State of the knowledge of bacterial resistance

Extended-spectrum beta-lactamase and ampicillin Class C beta lactamase-producing Escherichia coli from food animals: A review

Antimicrobial resistance has gained global notoriety due to its public health concern, the emergence of multiple drug-resistant bacteria, and lack of new antimicrobials. Extended-spectrum beta-lactamase (ESBL)/ampicillin Class C (AmpC)- producing Escherichia coli and other zoonotic pathogens can be transmitted to humans from animals either through the food chain, direct contact or contamination of shared environments. There is a surge in the rate of resistance to medically important antibiotics such as carbapenem, ESBL, aminoglycosides, and fluoroquinolones among bacteria of zoonotic importance. Factors that may facilitate the occurrence, persistence and dissemination of ESBL/AmpC-Producing E. coli in humans and animal includes; 1). o ral administration of antimicrobials to humans primarily (by physician and health care providers) and secondarily to animals, 2). importation of parent stock and day-old chickens, 3). farm management practice and lack of water acidification in poultry, 4). contamination of feed, water and environment, 5). contamination of plants with feces of animals. Understanding these key factors will help reduce the level of resistance, thereby boosting the therapeutic effectiveness of antimicrobial agents in the treatment of animal and human infections. This review highlights the occurrence, risk factors, and public health importance of ESBL/AmpC-beta-lactamase producing E. coli isolated from livestock.

Antimicrobial delivery systems for local infection prophylaxis in orthopedic- and trauma surgery

Infectious complications occur in a minor but significant portion of the patients undergoing joint replacement surgery or fracture fixation, particularly those with severe open fractures, those undergoing revision arthroplasty or those at elevated risk because of poor health status. Once established, infections are difficult to eradicate, especially in the case of bacterial biofilm formation on implanted hardware. Local antibiotic carriers offer the prospect of controlled delivery of antibiotics directly in target tissues and implant, without inducing toxicity in non-target organs. Polymeric carriers have been developed to optimize the release and targeting of antibiotics. Passive polymeric carriers release antibiotics by diffusion and/or upon degradation, while active polymeric carriers release their antibiotics upon stimuli provided by bacterial pathogens. Additionally, some polymeric carriers gelate in-situ in response to physiological stimuli to form a depot for antibiotic release. As antibiotic resistance has become a major issue, also other anti-infectives such as silver and antimicrobial peptides have been incorporated in research. Currently, several antibiotic loaded biomaterials for local infection prophylaxis are available for use in the clinic. Here we review their advantages and limitations and provide an overview of new materials emerging that may overcome these limitations.

Regulation of expression of abcA and its response to environmental conditions

The ATP-dependent transporter gene abcA in Staphylococcus aureus confers resistance to hydrophobic β-lactams. In strain ISP794, abcA is regulated by the transcriptional regulators MgrA and NorG and shares a 420-nucleotide intercistronic region with the divergently transcribed pbp4 gene, which encodes the transpeptidase Pbp4. Exposure of exponentially growing cells to iron-limited media, oxidative stress, and acidic pH (5.5) for 0.5 to 2 h had no effect on abcA expression. In contrast, nutrient limitation produced a significant increase in abcA transcripts. We identified three additional regulators (SarA, SarZ, and Rot) that bind to the overlapping promoter region of abcA and pbp4 in strain MW2 and investigated their role in the regulation of abcA expression. Expression of abcA is decreased by 10.0-fold in vivo in a subcutaneous abscess model. In vitro, abcA expression depends on rot and sarZ regulators. Moenomycin A exposure of strain MW2 produced an increase in abcA transcripts. Relative to MW2, the MIC of moenomycin was decreased 8-fold for MW2ΔabcA and increased 10-fold for the MW2 abcA overexpresser, suggesting that moenomycin is a substrate of AbcA.

