The successful treatment of multiresistant nonenteric salmonellosis with seven day oral ciprofloxacin

Salmonella gallinarum gyrA mutations associated with fluoroquinolone resistance

Salmonella enterica subsp. enterica serovar Gallinarum (S. gallinarum) is the causative organism of fowl typhoid, and an outbreak of fowl typhoid in Korea was confirmed in 1992. The aim of this study was to investigate possible changes in fluoroquinolone susceptibility among S. gallinarum isolates from 1995 to 2001, and to analyse mutations of the gyrA gene in fluoroquinolone-resistant isolates. Among 258 S. gallinarum isolates tested by the disk diffusion method, isolates from 1995 (n=18) were susceptible to all fluoroquinolones tested, whereas a number of isolates from 2001 (n=46) showed reduced susceptibility to enrofloxacin (6.5%), ciprofloxacin (10.9%), norfloxacin (52.5%) and ofloxacin (82.6%). The minimum inhibitory concentration range of enrofloxacin, ciprofloxacin, norfloxacin, ofloxacin and danofloxacin increased from < or =0.06 approximately 0.25 microg/ml in 1995 to 2 approximately 8 microg/ml in 2001. When amino acid changes in the gyrA were analysed by DNA sequencing, 22.5% and 14.7% among 258 isolates had a mutation at the Ser-83 and Asp-87 codons, respectively, and the prevalence of these mutants increased from 5.6% in 1995 to 89.1% in 2001. These mutants contained a change from Ser to Phe or Tyr at codon 83, or a change from Asp to Gly, Tyr or Asn at codon 87, and showed a range of minimum inhibitory concentrations of enrofloxacin from 0.5 to 8 microg/ml, ciprofloxacin from 0.25 to 4 microg/ml, norfloxacin from 2 to 32 microg/ml, ofloxacin from 0.5 to 4 microg/ml, and danofloxacin from 0.5 to 4 microg/ml. These results suggested an important association between the gyrA mutations and fluoroquinolone resistance of S. gallinarum.

The mechanism of ciprofloxacin resistance in dihydrogen peroxide-induced mutants of Salmonella enterica subsp. enterica serovar typhimurium consists mainly in mutations in gyrA gene and less in mutations affecting ciprofloxacin uptake

The effect of H(2)O(2) on the induction of ciprofloxacin (CFL) resistant mutants of Salmonella enterica subsp. enterica serovar Typhimurium was evaluated and determinants of CFL resistance in the mutants were analyzed. Factors associated with CFL resistance in H(2)O(2)-induced mutants included (i) mutations in gyrA gene, predominantly (63 %) Asp(87)-->Asn and less (37 %) Ser(83)-->Phe substitutions, (ii) mutations in the regulatory genes of MarRAB or SoxRS or in the individual structural genes of these operons. Such mutations are induced by H(2)O(2) in a much lower extent. Reduced OmpF expression simultaneously with enhanced efflux was detected only in one mutant strain and 20 % of mutant strains had increased CFL efflux from the cells.

Increasing ceftriaxone resistance in Salmonella isolates from a university hospital in Taiwan

OBJECTIVES

Salmonella infection is a distressing health problem worldwide. This study reports the changing epidemiology of Salmonella infections in Taiwan during 1999-2003, with emphasis on increasing ceftriaxone resistance.

METHODS

Records of Salmonella clinical isolates in Chang Gung Memorial Hospital during 1999-2003 were reviewed. All isolates were identified and antimicrobial susceptibility determined by standard methods. A total of 22 ceftriaxone-resistant isolates were investigated by PCR sequencing of the bla(TEM), bla(SHV), bla(CTX-M) and ampC genes. Southern-blot hybridization was used to localize the ampC gene. Infrequent-restriction-site PCR was used to genotype these isolates.

