidis infections in humans in our region.

Mutations in the gyrA gene in Salmonella enterica clinical isolates with decreased ciprofloxacin susceptibility

The incidence of resistance to nalidixic acid has increased in the University General Hospital of Elche, Spain, and this paper describes the investigation of this phenomenon. This increase was mainly due to an increase of nalidixic-resistant Salmonella enterica serotype Enteritidis. Resistance to nalidixic acid is an indicator of decreased ciprofloxacin susceptibility (sensitivity 100%, specificity 96.7%). Strains that were resistant to nalidixic acid and exhibited decreased susceptibility to ciprofloxacin had a single mutation in QRDR of gyrA: Asp87-Asn, Asp87-Tyr or Ser83-Phe. The sensitivity of S. enterica strains to nalidixic acid should be tested and the breakpoint of ciprofloxacin established by MENSURA applied, instead of that of the NCCLS for these strains.

Mutant prevention concentrations of ciprofloxacin and enrofloxacin for Salmonella enterica

OBJECTIVES

To determine the mutant prevention concentrations (MPCs) of ciprofloxacin and enrofloxacin against four strains of Salmonella enterica serovar Enteritidis and four strains of S. Typhimurium including one fully susceptible, one multiply resistant (MAR), one GyrA mutant and one GyrA/MAR mutant. Further, to examine mutants arising after exposure to sub-MPC concentrations of the antibiotics for susceptibility to ciprofloxacin and enrofloxacin, and cyclohexane tolerance.

METHODS

MICs were determined using the agar dilution method of the BSAC. The MPC was recorded as the lowest concentration of antibiotic to inhibit growth from an inoculum of 10(10) cfu.

RESULTS

The MPCs and resulting MPC/MIC ratios of enrofloxacin were generally two- to four-fold higher than for ciprofloxacin. At 24 h for both antibiotics, MPCs were lowest for the fully susceptible strains (0.25-0.5 mg/L), similar for the MAR (1-4 mg/L) and GyrA (2-4 mg/L) mutants and highest for the GyrA/MAR mutants (1-8 mg/L). MPC/MIC ratios at 24 h were 2-16 for all strains except those for the MAR strains without mutation in gyrA where the ratios were 8-64.

CONCLUSIONS

The ability to eradicate Salmonella in vivo depends on many factors such as antibiotic susceptibility of the strain, dose and route of administration. It is suggested that these MPC values will be useful when considering dosing strategies. In view of the high MPC/MIC ratio, MAR strains with wild-type gyrA, although susceptible to ciprofloxacin (MICs 0.06-0.13 mg/L), may give rise to treatment failures.

Emerging nalidixic acid and ciprofloxacin resistance in non-typhoidal Salmonella isolated from patients having acute diarrhoeal disease

BACKGROUND

Non-typhoidal Salmonella are one of the key etiological agents of diarrhoeal disease. The appearance of multiple drug resistance along with resistance to quinolones in this bacterium poses a serious therapeutic problem. We determined the prevalence of nalidixic acid and ciprofloxacin resistance in non-typhoidal Salmonella isolated from faecal samples of patients with acute diarrhoeal disease attending the outpatient and inpatient department of a hospital in Saudi Arabia during the years 1999 to 2002.

METHODS

Non-typhoidal Salmonella were isolated from faecal samples. Antimicrobial susceptibility was tested by the disc diffusion test. MICs to nalidixic acid and ciprofloxacin were determined by the agar dilution method.

RESULTS

During the study period, 524 strains of non-typhoidal Salmonella were isolated. Strains belonging to serogroup C1 were the commonest (41.4%) followed by serogroups B and D (15.6% and 14.5%, respectively). Resistance to ampicillin was observed in 22.9% and to trimethoprim/sulfamethoxazole in 18.5% of the strains. Nalidixic acid resistance was encountered in 9.9% and ciprofloxacin resistance in 2.3% of the strains. Resistance to nalidixic acid significantly increased from 0.1% in 1999 to 5.5% in 2002 (P=0.0007) and ciprofloxacin resistance increased significantly from 0.1% in 1999 to 0.9% in 2002 (P=0.0001). MICs to nalidixic acid and ciprofloxacin were determined among 29 nalidixic acid-resistant strains of non-typhoidal Salmonella isolated during 2002. The MIC was >256 microg/mL to nalidixic acid and 8 to 16 microg/mL to ciprofloxacin.

