Emergence of Streptococcus pneumoniae Serotype 12F after Sequential Introduction of 7- and 13-Valent Vaccines, Israel.

Israel implemented use of 7- and 13-valent pneumococcal vaccine in 2009 and 2010, respectively. We describe results of prospective, population-based, nationwide active surveillance of Streptococcus pneumoniae serotype 12F (Sp12F) invasive pneumococcal disease (IPD) dynamics in the 7 years after vaccine introduction. Of 4,573 IPD episodes during July 2009-June 2016, a total of 434 (9.5%) were caused by Sp12F. Sp12F IPD rates (cases/100,000 population) increased in children <5 years of age, from 1.44 in 2009-2010 to >3.9 since 2011-2012, followed by an increase in all ages. During 2011-2016, Sp12F was the most prevalent IPD serotype. Sp12F isolates were mostly penicillin nonsusceptible (MIC >0.06 µg/mL; MIC50 = 0.12) and predominantly of sequence type 3774), a clone exclusively found in Israel (constituting ≈90% of isolates in 2000-2009). The sharp increase, long duration, and predominance of Sp12F IPD after vaccine implementation reflect a single clone expansion and may represent more than a transient outbreak.

Outbreaks of Invasive Kingella kingae Infections in Closed Communities.

OBJECTIVES: To describe the results of the epidemiologic investigation of outbreaks of invasive Kingella kingae infections among attendees at daycare facilities located in 4 closed communities in Israel. STUDY DESIGN: The preschool-aged population of communities with clusters of Kingella cases had oropharyngeal cultures performed. K kingae isolates from infected patients and healthy contacts were genotyped by pulsed field gel electrophoresis to determine the spread of outbreak strains. RESULTS: The affected closed communities (3 military bases and 1 "kibbutz" commune) were characterized by tight social and family networks and intensive mingling. The outbreaks affected 9 of 51 attendees (attack rate: 17.6%) age 8-19 months (median: 12 months), within a 21-day period. Cases included skeletal system infections (n = 8) and bacteremia (n = 1); K kingae isolates were confirmed by the use of blood culture vials and selective media. Clinical presentation was mild and acute-phase reactants were usually normal or only moderately elevated. Thirty out of 55 (54.5%) asymptomatic children carried the outbreak strains. Analysis of the 3 clusters in which the entire preschool-aged population was cultured revealed that 31 of 71 (43.7%) children younger than 24 months of age were colonized with K kingae organisms compared with 8 of 105 (7.6%) older children (P < .001). CONCLUSIONS: Clusters of invasive K kingae infections characterized by sudden onset, high attack rate, and wide dissemination of the outbreak strain can occur in daycare facilities and closed communities. Because the mild clinical presentation of invasive K kingae infections and the fastidious nature of the organism, a high index of suspicion and use of sensitive detection methods are recommended.

Efficacy of 13-valent pneumococcal conjugate vaccine (PCV13) versus that of 7-valent PCV (PCV7) against nasopharyngeal colonization of antibiotic-nonsusceptible Streptococcus pneumoniae.

BACKGROUND: Pediatric respiratory infections caused by antibiotic-nonsusceptible Streptococcus pneumoniae (ANSP) continue to present an important challenge, even after introduction of 7-valent pneumococcal conjugate vaccine (PCV7). This randomized double-blind trial assessed the potential additional impact of PCV13 over PCV7 on reducing ANSP carriage. METHODS: Healthy infants were randomly assigned to receive PCV13 (n = 932) or PCV7 (n = 934) at ages 2, 4, 6, or 12 months. Eight nasopharyngeal specimens were collected by swabbing between ages 2 and 24 months. S. pneumoniae isolates were serotyped and tested for antimicrobial susceptibility by the disk-diffusion method and the Etest. Nasopharyngeal acquisition and prevalence of ANSP during ages 7-24 months were compared between the 2 vaccine groups. RESULTS: In general, new acquisition of pneumococci nonsusceptible to penicillin, erythromycin, clindamycin, penicillin plus erythromycin, and multiple drugs (≥3 antibiotics) was significantly lower in the PCV13 group compared with the PCV7 group; the main serotypes contributing to this significant decrease were serotype 19F, present in PCV13 and PCV7, and serotypes 6A and 19A, present in PCV13 only. CONCLUSIONS: PCV13 has a significant added benefit over PCV7 in reducing carriage of ANSP. Because carriage determines transmission, these results suggest that PCV13 will provide protection against ANSP disease that exceeds protection provided by PCV7. CLINICAL TRIALS REGISTRATION: NCT00508742.

