Quinolone resistance of Salmonella enterica serovar Virchow isolates from humans and poultry in Israel: evidence for clonal expansion

Salmonella enterica serovar Virchow is highly prevalent in humans and farm animals in Israel. In addition to high rates of resistance to multiple antibiotics, this serovar exhibits a high incidence of resistance to nalidixic acid. More than 90% of Salmonella serovar Virchow isolates of human and poultry origin obtained from 1997 to 2004 were resistant to nalidixic acid (MIC > or = 128 microg/ml), with reduced susceptibility to ciprofloxacin (MIC between 0.125 and 0.250 microg/ml). Most isolates belonged to two predominant, closely related pulsed-field gel electrophoresis image types. Investigation of the mechanisms of quinolone resistance revealed that this pathogen probably emerged from a parental clone that overproduced the AcrAB efflux pump and had a single point mutation in gyrA leading to the Asp87Tyr substitution. The close resemblance between human and poultry isolates points to poultry as a likely source of Salmonella serovar Virchow in the food chain.     

Geographically dependent distribution of gyrA gene mutations at codons 83 and 87 in Salmonella Hadar, and a novel codon 81 Gly to His mutation in Salmonella Enteritidis

In all, 90 nalidixic acid-resistant clinical strains of Salmonella Hadar and Salmonella Enteritidis isolated in Norway but of predominantly foreign origin were subjected to sequencing of the gyrA, gyrB, parC and parE genes. All the isolates contained at least one mutation in gyrA codon 83 or codon 87. A highly significant correlation between mutations in gyrA codon 83 and strains originating from Southeast Asia was found in S. Hadar but not in S. Enteritidis. A novel gyrA codon 81 Gly to His mutation was discovered in one S. Enteritidis isolate. One amino-acid (aa) changing mutation was found outside the quinolone resistance-determining region (QRDR) of S. Hadar parC at codon 57, which has previously only been observed once in Salmonellae.     

武汉社区腹泻病人粪便中致病菌的构成与耐药性研究

目的了解夏秋季武汉社区引起腹泻病原菌的流行性及耐药状况。方法收集2004年7月1日至10月31日武汉社区4所大型医院4536份门诊腹泻病人粪便标本进行鉴定及药敏试验;REP-PCR对主要致病菌进行基因分型。结果4536份粪便标本中,分离出非伤寒沙门菌64株（1.4%）,志贺菌29株（0.6%）,致病性大肠杆菌33株（0.7%）。其中主要致病菌是鼠伤寒沙门菌33株（52%）,D群志贺菌16株（55%）。挑选13种抗菌药物进行体外敏感试验,并将分离的致病菌对这13种抗生素的耐药率﹑敏感率﹑中介率进行比较,其中非伤寒沙门菌对喹诺酮类的耐药率较其他两种要高,但对第三代头孢的敏感性较强。分离的3种致病菌在第三代头孢抗生素的作用中对头孢他啶的敏感性最强。32株鼠伤寒沙门菌基因分型为9种,16株D群志贺菌基因分型为7种。结论武汉社区内感染性腹泻的致病菌主要以非伤寒沙门菌﹑致病性大肠杆菌和志贺菌为主,其中非伤寒沙门菌占了51%,基因分型提示有社区流行趋势,而且这些致病菌对肠道杆菌常用抗生素的耐药性较为严重。本次调查结果对该社区临床用药起到一定的提示作用。     

Detection of mutations in mtrR gene in quinolone resistant strains of N.gonorrhoeae isolated from India

