Low Levels of β-Lactam Antibiotics Induce Extracellular DNA Release and Biofilm Formation in <named-content content-type="genus-species">Staphylococcus aureus</named-content>
ABSTRACT Subminimal inhibitory concentrations of antibiotics have been shown to induce bacterial biofilm formation. Few studies have investigated antibiotic-induced biofilm formation in Staphylococcus aureus, an important human pathogen. Our goal was to measure S. aureus biofilm formation in the pre...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
American Society for Microbiology
2012-08-01
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| Series: | mBio |
| Online Access: | https://journals.asm.org/doi/10.1128/mBio.00198-12 |
| _version_ | 1818835494695337984 |
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| author | Jeffrey B. Kaplan Era A. Izano Prerna Gopal Michael T. Karwacki Sangho Kim Jeffrey L. Bose Kenneth W. Bayles Alexander R. Horswill |
| author_facet | Jeffrey B. Kaplan Era A. Izano Prerna Gopal Michael T. Karwacki Sangho Kim Jeffrey L. Bose Kenneth W. Bayles Alexander R. Horswill |
| author_sort | Jeffrey B. Kaplan |
| collection | DOAJ |
| description | ABSTRACT Subminimal inhibitory concentrations of antibiotics have been shown to induce bacterial biofilm formation. Few studies have investigated antibiotic-induced biofilm formation in Staphylococcus aureus, an important human pathogen. Our goal was to measure S. aureus biofilm formation in the presence of low levels of β-lactam antibiotics. Fifteen phylogenetically diverse methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) strains were employed. Methicillin, ampicillin, amoxicillin, and cloxacillin were added to cultures at concentrations ranging from 0× to 1× MIC. Biofilm formation was measured in 96-well microtiter plates using a crystal violet binding assay. Autoaggregation was measured using a visual test tube settling assay. Extracellular DNA was quantitated using agarose gel electrophoresis. All four antibiotics induced biofilm formation in some strains. The amount of biofilm induction was as high as 10-fold and was inversely proportional to the amount of biofilm produced by the strain in the absence of antibiotics. MRSA strains of lineages USA300, USA400, and USA500 exhibited the highest levels of methicillin-induced biofilm induction. Biofilm formation induced by low-level methicillin was inhibited by DNase. Low-level methicillin also induced DNase-sensitive autoaggregation and extracellular DNA release. The biofilm induction phenotype was absent in a strain deficient in autolysin (atl). Our findings demonstrate that subminimal inhibitory concentrations of β-lactam antibiotics significantly induce autolysin-dependent extracellular DNA release and biofilm formation in some strains of S. aureus. IMPORTANCE The widespread use of antibiotics as growth promoters in agriculture may expose bacteria to low levels of the drugs. The aim of this study was to investigate the effects of low levels of antibiotics on bacterial autoaggregation and biofilm formation, two processes that have been shown to foster genetic exchange and antibiotic resistance. We found that low levels of β-lactam antibiotics, a class commonly used in both clinical and agricultural settings, caused significant autoaggregation and biofilm formation by the important human pathogen Staphylococcus aureus. Both processes were dependent on cell lysis and release of DNA into the environment. The effect was most pronounced among multidrug-resistant strains known as methicillin-resistant S. aureus (MRSA). These results may shed light on the recalcitrance of some bacterial infections to antibiotic treatment in clinical settings and the evolution of antibiotic-resistant bacteria in agricultural settings. |
| first_indexed | 2024-12-19T02:51:37Z |
| format | Article |
| id | doaj.art-cbeec9a045684a409c51fa8ca80fe88b |
| institution | Directory Open Access Journal |
| issn | 2150-7511 |
| language | English |
| last_indexed | 2024-12-19T02:51:37Z |
| publishDate | 2012-08-01 |
| publisher | American Society for Microbiology |
| record_format | Article |
| series | mBio |
