Prevalence of the fimbrial operon mrkABCD, mrkA expression, biofilm formation and effect of biocides on biofilm formation in carbapenemase-producing Klebsiella pneumoniae isolates belonging or not to high-risk clones

Characterization of nontyphoidal Salmonella strains from a tertiary hospital in China: serotype diversity, multidrug resistance, and genetic insights

Objective

Nontyphoidal Salmonella is a significant public health concern due to its ability to cause foodborne illnesses worldwide. This study aims to characterize the nontyphoidal Salmonella strains isolated from patients in China.

Methods

A total of 19 nontyphoidal Salmonella strains were characterized through serovar identification, antimicrobial susceptibility testing (AST), biofilm formation assessment. Genetic relatedness was determined using pulsed-field gel electrophoresis (PFGE). WGS was employed to decipher the resistance mechanism and to contextualize the S. serovar Mbandaka strains among previously sequenced isolates in China. The biofilm associated mrkA gene was examined by PCR.

Results

The predominant serovar identified was S. Enteritidis, followed by S. Mbandaka, S. Thompson, S. Livingston, S. Alachua, and S. Infantis. PFGE analysis indicated a notable genetic similarity among the S. Mbandaka isolates. Phylogenetic analysis suggested that these strains were likely derived from a single source that had persisted in China for over five years. One multidrug resistance (MDR) S. Enteritidis isolate carried a highly transferable IncB/O/K/Z plasmid with bla CTX-M-15. One S. Thompson strain, harboring the mrkABCDF operon in an IncX1 plasmid, isolated from cutaneous lesions, demonstrated robust biofilm formation. However, no mrkABCDF loci were detected in other strains.

Conclusion

Our study emphasizes the importance of persisted surveillance and prompt response to Salmonella infections to protect public health. The dissemination of bla CTX-M-15-harboring IncB/O/K/Z plasmid and the spread of virulent mrkABCDF operon among Salmonella in China and other global regions warrant close monitoring.

Regulation of biofilm formation in Klebsiella pneumoniae

Klebsiella pneumoniae is an important Gram-negative opportunistic pathogen that is responsible for a variety of nosocomial and community-acquired infections. Klebsiella pneumoniae has become a major public health issue owing to the rapid global spread of extensively-drug resistant (XDR) and hypervirulent strains. Biofilm formation is an important virulence trait of K. pneumoniae. A biofilm is an aggregate of microorganisms attached to an inert or living surface by a self-produced exo-polymeric matrix that includes proteins, polysaccharides and extracellular DNA. Bacteria within the biofilm are shielded from antibiotics treatments and host immune responses, making it more difficult to eradicate K. pneumoniae-induced infection. However, the detailed mechanisms of biofilm formation in K. pneumoniae are still not clear. Here, we review the factors involved in the biofilm formation of K. pneumoniae, which might provide new clues to address this clinical challenge.

Benzoic acid derivatives as potent antibiofilm agents against Klebsiella pneumoniae biofilm

Klebsiella pneumoniae is responsible for a significant proportion of human urinary tract infections, and its biofilm is a major virulence. One potential approach to controlling biofilm-associated infections is targeting the adhesin MrkD1P to disrupt biofilm formation. We employed Schrodinger's Maestro tool with the OPLS 2005 force field to dock compounds with the target protein. Two benzoic acid derivatives, 3-hydroxy benzoic acid and 2,5-dihydroxybenzoic acid, had strong binding free energies (-55.57 and -18.68 kcal/mol) and were the most potent compounds. The in-vitro experiments were conducted to validate the in-silico results. The results showed that both compounds effectively inhibited biofilm formation at low concentrations (4 and 8 mg/mL, respectively) and had antibiofilm activity, restricting cell attachment. Both compounds demonstrated a strong biofilm inhibitory effect, with 97% and 89% reduction in biofilm by 3-hydroxy benzoic acid and 2,5-dihydroxybenzoic acid, respectively. These findings suggest that natural compounds can be a potential source of new drugs to combat biofilm-associated infections. The study highlights the potential of targeting adhesin MrkD1P as an effective approach to controlling biofilm-associated infections caused by K. pneumoniae. The results may have implications for the development of new therapies for biofilm-associated infections and pave the way for future research in this area.

Effects of chlorogenic acid on antimicrobial, antivirulence, and anti-quorum sensing of carbapenem-resistant Klebsiella pneumoniae

The rise in infections caused by the hypervirulent carbapenem-resistant Klebsiella pneumoniae (hv-CRKP) is an emergent threat to public health. We assessed the effects of chlorogenic acid (CA), a natural phenolic compound, on antibacterial, antivirulence, and anti-quorum sensing (QS) of hv-CRKP. Five hv-CRKP were selected for antimicrobial susceptibility test and confirmed to carry virulence genes and carbapenem-resistant genes by polymerase chain reaction (PCR). Subsequently, a series of time-kill assay, determinations of protease activity and capsule content, biofilm-related experiment, scanning electron microscopy (SEM) and transmission electron microscope (TEM) observation, G. mellonella infection model, quantitative real-time PCR (qRT-PCR) of QS-related genes and biofilm formation genes, as well as AI-2 binding test were conduct to verify the effect of CA on hv-CRKP. Five CRKP strains showed varying degrees of resistance to antibacterial agents. All strains carried the bla _KPC-2 gene, primarily carrying rmpA2, iucA, and peg-344. CA showed no effect on CRKP growth at the 1/2 minimum inhibitory concentration (MIC), 1/4 MIC, and 1/8 MIC, CA could reduce the production of extracellular protease and capsular polysaccharides, and improve the survival rate of larvae in Galleria mellonella (G. mellonella) infection model. By means of crystal violet staining and scanning electron microscopy experiments, we observed that CA can inhibit the formation of CRKP biofilm. On the quantitative real-time PCR analysis, the expression of the luxS, mrkA and wbbm genes in most CRKP strains appeared downregulated because of the CA treatment. Besides, CA significantly inhibited the effect of AI-2 activity of BB170. Our study suggests that CA can be an effective antimicrobial, antivirulent compound that can target QS in hv-CRKP infections, thus providing a new therapeutic direction for treating bacterial infections.