Background and Objectives: Emergence of multi-drug resistant Neisseria gonorrhoeae resulting from new genetic mutation is a serious threat in controlling gonorrhea. This study was undertaken to identify and characterise mutations in the mtrR genes in N.gonorrhoeae isolates resistant to six different antibiotics in the quinolone group. Materials and Methods: The Minimum inhibitory concentrations (MIC) of five quinolones for 64 N.gonorrhoeae isolates isolated during Jan 2007–Jun 2009 were determined by E-test method. Mutations in MtrR loci were examined by deoxyribonucleic acid (DNA) sequencing. Results: The proportion of N.gonorrhoeae strains resistant to anti-microbials was 98.4% for norfloxacin and ofloxacin, 96.8% for enoxacin and ciprofloxacin, 95.3% for lomefloxacin. Thirty-one (48.4%) strains showed mutation (single/multiple) in mtrR gene. Ten different mutations were observed and Gly-45 → Asp, Tyr-105 → His being the most common observed mutation. Conclusion: This is the first report from India on quinolone resistance mutations in MtrRCDE efflux system in N.gonorrhoeae. In conclusion, the high level of resistance to quinolone and single or multiple mutations in mtrR gene could limit the drug choices for gonorrhoea.     

Reduced susceptibility to ciprofloxacin and gyra gene mutation in North Indian strains of Salmonella enterica serotype Typhi and serotype Paratyphi A

The emergence of reduced susceptibility to ciprofloxacin among Salmonella enterica serotype Typhi and serotype Paratyphi A leading to clinical failure of treatment poses a great therapeutic challenge. The mechanism of fluoroquinolone resistance in clinical isolates of S. Typhi and S. Paratyphi A is not very well documented. The present study was carried out with the objective of molecular characterization of reduced quinolone susceptibility amongst the strains of S. Typhi and S. Paratyphi A isolated from the patients with enteric fever during January, 2000, to April, 2003, in a North Indian hospital. A total of 422 culture-positive cases of enteric fever were reported to the hospital during the period of study, of which S. Typhi was isolated from 350 cases and S. Paratyphi A from 72 cases. The antimicrobial susceptibility of these strains was determined by disk diffusion and agar dilution method according to NCCLS guidelines, and E-test method. A total of 140 randomly selected strains, isolated during the years 1993-1999, that were available from the laboratory stocks were also studied to compare with the present strains. To study the quinolone susceptibility, the strains were divided into nalidixic acid sensitive (NAS), nalidixic acid intermediate resistant, (NAI) and nalidixic acid resistant (NAR) on the basis of susceptibility to nalidixic acid. Clinical history was available from 174 patients, of which 93 needed hospitalization due to severe disease. Of these, 82 patients were infected with NAR strains and 22 patients had a documented evidence of clinical failure to ciprofloxacin therapy. The patients infected with NAR strains were younger and had a significantly longer duration of fever (p value < 0.05) than those infected with NAS strains. It was observed that the proportion of NAR strains increased gradually over the years. These strains had a significantly higher range of MIC of ciprofloxacin (0.023-1.0 microg/ml) as compared to the NAS strains (0.002-0.125 microg/ml) (p value < 0.05). The sequencing of quinolone resistance determining region (QRDR) of the gyrA gene showed the presence of mutation at either Ser 83 or at Asp 87 in all the NAR and NAI strains. None of the NAS strains had a mutation, suggesting that the gyrA gene mutation is sufficient to confer resistance to nalidixic acid and reduced susceptibility to ciprofloxacin. This mutation, although phenotypically expressed as decreased susceptibility to ciprofloxacin, goes undetected by the disk diffusion method using the present NCCLS guidelines. Hence, it can increase morbidity and mortality due to delay in appropriate antibiotic treatment.     

Clonal emergence of extended-spectrum beta-lactamase (CTX-M-2)-producing Salmonella enterica serovar Virchow isolates with reduced susceptibilities to ciprofloxacin among poultry and humans in Belgium and France (2000 to 2003)

