Biology subjects

Kang, K. N.

Publications and source records attributed to Kang, K. N..

4 recordsLinked to original sources

bioRxiv2026

Salmonella lipopolysaccharide stimulates uptake of long-chain fatty acids in the small intestine

Enteric bacterial pathogens profoundly alter intestinal physiology during infection, yet their effects on host lipid metabolism remain poorly understood. Using mass spectrometry lipidomics, we found that infection of the mouse intestine with the bacterial pathogen Salmonella enterica serovar Typhimurium (S. Typhimurium) stimulates uptake of long-chain fatty acids by small intestinal epithelial cells. This response coincided with increased expression of epithelial genes involved in lipid uptake and transport and required the long-chain fatty acid transporter CD36. Fatty acid uptake was triggered by S. Typhimurium lipopolysaccharide (LPS) and was impaired by bacterial mutations that alter LPS acyl chains. Mechanistically, S. Typhimurium induced lipid absorption through myeloid cell Toll-like receptor 4, a receptor for LPS. Escherichia coli, a related commensal bacterium, also induced intestinal lipid absorption through LPS, although to a lesser extent than S. Typhimurium. Finally, disruption of long-chain fatty acid absorption impaired host defense during bacterial stimulation, suggesting that bacteria-induced lipid uptake contributes to protection against enteric infection. Together, these findings identify LPS from Gram-negative intestinal bacteria as a key regulator of dietary lipid uptake by the intestinal epithelium. Significance StatementThe intestinal lining absorbs nutrients while also detecting bacteria that enter with food, but how these two functions intersect during infection is poorly understood. Salmonella is a food-borne bacterial pathogen that infects humans. By studying mice, we found that Salmonella infection rapidly enhances absorption of dietary lipids by intestinal epithelial cells. This response was triggered when immune cells beneath the gut lining detected lipopolysaccharide, a molecule in the outer coat of many Gram-negative bacteria. In mice with defective lipid absorption, more Salmonella spread beyond the intestine, suggesting that lipid uptake contributes to host defense. These findings reveal a previously unappreciated link between microbial sensing, nutrient absorption, and defense against intestinal infection.

microbiology↗

bioRxiv2022

PBP1A directly interacts with the divisome complex to promote septal peptidoglycan synthesis in Acinetobacter baumannii

The class A penicillin-binding proteins (aPBPs), PBP1A and PBP1B, are major peptidoglycan synthases that synthesize more than half of the peptidoglycan per generation in Escherichia coli. Whereas aPBPs have distinct roles in peptidoglycan biosynthesis during growth (i.e., elongation and division), they are semi-redundant; disruption of either is rescued by the other to maintain envelope homeostasis and promote proper growth. Acinetobacter baumannii is a nosocomial pathogen that demonstrated a high propensity to overcome antimicrobial treatment. A. baumannii encodes both PBP1A and PBP1B (encoded by mrcA and mrcB, respectively), but only mrcA deletion decreased fitness and contributed to colistin resistance through inactivation of lipooligosaccharide biosynthesis, indicating that PBP1B was not functionally redundant with PBP1A activity. While previous studies suggested a distinct role for PBP1A in division, it was unknown if its role in septal peptidoglycan biosynthesis was direct. Here, we show that A. baumannii PBP1A has a direct role in division through interactions with divisome components. PBP1A localizes to septal sites during growth, where it interacts with the transpeptidase, PBP3, an essential division component that regulates daughter cell formation. PBP3 overexpression was sufficient to rescue the division defect in {Delta}mrcA A. baumannii; however, PBP1A overexpression was not sufficient to rescue the septal defect when PBP3 was inhibited, suggesting their activity is not redundant. Overexpression of a major DD-carboxypeptidase, PBP5, also restored the canonical A. baumannii coccobacilli morphology in {Delta}mrcA cells. Together, these data support a direct role for PBP1A in A. baumannii division and highlights its role as a septal peptidoglycan synthase. ImportancePeptidoglycan biosynthesis is a validated target of {beta}-lactam antibiotics, and it is critical that we understand essential processes in multidrug resistant pathogens such as Acinetobacter baumannii. While model systems such as Escherichia coli have shown that PBP1A is associated with side wall peptidoglycan synthesis, we show herein that A. baumannii PBP1A directly interacts with the divisome component PBP3 to promote division, suggesting a unique role for the enzyme in the highly drug resistant nosocomial pathogen. A. baumannii demonstrated unanticipated resistance and tolerance to envelope-targeting antibiotics, which may be driven by rewired peptidoglycan machinery, and may underlie therapeutic failure during antibiotic treatment.

microbiology↗

bioRxiv2021

Peptidoglycan recycling contributes to outer membrane integrity and carbapenem tolerance in Acinetobacter baumannii