CONCLUSION

The increasing rates of antimicrobial resistance encountered among non-typhoidal Salmonella necessitate the judicious use of these drugs in humans. Moreover, these findings support the concern that the use of quinolones in animal feed may lead to an increase in resistance and should be restricted.

Emerging nalidixic acid and ciprofloxacin resistance in non-typhoidal Salmonella isolated from patients having acute diarrhoeal disease

BACKGROUND

Non-typhoidal Salmonella are one of the key etiological agents of diarrhoeal disease. The appearance of multiple drug resistance along with resistance to quinolones in this bacterium poses a serious therapeutic problem. We determined the prevalence of nalidixic acid and ciprofloxacin resistance in non-typhoidal Salmonella isolated from faecal samples of patients with acute diarrhoeal disease attending the outpatient and inpatient departments of a hospital in Saudi Arabia during the years 1999 to 2002.

METHODS

Non-typhoidal Salmonella were isolated from faecal samples. Antimicrobial susceptibility was tested by the disc diffusion test. MICs to nalidixic acid and ciprofloxacin were determined by the agar dilution method.

RESULTS

During the study period, 524 strains of non-typhoidal Salmonella were isolated. Strains belonging to serogroup C1 were the commonest (41.4%) followed by serogroups B and D (15.6% and 14.5%, respectively). Resistance to ampicillin was observed in 22.9% and to trimethoprim/sulfamethoxazole in 18.5% of the strains. Nalidixic acid resistance was encountered in 9.9% and ciprofloxacin resistance in 2.3% of the strains. Resistance to nalidixic acid significantly increased from 0.1% in 1999 to 5.5% in 2002 (P=0.0007) and ciprofloxacin resistance increased significantly from 0.1% in 1999 to 0.9% in 2002 (P=0.0001). MICs to nalidixic acid and ciprofloxacin were determined among 29 nalidixic acid-resistant strains of non-typhoidal Salmonella isolated during 2002. The MIC was >256 microg/mL to nalidixic acid and 8 to 16 microg/mL to ciprofloxacin.

CONCLUSION

The increasing rates of antimicrobial resistance encountered among non-typhoidal Salmonella necessitate the judicious use of these drugs in humans. Moreover, these findings support the concern that the use of quinolones in animal feed may lead to an increase in resistance and should be restricted.

Ciprofloxacin-resistant Salmonella enterica Typhimurium and Choleraesuis from pigs to humans, Taiwan

We evaluated the disk susceptibility data of 671 nontyphoid Salmonella isolates collected from different parts of Taiwan from March 2001 to August 2001 and 1,261 nontyphoid Salmonella isolates from the National Taiwan University Hospital from 1996 to 2001. Overall, ciprofloxacin resistance was found in 2.7% (18/671) of all nontyphoid Salmonella isolates, in 1.4% (5/347) of Salmonella enterica serotype Typhimurium and in 7.5% (8/107) in S. enterica serotype Choleraesuis nationwide. MICs of six newer fluoroquinolones were determined for the following isolates: 37 isolates of ciprofloxacin-resistant (human) S. Typhimurium (N = 26) and Choleraesuis (N = 11), 10 isolates of ciprofloxacin-susceptible (MIC <1 mg/mL) (human) isolates of these two serotypes, and 15 swine isolates from S. Choleraesuis (N = 13) and Typhmurium (N = 2) with reduced susceptibility to ciprofloxacin (MIC >0.12 microg/mL). Sequence analysis of the gryA, gyrB, parC, parE, and acrR genes, ciprofloxacin accumulation, and genotypes generated by pulsed-field gel electrophoresis with three restriction enzymes (SpeI, XbaI, and BlnI) were performed. All 26 S. Typhimurium isolates from humans and pigs belonged to genotype I. For S. Choleraesuis isolates, 91% (10/11) of human isolates and 54% (7/13) of swine isolates belonged to genotype B. These two genotypes isolates from humans all exhibited a high-level of resistance to ciprofloxacin (MIC 16-64 mg/mL). They had two-base substitutions in the gyrA gene at codons 83 (Ser83Phe) and 87 (Asp87Gly or Asp87Asn) and in the parC gene at codon 80 (Ser80Arg, Ser80Ile, or Ser84Lys). Our investigation documented that not only did these two S. enterica isolates have a high prevalence of ciprofloxacin resistance nationwide but also that some closely related ciprofloxacin-resistant strains are disseminated from pigs to humans.

