Multiple combination antibiotic susceptibility testing of nontypeable Haemophilus influenzae biofilms

Eradicating chronic ear, nose, and throat infections: a systematically conducted literature review of advances in biofilm treatment

OBJECTIVE

Bacteria can grow as individual, planktonic organisms or as complex biofilm communities that are more resistant to treatment. This review was designed to systematically search to identify recent laboratory studies on eradication of biofilms in otolaryngologic infections to highlight promising advances in biofilm treatment.

DATA SOURCES

A systematic electronic literature search of Medline/PubMed, CINHAL, and Web of Science was conducted for articles describing the treatment of biofilm infections in ear, nose, and throat (ENT) diseases through March 2010. English-language articles and articles with an English abstract that focused on biofilm treatment were considered for review.

REVIEW METHODS

Each included article was reviewed by one of the authors for study design, treatment intervention, and outcome. Data from in vitro and animal studies were considered separately from human studies.

RESULTS

A total of 30 articles were identified for this review, including 5 studies that included a human treatment component. In general, antibiotics were relatively ineffective for eradicating biofilm infections. Markedly higher antibiotic dosages were required to reduce biofilm presence compared with doses that were effective in eradicating planktonic bacteria. Mupirocin irrigation, gentian violet, and thiamphenicol glycinate acetylcysteine effectively eradicated biofilms. Physical disruption, surfactants, and probiotics were also shown to be beneficial in both nonhuman and human studies.

CONCLUSION

Eradicating ENT biofilms is difficult when treating single-organism or mixed flora biofilms. Antibiotic therapy is often ineffective against biofilms, and clinical treatment may need to focus on nonantibiotic therapies that reduce, disrupt, or eradicate ENT biofilms.

Divergent mechanisms for passive pneumococcal resistance to β-lactam antibiotics in the presence of Haemophilus influenzae

BACKGROUND

Otitis media, for which antibiotic treatment failure is increasingly common, is a leading pediatric public health problem.

METHODS

In vitro and in vivo studies using the chinchilla model of otitis media were performed using a β-lactamase-producing strain of nontypeable Haemophilus influenzae (NTHi 86-028NP) and an isogenic mutant deficient in β-lactamase production (NTHi 86-028NP bla) to define the roles of biofilm formation and β-lactamase production in antibiotic resistance. Coinfection studies were done with Streptococcus pneumoniae to determine if NTHi provides passive protection by means of β-lactamase production, biofilm formation, or both.

RESULTS

NTHi 86-028NP bla was resistant to amoxicillin killing in biofilm studies in vitro; however, it was cleared by amoxicillin treatment in vivo, whereas NTHi 86-028NP was unaffected in either system. NTHi 86-028NP protected pneumococcus in vivo in both the effusion fluid and bullar homogenate. NTHi 86-028NP bla and pneumococcus were both recovered from the surface-associated bacteria of amoxicillin-treated animals; only NTHi 86-028NP bla was recovered from effusion.

CONCLUSIONS

Based on these studies, we conclude that NTHi provides passive protection for S. pneumoniae in vivo through 2 distinct mechanisms: production of β-lactamase and formation of biofilm communities.

The activity of silver against Escherichia coli biofilm is increased by a lipopeptide biosurfactant

Biological contamination of surfaces, both in industry and in health care, plays an important role as a potential vector of disease transmission. Metals have been described to be effective antibiofilm agents, and the efficacy of silver ions as a disinfectant has been known for centuries. The activity of AgNO3 combined with the lipopeptide biosurfactant V9T14 has been studied against a preformed Escherichia coli biofilm on the Calgary Biofilm Device. Results indicated that the activity of silver can be synergistically enhanced by the presence of V9T14, both allowing for a reduction in the quantity of silver used and for greater antimicrobial activity. The concentration of silver needed to obtain this reduction in the silver-biosurfactant solution was from 129- to 258-fold less than the concentration of silver alone. To our knowledge, this is the first time that a synergistic interaction between a lipopeptide biosurfactant and silver has been observed.