Antibiotic treatment is not required in cases of Salmonella enterica gastroenteritis but is essential in cases of enteric fever or invasive salmonellosis or in immunocompromised patients. Although fluoroquinolones and extended-spectrum cephalosporins are the drugs of choice to treat invasive Salmonella, resistance to these antibiotics is increasing worldwide. During the period 2000 to 2003, 90 Salmonella enterica serovar Virchow poultry and poultry product isolates and 11 serovar Virchow human isolates were found to produce an extended-spectrum beta-lactamase, CTX-M-2, concomitantly with a TEM-1 beta-lactamase. The bla(CTX-M-2) gene was located on a large conjugative plasmid (>100 kb). Pulsed-field gel electrophoresis indicated a clonal relationship between the poultry and human isolates. All these isolates displayed additional resistance to trimethoprim-sulfamethoxazole and tetracycline as well as a reduced susceptibility to ciprofloxacin (MICs of between 0.5 and 1 mug/ml). CTX-M-2-producing Salmonella with a reduced susceptibility to fluoroquinolones constitutes a major concern, since such strains could disseminate on a large scale and jeopardize classical antibiotic therapy in immunocompromised patients.     

Salmonella bloodstream infection in Ghanaian children

Objective: To examine the frequency of community-acquired salmonella bloodstream infection in Ghanaian children and the occurrence of antibiotic resistance in salmonellae.
Methods: The study comprised 472 patients with a blood culture obtained within 48 h of admission to the pediatric department of Korle Bu Teaching Hospital in Accra, Ghana, over a 3-month period. All Salmonella isolates from blood cultures were speciated and antibiotic susceptibility tests were performed. Clinical data of children with salmonella bloodstream infection were compared to those of controls. Two control groups were identified: all children enrolled in the study without salmonella bloodstream infection (group 1), and those with bloodstream infection due to other organisms (group 2).
Results: A pathogen was isolated from 111 children (23.5%), and salmonellae were among the most common isolates ( n =24; 21.6%). Among Salmonella strains, S. enteritidis ( n =14;59%) predominated over S. typhi ( n =6;25%). Resistance to several antibiotics was only found in S. enteritidis isolates ( n =8;57%). Children with salmonella bloodstream infection presented more often than controls with severe anemia, jaundice, abdominal pain and distension as well as hepatomegaly and splenomegaly. They were also hospitalized for a significantly longer period, but the case-fatality rate was similar.
Conclusions: Salmonella bloodstream infection, especially due to non-typhoidal strains, is a potential health problem for Ghanaian children and may be complicated by resistance to the commonly available antibiotics.     

Molecular analysis of ampicillin-resistant sporadic Salmonella typhi and Salmonella paratyphi B clinical isolates

Objective: To study the mechanisms of antibiotic resistance in Salmonella typhi and Salmonella paratyphi B clinical isolates, and the clonality of resistant strains.
Method: Antibiotic susceptibility was tested by disk-agar diffusion. Conjugation experiments and plasmid analysis by agarose gel electrophoresis after Eco RI digestion were followed by hybridization to a digoxigenin-labeled TEM-type β-lactamase probe. DNA fingerprints were obtained by pulsed-field gel electrophoresis of Xba I-digested chromosomal DNA.
Results: Three S. typhi isolates (7% of the isolates studied), of which one was ampicillin resistant and the other two multiresistant (ampicillin, chloramphenicol, tetracycline, sulfamethoxazole/trimethoprim and streptomycin), and two ampicillin-resistant S. paratyphi B isolates (25% of the isolates studied) were further evaluated. A 34-MDa conjugative plasmid, previously isolated from Salmonella enteritidis , conferred ampicillin resistance. A 100-MDa conjugative plasmid encoded resistance to chloramphenicol, tetracycline and sulfamethoxazole/trimethoprim, as well as ampicillin. Chromosomal fingerprinting revealed two distinct resistant strains for each serovar which were different from a matched set of sensitive S. typhi strains.
Conclusions: Two conjugative, TEM-type β-lactamase-encoding plasmids conferred ampicillin resistance to S. typhi and S. paratyphi B. The 34-MDa plasmid was identical to that previously characterized from S. enteritidis , while the 100-MDa plasmid also encoded resistance to chloramphenicol, tetracycline and sulfamethoxazole/trimethoprim. Resistant isolates did not belong to a single clone but rather represented distinct strains.     

