Bacterial aetiology of recalcitrant acute otitis media in 62 children-high risk of pathogen colonisation after treatment

Amino Acid Starvation-Induced Glutamine Accumulation Enhances Pneumococcal Survival

Bacteria are known to cope with amino acid starvation by the stringent response signaling system, which is mediated by the accumulation of the (p)ppGpp alarmones when uncharged tRNAs stall at the ribosomal A site. While a number of metabolic processes have been shown to be regulatory targets of the stringent response in many bacteria, the global impact of amino acid starvation on bacterial metabolism remains obscure. This work reports the metabolomic profiling of the human pathogen Streptococcus pneumoniae under methionine starvation. Methionine limitation led to the massive overhaul of the pneumococcal metabolome. In particular, methionine-starved pneumococci showed a massive accumulation of many metabolites such as glutamine, glutamic acid, lactate, and cyclic AMP (cAMP). In the meantime, methionine-starved pneumococci showed a lower intracellular pH and prolonged survival. Isotope tracing revealed that pneumococci depend predominantly on amino acid uptake to replenish intracellular glutamine but cannot convert glutamine to methionine. Further genetic and biochemical analyses strongly suggested that glutamine is involved in the formation of a "prosurvival" metabolic state by maintaining an appropriate intracellular pH, which is accomplished by the enzymatic release of ammonia from glutamine. Methionine starvation-induced intracellular pH reduction and glutamine accumulation also occurred to various extents under the limitation of other amino acids. These findings have uncovered a new metabolic mechanism of bacterial adaptation to amino acid limitation and perhaps other stresses, which may be used as a potential therapeutic target for infection control. IMPORTANCE Bacteria are known to cope with amino acid starvation by halting growth and prolonging survival via the stringent response signaling system. Previous investigations have allowed us to understand how the stringent response regulates many aspects of macromolecule synthesis and catabolism, but how amino acid starvation promotes bacterial survival at the metabolic level remains largely unclear. This paper reports our systematic profiling of the methionine starvation-induced metabolome in S. pneumoniae. To the best of our knowledge, this represents the first reported bacterial metabolome under amino acid starvation. These data have revealed that the significant accumulation of glutamine and lactate enables S. pneumoniae to form a "prosurvival" metabolic state with a lower intracellular pH, which inhibits bacterial growth for prolonged survival. Our findings have provided insightful information on the metabolic mechanisms of pneumococcal adaptation to nutrient limitation during the colonization of the human upper airway.

Bacterial aetiology of chronic otitis media with effusion in children - risk factors

Background

Otitis media with effusion (OME) may occur spontaneously because of poor Eustachian tube function or as an inflammatory response following AOM. Bacterial involvement in OME has been widely reported, with various available methods to identify pathogens from middle ear effusion, including traditional culture methods and polymerase chain reaction (PCR).

Objectives

The primary goal of this study was to evaluate the bacteriological profile of middle ear effusion in OME. Risk factors of the bacterial OME aetiology were also identified.

Methods

Middle ear effusions (MEF) from 50 children, aged 2–8 years, diagnosed by ENT and undergoing routine tympanostomy tube placement were collected. MEF samples were streaked on standard microbiological media. Next, DNA was isolated from MEF samples and analysed with multiplex PCR for Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis and Alloiococcus otitidis.

Results

In multiplex PCR assay 37 (74%) of 50 children were positive for at least one of the four microorganisms. In 27.0% positive children multiple bacterial pathogens were identified. A. otitidis was the most frequently identified in positive MEF children (59.5%). By multiplex PCR, H. influenzae, S. pneumoniae and M. catarrhalis were detected in 24, 18 and 8% of OME patients, respectively. There was significant association between bilateral infection and H. influenzae aetiology of OME.

Conclusions

Overall we found OME predominantly a single otopathogen infection caused mainly by A. otitidis, which is difficult in identification using standard culture method, ahead to S. pneumoniae and H. influenzae. However, one third of MEF samples had multiple bacterial pathogens.

Resistant Streptococcus pneumoniae strains in children with acute otitis media- high risk of persistent colonization after treatment

Background

Despite advances in the development of pneumococcal conjugate vaccines, acute otitis media (AOM) is a common childhood infection, caused mainly by Streptococcus pneumoniae. It has been suggested that persistence of pneumococcal nasopharyngeal carriage is a risk factor for subsequent recurrent infections.

Methods

In this study we evaluate the relationship between 55 pneumococcal strains obtained from nasopharynx/oropharynx (NP/OP) and middle ear fluid (MEF) of 62 children, aged between 1 and 16 years, during AOM (including recurrent/treatment failure AOM, and post-treatment visits), based on their phenotypic and genotypic characteristics performed by analyses of serotype, antibiotic susceptibility patterns and multilocus sequence typing.

Results

S.pneumoniae was isolated from 27.4% of MEF samples; it constituted 43.6% of all positive bacterial samples from MEF samples. There was statistically significant concordance between isolation from the MEF sample and NP/OP colonization by S. pneumoniae (p < 0.0001). During post-treatment visits S.pneumoniae was isolated from 20.8% of children; 91% of them were positive in pneumococcal NP/OP culture during AOM. The serotypes belonging to 10- and 13-valent pneumococcal conjugated vaccines constituted 84% and 92% of the strains, respectively. Multidrug resistance was found in 84% of the strains. According to multivariate analysis, pneumococcal colonization after antibiotic therapy was significantly associated with shorter length of therapy in children with bilateral AOM.

Conclusions

High persistent prevalence of antibiotic-resistant S.pneumoniae strains in children with AOM after unsuccessful bacterial eradication may presumably be regarded as a predisposing factor of infection recurrence.

Electronic supplementary material

The online version of this article (10.1186/s12879-018-3398-9) contains supplementary material, which is available to authorized users.