A multiplex PCR assay was developed for the identification of major types and subtypes of staphylococcal cassette chromosome mec (SCCmec) in meticillin-resistant Staphylococcus aureus (MRSA) strains. The method uses a novel 9 valent multiplex PCR plus two primer pairs for S. aureus identification and detection of meticillin resistance. All 389 clinical MRSA isolates from Malaysia and 18 European isolates from the Harmony collection harbouring different SCCmec types that we tested were correctly characterized by our PCR assay. SCCmec type III and V were by far the most common types among both hospital- and community-acquired Malaysian MRSA isolates, with an apparent emergence of MRSA harbouring the IVh type.
A simple adherence test to detect IgM antibodies in patients with typhoid is described. The test utilises the IgM-"capture" approach, in which the test serum is applied to microtitration plate wells previously coated with anti-human IgM, followed by application of a stained Salmonella typhi antigen suspension which shows adherence in positive cases. By this test, 58 (95%) of 61 sera from confirmed cases of typhoid possessed IgM antibodies to the H or O or both antigens of S. typhi. In patients for whom a diagnosis of typhoid was based only on a significant Widal-test titre, 31 (41%) of 76 sera had IgM antibodies to the H or O or both antigens of S. typhi. Some cross-reactivity of the IgM antibodies was detected, especially with the O antigens of S. paratyphi A and B. A total of 82 sera from non-typhoidal fevers (leptospirosis, typhus, dengue fever) showed no reactivity in this test. In normal sera there was no detectable IgM to the O antigen of S. typhi and only a small number (3.9%) had low levels of IgM to the H antigen. The significance and potential importance of this simple, sensitive, specific and economical test is discussed.
In this study, we characterized 7C, a spontaneous mutant selected from tigecycline-susceptible Mycobacterium abscessus ATCC 19977. Whole-genome sequencing (WGS) was used to identify possible resistance determinants in this mutant. Compared to the wild-type, 7C demonstrated resistance to tigecycline as well as cross-resistance to imipenem, and had a slightly retarded growth rate. WGS and subsequent biological verifications showed that these phenotypes were caused by a point mutation in MAB_3542c, which encodes an RshA-like protein. In Mycobacterium tuberculosis, RshA is an anti-sigma factor that negatively regulates the heat/oxidative stress response mechanisms. The MAB_3542c mutation may represent a novel determinant of tigecycline resistance. We hypothesize that this mutation may dysregulate the stress-response pathways which have been shown to be linked to antibiotic resistance in previous studies.