Macrolides and β-Lactam Antibiotics Enhance C3b Deposition on the Surface of Multidrug-Resistant Streptococcus pneumoniae Strains by a LytA Autolysin-Dependent Mechanism

Abstract

The emergence of Streptococcus pneumoniae strains displaying high levels of multidrug resistance is of great concern worldwide and a serious threat for the outcome of the infection. Modifications of the bacterial envelope by antibiotics may assist the recognition and clearance of the pathogen by the host immune system. Recognition of S. pneumoniae resistant strains by the complement component C3b was increased in the presence of specific anti-pneumococcal antibodies and subinhibitory concentrations of different macrolides and ␤-lactam antibiotics for all the strains investigated. However, C3b levels were unchanged in the presence of serum containing specific antibodies and sub-MICs of levofloxacin. To investigate whether LytA, the main cell wall hydrolase of S. pneumoniae, might be involved in this process, lytA-deficient mutants were constructed. In the presence of antibiotics, loss of LytA was not associated with enhanced C3b deposition on the pneumococcal surface, which confirms the importance of LytA in this interaction. The results of this study offer new insights into the development of novel therapeutic strategies using certain antibiotics by increasing the efficacy of the host immune response to efficiently recognize pneumococcal resistant strains. Streptococcus pneumoniae, also termed pneumococcus, is the leading bacterial cause of acute otitis media in children, community-acquired pneumonia, and nonepidemic meningitis and a frequent cause of bacteremia (15). Despite appropriate antibiotic treatment, invasive pneumococcal disease (IPD) is a very common infection associated with high rates of morbidity and mortality worldwide. The widespread use of antibiotics has been one of the major reasons for the emergence of clinical isolates that exhibit resistance to multiple antibiotics. A major threat to fighting IPD is the appearance of strains harboring high levels of antibiotic resistance, as has been recently reported in Europe (19). The development of resistance to a wide variety of antimicrobial drugs has allowed S. pneumoniae to attain the status of a so-called "superbug" (11). The complement system is one of the first lines of defense against invading pathogens, such as S. pneumoniae, with an essential role in both innate and adaptive immunity (23). Activation of complement cascades leads to the formation of the key component C3b, which is crucial in host defense against pneumococcus by coating the microorganism and stimulating phagocytosis (23). In cases where the invading pathogen displays multidrug resistance, antimicrobial concentrations in serum may be insufficient, and therefore, the outcome of the infection largely depends on the interaction between bacterial virulence factors and host immune mechanisms. Using mice infected with a pneumococcal resistant strain and treated with subtherapeutic doses of ␤-lactam antibiotics, we previously found that bacterial clearance and survival were increased in mice immunized against S. pneumoniae, suggesting a synergistic effect between antimicrobial chemother...

Pleiotropic Effects of Cell Wall Amidase LytA on Streptococcus pneumoniae Sensitivity to the Host Immune Response

“…Bacterial strains and growth conditions. The S. pneumoniae clinical isolates used were D39 (NCTC 07466, serotype 2 [ST2]); strain S3 lytA (ST23F) and its complemented mutant, S3C (lytA ϩ ) (25); and strain 1515/97 (ST6B) and its lytA-deficient strain (26). Isogenic D39 mutants with mutations in lytA, ply, pspC, or lytB were constructed by transformation, using standard protocols (18,21,27,28), with DNA prepared from mutants previously characterized.…”

Poor Long-Term Efficacy of Prevnar-13 in Sickle Cell Disease Mice Is Associated with an Inability to Sustain Pneumococcal-Specific Antibody Titers

“…It has been observed that the administration of antibiotics enhances the deposition of complement components on the surface of S . pneumoniae , thereby enhancing protective phagocytic responses in conjunction with specific anti-pneumococcal antibodies [ 22 , 23 , 24 ]. It has also been previously shown in SCD patients that have reduced opsonization due to defects in the alternative complement pathway, which acts in conjunction with impaired anti-pneumococcal antibody responses to further inhibit opsonization [ 25 ].…”

Combination of Antibodies and Antibiotics as a Promising Strategy Against Multidrug-Resistant Pathogens of the Respiratory Tract

“…Once the complement cascade is activated and after numerous enzymatic reactions, the key component C3 is formed. In the presence of serum containing antibodies to pneumococcus and sub-inhibitory concentrations of β-lactam antibiotics or macrolides, C3 deposition on the surface of different MDR strains was markedly increased ( 33 , 66 ). Overall, activation of the recognition by acute phase proteins and complement proteins by certain antibiotics, such as β-lactams and macrolides in the presence of specific antibodies has functional consequences increasing the phagocytosis process and the clearance of the microorganism (Figure 1 ) ( 32 , 33 , 66 ).…”

“…In the presence of serum containing antibodies to pneumococcus and sub-inhibitory concentrations of β-lactam antibiotics or macrolides, C3 deposition on the surface of different MDR strains was markedly increased ( 33 , 66 ). Overall, activation of the recognition by acute phase proteins and complement proteins by certain antibiotics, such as β-lactams and macrolides in the presence of specific antibodies has functional consequences increasing the phagocytosis process and the clearance of the microorganism (Figure 1 ) ( 32 , 33 , 66 ). Previous studies using a sepsis model of infection in mice, have demonstrated that protective doses of amoxicillin and cefotaxime were, approximately, eight times lower in the presence of antibodies than in their absence ( 67 , 68 ).…”

“…It is important to mention that whatsoever, the possible benefit of the synergistic effect mediated by antibodies will not be based in a reduction of the antibiotic doses. The benefit would be to obtain a higher efficacy from the therapeutic perspective after the administration of the common doses used against IPD cases produced by clinical isolates with high MIC levels ( 32 , 33 , 66 , 67 ). Hence, vaccination reduces the magnitude of the pharmacodynamics indices (i.e., drug exposure defined from pharmacokinetic/pharmacodynamic ratio, ft > MIC, fCmax/MIC or fAUC/MIC), needed to reach a certain effect.…”