Glover, M. | bioRxiv Science

bioRxiv2019

Prospective evaluation of beta-lactamase detection in penicillin susceptible Staphylococcus aureus by interpretation of the penicillin disc edge

Penicillin susceptible Staphylococcus aureus (PSSA) may occasionally be encountered as a cause of complicated S. aureus infection, such as endocarditis or bloodstream infections. Clinicians may choose to treat these patients with penicillin over a semi-synthetic penicillin derivative, such as flucloxacillin or oxacillin, due to a favourable Pk/Pd profile. In this study, we prospectively evaluated the penicillin disc (1-IU) method for detection of blaZ, with interpretation of the penicillin edge according to EUCAST recommendations. 472 PSSA isolates were collected between September 2014 to December 2015 from three clinical microbiology laboratories in Queensland, Australia. Initial antimicrobial susceptibility testing was performed by the Vitek 2 system. Real-time PCR for blaZ was performed following phenotypic testing with the 1-IU penicillin disc and the PCR used as the gold standard for detection of penicillinase. The prevalence of blaZ amongst the isolates was 7%. The sensitivity, specificity, positive predictive value and negative predictive value of the penicillin disc method was 97%, 95%, 61% and 100% when compared to blaZ PCR. In summary, the penicillin disc zone size and edge interpretation is a reliable method for detection of blaZ in S. aureus isolates that otherwise test susceptible to penicillin by Vitek 2 AST.

microbiology↗

bioRxiv2019

Trickle infection and immunity to Trichuris muris

The majority of experiments investigating the immune response to gastrointestinal helminth infection use a single bolus infection. However, in situ individuals are repeatedly infected with low doses. Therefore, to model natural infection, mice were repeatedly infected (trickle infection) with low doses of Trichuris muris. Trickle infection resulted in the slow acquisition of immunity reflected by a gradual increase in worm burden followed by a partial expulsion. Flow cytometry revealed that the CD4+ T cell response shifted from Th1 dominated to Th2 dominated, which coincided with an increase in Type 2 cytokines. The development of resistance following trickle infection was associated with increased worm expulsion effector mechanisms including goblet cell hyperplasia, Muc5ac production and increased epithelial cell turn over. Depletion of CD4+ T cells reversed resistance confirming their importance in protective immunity following trickle infection. In contrast, depletion of group 2 innate lymphoid cells did not alter protective immunity. T. muris trickle infection resulted in a dysbiotic mircrobiota which began to recover alpha diversity following the development of resistance.\n\nThese data support trickle infection as a robust and informative model for analysis of immunity to chronic intestinal helminth infection more akin to that observed under natural infection conditions and confirms the importance of CD4+ T cell adaptive immunity in host protection.\n\nAuthor SummaryInfection with parasitic worms (helminths) is a considerable cause of morbidity in humans. Understanding how we respond to infection is crucial to developing novel therapies. Laboratory models of helminth infection have been a valuable tool in understanding fundamental immune responses to infection. However, typically an individual mouse will be infected with a large, single-dose of the parasite. This is in contrast to the natural scenario in which individuals will receive frequent low level exposures. What is unknown is how repeated infection alters the development of immunity to infection. We have developed a laboratory model to tackle this question. We infected mice with the model helminth Trichuris muris on a weekly basis and assessed a range of responses in comparison with a more traditional infection system. We found striking differences in the dynamics of the infection, the host immune response, and in changes to host gut microbial populations. Our study shows how resistance to helminth infection can develop over time in response to repeat infection, and provides a model system that better reflects human immunity to this parasite.

immunology↗