Increasing Incidence and Comparison of Nalidixic Acid-Resistant Salmonella enterica subsp. enterica Serotype Typhimurium Isolates from Humans and Animals

We determined the resistance to quinolone of 309 Salmonella enterica subsp. enterica serotype Typhimurium strains isolated from humans and animals (cattle, pigs, or poultry) in 1995 or 1996. Nalidixic acid resistance increased from 8.5% in 1995 to 18.6% in 1996. The highest resistance levels correlated with a mutation at Ser-83 (or Asp-82). All strains remained ciprofloxacin susceptible. Human and animal isolates were compared by pulsed-field gel electrophoresis, and the banding patterns of the human isolates most closely matched those of the bovine isolates.     

Comparison of plasmid profiles, phage types, and antimicrobial resistance patterns of Salmonella enteritidis isolates in the United States.

To evaluate the laboratory techniques for subtyping isolates of Salmonella enteritidis, we compared the plasmid profiles (PP), phage types (PT), and antimicrobial susceptibility patterns (AS) of two nationally representative samples of sporadic human S. enteritidis isolates from 1979 (n = 28) and 1984 (n = 37), 43 isolates from 20 outbreaks of S. enteritidis infections between 1983 and 1987, and 46 animal isolates selected from the U.S. Department of Agriculture Veterinary Services Laboratory in 1986 and 1987. Sporadic and outbreak isolates from humans showed similar rates of resistance to at least one of a panel of antimicrobial drugs (23 and 14%, respectively), PT (91 and 98%, respectively), and PP (97 and 100%, respectively). Sixteen different PP were identified in sporadic, outbreak, and animal isolates; two PP accounted for 76% of sporadic and outbreak isolates. Sporadic human isolates were of PT 8 (42%), of PT 13a (37%), nontypeable (9%), of PT 14b (8%), of PT 9a (3%), and of PT 13 (2%). Outbreak human isolates had similar distributions of PT. PT 8 was associated with poultry: 58% (7 of 12) of the poultry isolates but only 24% (8 of 34) of the isolates from other animals were of PT 8 (P less than 0.04). Although antimicrobial susceptibility patterns do not appear as useful as an epidemiologic marker, PP and PT effectively subtyped S. enteritidis.     

Prevalence and characterization of plasmid-mediated quinolone resistance genes in Salmonella isolated from poultry in Korea

The purpose of this study was to investigate the prevalence and characteristics of plasmid-mediated quinolone resistance (PMQR) genes qnr, aac(6′)-Ib-cr, and qepA in a total of 185 non-duplicate Salmonella spp. isolated from hatcheries, poultry farms, and poultry slaughterhouses during the period 2001 to 2010 in Korea. Additionally, mutation analysis of quinolone resistance determining regions (QRDRs), conjugation experiments, and plasmid analysis were performed in the PMQR-positive isolates. Among the 185 isolates, six (3.2%) contained qnr genes (two qnrB4 and four qnrS1) but none carried the aac(6′)-Ib-cr or qepA genes. Among the six PMQR-positive isolates, one showed a single mutation (Ser83-Phe substitution) in the QRDRs of gyrA. Among them, three were non-susceptible (intermediate or resistant) to nalidixic acid (minimum inhibitory concentration [MIC] ≥256 µg/ml), ciprofloxacin (MIC 2 µg/ml), and levofloxacin (MIC 4 µg/ml), but others were susceptible to all of the three fluoroquinolones. They were resistant to six or more antimicrobial agents tested and were able to transfer quinolone resistance to recipient Escherichia coli J53 by conjugation. By performing a hybridization test, plasmids harbouring qnrB4 and qnrS1 genes were less than 8 kb and about 70 kb in size, respectively. The horizontal dissemination of qnrS1 gene was mediated by IncN plasmid. Compared with the recipient strain, MICs of the transconjugants increased two-fold to four-fold for nalidixic acid, and eight-fold to 16-fold for ciprofloxacin and levofloxacin. This report is the first to describe the detection of qnr genes in Salmonella spp. isolated from poultry in Korea. Widespread horizontal transfer of these genes among bacteria may be a serious public health concern because these can rapidly increase fluoroquinolone resistance. To ensure the public health, it is essential to continuously survey and carefully monitor the spread of PMQR genes in Salmonella from poultry.     

