Ultrastructural cell wall characteristics of clinical gentamycin-resistant Staphylococcus aureus isolates

Suppressed distribution of protein A on the surface of Staphylococcus aureus as a morphological characteristic of erythromycin-resistant strain

To identify a new morphological phenotype of erythromycin (EM)-resistant Staphylococcus aureus (S. aureus) were isolated in vitro from EM-sensitive parent strain, and the distribution of staphylococcus specific protein A (SpA) on the surface of these strains was examined morphologically by using applied immunoelectron microscopy. The isolated EM-resistant strains had thickened cell walls, and the distribution of SpA on the surfaces of these strains was demonstrated to be lower than that of the parent strain. The SpA suppression was confirmed by enzyme-linked immunosorbent assay (ELISA) using fixed EM-resistant cells. Moreover, the spa gene of EM-resistant cells was detected by polymerase chain reaction (PCR) and confirmed by quantitative real-time PCR assay, showing that the expression of SpA was repressed at the transcriptional level in these strains. Furthermore, ELISA assay showed that whole EM-resistant cell SpA content was significantly decreased. Therefore, it was considered that the suppression of surface SpA on the EM-resistant strain was due to regulated SpA production, and not dependent on the conformational change in SpA molecule expression through cell wall thickening. These results strongly suggest that suppressed SpA distribution on the EM-resistant S. aureus is a phenotypical characteristic in these strains.

Migration of surface-associated microbial communities in spaceflight habitats

Astronauts are spending longer periods locked up in ships or stations for scientific and exploration spatial missions. The International Space Station (ISS) has been inhabited continuously for more than 20 years and the duration of space stays by crews could lengthen with the objectives of human presence on the moon and Mars. If the environment of these space habitats is designed for the comfort of astronauts, it is also conducive to other forms of life such as embarked microorganisms. The latter, most often associated with surfaces in the form of biofilm, have been implicated in significant degradation of the functionality of pieces of equipment in space habitats. The most recent research suggests that microgravity could increase the persistence, resistance and virulence of pathogenic microorganisms detected in these communities, endangering the health of astronauts and potentially jeopardizing long-duration manned missions. In this review, we describe the mechanisms and dynamics of installation and propagation of these microbial communities associated with surfaces (spatial migration), as well as long-term processes of adaptation and evolution in these extreme environments (phenotypic and genetic migration), with special reference to human health. We also discuss the means of control envisaged to allow a lasting cohabitation between these vibrant microscopic passengers and the astronauts.

In vitro characterisation of two Lactobacillus strains and evaluation of their suitability as probiotics for growing-finishing pigs

In this study, we evaluated the probiotic properties of two strains Lactobacillus reuteri ZLR003 and Lactobacillus salivarius ZLS006. The two strains displayed tolerance of acid and heat, and demonstrated antimicrobial ability in vitro. Furthermore, their potential functions in vivo were also tested. A total of 120 crossbred (Landrace × Large White) growing pigs were divided into three groups: a control diet, the same diet supplemented with L. reuteri ZLR003 (2.0 × 109 cfu/kg of diet) or L. salivarius ZLS006 (3.50 × 109 cfu/kg of diet). The results showed that the average daily gain and feed conversion ratio were significantly improved in L. reuteri ZLR003- (1–5 weeks and 1–9 weeks) (P < 0.05) and L. salivarius ZLS006-treated pigs (1–5 weeks, 6–9 weeks and 1–9 weeks) (P < 0.05) compared with the control group. Dietary supplementation with L. salivarius ZLS006 increased the apparent digestibility of nitrogen at Week 9 (P < 0.05). The faecal Lactobacillus populations increased at the end of experiment, and the Escherichia coli and Staphylococcus aureus in faeces decreased in the two Lactobacillus treatments compared with the control at Week 5 (P < 0.05) and Week 9 (P < 0.05), respectively. Furthermore, the total cholesterol, alanine transferase, aspartate transferase, blood urea nitrogen and haptoglobin levels in serum were significantly decreased following L. reuteri ZLR003 and L. salivarius ZLS006 treatments (P < 0.05). In conclusion, these data suggest that the two Lactobacillus strains may be promising candidates for probiotic products in growing-finishing pigs.

Correlation between resistance mechanisms in Staphylococcus aureus and cell wall and septum thickening

Purpose

The aim of the present study is to examine cell wall and septum thickening of methicillin-sensitive Staphylococcus aureus (MSSA), methicillin-resistant S. aureus (MRSA), and methicillin- and linezolid-resistant S. aureus (MLRSA) isolates by transmission electron microscopy to correlate the association of resistance mechanisms with major changes in the morphology of membrane or septum.

Materials and methods

MSSA, MRSA, and MLRSA strains obtained from clinical samples of an outbreak that occurred in 2010 at the Intensive Care Unit of our Hospital were thawed and sown at 37°C in blood agar overnight. After that, they were washed, pelleted, and treated with a fixer solution. Pellets were dehydrated and finally embedded in resin. Transmission electron microscopy was used to characterize cell wall and septum thickening in all isolates. The comparison between the measurements obtained for each group was performed by a Kruskal–Wallis test and a post hoc Dunn–Bonferroni’s pairwise comparison method.

Results

Differences in cell wall and septum thickness were statistically significant (P<0.001 and P<0.001, respectively) between the three groups. Moreover, significant differences were detected in wall and septum thickness between the MSSA and MRSA strains (P<0.001 and P<0.001, respectively) and between the MSSA and MLRSA strains (P<0.001 and P<0.001, respectively) but not between the MRSA and MLRSA strains (P=0.386 and P=0.117).

