Description of two new isolates of Streptococcus pneumoniae in spain that are highly resistant to cefotaxime

Breakthrough in penicillin resistance? Streptococcus pneumoniae isolates with penicillin/cefotaxime MICs of 16 mg/L and their genotypic and geographical relatedness

OBJECTIVES

To phenotypically and genotypically characterize 11 strains (isolated in four different centres) exhibiting penicillin MIC of 8-32 mg/L among isolates of the SPICE project. Nine isolates were from Romania (9/162; 5.56%) and two from Poland (2/305; 0.66%).

METHODS

In vitro susceptibility was determined in triplicate by microdilution (CLSI guidelines), and additionally, MICs of penicillin, cefotaxime and amoxicillin were confirmed in triplicate by agar dilution. Multilocus sequence typing (MLST), PFGE and gene amplification and sequencing were performed.

RESULTS

For the nine Romanian isolates, MICs were >/=16 mg/L for penicillin, cefotaxime and amoxicillin, >/=32 mg/L for cefuroxime and cefpodoxime, 4-8 mg/L for cefditoren and >/=128 mg/L for erythromycin and gentamicin. All isolates were non-susceptible to imipenem (MIC = 0.5-1 mg/L) and susceptible to levofloxacin (MIC = 0.5-1 mg/L) and vancomycin (MIC = 0.25-0.5 mg/L). These Romanian strains presented a new cluster in the 595-600 region of PBP2X (YSGIQL-->LSTPWF) conferring 98% homology with Streptococcus mitis PBP2X, with a new MurM allele (seven strains) with eight amino acid changes versus R6. PBP nucleotide sequences were highly conserved suggesting a common origin. Allelic profiles of two strains gave sequence type 321, three strains exhibited a single- and four a double-locus variance. MLST-predicted serotype was 23F in all but one strain (19F), but three strains were 19A by Quellung.

CONCLUSIONS

The multidrug high resistance (precluding adequate oral therapy in children), its origin, the prevalence found in Romania and the presence of non-vaccine (7-valent) serotypes should worry the medical community because of a possible clonal diffusion that would limit therapeutic alternatives.

Evaluation of ceftriaxone, vancomycin and rifampicin alone and combined in an experimental model of meningitis caused by highly cephalosporin-resistant Streptococcus pneumoniae ATCC 51916

OBJECTIVES

The aim of the study was to assess the in vitro and in vivo efficacy of ceftriaxone, vancomycin and rifampicin alone and combined against Streptococcus pneumoniae ATCC 51916 (MIC of ceftriaxone: 32 mg/L).

METHODS

In vitro killing curves were performed with clinically achievable CSF antibiotic concentrations. In the rabbit model of pneumococcal meningitis, we studied the efficacy of and effects on inflammation of treatment with ceftriaxone 100 mg/kg/day, vancomycin 30 mg/kg/day and rifampicin 15 mg/kg/day, alone and combined, over a 26 h period.

RESULTS

Time-kill curves showed that vancomycin was bactericidal, and ceftriaxone and rifampicin produced a bacteriostatic effect. An additive effect was observed when combinations of ceftriaxone plus vancomycin were studied at subinhibitory concentrations. Emergence of resistance to rifampicin was detected both when rifampicin was studied alone and when combined with ceftriaxone or vancomycin. In the rabbit meningitis model, ceftriaxone was bacteriostatic, whereas rifampicin and vancomycin were bactericidal at 24 h. Although not synergistic, the combinations of ceftriaxone plus vancomycin or rifampicin, and vancomycin plus rifampicin, improved the efficacy of any antibiotic tested alone--all combinations were bactericidal from 6 h--and significantly decreased inflammatory parameters in CSF compared with control and ceftriaxone groups.

CONCLUSION

Ceftriaxone plus vancomycin, and vancomycin plus rifampicin appeared to be effective in the therapy of experimental pneumococcal meningitis caused by highly cephalosporin-resistant strains such as ATCC 51916. Our results provide an experimental basis for using these combinations as empirical therapy for pneumococcal meningitis, regardless of the degree of cephalosporin resistance of the causative strain.

Characterisation of invasive pneumococcal isolates in Catalan children up to 5 years of age, 1989–2000

Ninety-six Streptococcus pneumoniae strains isolated between January 1989 and December 2000 from usually sterile sites of children aged < 5 years of age were included in the study. Resistance to penicillin (38.6% intermediate, 10.4% high-level), cefotaxime (20.8%), tetracycline (41.7%), chloramphenicol (33.3%) and erythromycin (27.1%), as well as serogroup/type, were related to age and pathology. Strains from children aged < 2 years showed the highest penicillin resistance rate. Resistance to penicillin, tetracycline, chloramphenicol and erythromycin was the most common pattern (18.8% of strains). Most isolates (80.2%) belonged to serogroups/types included in the heptavalent conjugate vaccine.

A novel multiresistant Streptococcus pneumoniae serogroup 19 clone from Washington State identified by pulsed-field gel electrophoresis and restriction fragment length patterns

In 1997, a cluster of multiresistant invasive serogroup 19 pneumococcus infections, including two fatalities, was reported in Washington State. Further investigation identified other cases. Fourteen Washington Streptococcus pneumoniae isolates, four from Alaska, and eight isolates from eastern Canada with reduced penicillin susceptibility (MIC of > or =1 microg/ml) were included in the study. Pulsed-field gel electrophoresis (PFGE) with ApaI, SacII, and SmaI restriction enzymes and IS1167 and mef restriction fragment length polymorphism (RFLP) pattern analysis were performed. Twenty of the 26 isolates had identical or related PFGE patterns, with two or all three enzymes, and identical or related IS1167 RFLP patterns, indicating that they were genetically related. These 20 isolates contained the mef gene conferring erythromycin resistance and had identical mef RFLP patterns. The PFGE and RFLP patterns were distinct from those of six multiresistant clones previously described and suggest that a new multiresistant clone has appeared in Washington, Alaska, and eastern Canada. This newly characterized clone should be included in the Pneumococcal Molecular Epidemiology Network.