Fluoroquinolones in paediatrics: a risk for the patient or for the community?

Fluoroquinolones are an important group of antibiotics widely used in adult patients because of their excellent tissue penetration and their bactericidal activity. They are not authorised for paediatric use (except the limited indication of pseudomonas infections in cystic fibrosis), however, because of the potential for joint toxicity reported from experiments with young animals. Despite the absence of official approval, fluoroquinolones are widely used in paediatrics as second-line antibiotics when all other treatments have failed. Most of the information available about paediatric use concerns ciprofloxacin, which is used in children much more often than the other members of this class. The published paediatric series have shown that frequency of articular side-effects varies according to age: all the surveys have reported frequencies of around 0.1% in adults and 2-3% in children. Outside of cystic fibrosis and severe infections in which no other treatment is possible, the only paediatric situations where fluoroquinolones are superior to standard treatments for children, in speed of recovery and comfort as well as in efficacy, are typhoid fever, severe shigella dysenteries, and enterobacteria meningitis. Should the use of new fluoroquinolones active against pneumococci be authorised for upper respiratory infections (including recurrent otitis) in children, the potential emergence and dissemination of pneumococci strains in which multidrug resistance includes fluoroquinolones would create a real risk in the community. It is, therefore, important to continue the policy of second-line use in children, only after failure of an earlier treatment, and when other antibiotics approved for paediatric use cannot be used.

Incidence of Salmonella from poultry products and their susceptibility to antimicrobial agents

The incidence of Salmonella in 60 samples of poultry products of national origin available for consumers obtained from two local butcher shops and one canteen of the city of Porto and the susceptibility to antimicrobial agents allowed for human or animal therapy were evaluated. The results show that poultry samples are frequently contaminated with Salmonella (60%), belonging to 10 different serotypes. Salmonella enteritidis and S. hadar were the most prevalent serotypes. In addition, a high number (75%) of the Salmonella isolates was resistant to one or more antimicrobial agents and eight different resistance profiles were recorded. Resistance to nalidixic acid and enrofloxacin was demonstrated for 50% of the isolates and the occurrence of resistant and multiresistant S. enteritidis isolates were less frequent than for S. hadar. This study suggests a high incidence of Salmonella on Portuguese poultry products and shows that they could be a potential vehicle of resistant Salmonella foodborne infections.

Life-threatening infantile diarrhea from fluoroquinolone-resistant Salmonella enterica typhimurium with mutations in both gyrA and parC

Salmonella Typhimurium DT12, isolated from a 35-day-old infant with diarrhea, was highly resistant to ampicillin, tetracycline, chloramphenicol, streptomycin, gentamycin, sulfamethoxazole/trimethoprim, nalidixic acid, and fluoroquinolones. The patient responded to antibiotic therapy with fosfomycin. Multidrug-resistance may become prevalent in Salmonella infections in Japan, as shown in this first case of a patient infected with fluoroquinolone-resistant Salmonella.

Multiresistant clones of Salmonella enterica: The importance of dissemination

Increasing anitmicrobial resistance among foodborne pathogens has prompted calls for the reduction of anitmicrobial use in livestock to prevent future emergence or resistance. In the case of Salmonella enterica, clonal dissemination may play a more critical role in regional changes in antimicrobial resistance in Salmonellae than antimicrobial selection pressure. Multi-resistant Salmonella Typhimurium definitive type 104 (mr-DT104) emerged from an unknown location and was disseminated globally during the 1980s and 1990s. Other clones of Salmonella Typhimurium and non-Typhimurium Salmonellae have demonstrated an ability to disseminate widely. The clonal epidemiology of mr-DT104 is in contrast with that of Campylobacter jejuni, in which antimicrobial resistance is polyclonal and seems to develop in response to local antimicrobial pressures. The epidemiology of mr-DT104 is more similar to that of methicillin resistant Staphylococcus aureus, which is also characterized by international transmission of a few clonal subtypes. Control measures for multiresistant disseminated clones of Salmonellae must focus on the interruption of dissemination in order to be effective.