Microtiter susceptibility testing of microbes growing on peg lids: a miniaturized biofilm model for high-throughput screening

Batch culture of biofilms on peg lids is a versatile method that can be used for microtiter determinations of biofilm antimicrobial susceptibility. In this paper, we describe a core protocol and a set of parameters (surface composition, the rate of rocking or orbital motion, temperature, cultivation time, inoculum size, atmospheric gases and nutritional medium) that can be adjusted to grow single- or multispecies biofilms on peg surfaces. Mature biofilms formed on peg lids can then be fitted into microtiter plates containing test agents. After a suitable exposure time, biofilm cells are disrupted into a recovery medium using sonication. Microbicidal endpoints can be determined qualitatively using optical density measurements or quantitatively using viable cell counting. Once equipment is calibrated and growth conditions are at an optimum, the procedure requires approximately 5 h of work over 4-6 d. This efficient method allows antimicrobial agents and exposure conditions to be tested against biofilms on a high-throughput scale.

Microbial interactions in the respiratory tract

Upper respiratory tract infections are caused by the synergistic and antagonistic interactions between upper respiratory tract viruses and 3 predominant bacterial pathogens: Streptococcus pneumoniae, nontypeable Haemophilus influenzae (NTHi), and Moraxella catarrhalis, which are members of the commensal flora of the nasopharynx. For many bacterial pathogens, colonization of host mucosal surfaces is a first and necessary step in the infectious process. S. pneumoniae and H. influenzae have intricate interactions in the nasopharynx. The host innate immune response may influence these interactions and therefore influence the composition of the colonizing flora and the invading bacteria. S. pneumoniae, nontypeable H. influenzae, and M. catarrhalis can behave as opportunistic pathogens of the middle ear when conditions are optimal. Chronic otitis media (OM) and recurrent OM include a biofilm component. Each of the 3 predominant pathogens of OM can form a biofilm and have been shown to comprise biofilms present on middle ear mucosa specimens recovered from children with recurrent or chronic OM. Some of these characterized biofilms are of mixed bacterial etiology, suggesting that progress made on single-microbe directed strategies for treatment and/or prevention of OM, although highly encouraging, are likely to be inadequate. A significantly greater understanding about microbial physiology is required as it relates to the involvement of biofilms in OM, to identify points in the natural course of the disease that are perhaps more amenable to treatment strategies, as well as to identify biofilm-relevant antigenic targets that would be helpful in the rational design of vaccines to prevent OM.

Chinchilla as a robust, reproducible and polymicrobial model of otitis media and its prevention

There is compelling evidence that many infectious diseases of humans are caused by more than one microorganism. Multiple diverse in vitro systems have been used to study these complex diseases, and although the data generated have contributed greatly to our understanding of diseases of mixed microbial etiology, having rigorous, reproducible and relevant animal models of human diseases are essential for the development of novel methods to treat or prevent them. All animal models have inherent limitations; however, they also have important advantages over in vitro methods, including the presence of organized organ systems and an intact immune system, which promote our ability to characterize the pathogenesis of, and the immune response to, sequential or coinfecting microorganisms. For the highly prevalent pediatric disease otitis media, or middle-ear infection, the chinchilla (Chinchilla lanigera) has served as a gold-standard rodent host system in which to study this multifactorial and polymicrobial disease.

Intercellular adhesion and biocide resistance in nontypeable Haemophilus influenzae biofilms

Respiratory infections caused by nontypeable Haemophilus influenzae (NTHi) are a major medical problem. Evidence suggests that the ability to form biofilms on mucosal surfaces may play a role in NTHi pathogenesis. However, the factors that contribute to NTHi biofilm cohesion remain largely unknown. In this study we investigated the biofilm growth and detachment phenotypes of eight NTHi clinical strains in vitro. We found that the majority of strains produced biofilms within 6h when cultured statically in tubes. Biofilm formation was inhibited when culture medium was supplemented with proteinase K or DNase I. Both enzymes also caused significant detachment of pre-formed NTHi biofilms. These findings indicate that both proteinaceous adhesins and extracellular DNA contribute to NTHi biofilm cohesion. Treatment of NTHi biofilms cultured in centrifugal filter devices with DNase I, but not with proteinase K, caused a significant decrease in fluid convection through the biofilms. These results suggest that extracellular DNA is the major volumetric component of the NTHi biofilm matrix. Mechanical or enzymatic disruption of NTHi biofilms cultured in microtiter plates significantly increased their sensitivity to killing by SDS, cetylpyridinium chloride, chlorhexidine gluconate, povidone iodine and sodium hypochlorite. These findings indicate that biocide resistance in NTHi biofilms is mediated to a large part by the cohesive and protective properties of the biofilm matrix. Understanding the mechanisms of biofilm cohesion and biocide resistance in NTHi biofilms may lead to new methods for treating NTHi-associated infections.

