S. pneumoniae strains increasingly resistant in post-PCV13 era
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Researchers observed a “rapid and steady erosion of antibiotic susceptibility” among Streptococcus pneumoniae strains in the years since the 13-valent pneumococcal conjugative vaccine, or PCV13, was introduced, according to study findings.
The rise is due mostly to serotypes not included in the vaccine and mirrors the emergence of resistance after the introduction of PCV7 years earlier, the researchers noted.
“History repeats itself,” Michael E. Pichichero, MD, clinical professor of pediatrics at the University of Rochester Medical Center, told Healio. “Antibiotic resistance among Streptococcus pneumoniae strains isolated from children is rising since 2013 due to serotypes not included in the PCV13 and strains have a different profile of susceptibility compared to the pre-PCV13 era.”
In a prospective cohort study, Pichichero and colleagues collected more than 1,200 S. pneumoniae isolates between 2006 and 2016 from patients aged 6 to 36 months at pediatric primary care practices in Rochester, New York, to characterize antibiotic susceptibility of the isolates.
They found capsular serotypes not included in PCV13, especially 11A, 35B and 35F, accounted for much of the change in susceptibility.
“As occurred during the PCV7 era, the dominant emerging serotypes —35B, 35F and 11A — have a competitive advantage due to multiple antibiotic resistance so antibiotic use among the population selects out the 35B, 35F and 11A strains to predominate,” Pichichero said.
According to the study, resistance to penicillin decreased initially following the introduction of PCV13 but rebounded to levels similar to those before the introduction of the vaccine. Pichichero and colleagues also reported observing resistance to third generation cephalosporins, fluoroquinolones and carbapenems.
“Resistance among 35B and 35F isolates to penicillin and amoxicillin is notable,” Pichichero said. “Importantly, we found the minimum concentration of third-generation cephalosporins and carbapenems needed to kill 35B and 35F pneumococci rapidly increased since 2013 through end of 2016.”
Pichichero said that resistance to fluoroquinolones had increased among serotype 11A strains and that physicians rely on fluoroquinolones — as well as cephalosporins and carbapenems — to empirically treat sepsis of unknown cause in patients admitted to the ICU.
“Our study suggests that these incredibly valuable broad-spectrum antibiotics may soon lose their effectiveness against serotype 35B, 35F and/or 11A strains,” he said. “Unfortunately, neither PCV15 (Merck) nor PCV20 (Pfizer) include a serotype 35B or 35F strain as an ingredient; PCV20 will include serotype 11A.” – by Ken Downey Jr.
Disclosures: The authors report no relevant financial disclosures.
Perspective
Back to TopEugene Shapiro, MD
In this article, the authors found that since the introduction of PCV13, an increasing number of isolates of pneumococci from young children, recovered primarily from swabs of the nasopharynx, have been either resistant or relatively resistant to penicillin and to a number of other antimicrobial agents, most notably azithromycin.
The authors indicate that the increase in resistant strains likely occurred, in part, because serotypes in PCV13 that typically are susceptible to penicillin and to other antimicrobials were replaced by serotypes more likely to be resistant, and in part because even strains that usually were highly susceptible to penicillin were becoming more resistant.
There are more than 90 different serotypes of pneumococci, the pathogenic potential of which vary. Unlike the pneumococcal polysaccharide vaccine, not only does PCV13 provide protection against invasive pneumococcal infections such as bacteremia, it also causes a marked decrease in nasopharyngeal colonization with vaccine serotypes.
However, there typically is a concomitant increase in colonization with non-vaccine serotypes that, although they certainly can cause disease, fortunately tend to be less likely to do so, especially in children.
The clinical importance of the apparent increase in the antimicrobial resistance of these pneumococci remains to be determined, but the observation certainly raises concerns. It will be important to determine whether a similar change in antimicrobial susceptibility is occurring in other geographic locations and in other demographic groups, and whether it is also observed in strains of pneumococci that are isolated from sites of infection, rather than primarily from sites of colonization. Continuing surveillance of this potential problem is important.
Disclosure: Shapiro reports no relevant financial disclosures.
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