Persistence and complex evolution of fluoroquinolone-resistant Streptococcus pneumoniae clone.

Prolonged outbreaks of multidrug-resistant Streptococcus pneumoniae in health care facilities are uncommon. We found persistent transmission of a fluroquinolone-resistant S. pneumoniae clone during 2006-2011 in a post-acute care facility in Israel, despite mandatory vaccination and fluoroquinolone restriction. Capsular switch and multiple antimicrobial nonsusceptibility mutations occurred within this single clone. The persistent transmission of fluoroquinolone-resistant S. pneumoniae during a 5-year period underscores the importance of long-term care facilities as potential reservoirs of multidrug-resistant streptococci.

Comparative immunogenicity and efficacy of 13-valent and 7-valent pneumococcal conjugate vaccines in reducing nasopharyngeal colonization: a randomized double-blind trial.

BACKGROUND: The 13-valent pneumococcal conjugate vaccine (PCV13) was licensed to replace the 7-valent pneumococcal conjugate vaccine (PCV7) based on serological noninferiority criteria. To date no randomized PCV13 pediatric trial has included clinical endpoints. METHODS: This randomized double-blind trial compared the impact of PCV13 versus PCV7 on nasopharyngeal (NP) colonization and immunogenicity. Healthy infants were randomized (1:1) to receive PCV7 or PCV13 at ages 2, 4, 6, and 12 months; NP swabs were collected at 2, 4, 6, 7, 12, 13, 18, and 24 months, and blood was drawn at 7 and 13 months. Rates of NP acquisition and prevalence, and serotype-specific immunoglobulin G (IgG) concentrations were assessed. RESULTS: The per protocol analysis population included 881 PCV13 and 873 PCV7 recipients. PCV13 significantly reduced NP acquisition of the additional PCV13 serotypes 1, 6A, 7F, and 19A; the cross-reacting serotype 6C; and the common PCV7 serotype 19F. For serotype 3, and the other PCV7 serotypes, there were no significant differences between the vaccine groups. There were too few serotype 5 events to draw inference. The impact on prevalence at predefined time points was similar to that observed with NP acquisition. PCV13 elicited significantly higher IgG responses for PCV13 additional serotypes and serotype 19F, and similar or lower responses for 6/7 PCV7 serotypes. CONCLUSIONS: PCV13 resulted in lower acquisition and prevalence of NP colonization than PCV7 did for 4 additional PCV13 serotypes, and serotypes 6C and 19F. It was comparable with PCV7 for all other common serotypes. These findings predict vaccine effectiveness through both direct and indirect protection. CLINICAL TRIALS REGISTRATION: NCT00508742.

Baseline epidemiology and genetic structure of Streptococcus pneumoniae serotype 6D in southern Israel prior to introduction of pneumococcal conjugate vaccines.

We characterized Streptococcus pneumoniae serotype 6D from among previously identified S. pneumoniae serotype 6B strains from Jewish and Bedouin children in southern Israel during a decade before vaccination. S. pneumoniae serotype 6D isolates constituted 6.7% of the presumed S. pneumoniae serotype 6B isolates. S. pneumoniae serotype 6D strains belonged to 20 sequence types that were differentially distributed between the two ethnic groups.

Thiol peroxidase is an important component of Streptococcus pneumoniae in oxygenated environments.