Subtyping of Salmonella typhimurium by pulsed-field gel electrophoresis and comparisons with phage types and resistance types

One-hundred and sixty-eight Salmonella enterica subsp. enterica serotype Typhimurium isolates have been analysed by phage typing, by pulsed-field gel electrophoresis and for their antimicrobial susceptibility. Those independent strains, isolated from food animal production including cattle, poultry and pig sectors have been collected by the French non human Salmonella network, during the first semester in 1999. Isolates encompassed 14 phage types. The majority of S. Typhimurium isolates was found to be definitive phage type DT104, representing 39% of all isolates. Other phage types were mainly DT8, PT U302, DT120, DT193 and DT135. Forty-six pulsotypes were obtained using Xbal restriction enzyme, and amongst them, ten were associated to the DT104 phage type. A major pulsotype (px1), was represented by 79% of DT104 isolates and was also found among DT120. Forty-eight percent of isolates showed a classic DT104 resistance profile to ampicillin, streptomycin, chloramphenicol, tetracycline, sulfonamides (ASCTSu). Among this resistance type, 84% were DT104 and 12% were DT120. Some pulsotypes were found associated to this resistant type. The pulsed field gel electrophoresis showed to be a useful typing method for discrimination of S. Typhimurium strains and for tracing clone through different sectors of origin in order to control their spread.

Fluoroquinolones in paediatrics

The fluoroquinolones are an important group of antibiotics, which are widely used in adult patients because of their high penetration in tissues and bactericidal activity. However, they are not licensed for paediatric use (except the limited indication of Pseudomonas infection in cystic fibrosis) because of their potential to cause joint toxicity (observed in experiments using juvenile animal models). In recent years, there has been a change in the susceptibility of pathogens to widely used antibiotics; however, many of these pathogens remain sensitive to the fluoroquinolones (agents which can often be administered orally to treat severe infections). Fluoroquinolones have a number of potential indications in children: cystic fibrosis, intestinal infections due to resistant strains of Salmonella spp. and Shigella spp., severe infections due to Enterobacteriaceae (including the neonatal period), complicated urinary tract infections, the immunocompromised host, and some mycobacterial infections. The third generation fluoroquinolones have improved activity against Gram-positive bacteria and could be useful in respiratory tract, and ear, nose and throat infections in adult patients. Their potential role in routine use for paediatric patients will remain limited because of potential joint complications and the availability of other treatment options. However, available clinical data does indicate that the incidence of arthrotoxicity in children treated with ciprofloxacin appears to be the same as that in adult patients. The use of other fluoroquinolones is too rare to obtain meaningful information on their toxicity in children. For future fluoroquinolones, pneumococcal meningitis will probably be a potential indication. Despite their important activity, fluoroquinolones remain a second-line treatment in children, for use following the failure of a well established antibiotic treatment, to avoid potential adverse effects and the emergence of resistant strains.

Epidemiological analysis of Salmonella enterica serotype typhimurium from Hong Kong by ribotyping and pulsed-field gel electrophoresis

We investigated the antimicrobial susceptibilities and molecular epidemiology of 200 strains of Salmonella enterica serotype typhimurium isolated from 1989 to 1996 in Hong Kong. Only 22% of strains were susceptible to all 19 antibiotics tested but all were susceptible to second- and third-generation cephalosporins. Up to 9% of strains were resistant to 0.12 mg/l concentrations of ciprofloxacin or ofloxacin but none were resistant to 1 or 2 mg/l concentrations of these 2 drugs, respectively. The isolates were grouped into 15 types by ribotyping with restriction endonuclease EcoRI and into 53 types by pulsed-field gel electrophoresis of XbaI-restricted DNA fragments. When DNA fragments of the ribotypes and pulsotypes were pooled and analyzed 87 types resulted, 76 (87%) of which were of > 90% similarity and were grouped into 15 clusters. About 60% of the isolates belonged to 3 clusters, which probably represented 3 clones endemic in the community. The rest of the isolates were of a large variety of types or clusters. For epidemiological purposes analysis of pooled results from different molecular techniques would be more discriminative than results from individual techniques alone.