Conclusion

In this analysis, we correlate the resistance mediated by alterations in the cell membrane of S. aureus (methicillin-resistant, for example) with a greater thickness of the wall or septum. The resistance added to linezolid did not determine significant changes in the characteristics of the wall or septum with respect to those strains resistant only to methicillin.

Phenotypic Changes Exhibited by E. coli Cultured in Space

Bacteria will accompany humans in our exploration of space, making it of importance to study their adaptation to the microgravity environment. To investigate potential phenotypic changes for bacteria grown in space, Escherichia coli was cultured onboard the International Space Station with matched controls on Earth. Samples were challenged with different concentrations of gentamicin sulfate to study the role of drug concentration on the dependent variables in the space environment. Analyses included assessments of final cell count, cell size, cell envelope thickness, cell ultrastructure, and culture morphology. A 13-fold increase in final cell count was observed in space with respect to the ground controls and the space flight cells were able to grow in the presence of normally inhibitory levels of gentamicin sulfate. Contrast light microscopy and focused ion beam/scanning electron microscopy showed that, on average, cells in space were 37% of the volume of their matched controls, which may alter the rate of molecule–cell interactions in a diffusion-limited mass transport regime as is expected to occur in microgravity. TEM imagery showed an increase in cell envelope thickness of between 25 and 43% in space with respect to the Earth control group. Outer membrane vesicles were observed on the spaceflight samples, but not on the Earth cultures. While E. coli suspension cultures on Earth were homogenously distributed throughout the liquid medium, in space they tended to form a cluster, leaving the surrounding medium visibly clear of cells. This cell aggregation behavior may be associated with enhanced biofilm formation observed in other spaceflight experiments.

Intracellular morphological changes in Staphylococcus aureus induced by treatment with sodium hypochlorite

Sodium hypochlorite (NaOCl) is commonly used as a disinfectant; however, its bactericidal mechanism has not yet been clarified. In the present study, the bactericidal mechanism of NaOCl was examined using microscopy and gel electrophoresis techniques with Staphylococcus aureus strain 209P. S. aureus cells treated with 500 and 1000 ppm NaOCl for 5 and 15 min were observed by SEM and TEM. SEM images of the bacterial cells treated with NaOCl showed an irregular surface, with cells being partially invaginated. TEM images of the bacterial cells showed cytoplasmic alterations, accompanied by a partially irregular cellular surface. Under a fluorescence microscope, we clearly observed fluorescence quenching in the 1000 ppm NaOCl-treated cells. Based on these observations, which indicated that NaOCl damaged chromosomal DNA, we next extracted chromosomal DNA from bacterial cells treated with NaOCl and performed agarose gel electrophoresis. Chromosomal DNA was absent in the DNA sample from the bacterial cells treated with 500 ppm NaOCl. From these biochemical results, it was strongly suggested that NaOCl degrades the chromosomal DNA of S. aureus. We consider that the morphological changes in the cytoplasm induced by NaOCl may be related to NaOCl-induced degradation of S. aureus chromosomal DNA.

Vancomycin tolerant, methicillin-resistant Staphylococcus aureus reveals the effects of vancomycin on cell wall thickening

Methicillin-resistant Staphylococcus aureus (MRSA) is an important opportunistic pathogen that causes both healthcare- and community-acquired infections. An increase in the incidence of these infections may lead to a substantial change in the rate of vancomycin usage. Incidence of reduced susceptibility to vancomycin has been increasing worldwide for the last few years, conferring different levels of resistance to vancomycin as well as producing changes in the cell wall structure. The aim of the present study was to determine the effect of vancomycin on cell wall thickening in clinical isolates of vancomycin-tolerant (VT) MRSA obtained from pediatric patients. From a collection of 100 MRSA clinical isolates from pediatric patients, 12% (12/100) were characterized as VT-MRSA, and from them, 41.66% (5/12) exhibited the heterogeneous vancomycin-intermediate S. aureus (hVISA) phenotype. Multiplex-PCR assays revealed 66.66% (8/12), 25% (3/12), and 8.33% (1/12) of the VT-MRSA isolates were associated with agr group II, I, and III polymorphisms, respectively; the II-mec gene was amplified from 83.3% (10/12) of the isolates, and the mecIVa gene was amplified from 16.66% (2/12) of the isolates. Pulsed field electrophoresis (PFGE) fingerprint analysis showed 62% similarity among the VT-MRSA isolates. Thin transverse sections analyzed by transmission electron microscopy (TEM) revealed an average increase of 24 nm (105.55%) in the cell wall thickness of VT-MRSA compared with untreated VT-MRSA isolates. In summary, these data revealed that the thickened cell walls of VT-MRSA clinical isolates with agr type II and SCCmec group II polymorphisms are associated with an adaptive resistance to vancomycin.

Thickening of the cell wall in macrolide-resistant Staphylococcus aureus

Macrolides are widely used at low dosage for long-term therapy of chronic sinusitis. Twenty clinical macrolide-resistant Staphylococcus aureus strains were morphologically compared with 10 clinical macrolide-sensitive strains. PCR amplification was performed to determine the presence of four known macrolide resistance genes. Transmission electron microscopy revealed significantly thicker cell walls in clinical macrolide-resistant strains. Even though the ultrastructural characteristics were shared by all macrolide-resistant strains, they were not associated with the presence or absence of the known macrolide-resistance genes. We also demonstrated that macrolide-resistant mutant strains derived in vitro from a macrolide-sensitive parent strain had thickened cell walls and did not harbor the known macrolide-resistance genes. These results, therefore, revealed that macrolide-resistant S. aureus strains have thickened cell walls as a common ultrastructural characteristic and that cell wall thickening is likely mediated by an unknown gene which is unrelated to any known macrolide resistance gene.