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Background: Chlorhexidine bathing reduces bacterial skin colonization and prevents infections in specific patient populations. As chlorhexidine use becomes more widespread, concerns about bacterial tolerance to chlorhexidine have increased; however, testing for chlorhexidine minimum inhibitory concentrations (MICs) is challenging. We adapted a broth microdilution (BMD) method to determine whether chlorhexidine MICs changed over time among 4 important healthcare-associated pathogens. Methods: Antibiotic-resistant bacterial isolates (Staphylococcus aureus from 2005 to 2019 and Escherichia coli, Klebsiella pneumoniae, and Enterobacter cloacae complex from 2011 to 2019) were collected through Emerging Infections Program surveillance in 2 sites (Georgia and Tennessee) or through public health reporting in 1 site (Orange County, California). A convenience sample of isolates were collected from facilities with varying amounts of chlorhexidine use. We performed BMD testing using laboratory-developed panels with chlorhexidine digluconate concentrations ranging from 0.125 to 64 μg/mL. After successfully establishing reproducibility with quality control organisms, 3 laboratories performed MIC testing. For each organism, epidemiological cutoff values (ECVs) were established using ECOFFinder. Results: Among 538 isolates tested (129 S. aureus, 158 E. coli, 142 K. pneumoniae, and 109 E. cloacae complex), S. aureus, E. coli, K. pneumoniae, and E. cloacae complex ECVs were 8, 4, 64, and 64 µg/mL, respectively (Table 1). Moreover, 14 isolates had an MIC above the ECV (12 E. coli and 2 E. cloacae complex). The MIC50 of each species is reported over time (Table 2). Conclusions: Using an adapted BMD method, we found that chlorhexidine MICs did not increase over time among a limited sample of S. aureus, E. coli, K. pneumoniae, and E. cloacae complex isolates. Although these results are reassuring, continued surveillance for elevated chlorhexidine MICs in isolates from patients with well-characterized chlorhexidine exposure is needed as chlorhexidine use increases.
Differential susceptibility theory (DST) posits that individuals differ in their developmental plasticity: some children are highly responsive to both environmental adversity and support, while others are less affected. According to this theory, “plasticity” genes that confer risk for psychopathology in adverse environments may promote superior functioning in supportive environments. We tested DST using a broad measure of child genetic liability (based on birth parent psychopathology), adoptive home environmental variables (e.g., marital warmth, parenting stress, and internalizing symptoms), and measures of child externalizing problems (n = 337) and social competence (n = 330) in 54-month-old adopted children from the Early Growth and Development Study. This adoption design is useful for examining DST because children are placed at birth or shortly thereafter with nongenetically related adoptive parents, naturally disentangling heritable and postnatal environmental effects. We conducted a series of multivariable regression analyses that included Gene × Environment interaction terms and found little evidence of DST; rather, interactions varied depending on the environmental factor of interest, in both significance and shape. Our mixed findings suggest further investigation of DST is warranted before tailoring screening and intervention recommendations to children based on their genetic liability or “sensitivity.”
In the epilogue, we reflect on some of the major themes linked to the questions driving research in second language acquisition and return to the question that started the field in the 1970s: Are first and second language acquisition similar or different?
This chapter centers on the major descriptive findings of second language research, focusing on ordered and systematic development. We review and discuss such things as morpheme orders, developmental stages/sequences, unmarked before marked, U-shaped development, among others. We also review the evidence for L1 influence on ordered development. We touch on the nature of internal (e.g., Universal Grammar, general learning mechanisms) and external constraints (e.g., quantity and quality of input and interaction with that input, frequency) as underlying factors in ordered development. We also briefly discuss variability during staged development.
In this chapter we discuss the qualitative difference between explicit knowledge and implicit knowledge (underlying mental representation). The chapter focuses on whether instruction affects the latter. We review the accepted finding that instruction does not affect ordered development. We also review the issue of whether instruction affects rate of development and ultimate attainment. We look at important variables in the research on instructed acquisition, including type of knowledge measured, the nature of assessments used in the research, and short-term vs. long-term studies, among others.
In this chapter we review the competing perspectives on the starting point for second language acquisition. Do learners begin with the L1 and transfer all properties and processes into second language acquisition? Or is transfer partial and selective at the outset? Or do second language learners not transfer any aspects of the L1 and begin with universal properties of language and universal processes for acquiring language? We review such key hypotheses as Full Access and Full Transfer/Full Access, as well as important constructs such as minimal trees, input processing, and processability.
This chapter lays the foundation for how the field of second language acquisition arose. We briefly review the pioneering work in the late 1950s and 1960s in first language acquisition (e.g., Berko Gleason, Brown, Klima & Bellugi). We also review the generative revolution in linguistics and how it laid the groundwork for the idea of constrained language acquisition. We then review the seminal articles by S. Pit Corder (1967) and Larry Selinker (1972) that posited the major questions in second language acquisition, and end with the pioneering work that mirrored first language acquisition (e.g., Dulay & Burt, Krashen, Wode). We end the chapter with the major question that launched second language research in the early 1970s: Are first and second language acquisition similar or different?
This chapter defines what kind of input contains the data necessary for acquisition (communicatively embedded input) and focuses on its fundamental role in acquisition. Subsequently, we review the claims on the role of output and interaction, focusing on these major issues: comprehensible output is necessary for acquisition; comprehensible output is beneficial for acquisition; comprehensible output does little to nothing for acquisition. We also discuss the nature of interaction more generally, focusing on whether interaction affects the acquisition of formal features of language.
In this chapter we touch on the idea of inter-learner variability in outcome (i.e., how far learners get) as well as rate of acquisition among different learners. We then link these issues to the idea of individual differences as explanatory factors. We focus on the most studied: motivation, aptitude, and working memory.
This chapter covers three different ideas about nativelikeness in second language acquisition. The first is that learners can become nativelike in all domains of language and language processing. The opposite idea we will cover is that learners cannot become nativelike in any area of second language acquisition. The final idea we will treat is that learners can become nativelike in some domains of language but not others. We discuss what “nativelike” means and what kinds of measures are used to assess learner knowledge and ability. We also review key hypotheses and constructs such as The Fundamental Difference Hypothesis, The Shallow Structure Hypothesis, Full Transfer/Full Access, the critical period, and others.
In this chapter we address the question of whether or not language acquisition is largely implicit in nature. After reviewing key constructs (e.g., explicit and implicit knowledge, explicit and implicit processing/learning, intentional and unintentional learning), we discuss the major positions currently under scrutiny in the field: (1) explicit learning is necessary; (2) explicit learning is beneficial; (3) explicit learning does little to nothing (i.e., acquisition is largely if not exclusively implicit in nature). A key issue in this chapter is how one defines “language” and how one construes “input processing.” We will review how definitions of these constructs color the researcher’s perspective on the issues.