The Staphylococcus aureus thiol/oxidative stress global regulator Spx controls trfA, a gene implicated in cell wall antibiotic resistance

S. aureus combats cell wall antibiotic stress by altered gene expression mediated by various environmental signal sensors. In this study, we examined the transcriptional regulation of trfA, a gene related to mecA of Bacillus subtilis encoding an adaptor protein implicated in multiple roles, notably, proteolysis and genetic competence. Despite strong sequence similarity to B. subtilis mecA, the function of S. aureus trfA remains largely unexplored; however, its deletion leads to almost complete loss of resistance to oxacillin and glycopeptide antibiotics in glycopeptide-intermediate S. aureus (GISA) derivatives of methicillin-susceptible or methicillin-resistant S. aureus (MRSA) clinical or laboratory isolates. Northern blot analysis and 5' rapid amplification of cDNA ends (RACE) mapping revealed that trfA was expressed monocistronically by three promoters. Cell wall-active antibiotic exposure led to both increased trfA transcription and enhanced steady-state TrfA levels. trfA promoter regulation was not dependent upon the cell wall stress sentinel VraSR and other sensory stress systems, such as GraRS, WalkRK, Stk1/Stp1, and SigB. Notably, we discovered that the global oxidative-stress regulator Spx controlled trfA transcription. This finding was also confirmed using a strain with enhanced Spx levels resulting from a defect in yjbH, encoding a Spx-interacting protein governing Spx proteolytic degradation. A cohort of clinical GISA strains revealed significant steady-state upregulation of trfA compared to corresponding susceptible parental strains, further supporting a role for trfA in antibiotic resistance. These data provide strong evidence for a link between cell wall antibiotic stress and evoked responses mediated by an oxidative-stress sensor.

Whole genome sequencing and complete genetic analysis reveals novel pathways to glycopeptide resistance in Staphylococcus aureus

The precise mechanisms leading to the emergence of low-level glycopeptide resistance in Staphylococcus aureus are poorly understood. In this study, we used whole genome deep sequencing to detect differences between two isogenic strains: a parental strain and a stable derivative selected stepwise for survival on 4 µg/ml teicoplanin, but which grows at higher drug concentrations (MIC 8 µg/ml). We uncovered only three single nucleotide changes in the selected strain. Nonsense mutations occurred in stp1, encoding a serine/threonine phosphatase, and in yjbH, encoding a post-transcriptional negative regulator of the redox/thiol stress sensor and global transcriptional regulator, Spx. A missense mutation (G45R) occurred in the histidine kinase sensor of cell wall stress, VraS. Using genetic methods, all single, pairwise combinations, and a fully reconstructed triple mutant were evaluated for their contribution to low-level glycopeptide resistance. We found a synergistic cooperation between dual phospho-signalling systems and a subtle contribution from YjbH, suggesting the activation of oxidative stress defences via Spx. To our knowledge, this is the first genetic demonstration of multiple sensor and stress pathways contributing simultaneously to glycopeptide resistance development. The multifactorial nature of glycopeptide resistance in this strain suggests a complex reprogramming of cell physiology to survive in the face of drug challenge.

Nocardia osteomyelitis: a rare complication after intramedullary nailing of a closed tibial shaft fracture

Posttraumatic osteomyelitis of the tibia represents a major therapeutic challenge and continues to be associated with poor outcomes. In this article, we report on the successful management of a rare case of a Nocardia osteomyelitis of the tibial shaft secondary to intramedullary nailing of a closed fracture in a 19-year-old immunocompetent patient. In addition, we provide a review of the literature in the field and discuss optimized treatment strategies.

In vivo release of the antimicrobial peptide hLF1-11 from calcium phosphate cement

We studied the release of human lactoferrin 1-11 (hLF1-11), a potent antimicrobial peptide, in an animal model. Calcium phosphate cement with 50 mg/g hLF1-11 was injected into the femoral canal of 12 rabbits. One, 3, and 7 days later, four animals were terminated, and the femora excised. Sections of bone and cement were removed for histological analysis. We used liquid chromatography-mass spectrometry/mass spectrometry for semiquantitative determination of the hLF1-11 concentration. Blood samples were drawn for leukocyte count and differentiation to identify a potential immunomodulating effect of hLF1-11. After an initial burst release, the hLF1-11 concentration in cement and bone decreased steadily. This in vivo release profile is consistent with earlier in vitro studies. Tissue ingrowth into the cement, without signs of inflammation or necrosis, was observed. Leukocytosis or a shift in leukocyte differentiation did not occur. The carrier released over 99% of the hLF1-11, resulting in peak concentrations at the cement-bone interface. This indicates that hLF1-11 could become a valuable prophylactic agent in osteomyelitis treatment.