RESULTS

A total of 3635 Salmonella isolates, including 3592 (98.8%) non-typhoid Salmonella, were identified. Serogroup B (55.6%) remained the most predominant, but the prevalence has been decreasing. In contrast, serogroup D infections have increased significantly from 13.6 to 22.8%. Overall resistance to ampicillin and chloramphenicol remained high, with the highest rate (91% to both drugs) observed in Salmonella enterica serotype Choleraesuis in 2003. A sudden upsurge of ciprofloxacin resistance from zero to 69% was found in S. Choleraesuis. Ceftriaxone resistance increased in several serogroups (0.8-2.1%; average, 1.5%). The resistance was associated with plasmid-mediated bla(CMY-2) in 14 cases and extended-spectrum beta-lactamases (ESBLs), including CTX-M-3 (n=6), SHV-2a (n=1) and SHV-12 (n=1), in others. Diverse serotypes and genotypes were found among the ceftriaxone-resistant isolates.

CONCLUSIONS

Increasing ceftriaxone resistance in non-typhoid Salmonella appears to link to the spread of plasmid-mediated ampC or ESBL genes. Effective measures should be taken to prevent the problem worsening.

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.

Salmonella enterica serotype Choleraesuis: epidemiology, pathogenesis, clinical disease, and treatment

Nontyphoid Salmonella strains are important causes of reportable food-borne infection. Among more than 2,000 serotypes, Salmonella enterica serotype Choleraesuis shows the highest predilection to cause systemic infections in humans. The most feared complication of serotype Cholearesuis bacteremia in adults is the development of mycotic aneurysm, which previously was almost uniformally fatal. The advances in diagnostic techniques, surgical care, and antimicrobial therapy have greatly improved the survival of these patients. However, the recent emergence of serotype Choleraesuis that is resistant to ampicillin, chloramphenicol, trimethoprim-sulfamethoxazole, and, notably, fluoroquinolone antibiotics has aroused concern about the use of these agents for the empirical treatment of systemic infection caused by this organism. In view of the serious implications of the situation, the chain of transmission and mechanism of resistance should be carefully studied to reduce the spread of infection and threat to human health. To date, there are no vaccines available to prevent serotype Choleraesuis infections in humans. The availability, in the near future, of the genome sequence of serotype Cholearesuis will facilitate the development of effective vaccines as well as the discovery of new targets for novel antimicrobial agents.

Fluoroquinolone resistance in Salmonella serovars isolated from humans and food animals

Quinolone-resistant Salmonella enterica usually contain a mutation in gyrA within the region encoding the quinolone resistance determining region of the A subunit of DNA gyrase. These mutations confer substitutions analogous to Escherichia coli Ser83-->Phe and Asp87-->Gly or Tyr, or a novel mutation resulting in Ala119-->Glu or Val. Mutations in gyrB are rare, and no mutations in parC or parE have been described. Quinolone-resistant Salmonella can also be cross-resistant to other agents including chloramphenicol and tetracycline. Increased efflux has been demonstrated and for some strains this has been associated with increased expression of acrB. Mutation in soxR has also been shown for one isolate. Detection of low level resistance (minimum inhibitory concentrations <0.5 microg ml(-1)) to fluoroquinolones is proving an increasing problem in the treatment of invasive Salmonella infections.

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.

Comparative studies of mutations in animal isolates and experimental in vitro- and in vivo-selected mutants of Salmonella spp. suggest a counterselection of highly fluoroquinolone-resistant strains in the field

