Bacterial Resistance to Hospital Disinfection

Biochemical and molecular mechanisms of antibiotic resistance in Salmonella spp

Salmonella is a diverse Gram-negative bacterium that represents the major disease burden worldwide. According to WHO, Salmonella is one of the fourth global causes of diarrhoeal disease. Antibiotic resistance is a worldwide health concern, and Salmonella spp. is one of the microorganisms that can evade the toxicity of antimicrobials via antibiotic resistance. This review aims to deliver in-depth knowledge of the molecular mechanisms and the underlying biochemical alterations perceived in antibiotic resistance in Salmonella. This information will help understand and mitigate the impact of antibiotic-resistant bacteria on humans and contribute to the state-of-the-art research developing newer and more potent antibiotics.

Priming with biocides: A pathway to antibiotic resistance?

AIMS

To investigate the priming effects of sub-inhibitory concentrations of biocides on antibiotic resistance in bacteria.

METHODS AND RESULTS

Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus were exposed to sub-inhibitory concentrations of biocides via a gradient plate method. Minimum inhibitory concentration (MIC) and antibiotic susceptibility were determined, and efflux pump inhibitors (thioridazine and chlorpromazine) were used to investigate antibiotic resistance mechanism(s). Escherichia coli displayed a twofold increase in MIC (32-64 mg l-1 ) to H2 O2 which was stable after 15 passages, but lost after 6 weeks, and P. aeruginosa displayed a twofold increase in MIC (64-128 mg l-1 ) to BZK which was also stable for 15 passages. There were no other tolerances observed to biocides in E. coli, P. aeruginosa or S. aureus; however, stable cross-resistance to antibiotics was observed in the absence of a stable increased tolerance to biocides. Sixfold increases in MIC to cephalothin and fourfold to ceftriaxone and ampicillin were observed in hydrogen peroxide primed E. coli. Chlorhexidine primed S. aureus showed a fourfold increase in MIC to oxacillin, and glutaraldehyde-primed P. aeruginosa showed fourfold (sulphatriad) and eightfold (ciprofloxacin) increases in MIC. Thioridazine increased the susceptibility of E. coli to cephalothin and cefoxitin by fourfold and twofold, respectively, and both thioridazine and chlorpromazine increased the susceptibility S. aureus to oxacillin by eightfold and fourfold, respectively.

CONCLUSIONS

These findings demonstrate that sub-inhibitory concentrations of biocides can prime bacteria to become resistant to antibiotics even in the absence of stable biocide tolerance and suggests activation of efflux mechanisms may be a contributory factor.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates the effects of low-level exposure of biocides (priming) on antibiotic resistance even in the absence of obvious increased biocidal tolerance.

Highly Active, Entirely Biobased Antimicrobial Pickering Emulsions

We present the development of surfactant-free, silica-free and fully biobased oil-in-water antimicrobial Pickering emulsions, based on the self-assembly of β-cyclodextrin and phytoantimicrobial oils (terpinen-4-ol or carvacrol). Undecylenic acid (UA), derived from castor oil, can be used as bio-based drug to treat fungal infection, but is less effective than petroleum-based drugs as azole derivatives. To maximize its antifungal potential, we have incorporated UA in fully biobased Pickering emulsions. These emulsions are effective against fungi, Gram-positive and Gram-negative bacteria. The carvacrol emulsion charged with UA is +390 % and +165 % more potent against methicillin-resistant S. aureus (MRSA), compared to UA and azole-based commercial formulations. Moreover, this emulsion is up to +480 % more efficient that UA ointment against C. albicans. Finally, remarkable eradication of E. coli and MRSA biofilms was obtained with this environmental-friendly emulsion.

Assembly and regulation of the chlorhexidine-specific efflux pump AceI

Acinetobacter baumannii has become challenging to treat due to its multidrug resistance mediated by active drug efflux pumps. The prototype member of the proteobacterial antimicrobial compound efflux (PACE) family, AceI of A. baumannii, is implicated in the transport of widely used antiseptic chlorhexidine, while AceR is associated with regulating the expression of the aceI gene. Here we apply native mass spectrometry to show that AceI forms dimers at high pH, and that chlorhexidine binding facilitates the functional form of the protein. Also, we demonstrate how AceR affects the interaction between RNA polymerase and promoter DNA both in the presence and in the absence of chlorhexidine. Overall, these results provide insight into the assembly and regulation of the PACE family.

Few antibiotics are effective against Acinetobacter baumannii, one of the most successful pathogens responsible for hospital-acquired infections. Resistance to chlorhexidine, an antiseptic widely used to combat A. baumannii, is effected through the proteobacterial antimicrobial compound efflux (PACE) family. The prototype membrane protein of this family, AceI (Acinetobacter chlorhexidine efflux protein I), is encoded for by the aceI gene and is under the transcriptional control of AceR (Acinetobacter chlorhexidine efflux protein regulator), a LysR-type transcriptional regulator (LTTR) protein. Here we use native mass spectrometry to probe the response of AceI and AceR to chlorhexidine assault. Specifically, we show that AceI forms dimers at high pH, and that binding to chlorhexidine facilitates the functional form of the protein. Changes in the oligomerization of AceR to enable interaction between RNA polymerase and promoter DNA were also observed following chlorhexidine assault. Taken together, these results provide insight into the assembly of PACE family transporters and their regulation via LTTR proteins on drug recognition and suggest potential routes for intervention.

Comparative assessment of the effectiveness of three disinfection protocols for reducing bacterial contamination of stethoscopes

In a crossover study, 30 stethoscopes were assessed and disinfected using 3 protocols: isopropyl alcohol, a quaternary ammonia or biguanide disinfectant, and ultraviolet germicidal irradiation (UVGI). All protocols effectively reduced bacterial loads, but UVGI was less effective at higher contamination levels (P = .0004). The effectiveness of each intervention was short in duration.

Can probiotic cleaning solutions replace chemical disinfectants in dental clinics?

Objectives:

We aim to assess the antibacterial effectiveness of probiotic cleaning in a dental clinic at the University Dental Hospital Sharjah (UDHS), UAE.

Materials and Methods:

The current cleaning protocol of UDHS was evaluated by the surface swabbing of three dental clinics routinely cleaned using regular chemical disinfectants. Then, a new probiotic cleaning solution containing Bacillus subtilis was applied for 3 weeks in a selected clinic. Bacteria were grown onto selective culture media for colony counting from surfaces cleaned with probiotic solution compared to those obtained from the same surfaces cleaned with the regular chemical solutions. Isolates identity was confirmed by biochemical tests or polymerase chain reaction.

Results:

There was a significant reduction of the bacterial counts of various bacterial species (Staphylococci, Streptococci, and Gram-negative rods) from almost all the surfaces in the dental clinic after the application of the probiotic solution compared to the same surfaces cleaned with the regular chemical solutions. However, the antibiotic resistance rates were not significantly reduced within the short period of 3 weeks of using the new probiotic cleaning product.

Conclusions:

This study demonstrated that the use of probiotic cleaning is effective in reducing microbial growth in dental settings. This approach may be tested further to examine the long-term effect and to evaluate the opportunity of applying this novel biotechnology as part of the infection control routine in dental settings instead of the chemical disinfectants which are known to cause serious health problems. This is the first study testing the application of probiotic-based solution in dental settings.