PCR fingerprinting analysis for differentiation of Streptococcus pneumoniae reinfection versus relapse

Recurrent pneumococcal invasive disease in the region of Madrid during a five-year period

PURPOSE

The aim of this study was to describe the clinical and microbiological characteristics of recurrent invasive pneumococcal disease (RIPD) cases identified in the Region of Madrid between January 2007 and December 2011.

METHODS

Streptococcus pneumoniae serotyping was performed by Pneumotest-Latex and Quellung reaction. Molecular typing was carried out by pulsed-field gel electrophoresis (PFGE). A relapse was defined as any case of RIPD caused by strains with similar PFGE profile. Re-infections were defined by detection of recurrent episodes caused by strains with different PFGE patterns.

RESULTS

During the study period, 2,929 S. pneumoniae strains isolated from 2,858 patients with invasive pneumococcal disease (IPD) were studied. In 61 patients (2.1 %), 132 episodes of RIPD were detected (two episodes in 52 patients, three in 8 and four in 1). Twelve patients had relapses, 47 had re-infections and two had re-infections followed by relapses. Common risk factors to developing RIPD were HIV (42.6 %) and haematological malignancies (16.4 %). The most frequent serotypes were 8 (16 episodes) and 19A (15 episodes). Fourteen strains that were resistant to levofloxacin were also resistant to erythromycin. The proportion of strains co-resistant to erythromycin and levofloxacin was significantly higher in relapses (11/29) than in re-infections (3/103).

CONCLUSIONS

The occurrence of repeated episodes of IPD in the same patient over the time is not an exceptional issue. Some underlying conditions that may favour these recurrences, mainly immunosuppression, need to be considered in patients having an episode of IPD.

Recurrence of occult pneumococcal bacteremia by an identical strain in an apparently healthy child

This is the first report to describe an apparently healthy girl, who developed recurrent occult bacteremia by the same Streptococcus pneumoniae strain, at 11 and 15 months of age. The two separately isolated organisms were demonstrated to have the identical serotype (type 6B), antibiotic susceptibility (intermediately penicillin-resistant), genotypes of penicillin-binding proteins, and patterns of pulse-field gel electrophoresis. The serum levels of anti-type 6B antibodies showed poor responses after both bacteremic episodes, but other immunological workups did not demonstrate any abnormalities. This case indicates that occult bacteremia may recur due to an identical pneumococcal strain in an immunocompetent infant, and that early introduction of pneumococcal conjugate vaccine is necessary in Japan.

Pasteurella multocida subsp. multocida and P. multocida subsp. septica differentiation by PCR fingerprinting and alpha-glucosidase activity

Pasteurella multocida is composed of three subspecies that are often differentiated by fermentation of sorbitol and dulcitol. We studied 35 dulcitol-negative P. multocida isolates from infected dog and cat bite wounds, 16 of which yielded weak and/or conflicting fermentation reactions in Andrades sorbitol, thus making it difficult to distinguish between the two dulcitol-negative subspecies of P. multocida, i.e., P. multocida subsp. multocida and P. multocida subsp. septica. All isolates and two control strains were further analyzed using a PCR fingerprinting technique with a single primer (M13 core) and assessed for alpha-glucosidase (alpha-Glu) activity. Although the PCR fingerprint patterns and alpha-Glu activity did not correlate well with the sorbitol fermentation reactions, they did correlate well with each other. All strains identified as P. multocida subsp. septica were positive for alpha-Glu activity and exhibited the group I PCR fingerprint profile. All strains categorized as P. multocida subsp. multocida displayed either the group II or group III PCR fingerprint profile; 9 of 11 of these isolates were alpha-Glu negative. These data suggest that both PCR fingerprinting and alpha-Glu activity provide reliable means for differentiating P. multocida subsp. multocida from P. multocida subsp. septica, particularly in strains that produce weak and/or discrepant sorbitol fermentation reactions.

A commented dictionary of techniques for genotyping

Several tools, differing in their technical and practical parameters, are available for the detection of point mutations as well as small deletions and insertions. In this article, a dictionary featuring over fifty methods for detection of mutation is presented. The distinguishing principle for each method is briefly explained. Sorting of and discussion on the methods give the reader a brief introduction to the field of genotyping.