Molecular characterization of genes encoding the quinolone resistance determining regions of Malaysian Streptococcus pneumoniae strains

Genes encoding the quinolones resistance determining regions (QRDRs) in Streptococcus pneumoniae were detected by PCR and the sequence analysis was carried out to identify point mutations within these regions. The study was carried out to observe mutation patterns among S. pneumoniae strains in Malaysia. Antimicrobial susceptibility testing of 100 isolates was determined against various antibiotics, out of which 56 strains were categorised to have reduced susceptibility to ciprofloxacin (>or=2 microg/mL). These strains were subjected to PCR amplification for presence of the gyrA, parC , gyrB and parE genes. Eight representative strains with various susceptibilities to fluoroquinolones were sequenced. Two out of the eight isolates that were sequenced were shown to have a point mutation in the gyrA gene at position Ser81. The detection of mutation at codon Ser81 of the gyrA gene suggested the potential of developing fluoroquinolone resistance among S. pneumoniae isolates in Malaysia. However, further experimental work is required to confirm the involvement of this mutation in the development of fluoroquinolone resistance in Malaysia.     

Plasmid-mediated quinolone resistance determinant qnrS in Enterobacter cloacae

PCR was used to investigate the occurrence of the plasmid-encoded quinolone resistance determinants qnrA and qnrS among diarrhoeagenic enterobacterial isolates recovered from Hanoi, Vietnam, during the period March 2001 to April 2002. In total, 162 Escherichia coli isolates, 28 Shigella isolates and three Enterobacter cloacae isolates were negative for qnrA, while a single Ent. cloacae isolate harboured a 50-kb qnrS-positive conjugative plasmid. Cloning and sequencing identified a qnrS gene bracketed by open reading frames identical to those surrounding the qnrS gene of a Shigella flexneri isolate from Japan, thereby suggesting a common mechanism of acquisition.     

Observation of a New Pattern of Mutations in gyrA and parC within Escherichia coli Exhibiting Fluroquinolone Resistance

Therapeutic options with quinolones are severely compromised in infections caused by members of Enterobacteriaceae family. Mutations in chromosomal region are one of the major reasons for bacterial resistance towards this group of antibiotic. The aim of the study is to detect the mutations in gyrA and parC responsible for quinolone resistance among clinical isolates of Escherichia coli. A total of 96 quinolone-resistant clinical isolates of E. coli were collected from a tertiary care hospital of North-east India during March 2015 to August 2015. All the quinolone-resistant E. coli strains were investigated for mutations in the topoisomerases genes gyrA and parC by amplifying and sequencing the quinolone resistance determining regions. Among the 96 E. coli isolates, 83.3% were resistant to nalidixic acid and 80.2%, 66.6%, 23.9% and 50% to ciprofloxacin, norfloxacin, levofloxacin and ofloxacin, respectively. Several alterations were detected in gyrA and parC genes. Three new patterns of amino acid substitution are reported in E. coli isolates. The findings of this study warrant a review in quinolone-based therapy in this region of the world to stop or slow down the irrational use this drug.     