Antibiotic resistance in Salmonella enterica subsp. enterica strains isolated in Poland from 1998 to 1999

A total of 326 Salmonella enterica subsp. enterica strains representing 29 serotypes, isolated from human stool specimens during 1998-1999 in sanitary-epidemiological units in Poland were tested for antibiotic susceptibility by a standard disk diffusion method. The antibiotics used were ampicillin, cefotaxime, chloramphenicol, tetracycline, streptomycin, gentamicin, kanamycin, nalidixic acid, ciprofloxacin, furazolidone, cotrimoxazole, sulphonamides and trimethoprim. In addition, 201 strains belonging to the five most commonly isolated serotypes (S. Enteritidis, S. Typhimurium, S. Hadar, S. Infantis and S. Virchow) also had minimal inhibitory concentrations (MICs) determined for amoxycillin/clavulanic acid. Selected strains were screened for production of extended spectrum beta-lactamases (ESBLs). There were 49.4% of Salmonella enterica subsp. enterica strains resistant to two or more antibiotics, with the highest prevalence of multiple resistant strains among serotypes Typhimurium, Hadar and Virchow. Resistance to ampicillin, streptomycin, tetracycline, nalidixic acid, furazolidone and sulphonamides occurred most frequently. Over 93% of S. Virchow strains were resistant to furazolidone. No strains resistant to ciprofloxacin by disk-diffusion method were detected but 31.3% of isolates of the 201 strains representing the five most common serotypes had reduced ciprofloxacin susceptibility (MICs ranging 0.125-0.5 mg/l). One strain (S. Mbandaka) was resistant to cefotaxime and produced ESBL.

Antimicrobial susceptibility of nontyphoidal Salmonella isolated from humans in Belgium

Human nontyphoidal Salmonella infections are the primary cause of foodborne disease in developed countries, resulting in considerable morbidity and occasionally death, especially in immunocompromised patients. Strains of Salmonella that are resistant to antimicrobial agents have become a world-wide health problem. Fluoroquinolones are drugs of choice for treatment of human invasive salmonellosis, and have been useful for the treatment of infections caused by multi-resistant strains. However, strains resistant to ciprofloxacin have been noted. A random sample of 378 Salmonella strains of human origin was collected during 1998. Their susceptibility to 11 antimicrobial agents was determined by the agar dilution method according to NCCLS standards. In total, 38 serotypes were represented of which S. Enteritidis (20.4%), S. Typhimurium (20.4%), S. Hadar (9.0%), S. Brandenburg (7.9%), S. Infantis (7.7%), and S. Virchow (5.3%) were the most common. All strains were susceptible to ceftriaxone and ciprofloxacin. For nalidixic acid the rate of resistance was 19.0%. Of the 72 strains resistant to nalidixic acid, 31 were S. Hadar, and thus 91.2% (31/34) of the S. Hadar isolates showed resistance to nalidixic acid. Most of the S. Hadar strains were also resistant to ampicillin, tetracycline and sulphamethoxazole, and an elevated MIC50 (0.25 microgram/ml) and MIC90 (1 microgram/ml) was observed for ciprofloxacin. The high rate of resistance to nalidixic acid can be a first step towards the development of resistance to ciprofloxacin.

Genotypic analysis of Escherichia coli strains from poultry carcasses and their susceptibilities to antimicrobial agents

Plasmid profiling and amplified fragment length polymorphism (AFLP) analysis were used to genotype 50 Escherichia coli strains from poultry carcasses. Thirty different plasmid profiles were evident, and clustering of the AFLP data showed that they were a distinctly heterogeneous group of strains. Susceptibility testing against five antimicrobial agents used in the South African poultry industry showed all strains to be susceptible to danofloxacin and colistin, while the majority (96%) were resistant to two tetracyclines.