The occurrence of mutations in the genes coding for gyrase (gyrA and gyrB) and topoisomerase IV (parE and parC) of Salmonella typhimurium experimental mutants selected in vitro and in vivo and of 138 nalidixic acid-resistant Salmonella field isolates was investigated. The sequencing of the quinolone resistance-determining region of these genes in highly fluoroquinolone-resistant mutants (MICs of 4 to 16 microg/ml) revealed the presence of gyrA mutations at codons corresponding to Gly-81 or Ser-83, some of which were associated with a mutation at Asp-87. No mutations were found in the gyrB, parC, and parE genes. An assay combining allele-specific PCR and restriction fragment length polymorphism was developed to rapidly screen mutations at codons 81, 83, and 87 of gyrA. The MICs of ciprofloxacin for the field isolates reached only 2 microg/ml, versus 16 microg/ml for some in vitro-selected mutants. The field isolates, like the mutants selected in vivo, had only a single gyrA mutation at codon 83 or 87. Single gyrA mutations were also found in highly resistant in vitro-selected mutants (MIC of ciprofloxacin, 8 microg/ml), which indicates that mechanisms other than the unique modification of the intracellular targets could participate in fluoroquinolone resistance in Salmonella spp. A comparison of experimental mutants selected in vitro, field strains, and mutants selected in vivo suggests that highly fluoroquinolone-resistant strains are counterselected in field conditions in the absence of selective pressure.

Mutations in gyrA gene of quinolone-resistant Salmonella serotypes isolated from humans and animals

The quinolone resistance-determining regions (QRDRs) of the gyrA genes of quinolone-resistant clinical and veterinary salmonella isolates were sequenced. Substitutions analogous to a substitution of a Ser to a Phe at position 83 (Ser83-->Phe) and Asp87-->Gly or Tyr in Escherichia coli were found, as was a single novel mutation outside of the QRDR resulting in Ala119-->Glu. The data suggest that gyrA mutations are associated with quinolone resistance in veterinary and clinical salmonella isolates and that the limits of the QRDR may require revision.

Ciprofloxacin. A review of its pharmacological profile and therapeutic use in the elderly

Ciprofloxacin belongs to the fluoroquinolone class of antimicrobial agents which primarily inhibit bacterial DNA gyrase. It is effective after oral or intravenous administration, demonstrating potent antibacterial activity against most Gram-negative, and many Gram-positive bacteria. Although most bacterial strains have remained susceptible to the drug, low rates of resistance have been observed in some strains of Pseudomonas aeruginosa and enterococci and higher rates in methicillin-resistant Staphylococcus aureus. Ciprofloxacin attains concentrations in most tissues and body fluids sufficient to inhibit the majority of susceptible pathogens. Its pharmacokinetic profile in the elderly (> or = 65 years) is broadly similar to that reported in younger persons, although plasma concentrations are higher, and renal clearance is decreased in elderly persons. Ciprofloxacin is an effective treatment for those infections most common in elderly patients, including infections of the urinary tract, lower respiratory tract, skin and soft-tissues, and bone and joints, and is an effective agent for prophylaxis in transurethral surgery. Orally administered ciprofloxacin appeared to be at least as effective as alternative orally administered antimicrobial agents (trimethoprim, cotrimoxazole [trimethoprim/sulfamethoxazole], amoxicillin, amoxicillin/clavulanic acid) and also as effective as various parenteral agents (ceftriaxone, cefamandole, ceftazidime, cefotaxime) in a small number of comparative clinical trials. However, further studies are needed to clarify the comparative efficacy of ciprofloxacin with that of other oral and parenteral agents in the elderly. Initial trials have also indicated therapeutic efficacy of oral ciprofloxacin in malignant external otitis and bacterial prostatitis. Nevertheless, with its good tolerability profile and potent antimicrobial activity following oral administration, ciprofloxacin appears to offer a valuable alternative for treating various acute and chronic infections in elderly patients. Causative pathogens are frequently multiresistant in this patient group, and ciprofloxacin avoids or minimises the need for parenteral therapy.

Salmonella prosthetic valve endocarditis

Four cases of Salmonella prosthetic valve endocarditis have been reported previously in the English medical literature (Fraser et al. 1967; Yamamoto et al., 1974; Shanson et al., 1977; Bassa et al., 1989). This report describes a fifth case in a 62-year-old woman who developed tricuspid valve endocarditis after an episode of Salmonella gastroenteritis, and reviews prior cases of Salmonella prosthetic valve endocarditis.