Effectiveness of honey on Staphylococcus aureus and Pseudomonas aeruginosa biofilms

OBJECTIVES

Biofilms formed by Pseudomonas aeruginosa (PA) and Staphylococcus aureus (SA) have been shown to be an important factor in the pathophysiology of chronic rhinosinusitis (CRS). As well, honey has been used as an effective topical antimicrobial agent for years. Our objective is to determine the in vitro effect of honey against biofilms produced by PA and SA.

STUDY DESIGN

In vitro testing of honey against bacterial biofilms.

METHODS

We used a previously established biofilm model to assess antibacterial activity of honey against 11 methicillin-susceptible SA (MSSA), 11 methicillin-resistant SA (MRSA), and 11 PA isolates. Honeys were tested against both planktonic and biofilm-grown bacteria.

RESULTS

Honey was effective in killing 100 percent of the isolates in the planktonic form. The bactericidal rates for the Sidr and Manuka honeys against MSSA, MRSA, and PA biofilms were 63-82 percent, 73-63 percent, and 91-91 percent, respectively. These rates were significantly higher (P<0.001) than those seen with single antibiotics commonly used against SA.

CONCLUSION

Honey, which is a natural, nontoxic, and inexpensive product, is effective in killing SA and PA bacterial biofilms. This intriguing observation may have important clinical implications and could lead to a new approach for treating refractory CRS.

Formation of biofilm by Haemophilus influenzae isolated from pediatric intractable otitis media

OBJECTIVES

The aims of this study are to evaluate biofilm formation by nontypeable Haemophilus influenzae (NTHi) isolated from children with acute otitis media (AOM) and its relation with clinical outcome of the disease.

METHODS

Biofilm formations by NTHi clinical isolates from pediatric AOM patients were evaluated by a crystal violet microtiter plate and a 98 well pin-replicator assay with a confocal laser scanning microscopy (CLSM). Optical density values of clinical isolates were compared with a positive control and the ratio of clinical isolates to a positive control was defined as biofilm formation index (BFI).

RESULTS

84.3% clinical isolates of NTHi were biofilm forming strains (BFI> or =0.4). The BFI represented the levels of biofilm formation and adherence on the surface. The identical strains isolated from both middle ear fluids (MEFs) and nasopharynx showed biofilm formation at the same level. The prevalence of biofilm forming isolates was significantly higher among the susceptible strains than resistant strains. The level of biofilm formation of NTHi isolated from AOM cases who was not improved by amoxicillin (AMPC) was significantly higher than that of NTHi isolated from AOM cases who was improved by AMPC.

CONCLUSION

We clearly showed the biofilm formation of clinical NTHi isolates from AOM children. In addition, the biofilm formed by NTHi would play an important role in persistent or intractable clinical course of AOM as a result of lowered treatment efficacy of antibiotics.

Nontypeable Haemophilus influenzae as a pathogen in children

Nontypeable Haemophilus influenzae is a significant pathogen in children, causing otitis media, sinusitis, conjunctivitis, pneumonia, and occasionally invasive infections. H. influenzae type b conjugate vaccines have no effect on infections caused by nontypeable strains because nontypeable strains are nonencapsulated. Approximately, one-third of episodes of otitis media are caused by nontypeable H. influenzae and the bacterium is the most common cause of recurrent otitis media. Recent progress in elucidating molecular mechanisms of pathogenesis, understanding the role of biofilms in otitis media and an increasing understanding of immune responses have potential for development of novel strategies to improve prevention and treatment of otitis media caused by nontypeable H. influenzae. Feasibility of vaccination for prevention of otitis media due to nontypeable H. influenzae was recently demonstrated in a clinical trial with a vaccine that included the surface virulence factor, protein D.

