Searching for a potential antibacterial lead structure against bacterial biofilms among new naphthoquinone compounds.

AIMS: The aims of this study were to design, synthesize and to evaluate 2-hydroxy-3-phenylsulfanylmethyl-[1,4]-naphthoquinones against Gram-negative and Gram-positive bacterial strains, including methicillin-resistant Staphylococcus aureus (MRSA) and its biofilm, to probe for potential lead structures. METHODS AND RESULTS: Thirty-six new analogues were prepared with good yields using a simple, fast, operational three-procedure reaction and a thiol addition to an ο-quinone methide using microwave irradiation. All compounds were tested against Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Proteus mirabilis ATCC 15290, Serratia marcescens ATCC 14756, Klebsiella pneumoniae ATCC 4352, Enterobacter cloacae ATCC 23355, Enterococcus faecalis ATCC 29212, S. aureus ATCC 25923, Staphylococcus simulans ATCC 27851, Staphylococcus epidermidis ATCC 12228 and a hospital strain of MRSA. Their antibacterial activity was determined using the disc diffusion method, revealing the activity of 19 compounds, mainly against Gram-positive strains. Interestingly, the minimal inhibitory concentration ranges detected for the hit molecules (32-128 µg ml-1 ) were within Clinical and Laboratory Standards Institute levels. Promisingly, compound 15 affected the MRSA strain, with a reduction of up to 50% in biofilm formation, which is better than vancomycin as biofilm forms a barrier against the antibiotic that avoids its action. CONCLUSIONS: After probing 36 naphthoquinones for a potential antibacterial lead structure against the bacterial biofilm, we found that compound 15 should be explored further and also should be structurally modified in the near future to test against Gram-negative strains. SIGNIFICANCE AND IMPACT OF THE STUDY: Since vancomycin is one of the last treatment options currently available, and it is unable to inhibit biofilm, the research of new antimicrobials is urgent. In this context, 2-hydroxy-3-phenylsulfanylmethyl-[1,4]-naphthoquinones proved to be a promising lead structure against MRSA and bacterial biofilm.

Multiple methicillin-resistant Staphylococcus aureus strains as a cause for a single outbreak of severe disease in hospitalized neonates.

Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of nosocomial infection. Outbreaks of infection caused by these pathogens are generally considered to be traceable to introduction of single strains into a hospital population. A large outbreak of bacteremic disease that recently occurred in our neonatal intensive care unit (11 episodes in 10 patients) involved 9 low birth weight infants and was associated with serious infection (4 episodes of meningitis). To determine the role of a single point source in this outbreak, isolates were characterized based on phenotypic and genotypic analyses. Phenotypic analysis included assessing hemolytic activity, phage typing, antimicrobial susceptibility testing and methicillin resistance population analysis. Genotypic analysis included assessment of plasmid profiles, dot-blot hybridization, restriction enzyme fragment pattern analysis and hybridization analysis of chromosomal DNA using a panel of staphylococcal gene probes. This analysis established that at least two distinct strains of MRSA were responsible for disease during this outbreak. This experience demonstrates the potential for MRSA to cause severe disease in the neonatal intensive care unit and indicates that the epidemiology of MRSA outbreaks is more complex than the spread of a single strain of bacteria.

Drastic changes in the peptidoglycan composition of penicillin resistant laboratory mutants of Streptococcus pneumoniae.

The penicillin MIC of 2 Streptococcus pneumoniae clinical isolates was increased 100-fold (from 0.02 to 2.0 micromilligrams) and 20-fold (from 0.5 to 10.0 micromilligrams) through gradual exposure of the bacteria to increasing concentrations of penicillin in the laboratory. In both mutants the affinity of all four high molecular mass penicillin binding proteins (PBPs) for penicillin was drastically reduced accompanied by major changes in the composition of peptidoglycan as resolved by HPLC. The ratio of crosslinked to monomeric peptides became virtually inverted in the resistant cell walls with monomers representing two-thirds of the muropeptide species. The proportion of the crosslinked tri-tetra dimer, a major component of the cell wall of the original isolates, decreased to one-third or one-sixth of its normal representation, while the amounts of tripeptide monomers with an alanyl-serine substitution on the lysine epsilon amino group increased by close to a factor of two. The growth rates of both mutants decreased by a factor of approximately two, as compared to the original bacteria.

Multiple mechanisms of methicillin resistance and improved methods for detection in clinical isolates of Staphylococcus aureus.

The mec gene of a number of clinical methicillin-resistant Staphylococcus aureus isolates exhibiting a variety of heterogeneous expression modes was selectively inactivated by allelic replacement mutagenesis. While the resistance level of each of the transformants was reduced, the methicillin MIC for these transformants was well above the MIC for susceptible laboratory strains of S. aureus and was similar to the methicillin MIC for many contemporary clinical isolates which did not react with the mec-specific DNA probe but which showed a low or borderline level of resistance to methicillin. A number of those strains had no detectable beta-lactamase, and for about half of the isolates that did carry plasmid-borne beta-lactamase, elimination of the plasmid caused only partial reduction of the methicillin MIC or no reduction at all. The findings suggest that many contemporary strains of staphylococci harbor a combination of at least three distinct beta-lactam resistance mechanisms: (i) the mechanism related to the acquisition of the foreign mec gene and (ii) a beta-lactamase-dependent and (iii) a beta-lactamase-independent mechanism, each one of which can provide a certain degree of resistance against penicillinase-resistant beta-lactam antibiotics.

Hyaluronidase production by groups A, B, C, and G streptococci: a statistical analysis.

Production of hyaluronidase by 147 strains of beta hemolytic streptococci was studied employing a sensitive dye-binding assay and levels of enzyme activity were evaluated statistically. The analysis of variance showed that group A strains isolated in Rio de Janeiro produced significantly smaller amounts of enzyme than group A strains from a Minneapolis (USA) collection or than groups B and G brazilian isolates. The t test revealed that M not typable nose/throat group A strains produced more hyaluronidase than skin isolates. The analysis of variance did not show a significant difference in the enzyme production between M typable and not typable brazilian strains of group A streptococci. High enzyme--producing strains were not restricted to a few serotypes of group B streptococci.