The effect of broth media on pneumococcal growth and the latex serotyping result

Validation of Fourier Transform Infrared Spectroscopy for Serotyping of Streptococcus pneumoniae

Fourier transform infrared (FT-IR) spectroscopy (IR Biotyper; Bruker) allows highly discriminatory fingerprinting of closely related bacterial strains. In this study, FT-IR spectroscopy-based capsular typing of Streptococcus pneumoniae was validated as a rapid, cost-effective, and medium-throughput alternative to the classical phenotypic techniques. A training set of 233 strains was defined, comprising 34 different serotypes and including all 24 vaccine types (VTs) and 10 non-vaccine types (NVTs). The acquired spectra were used to (i) create a dendrogram where strains clustered together according to their serotypes and (ii) train an artificial neural network (ANN) model to predict unknown pneumococcal serotypes. During validation using 153 additional strains, we reached 98.0% accuracy for determining serotypes represented in the training set. Next, the performance of the IR Biotyper was assessed using 124 strains representing 59 non-training set serotypes. In this setting, 42 of 59 serotypes (71.1%) could be accurately categorized as being non-training set serotypes. Furthermore, it was observed that comparability of spectra was affected by the source of the Columbia medium used to grow the pneumococci and that this complicated the robustness and standardization potential of FT-IR spectroscopy. A rigorous laboratory workflow in combination with specific ANN models that account for environmental noise parameters can be applied to overcome this issue in the near future. The IR Biotyper has the potential to be used as a fast, cost-effective, and accurate phenotypic serotyping tool for S. pneumoniae.

Pneumococcal disease burden, clinical presentations and vaccine coverage in the Jamaican population

BACKGROUND

Pneumococcal serotypes circulating in any population vary over time and between countries and impacts the effectiveness of pneumococcal vaccination.

OBJECTIVE

This study investigated the epidemiology of pneumococcal disease in Jamaica.

METHODS

Streptococcus pneumoniae isolates (n= 349) along with demographic and clinical information were collected from patients presenting at the 4 major hospitals in Jamaica over a 2-year period. Serotyping was done using latex agglutination tests and the Quellung reaction assay.

RESULTS

Invasive pneumococcal disease (IPD) incidence was 45.4/100,000 in children under 5 yrs and 16.3/100,000 in adults over 65 yrs. Thirteen serogroups were identified among the 120 isolates subjected to grouping; the most common being serogroups: 19 (22/120,18.3%), 6 (20/120,16.7%), 14 (20/120,16.7%), 23 (18/120,15.0%), 3 (11/120,9.2%) and nontypeable (8/120,2.3%). The estimated vaccine coverage rates for the PCV7 and PCV13 vaccines in children less than 5 yrs were 82.5% and 88.7% respectively. The 23-valent PPV23 provided 100% coverage rate in adults over 65 yrs and 82.9% coverage rate for the entire population.

CONCLUSIONS

Pneumococcal vaccine coverage rates in Jamaica are comparable to those reported in certain developed countries and higher than in other developing countries. The high incidence of IPD in the paediatric population indicates that routine vaccination would be beneficial.

In vitro growth of pneumococcal isolates representing 23 different serotypes

Background

Although there are established methodologies for pneumococcal carriage studies, recent studies have extended these by conducting a culture amplification step prior to pneumococcal identification or serotyping. However, few data are available comparing the growth of different serotypes.

Findings

We compared the growth of individual isolates representing 23 serotypes in serum broth, and Todd-Hewitt broth from four different manufacturers. Following overnight incubation of low inocula, there were differences in the final growth densities of individual isolates. These can be minimised with the use of optimal media.

Conclusions

These data caution against using broth culture amplification of nasopharyngeal samples for some applications.

Direct serogrouping of Streptococcus pneumoniae strains in clinical samples by use of a latex agglutination test

Pneumotest-Latex (Statens Seruminstitut) was evaluated for direct serogrouping of Streptococcus pneumoniae strains in clinical samples from patients with invasive disease. The technique was accurate to its level of discrimination for 62 of 67 clinical samples (92.5%). Pneumotest-Latex would be a useful alternative for direct serogrouping of pneumococci in clinical samples.

Serotype-specific invasiveness and colonization prevalence in Streptococcus pneumoniae correlate with the lag phase during in vitro growth

Serotypes of Streptococcus pneumoniae differ in colonization prevalence and the likelihood of causing disease. In vitro growth in brain heart infusion broth with or without 5% fetal calf serum (FCS) was compared for 47 clinical isolates representing 15 pneumococcal serotypes. Serotype-specific colonization prevalence and odds ratios for the invasive potential were obtained from an international and a local epidemiological study. The duration of the lag phase increased with the invasiveness and was inversely associated with the colonization prevalence of a serotype. Supplementation with FCS shortened the lag phase preferentially in serotypes associated with invasive disease (P=0.007). Reduction of oxidative stress by addition of manganese (Mn(2+)), Tiron, mannitol or catalase did not influence the duration of the lag phase significantly. Serotype specific invasiveness and colonization prevalence of S. pneumoniae are associated with the length of the lag phase during in vitro growth. This may correlate with serotype specific selection in vivo.