TY - JOUR
T1 - A comprehensive comparison of biofilm formation and capsule production for bacterial survival on hospital surfaces
AU - Nunez, Charles
AU - Kostoulias, Xenia
AU - Peleg, Anton
AU - Short, Francesca
AU - Qu, Yue
N1 - Funding Information:
When grown as planktonic cells, both A. baumannii and K. pneumoniae WT strains demonstrated drastic decreases in CFU enumeration under environmental desiccation, with an ∼2-log reduction and ∼4-log reduction respectively after 7-day treatment (Fig. 3A and B). Qualitative SEM of post-desiccation planktonic growths (Fig. 3E) supported our CFU enumeration results, with most K. pneumoniae cells on the MCE membranes showing shriveled appearance and A. baumannii presenting cell debris. In contrast, biofilm growth of A. baumannii and K. pneumoniae conferred significant protection to bacterial cells, with no reduction of CFU enumeration even after 28-day desiccation (Fig. 3C, D and 3E).Using CLSI-recommended broth microdilution assay for planktonic cells, A. baumannii and K. pneumoniae had MICs to BAC of 32 and 64 μg/mL respectively, with no difference between WT and capsule-deficient mutant strains (Table 2). XTT assay revealed that biofilms formed by WT A. baumannii and K. pneumoniae had BAC BMIC75 of 64 μg/mL compared to 128 μg/mL for their isogenic capsule-deficient mutants (Table 2), only marginally higher than the CLSI MICs for their planktonic counterparts (≤2-fold). It was speculated that biofilm resistance to BAC might have been complicated by the intrinsic BAC resistance of A. baumannii and K. pneumoniae strains used in this study. We thus introduced other biofilm-forming bacterial species that were sensitive to BAC into this study to clarify the role of biofilm formation on BAC resistance. Biofilms formed by S. aureus ATCC 25923 and S. epidermidis had higher resistance to BAC than their planktonic counterparts, supported by high biofilm MIC75 of 64 μg/mL and 128 μg/mL respectively, relative to CLSI MIC of 4 μg/mL for planktonic cultures. Another Gram-negative bacterium P. aeruginosa PAO1 also showed at least a 4-fold increase in MICs when its growth mode changed from planktonic cells to biofilms (Table 2).Biofilm formation completely mitigated the impact of UV disinfection, as supported by negligible loss of cell viability following UV exposure. This agrees with results from another published study that was conducted for water distribution systems [42]. It is possible that the anti-UV effects of biofilms are likely lent by the thick biofilm EPS matrix, which limits UV penetration towards the embedded bacterial cells. Surprisingly, capsule production promoted the effectiveness of UV radiation against A. baumannii and K. pneumoniae, rather than protecting bacterial cells from UV-mediated damage. To the best of our knowledge, this is the first study examining the linkage between capsule production and bacterial resistance to UV radiation. The exact mechanism by which capsule promotes susceptibility to UV is currently unknown. It is speculated that the capsule absorbs more UV radicals that contributes to more UV damage of its target, the bacterial DNA [43]. The ESKAPE pathogens isolated from the hospital environment often exhibit an encapsulated phenotype and higher virulence [44,45]. Given the abundance of encapsulated bacteria in the hospital environment, the value of UV radiation in hospital disinfection may be under-estimated.The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Francesca Short reports financial support was provided by the Australian Research Council.
Publisher Copyright:
© 2023 The Authors
PY - 2023/12
Y1 - 2023/12
N2 - Biofilm formation and capsule production are known microbial strategies used by bacterial pathogens to survive adverse conditions in the hospital environment. The relative importance of these strategies individually is unexplored. This project aims to compare the contributory roles of biofilm formation and capsule production in bacterial survival on hospital surfaces. Representative strains of bacterial species often causing hospital-acquired infections were selected, including Acinetobacter baumannii, Klebsiella pneumoniae, Staphylococcus aureus, Staphylococcus epidermidis and Pseudomonas aeruginosa. The importance of biofilm formation and capsule production on bacterial survival was evaluated by comparing capsule-positive wild-type and capsule-deficient mutant strains, and biofilm and planktonic growth modes respectively, against three adverse hospital conditions, including desiccation, benzalkonium chloride disinfection and ultraviolet (UV) radiation. Bacterial survival was quantitatively assessed using colony-forming unit (CFU) enumeration and the 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) assay and qualitatively by scanning electron microscopy (SEM). Correlations between capsule production and biofilm formation were further investigated. Biofilm formation contributed significantly to bacterial survival on hospital surface simulators, mediating high resistance to desiccation, benzalkonium chloride disinfection and UV radiation. The role of capsule production was minor and species-specific; encapsulated A. baumannii but not K. pneumoniae cells demonstrated slightly increased resistance to desiccation, and neither showed enhanced resistance to benzalkonium chloride. Interestingly, capsule production sensitized K. pneumoniae and A. baumannii to UV radiation. The loss of capsule in K. pneumoniae and A. baumannii enhanced biofilm formation, possibly by increasing cell surface hydrophobicity. In summary, this study confirms the crucial role of biofilm formation in bacterial survival on hospital surfaces. Conversely, encapsulation plays a relatively minor role and may even negatively impact bacterial biofilm formation and hospital survival.
AB - Biofilm formation and capsule production are known microbial strategies used by bacterial pathogens to survive adverse conditions in the hospital environment. The relative importance of these strategies individually is unexplored. This project aims to compare the contributory roles of biofilm formation and capsule production in bacterial survival on hospital surfaces. Representative strains of bacterial species often causing hospital-acquired infections were selected, including Acinetobacter baumannii, Klebsiella pneumoniae, Staphylococcus aureus, Staphylococcus epidermidis and Pseudomonas aeruginosa. The importance of biofilm formation and capsule production on bacterial survival was evaluated by comparing capsule-positive wild-type and capsule-deficient mutant strains, and biofilm and planktonic growth modes respectively, against three adverse hospital conditions, including desiccation, benzalkonium chloride disinfection and ultraviolet (UV) radiation. Bacterial survival was quantitatively assessed using colony-forming unit (CFU) enumeration and the 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) assay and qualitatively by scanning electron microscopy (SEM). Correlations between capsule production and biofilm formation were further investigated. Biofilm formation contributed significantly to bacterial survival on hospital surface simulators, mediating high resistance to desiccation, benzalkonium chloride disinfection and UV radiation. The role of capsule production was minor and species-specific; encapsulated A. baumannii but not K. pneumoniae cells demonstrated slightly increased resistance to desiccation, and neither showed enhanced resistance to benzalkonium chloride. Interestingly, capsule production sensitized K. pneumoniae and A. baumannii to UV radiation. The loss of capsule in K. pneumoniae and A. baumannii enhanced biofilm formation, possibly by increasing cell surface hydrophobicity. In summary, this study confirms the crucial role of biofilm formation in bacterial survival on hospital surfaces. Conversely, encapsulation plays a relatively minor role and may even negatively impact bacterial biofilm formation and hospital survival.
KW - Biofilm formation
KW - Capsule
KW - Desiccation
KW - Disinfectant
KW - Encapsulation
KW - Hospital surfaces
KW - UV radiation
UR - http://www.scopus.com/inward/record.url?scp=85146868877&partnerID=8YFLogxK
U2 - 10.1016/j.bioflm.2023.100105
DO - 10.1016/j.bioflm.2023.100105
M3 - Article
C2 - 36711324
AN - SCOPUS:85146868877
SN - 2590-2075
VL - 5
JO - Biofilm
JF - Biofilm
M1 - 100105
ER -