Reduced fluoroquinolone susceptibility in Salmonella enterica serotypes in travelers returning from Southeast Asia

During 1995 to 1999, we collected 1,210 Salmonella isolates; 629 were from Finnish travelers returning from abroad. These isolates were tested for susceptibility by determining MICs to ciprofloxacin, nalidixic acid, and seven additional antimicrobial agents. From 1995 to 1999, the annual proportion of reduced ciprofloxacin susceptibility (MIC > 0.125 microg/mL) among all travelers' isolates increased from 3.9% to 23.5% (p<0.001). The increasing trend was outstanding among the isolates from Southeast Asia; isolates from Thailand alone increased from 5.6% to 50.0% (p<0.001). The reduced fluoroquinolone susceptibility was nonclonal in character and significantly associated with multidrug resistance. A point mutation in the quinolone resistance-determining region of gyrA was present in all isolates with reduced susceptibility. These data provide further evidence for the rapid spread of multidrug-resistant pathogens from one continent to another.

A between-species comparison of antimicrobial resistance in enterobacteria in fecal flora

Enterobacteria in fecal flora are often reported to be highly resistant. Escherichia coli is the main species; resistance data on other species are rare. To assess the effect of the host's environment, antimicrobial resistance was determined in fecal species of the family Enterobacteriaceae from three populations: healthy people (HP)(n = 125) with no exposure to antimicrobials for 3 months preceding sampling, university hospital patients (UP) (n = 159) from wards where the antibiotic use was 112 defined daily doses (DDD)/bed/month, and geriatric long-term patients (LTP) (n = 74) who used 1.8 DDD/bed/month. The mean length of hospital stay was 5 days for the UP and 22 months for the LTP. The isolates were identified to at least genus level, and MICs of 16 antimicrobials were determined. From the university hospital, resistance data on clinical Enterobacteriaceae isolates were also collected. Resistance data for on average two different isolates per sample (range, 1 to 5) were analyzed: 471 E. coli isolates and 261 other Enterobacteriaceae spp. Resistance was mainly found among E. coli; even in HP, 18% of E. coli isolates were resistant to two or more antimicrobial groups, with MIC patterns indicative of transferable resistance. Other fecal enterobacteria were generally susceptible, with little typically transferable multiresistance. Clinical Klebsiella and Enterobacter isolates were significantly more resistant than fecal isolates. The resistance patterns at both hospitals mirrored the patterns of antibiotic use, but LTP E. coli isolates were significantly more resistant than those from UP. Conditions permitting an efficient spread may have been more important in sustaining high resistance levels in the LTP. E. coli was the main carrier of antimicrobial resistance in fecal flora; resistance in other species was rare in the absence of antimicrobial selection.

Detection of decreased fluoroquinolone susceptibility in Salmonellas and validation of nalidixic acid screening test

We evaluated 1,010 Salmonella isolates classified as fluoroquinolone susceptible according to the National Committee for Clinical Laboratory Standards guidelines for susceptibility to nalidixic acid and three fluoroquinolones. These isolates were divided into two distinct subpopulations, with the great majority (n = 960) being fully ciprofloxacin susceptible and a minority (n = 50) exhibiting reduced ciprofloxacin susceptibility (MICs ranging between 0.125 and 0.5 microg/ml). The less ciprofloxacin-susceptible isolates were uniformly resistant to nalidixic acid, while only 12 (1.3%) of the fully susceptible isolates were nalidixic acid resistant. A similar association was observed between resistance to nalidixic acid and decreased susceptibility to ofloxacin or norfloxacin. A mutation of the gyrA gene could be demonstrated in all isolates for which the ciprofloxacin MICs were >/= 0.125 microg/ml and in 94% of the nalidixic acid-resistant isolates but in none of the nalidixic acid-susceptible isolates analyzed. Identification of nalidixic acid resistance by the disk diffusion method provided a sensitivity of 100% and a specificity of 87.3% as tools to screen for isolates for which the MICs of ciprofloxacin were >/= 0.125 microg/ml. We regard it as important that microbiology laboratories endeavor to recognize these less susceptible Salmonella strains, in order to reveal their clinical importance and to survey their epidemic spread.