Antimicrobial effect of fluoroquinolones for the eradication of nontypeable Haemophilus influenzae isolates within biofilms

Biofilms can be defined as communities of microorganisms attached to a surface. Those bacterial biofilms cause serious problems, such as antibiotic resistance and medical device-related infections. Nontypeable Haemophilus influenzae (NTHi) is an important pathogen in respiratory infections, as it forms biofilms both in vitro and in vivo such as human middle ear. Recent reports indicate that otitis media, paranasal sinusitis and lower respiratory tract infections caused by Haemophilus influenzae have become more difficult to treat with oral antibiotic therapy. However, there has been no attention given to antibiotic eradication of NTHi biofilm. To investigate the antimicrobial effect of various antibiotics against NTHi biofilm formation, we conducted the following comparative study using both beta-lactamase-negative ampicillin (AMP)-susceptible (BLNAS) and AMP-resistant (BLNAR) NTHi strains. In a microtiter biofilm assay, both levofloxacin and gatifloxacin, of the fluoroquinolone antibiotic group, significantly inhibited biofilm formation by BLNAS and BLNAR NTHi in a dose-dependent fashion compared to ampicillin of the penicillin antibiotic group, cefotaxime of the cephalosporin antibiotic group, and both erythromycin and clarithromycin of the macrolide antibiotic group. Furthermore, in flow cell chamber studies, confocal laser scanning microscopy counted survival bacteria in mature biofilm had been treated with gatifloxacin, ampicillin, cefotaxime and erythromycin. Only gatifloxacin completely killed the BLNAR NTHi isolates within biofilms without regard to the thickness of biofilm formation. The results of this study suggest that fluoroquinolones potentially have a role in therapy against diseases caused by both BLNAS and BLNAR NTHi isolates within biofilms.

Haemophilus influenzae biofilms: hypothesis or fact?

Many publications state that nontypeable Haemophilus influenzae (NTHi) produces biofilms. Here, we review many of the publications that have led to acceptance by some that NTHi expresses a biofilm-specific phenotype as a distinct part of its life cycle. Biofilm formation was originally invoked to explain the failure to culture NTHi from middle-ear effusions, recalcitrance to antibiotics and its pathogenic behaviour. We argue that the current evidence for NTHi biofilm formation in vitro and in vivo is inconclusive. We consider that NTHi biofilm is hypothesis not fact, and although it might yet prove to be correct, there has been little or no consideration of alternative interpretations for the in vitro and in vivo observations. Uncritical acceptance of a distinctive NTHi biofilm phenotype has the potential to mislead and could confuse and compromise research efforts aimed at improving management and prevention of NTHi diseases of the human respiratory tract.

Bacterial biofilms in otitis media: evidence and relevance

A biofilm is a highly organized, multicellular network of bacteria encased in a matrix and found in close association with a surface. Substantial effort in understanding the biologic and biochemical nature of biofilms has resulted in evidence supporting their importance in otitis media (OM), both from the perspective how pathogens develop viable communities in the middle ear as well as how this structure impedes successful antibiotic therapy. This new understanding may explain the recurrent nature of OM, and the persistence of middle ear fluid after infection. This article looks closely at biofilms in OM and suggests that an improved understanding of the unique properties of bacteria resident within a biofilm and the proteins they express while part of this organized community has the potential to identify novel and perhaps biofilm-specific molecular targets for the design of vaccine candidates for the prevention of OM.

In vitro effects of antimicrobial agents on planktonic and biofilm forms of Staphylococcus lugdunensis clinical isolates

Staphylococcus lugdunensis is an atypically virulent coagulase-negative staphylococcal species associated with acute and destructive infections that often resemble Staphylococcus aureus infections. Several types of infection caused by S. lugdunensis (e.g., native valve endocarditis, prosthetic joint infection, and intravascular catheter infection) are associated with biofilm formation, which may lead to an inability to eradicate the infection due to the intrinsic nature of biofilms to resist high levels of antibiotics. In this study, planktonic MICs and MBCs and biofilm bactericidal concentrations of 10 antistaphylococcal antimicrobial agents were measured for 15 S. lugdunensis isolates collected from patients with endocarditis, medical device infections, or skin and soft tissue infections. Planktonic isolates were susceptible to all agents studied, but biofilms were resistant to high concentrations of most of the drugs. However, moxifloxacin was able to kill 73% of isolates growing in biofilms at </=0.5 mug/ml. Relative to the effect on cell density, subinhibitory concentrations of nafcillin substantially stimulated biofilm formation of most isolates, whereas tetracycline and linezolid significantly decreased biofilm formation in 93 and 80% of isolates, respectively. An unexpected outcome of MBC testing was the observation that vancomycin was not bactericidal against 93% of S. lugdunensis isolates, suggesting widespread vancomycin tolerance in this species. These data provide insights into the response of S. lugdunensis isolates when challenged with various levels of antimicrobial agents in clinical use.