Population structure of mixed Mycobacterium tuberculosis infection is strain genotype and culture medium dependent.
BACKGROUND
Molecular genotyping methods have shown infection with more than one Mycobacterium tuberculosis strain genotype in a single sputum culture, indicating mixed infection.


OBJECTIVE
This study aimed to develop a PCR-based genotyping tool to determine the population structure of M. tuberculosis strain genotypes in primary Mycobacterial Growth Indicator Tubes (MGIT) and Löwenstein-Jensen (LJ) cultures to identify mixed infections and to establish whether the growth media influenced the recovery of certain strain genotypes.


METHODS
A convenience sample of 206 paired MGIT and LJ M. tuberculosis cultures from pulmonary tuberculosis patients resident in Khayelitsha, South Africa were genotyped using an in-house PCR-based method to detect defined M. tuberculosis strain genotypes.


RESULTS
The sensitivity and specificity of the PCR-based method for detecting Beijing, Haarlem, S-family, and LAM genotypes was 100%, and 75% and 50% for detecting the Low Copy Clade, respectively. Thirty-one (15%) of the 206 cases showed the presence of more than one M. tuberculosis strain genotype. Strains of the Beijing and Haarlem genotypes were significantly more associated with a mixed infection (on both media) when compared to infections with a single strain (Beijing MGIT p = 0.02; LJ, p<0.01) and (Haarlem: MGIT p<0.01; LJ, p = 0.01). Strains with the Beijing genotype were less likely to be with "other genotype" strains (p<0.01) while LAM, Haarlem, S-family and LCC occurred independently with the Beijing genotype.


CONCLUSIONS
The PCR-based method was able to identify mixed infection in at least 15% of the cases. LJ media was more sensitive in detecting mixed infections than MGIT media, implying that the growth characteristics of M. tuberculosis on different media may influence our ability to detect mixed infections. The Beijing and Haarlem genotypes were more likely to occur in a mixed infection than any of the other genotypes tested suggesting pathogen-pathogen compatibility.
Division of Anatomy and Histology, Faculty of Health Sciences, Tygerberg, Stellenbosch University, Stellenbosch, Western Cape, South Africa. hanekom@sun.ac.za
Madeleine
M
Hanekom
Elizabeth M
EM
Streicher
Doreen
D
Van de Berg
Helen
H
Cox
Cheryl
C
McDermid
Marlein
M
Bosman
Nicolaas C
NC
Gey van Pittius
Tommie C
TC
Victor
Martin
M
Kidd
Dick
D
van Soolingen
Paul D
PD
van Helden
Robin M
RM
Warren
D060085:Coinfection; D003430:Cross-Sectional Studies; D003470:Culture Media; D005838:Genotype; D006801:Humans; D009169:Mycobacterium tuberculosis / Q000235:genetics* / Q000254:growth & development; D016133:Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D013183:Sputum / Q000382:microbiology; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis / Q000382:microbiology*
D003470:Culture Media