耐喹诺酮类铜绿假单胞菌的耐药机制研究

目的探讨广州地区铜绿假单胞菌对喹诺酮类药物的耐药机制。方法对喹诺酮耐药株的gyrA和parC基因进行限制性片段长度多态性分析（PCR-RFLP）,并对其中的高水平耐药株gyrB和parE基因进行测序;用琼脂稀释法测定加入碳酰氰基-对-氯苯腙（CCCP）前后环丙沙星的最小抑菌浓度（MIC）;同时用SDS-PAGE对高水平耐药株的外膜蛋白进行电泳分析。结果有72.7%（72/99）的菌株发生gyrA突变,主要为Thr-83-Ile;25.3%（25/99）的菌株发生parC突变,主要为Ser-87-Leu,且均是gyrA和parC双基因突变;gyrB和parE突变较少见。53.3%（53/99）的菌株的MIC可被CCCP逆转,其MIC能明显降低;7%（7/10）的高水平耐药株的外膜蛋白在43～67kDa间条带增多,其蛋白含量有差异。结论抗菌药物作用靶位的改变和外排泵机制是本地区铜绿假单胞菌对喹诺酮类耐药的重要机制。     

Molecular epidemiology and mutations at gyrA and parC genes of ciprofloxacin-resistant Escherichia coli isolates from a Taiwan medical center

Sixty-five ciprofloxacin-resistant clinical Escherichia coli isolates were collected from a Taiwan Medical Center from December 1998 to February 1999. All 65 clinical isolates were resistant (MICs > or = 4 microg/mL) to the following fluoroquinolones: ofloxacin, levofloxacin, sparfloxacin, and trovafloxacin. These isolates were cross-resistant to chloramphenicol (65 isolates, 100%), tetracycline (65 isolates, 100%), cefuroxime (64 isolates, 98.5%), ampicillin (57 isolates, 87.7%), gentamicin (53 isolates, 81.5%), and cephalothin (24 isolates, 36.9%). Pulsed-field gel electrophoresis (PFGE) revealed a high diversity among the genomes of these isolates and indicated that clonal spread was not responsible for the prevalence of ciprofloxacin resistance in the hospital. Sequencing of the polymerase chain reaction (PCR) amplified products of the quinolone resistance determining regions (QRDRs) of gyrA and parC showed that all isolates carrying double mutations in gyrA at codon 83 and 87 and at least one parC mutation at codon 80 and/or 84. The mutation at codon 83 of GyrA from serine to leucine (S83L) was present in all the clinical isolates. The most prevalent pattern was the S83L mutation and the mutation at codon 87 from an aspartate to an asparagine (D87N) of GyrA plus a mutation from a serine to an isoleucine (S80I) at codon 80 of ParC (63.2%). This indicated that the presence of high-level resistance to quinolones in clinical E. coli isolates were associated with mutations at hot spots, codon 83 and 87 in GyrA and followed by subsequent mutation in either codon 80 and/or 84 in ParC.     

Molecular epidemiology and antimicrobial susceptibility of Salmonella enterica serotype Stanley isolates in Taiwan.

BACKGROUND AND PURPOSE: Salmonella enterica serotype Stanley became the third most common non-typhoidal Salmonella serotype among human isolates in 2004. The present study was conducted to gain further understanding of the epidemiology and antimicrobial suseptibility of S. Stanley. METHODS: A total of 20 culture-confirmed cases were retrieved from the Center for Disease Control collection and analyzed. Clinical features and demographic data of the cases were analyzed. Laboratory investigation of the isolates included antimicrobial susceptibility testing and molecular typing by pulsed-field gel electrophoresis. Ceftriaxone-non-susceptible isolates were further examined by polymerase chain reaction, sequencing, and Southern blot hybridization. RESULTS: The cases studied were distributed widely across Taiwan, suggesting that the infection was an island-wide problem. S. Stanley predominantly caused infections in patients under the age of 5 years (75%). The most common type of illness was uncomplicated enterocolitis. Molecular typing showed 1 predominant genotype with 5 subtypes among these isolates. Antimicrobial resistance to ampicillin (75%), chloramphenicol (95%), and trimethoprim-sulfamethoxazole (95%) was common. Two isolates expressed non-susceptibility to ceftriaxone, and a bla(CMY-2) gene was identified on an 80-kb plasmid in both isolates. CONCLUSION: The increase in S. Stanley infections may be associated with the spread of an epidemic clone, although this requires further epidemiological surveillance. In view of the high rate of antimicrobial resistance, especially the emergence of resistance to third-generation cephalosporins, continued surveillance of the infections caused by this bacterium should be undertaken.     