| spelling | doaj.art-cbeec9a045684a409c51fa8ca80fe88b2022-12-21T20:38:36ZengAmerican Society for MicrobiologymBio2150-75112012-08-013410.1128/mBio.00198-12Low Levels of β-Lactam Antibiotics Induce Extracellular DNA Release and Biofilm Formation in <named-content content-type="genus-species">Staphylococcus aureus</named-content>Jeffrey B. Kaplan0Era A. Izano1Prerna Gopal2Michael T. Karwacki3Sangho Kim4Jeffrey L. Bose5Kenneth W. Bayles6Alexander R. Horswill7Department of Oral Biology, New Jersey Dental School, Newark, New Jersey, USADepartment of Oral Biology, New Jersey Dental School, Newark, New Jersey, USADepartment of Oral Biology, New Jersey Dental School, Newark, New Jersey, USADepartment of Oral Biology, New Jersey Dental School, Newark, New Jersey, USADepartment of Oral Biology, New Jersey Dental School, Newark, New Jersey, USADepartment of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, Nebraska, USADepartment of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, Nebraska, USADepartment of Microbiology, Carver College of Medicine, University of Iowa, Iowa City, Iowa, USAABSTRACT Subminimal inhibitory concentrations of antibiotics have been shown to induce bacterial biofilm formation. Few studies have investigated antibiotic-induced biofilm formation in Staphylococcus aureus, an important human pathogen. Our goal was to measure S. aureus biofilm formation in the presence of low levels of β-lactam antibiotics. Fifteen phylogenetically diverse methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) strains were employed. Methicillin, ampicillin, amoxicillin, and cloxacillin were added to cultures at concentrations ranging from 0× to 1× MIC. Biofilm formation was measured in 96-well microtiter plates using a crystal violet binding assay. Autoaggregation was measured using a visual test tube settling assay. Extracellular DNA was quantitated using agarose gel electrophoresis. All four antibiotics induced biofilm formation in some strains. The amount of biofilm induction was as high as 10-fold and was inversely proportional to the amount of biofilm produced by the strain in the absence of antibiotics. MRSA strains of lineages USA300, USA400, and USA500 exhibited the highest levels of methicillin-induced biofilm induction. Biofilm formation induced by low-level methicillin was inhibited by DNase. Low-level methicillin also induced DNase-sensitive autoaggregation and extracellular DNA release. The biofilm induction phenotype was absent in a strain deficient in autolysin (atl). Our findings demonstrate that subminimal inhibitory concentrations of β-lactam antibiotics significantly induce autolysin-dependent extracellular DNA release and biofilm formation in some strains of S. aureus. IMPORTANCE The widespread use of antibiotics as growth promoters in agriculture may expose bacteria to low levels of the drugs. The aim of this study was to investigate the effects of low levels of antibiotics on bacterial autoaggregation and biofilm formation, two processes that have been shown to foster genetic exchange and antibiotic resistance. We found that low levels of β-lactam antibiotics, a class commonly used in both clinical and agricultural settings, caused significant autoaggregation and biofilm formation by the important human pathogen Staphylococcus aureus. Both processes were dependent on cell lysis and release of DNA into the environment. The effect was most pronounced among multidrug-resistant strains known as methicillin-resistant S. aureus (MRSA). These results may shed light on the recalcitrance of some bacterial infections to antibiotic treatment in clinical settings and the evolution of antibiotic-resistant bacteria in agricultural settings.https://journals.asm.org/doi/10.1128/mBio.00198-12 |
| spellingShingle | Jeffrey B. Kaplan Era A. Izano Prerna Gopal Michael T. Karwacki Sangho Kim Jeffrey L. Bose Kenneth W. Bayles Alexander R. Horswill Low Levels of β-Lactam Antibiotics Induce Extracellular DNA Release and Biofilm Formation in <named-content content-type="genus-species">Staphylococcus aureus</named-content> mBio |
| title | Low Levels of β-Lactam Antibiotics Induce Extracellular DNA Release and Biofilm Formation in <named-content content-type="genus-species">Staphylococcus aureus</named-content> |
| title_full | Low Levels of β-Lactam Antibiotics Induce Extracellular DNA Release and Biofilm Formation in <named-content content-type="genus-species">Staphylococcus aureus</named-content> |
| title_fullStr | Low Levels of β-Lactam Antibiotics Induce Extracellular DNA Release and Biofilm Formation in <named-content content-type="genus-species">Staphylococcus aureus</named-content> |
| title_full_unstemmed | Low Levels of β-Lactam Antibiotics Induce Extracellular DNA Release and Biofilm Formation in <named-content content-type="genus-species">Staphylococcus aureus</named-content> |
| title_short | Low Levels of β-Lactam Antibiotics Induce Extracellular DNA Release and Biofilm Formation in <named-content content-type="genus-species">Staphylococcus aureus</named-content> |
| title_sort | low levels of β lactam antibiotics induce extracellular dna release and biofilm formation in named content content type genus species staphylococcus aureus named content |
| url | https://journals.asm.org/doi/10.1128/mBio.00198-12 |
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