Tag Archive for: methicillin-resistant Staphylococcus aureus

Staphylococcus aureus

Microbiological diagnoses and clinical outcomes for acute hematogenous osteomyelitis

Staphylococcus aureus

Acute hematogenous osteomyelitis is an infection that occurs in the bone and is most commonly caused by the pathogen Staphylococcus aureus.

Hospital length of stay (LOS) was shorter and odds of receiving three or more unique antibiotics for acute hematogenous osteomyelitis (AHO) was lower in culture-negative patients versus culture-positive patients, according to findings presented by researchers at Children’s National Hospital. The data was presented as part of a poster presentation at the ID Week 2022 conference.

AHO is an infection that occurs in the bone and is most commonly caused by the pathogen Staphylococcus aureus. AHO affects about 2-13 children per 100,000 in developed countries each year.

“For most patients with acute hematogenous osteomyelitis, the antibiotics we treat them with are empiric antibiotics – that is, our “best guess” at what antibiotic they should be on – as opposed to “definitive” antibiotics based on microbiologic results,” says Rana Hamdy, M.D., M.S.C.E., M.P.H., director of the Antimicrobial Stewardship Program at Children’s National Hospital and one of the authors of the study. “But with increasing antibiotic resistance, sometimes our “best guess” is wrong and that could lead to longer hospital length of stay and multiple changes in antibiotic regimens for some patients.”

She continues, “For this reason, the 2021 Pediatric Infectious Diseases Society clinical practice guidelines for patients with bone and joint infections suggest performing a bone biopsy when feasible to be able to have culture results to help guide the antibiotic choices.”

Blood and bone cultures may identify causative pathogens and determine antibiotic susceptibilities but obtaining bone cultures is an invasive procedure that carries risks including bleeding and the risk of sedation for the procedure.

The retrospective study included 367 patients under age 21 admitted to Children’s National Hospital from January 2010 – June 2020 with a final clinician’s diagnosis of AHO. Of the 367 patients, 210 (57.2%) had at least one positive culture result, 151 patients (41.1%) had all negative cultures, and 6 (1.6%) patients had no blood, bone or synovial fluid cultures obtained. About 83% of patients with positive culture were identified as having Staphylococcus aureus infections. Specifically, about 24% of identified pathogens were methicillin-resistant Staphylococcus aureus (MRSA).

In this population being culture-negative was associated with shorter LOS and lower odds of receiving three or more unique antibiotics.

“Our study disproved our hypothesis that patients without positive cultures would have longer hospital length of stay; however, because it was a retrospective study, there was the potential for additional confounding factors that we may not have been able to adjust for,” Dr. Hamdy adds.

Staphylococcus aureus

Understanding antibiotic resistance in patients with cystic fibrosis

Staphylococcus aureus

Patients with cystic fibrosis who carried antibiotic-resistant bacteria, such as Staphylococcus aureus, in their lungs had significantly lower microbial diversity and more aggressive disease, according to a small study published in Heliyon.

A defective gene causes thick, sticky mucus to build up in the lungs of patients with cystic fibrosis (CF). There, it traps bacteria, causing patients to develop frequent lung infections that progressively damage these vital organs and impair patients’ ability to breathe.

Most patients with this progressive genetic disorder die by the fourth decade of life. A key to helping patients live even that long – a vast improvement from an average lifespan of 10 years  just decades ago – is judicious use of antibiotics, explains Andrea Hahn, M.D., a pediatric infectious diseases specialist at Children’s National Health System.

But antibiotics are a double-edged sword, Dr. Hahn adds: Although they’re necessary to eradicate lung infections, repeated use of these drugs can lead to antibiotic resistance, making it tougher to treat future infections. Also, antibiotic use can kill the nonpathogenic bacteria living in the lungs as well. That decreases the diversity of the microbial community that resides in the lungs, a factor associated with disease progression. But how antibiotic resistance impacts the relationship between lung bacterial diversity and CF patients’ pulmonary function has been unknown.

Dr. Hahn and colleagues investigated this question in a small study that was published online Sept. 17, 2018, in Heliyon. Their findings suggest that the presence of multidrug resistant bacteria in the airways of patients with CF is associated with decreased microbial diversity and decreased pulmonary function.

In the study, the researchers recruited six patients with CF from Children’s National during well-child visits. During those appointments, the research team collected respiratory secretions from these volunteers. They collected more samples at subsequent visits, including:

  • When patients were admitted to the hospital for pulmonary exacerbations (periods when infections inflamed their airways, making it difficult to breathe);
  • Just after intravenous antibiotic courses to treat these infections; and
  • Thirty days after patients completed antibiotic therapy, when their lungs’ bacterial flora had some time to bounce back.

Over the 18-month study period, these patients made multiple visits for exacerbations and antibiotic treatments, leading to samples from 19 patient encounters overall.

The scientists then analyzed each sample in two different ways. They used some to grow cultures in petri dishes, the classic method that labs use to figure out which bacterial species are present and to determine which antibiotics are effective in tamping them down. They used another part of the sample to run genetic analyses that searched for antibiotic resistance genes. Both methods were necessary to gather a complete inventory of which antibiotic-resistant bacteria were present, Dr. Hahn explains.

“Laboratory cultures are designed to grow certain types of bacteria that we know are problematic, but they don’t show everything,” she says. “By genetically sequencing these samples, we can see everything that’s there.”

Their results revealed a host of bacterial species present in these patients’ airways, including methicillin-resistant Staphylococcus aureus, a notoriously hard-to-treat microbe. Patients who carried this or other antibiotic-resistant bacteria had significantly lower microbial diversity in their samples and more aggressive disease. Their samples also were more likely to contain bacteria of the genus Alcaligenes, whose role in CF is not yet known.

Although heavy antibiotic use probably contributed to both the antibiotic resistance and lowered microbial diversity, Dr. Hahn says, the answer isn’t to reduce use of these drugs: They’re necessary to help patients with CF recover after each bout with pulmonary exacerbations. Rather, she says, using methods beyond a simple lab culture can help doctors target infectious bacteria more selectively, perhaps avoiding collateral damage.

“We can’t stop using antibiotics,” she says, “but we can learn to use them better.”

In addition to Dr. Hahn, Children’s co-authors include Aszia Burrell; Hani Fanous; Hollis Chaney, M.D.; Iman Sami Zakhari, M.D.; Geovanny F. Perez, M.D.; Anastassios C. Koumbourlis, M.D., MPH; and Robert J. Freishtat, M.D., MPH; and Senior Author, Keith A. Crandall, of The George Washington University.

Financial support for the research described in this post was provided by the National Institutes of Health National Center for Advancing Translational Sciences under award number UL1TR000075 and the National Heart, Lung and Blood Institute under award number K12HL119994.