The Gram-negative cell envelope is an essential structure that not only protects the cell against lysis from the internal turgor, but also forms a barrier to limit entry of antibiotics. Some of our most potent bactericidal antibiotics, the {beta}-lactams, exploit the essentiality of the cell envelope by inhibiting its biosynthesis, typically inducing lysis and rapid death. However, many Gram-negative bacteria exhibit "antibiotic tolerance", the ability to sustain viability in the presence of {beta}-lactams for extended time periods. Despite several studies showing that antibiotic tolerance contributes directly to treatment failure, and is a steppingstone in acquisition of true resistance, the molecular factors that promote intrinsic tolerance are not well-understood. Acinetobacter baumannii is a critical-threat nosocomial pathogen notorious for its ability to rapidly develop multidrug resistance. While typically reserved to combat multidrug resistant infections, carbapenem {beta}-lactam antibiotics (i.e., meropenem) are first-line prescriptions to treat A. baumannii infections. Meropenem tolerance in Gram-negative pathogens is characterized by morphologically distinct populations of spheroplasts, but the impact of spheroplast formation is not fully understood. Here, we show that susceptible A. baumannii clinical isolates demonstrate high intrinsic tolerance to meropenem, form spheroplasts with the antibiotic and revert to normal growth after antibiotic removal. Using transcriptomics and genetics screens, we characterized novel tolerance factors and found that outer membrane integrity maintenance, drug efflux and peptidoglycan homeostasis collectively contribute to meropenem tolerance in A. baumannii. Furthermore, outer membrane integrity and peptidoglycan recycling are tightly linked in their contribution to meropenem tolerance in A. baumannii. ImportanceCarbapenem treatment failure associated with "superbug" infections has rapidly increased in prevalence, highlighting an urgent need to develop new therapeutic strategies. Antibiotic tolerance can directly lead to treatment failure but has also been shown to promote acquisition of true resistance within a population. While some studies have addressed mechanisms that promote tolerance, factors that underlie Gram-negative bacterial survival during carbapenem treatment are not well-understood. Here, we characterized a role for peptidoglycan recycling in outer membrane integrity maintenance and carbapenem tolerance in A. baumannii. These studies suggest that the pathogen limits antibiotic concentrations in the periplasm and highlights physiological processes that could be targeted to improve antimicrobial treatment.

microbiology↗

bioRxiv2019

Colistin heteroresistance in Enterobacter cloacae is mediated by PmrAB-independent 4-amino-4-deoxy-l-arabinose addition to lipid A

The Enterobacter cloacae complex (ECC) consists of closely-related, but genetically distinct bacteria commonly associated with the human microbiota. ECC have been increasingly isolated from healthcare-associated infections, demonstrating that these Enterobacteriaceae are emerging nosocomial pathogens. ECC strains can rapidly acquire multidrug resistance to conventional antibiotics. Cationic antimicrobial peptides (CAMPs) have served as therapeutic alternatives because they target the highly conserved lipid A component of the Gram-negative outer membrane to lyse the bacterial cell. Many Gram-negative Enterobacteriaceae fortify their outer membrane with cationic amine-containing moieties to protect from CAMP-inflicted lysis. The PmrAB two-component system (TCS) transcriptionally activates 4-amino-4-deoxy-O_SCPCAPLC_SCPCAP-arabinose (O_SCPCAPLC_SCPCAP-Ara4N) biosynthesis to result in amine moiety addition to lipid A in many Enterobacteriaceae such as E. coli and Salmonella. In contrast, PmrAB in E. cloacae is dispensable for CAMP resistance. Instead, fitness against CAMPs presents as heteroresistance, or a subpopulation of cells that exhibit clinically significant increases in resistance levels compared to the majority population. We demonstrate that E. cloacae lipid A is modified with O_SCPCAPLC_SCPCAP-Ara4N to induce CAMP heteroresistance and that the regulatory mechanism is independent of the PmrABEcl TCS. We show that the response regulator, PhoPEcl, directly binds to the arnBEcl promoter to induce expression of O_SCPCAPLC_SCPCAP-Ara4N biosynthesis and PmrAB-independent addition to the lipid A disaccharolipid. Therefore, we have identified a mechanism of ECC colistin heteroresistance that directly involves the PhoPQ system.\n\nImportanceMembers of the Enterobacter cloacae complex (ECC) are Gram-negative nosocomial pathogens that have emerged within healthcare facilities around the world. ECC infections are associated with immunocompromised patients and infections are often life threatening. The cationic antimicrobial peptide, colistin (polymyxin E), is a last-line treatment option to combat Gram-negative multidrug resistant infections. However, many ECC intrinsically encode a colistin heteroresistance mechanism. Our analysis to characterize colistin heteroresistance in E. cloacae revealed that 4-amino-4-deoxy-O_SCPCAPLC_SCPCAP-arabinose is conjugated to the lipid A disaccharolipid to protect from colistin-mediated lysis. Additionally, this mechanism is directly regulated by the PhoPQEcl two-component system. Elucidation of outer membrane antimicrobial resistance modifications and their regulatory pathways in E. cloacae isolates will advance our understanding of CAMP heteroresistance.

microbiology↗