Diversity in the antimicrobial susceptibility patterns of methicillin-resistant Staphylococcus aureus clones

Mechanisms of Resistance to Macrolide Antibiotics among Staphylococcus aureus

Methicillin resistant Staphylococcus aureus strains pose a serious treatment problem because of their multi-drug resistance (MDR). In staphylococcal strains, resistance to macrolides, lincosamides, and streptogramin B (MLS_B) correlates with resistance to methicillin. The rapid transmission of erm genes responsible for MLS_B resistance has strongly limited the clinical application of traditional macrolides such as erythromycin. On the other hand, in the age of increasing insensitivity to antibiotics the idea of implementing a therapy based on older generation drugs brings hope that the spread of antibiotic resistance will be limited. A thorough understanding of the resistance mechanisms contributes to design of antibiotics that avoid bacterial insensitivity. This review highlights the mechanisms of action of macrolides and mechanism of resistance to these antibiotics among Staphylococcus aureus.

Emergence of Highly Multidrug-Resistant Bacteria Isolated from Patients with Infections Admitted to Public Hospitals in Southwest Iran

Background

The emergence of multidrug-resistant (MDR) microorganisms causing infections is increasing worldwide and becoming more serious in developing countries. Among those, Acinetobacter species are becoming prominent.

Objectives

The aim of this study was to determine the rate of antimicrobial resistance of the bacteria causing infections, Acinetobacter species in particular, in local public hospitals in Firuzabad, Fars province, Iran.

Methods

This cross-sectional study was performed on different clinical specimens collected from patients who were suspected of infections hospitalized from March 2016 to March 2019 in local hospitals of Firuzabad, Fars province, Iran. The bacterial isolates were identified following standard microbiological methods. Clinical and Laboratory Standards Institute guidelines were used to identify the antibiotic susceptibility of these isolates.

Results

Overall, 1778 bacterial etiologies were isolated from 1533 patients diagnosed with infection. Of these, 1401 (78.8%) were Gram-negative and the remaining were Gram-positive bacteria. Escherichia coli (37.1%), Klebsiella spp. (13.9%), and Acinetobacter species (10.4%) were the most common isolated bacteria. Antibiotic sensitivity testing in this study showed a high resistance rate of Acinetobacter species to all antibiotics tested except Colistin. During the study period, the rate of infection with highly multidrug-resistant Acinetobacter species increased from 7.2% to 13.3%.

Conclusions

This study highlights the emergence of MDR bacterial agents such as Acinetobacter species as a new threat in our region. However, a decrease in the rate of infection with Pseudomonas aeruginosa was noticeable.

High prevalence of clindamycin resistance in Staphylococcus aureus blood culture isolates in São Paulo, Brazil

BACKGROUND:

Clindamycin has become an important antimicrobial option for the treatment of Staphylococcus aureus. However, little is known about the current patterns of clindamycin-susceptibility in S. aureus invasive isolates, both in our country and in other developing countries in the world.

AIMS:

The aim of this study was to determine the prevalence of constitutive and inducible clindamycin resistance in methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) blood culture isolates in São Paulo, Brazil.

MATERIALS AND METHODS:

From July 2011 to June 2012, all S. aureus isolates from blood cultures collected at our hospital were included in the study. Antimicrobial susceptibility testing was performed according to recommendations of the Clinical and Laboratory Standards Institute.

RESULTS:

Total prevalence of clindamycin resistance was 68%, including 7.2% with inducible resistance. In MRSA resistance rate was 90.8% whereas in MSSA the rate was 32.7%.

CONCLUSIONS:

Our high prevalence of clindamycin resistance highlights the importance of performing D-test in a routine base, as well of maintaining continued surveillance for the prevalence of clindamycin resistance.

Community-associated methicillin-resistant Staphylococcus aureus case studies

Over the past decade, the emergence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has changed the landscape of S. aureus infections around the globe. Initially recognized for its ability to cause disease in young and healthy individuals without healthcare exposures as well as for its distinct genotype and phenotype, this original description no longer fully encompasses the diversity of CA-MRSA as it continues to expand its niche. Using four case studies, we highlight a wide range of the clinical presentations and challenges of CA-MRSA. Based on these cases we further explore the globally polygenetic background of CA-MRSA with a special emphasis on generally less characterized populations.

Genotypically different clones of Staphylococcus aureus are diverse in the antimicrobial susceptibility patterns and biofilm formations

This study evaluated whether genotypically different clinical isolates of S. aureus have similar susceptibilities to individual antibiotics. It further aims to check the impact of biofilm on the in vitro activity of vancomycin, daptomycin, linezolid, and tigecycline against S. aureus clones. The study used a total of 60 different clinical MSSA and MRSA isolates. Susceptibilities were performed in planktonic cultures by macrobroth dilution and epsilon-test (E test) system. Biofilm production was determined using an adherent plate assay. The efficacy of antimicrobial activities against biofilms formation was checked using confocal laser scanning microscopy (CLSM). The study found that similar and different spa, MLST, and SCCmec types displayed high variation in their susceptibilities to antibiotics with tigecycline and daptomycin being the most effective. The biofilms were found resistant to high concentrations of most antibiotics tested with daptomycin being the most effective drug used in adhesive biofilms. A considerable difference exists among similar and various clone types against antibiotics tested. This variation could have contributed to the degree of virulence even within the same clonal genotype and enhanced heterogeneity in the infection potential. Thus, the development of a rapid and precise identification profile for each clone in human infections is important.