3.3 Miscellaneous pathogens of interest
3.3.1 Respiratory and central nervous system pathogens
High-level penicillin resistance in S. pneumoniae can lead to treatment failure in respiratory tract infections. Even low-level resistance is a problem for infections of the central nervous system, for example meningitis. This is because only small concentrations of drug can be achieved in the brain because of the presence of the blood-brain barrier (Linares et al., 2010).
Penicillin resistance in S. pneumoniae is acquired differently to the resistance mechanisms described so far. It is generally the result of cumulative mutations and resistance acquisition leading to resistant strains, rather than by a single transmissible genetic element. An association has often been observed between rates of antimicrobial use and prevalence of resistance in this organism (Albrich et al., 2004; WHO, 2001).
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Why is this organism in the ‘medium’ WHO priority R&D category and not in the ‘high’ category?
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Although this organism is responsible for life-threatening pneumonia and meningitis, antimicrobial resistance is not as readily transmissible as for some of the other organisms. The resistant strains themselves are transmissible but infection can be controlled by vaccination, and as the strain is removed from circulation so too is its resistance. Most resistant strains remain susceptible to some antimicrobials so can still be treated. MDR S. pneumoniae is an emerging problem (Cillóniz et al., 2018) though, so it could be upgraded in a future list (WHO, 2001).
Haemophilus influenzae is a cause of vaccine-preventable invasive disease (HiB) in children, mainly causing respiratory tract infection or meningitis. Despite the ongoing success of the global vaccine programme, resistance to amoxicillin, in both HiB and non-typeable H. influenzae (NTHi) strains, remains a problem as amoxicillin would normally be the treatment of choice (Su et al., 2020; Van Eldere et al., 2014).
3.2.3 Vancomycin-resistant Enterococci