Resistance to ciprofioxacin in non-typhoidal salmonellas from humans in England and Wales—the current situation

Objective: To report on the prevalence of isolates with ciprofloxacin resistance in non-typhoidal salmonellas from humans in England and Wales in 1997.
Methods: All non-typhoidal salmonellas referred to the Laboratory of Enteric Pathogens in 1997 were screened for resistance to ciprofloxacin at 0.125 and 1.0 mg/L and nalidixic acid at 16 mg/L, and results were compared to those for 1994. Full minimal inhibitory concentrations (MICs) of these antimicrobials were also determined for a selection of isolates resistant to ciprofloxacin at 0.125 mg/L but sensitive at 1.0 mg/L, and for all isolates resistant at 1.0 mg/L.
Results: Since 1994 there have been increases in the occurrence of resistance to ciprofloxacin (MICs: 0.25–1.0 mg/L) in Salmonella enterica serotypes Enteritidis, Typhimurium, Virchow and Hadar. Of particular importance have been increases in the occurrence of resistance in multiresistant S. Typhimurium DT 104, and also in S. virchow, a serotype with a propensity for causing extraintestinal infections in humans. High-level resistance (MIC≥2.0 mg/L) was uncommon and was identified in only a few strains, all from patients with a history of recent foreign travel.
Conclusions: There is a strong temporal association between increases in the occurrence of ciprofloxacin resistance in Salmonella serotypes Typhimurium, Virchow and Hadar from humans in England and Wales and with the licensing for use in food animals in the UK of the related fluoroquinolone antibiotic enrofloxacin; in contrast, for S. enteritidis ciprofloxacin resistance was most common in a phage type associated with foreign travel. It is hoped that recent recommendations for the use of fluoroquinolone antimicrobials in food animals in the UK will result in a reduction in the occurrence of resistance to ciprofloxacin in zoonotic salmonellas causing infections in humans.     

Phenotypic and genotypic characterization of food animal isolates of Salmonella with reduced sensitivity to ciprofloxacin

Reports of nontyphoidal Salmonella enterica subsp. enterica showing reduced sensitivity to ciprofloxacin (RSC) have increased rapidly during the past decade. Infection in humans with Salmonella possessing RSC may compromise the effectiveness of ciprofloxacin therapy. Nineteen among 4,357 Salmonella strains isolated from food animals in Canada from 1998 to 1999 showed RSC; 17 were from turkeys and 2 from chickens. All were resistant to nalidixic acid and sulfisoxazole and possessed RSC at a level of 0.125-0.5 microg/ml. PCR-RFLP of the gyrA quinolone resistance-determining region (QRDR) with Hinfl revealed that S. Bredeney and S. Heidelberg isolates possessed a mutation in this region. Single-strand conformational polymorphism (SSCP) analysis showed that S. Schwarzengrund and S. Senftenberg isolates also possessed a point mutation in the QRDR. DNA sequencing confirmed the findings and showed that all isolates possessed a base substitution in the gyrA QRDR. Sequencing revealed no mutations in the gyrB and silent wobble mutations in the parC QRDR. Reserpine, a known efflux pump inhibitor, did not effect the MICs for ciprofloxacin, nalidixic acid, and tetracycline. The mar operon could be induced in all isolates at 37 degrees C and in 18 of 19 at 30 degrees C; induction resulted in a two- to four-fold increase in the MIC of ciprofloxacin. In 14 of the 19 isolates, the mutation rate was two-fold or higher than in a ciprofloxacin sensitive S. Bredeney and S. Typhimurium LT2 control strain. Examination of clonal relatedness using pulsed-field gel electrophoresis (PFGE) and plasmid profiles indicated that some degree of clonal dispersion may have occurred, but the majority of isolates may have arisen from de novo mutations.