Streptococcus pneumoniae is an aerotolerant gram-positive bacterium that causes an array of diseases, including pneumonia, otitis media, and meningitis. During aerobic growth, S. pneumoniae produces high levels of H(2)O(2). Since S. pneumoniae lacks catalase, the question of how it controls H(2)O(2) levels is of critical importance. The psa locus encodes an ABC Mn(2+)-permease complex (psaBCA) and a putative thiol peroxidase, tpxD. This study shows that tpxD encodes a functional thiol peroxidase involved in the adjustment of H(2)O(2) homeostasis in the cell. Kinetic experiments showed that recombinant TpxD removed H(2)O(2) efficiently. However, in vivo experiments revealed that TpxD detoxifies only a fraction of the H(2)O(2) generated by the pneumococcus. Mass spectrometry analysis demonstrated that TpxD Cys(58) undergoes selective oxidation in vivo, under conditions where H(2)O(2) is formed, confirming the thiol peroxidase activity. Levels of TpxD expression and synthesis in vitro were significantly increased in cells grown under aerobic versus anaerobic conditions. The challenge with D39 and TIGR4 with H(2)O(2) resulted in tpxD upregulation, while psaBCA expression was oppositely affected. However, the challenge of ΔtpxD mutants with H(2)O(2) did not affect psaBCA, implying that TpxD is involved in the regulation of the psa operon, in addition to its scavenging activity. Virulence studies demonstrated a notable difference in the survival time of mice infected intranasally with D39 compared to that of mice infected intranasally with D39ΔtpxD. However, when bacteria were administered directly into the blood, this difference disappeared. The findings of this study suggest that TpxD constitutes a component of the organism's fundamental strategy to fine-tune cellular processes in response to H(2)O(2).

Differential occurrence of Streptococcus pneumoniae serotype 11E between asymptomatic carriage and invasive pneumococcal disease isolates reflects a unique model of pathogen microevolution.

BACKGROUND: Streptococcus pneumoniae is a commensal colonizer of the human nasopharynx (NP) that causes disease after evasion of host defenses and dissemination. Pneumococcal strains expressing the newly identified serotype 11E arise from antigenically similar 11A progenitors by genetic inactivation of the O-acetyltransferase gene wcjE. Each 11E strain contains a distinct mutation to wcjE, suggesting that 11E strains are not transmitted among hosts despite their recovery from multiple patients with pneumococcal disease. We investigated whether the presumed lack of transmission of serotype 11E is consistent with its inability to survive in the NP. METHODS: More than 400 pneumococcal carriage, middle ear, conjunctiva, and blood isolates, serotyped as 11A by Quellung reaction, were reexamined for reactivity to 11A- and 11E-specific antibodies. We confirmed serotyping of isolates with sequencing of wcjE alleles. RESULTS: Serotype 11E strains were statistically more likely to occur among blood (4 of 15), conjunctiva (1 of 14), or middle ear (2 of 21) isolates than among carriage isolates (2 of 355). All 11E isolates contained unique mutations that putatively decrease wcjE expression. CONCLUSIONS: The lack of a circulating 11E clone and the increased occurrence of 11E strains among disease isolates supports the idea that serotype 11E independently arises during infection after initial colonization with a serotype 11A progenitor. Factors encountered in the NP likely contribute to relative rarity of 11E among carriage isolates, whereas selective pressures in deeper tissues possibly promote 11E emergence. These findings illustrate a novel model of microevolution that transpires during the span of a single encounter with serotype 11A, highlighting the adaptability of bacterial pathogens within hosts.

Genotyping of invasive Kingella kingae isolates reveals predominant clones and association with specific clinical syndromes.

BACKGROUND: Despite the increasing recognition of Kingella kingae as an important pathogen of early childhood, the relative frequency and invasiveness of different strains of the organism has not been investigated. A study was conducted to determine the association of K. kingae genotypes with specific clinical syndromes and the temporal and geographic distribution of invasive clones. METHODS: A collection of 181 invasive K. kingae strains, isolated between 1991 and 2012 from Israeli patients with bacteremia, skeletal system infections, or endocarditis, were typed by pulsed-field gel electrophoresis (PFGE). In addition, the correspondence between PFGE, multilocus sequence types (MLSTs), and rtxA gene sequencing results was also examined for organisms belonging to the predominant PFGE clones isolated from asymptomatic carriers and patients with invasive infections. RESULTS: A total of 32 different K. kingae clones were identified by PFGE, of which 5 (B, H, K, N, and P) caused 72.9% of all invasive infections, and were recovered during the 21-year period from different regions of the country. Clone K was significantly associated with bacteremia, clone N with skeletal system infections, and clone P with bacterial endocarditis. Strains belonging to the same PFGE clone, either carried asymptomatically or causing different invasive infections, shared MLST complexes and exhibited identical or closely related rtxA alleles. CONCLUSIONS: Although K. kingae exhibits noteworthy genetic heterogeneity, a limited number of distinct clones cause the majority of invasive infections in Israel, exhibiting genetic stability, long-term persistence, and wide geographic dispersal. K. kingae strains also show significant association with specific clinical syndromes.

Clonal distribution of common pneumococcal serotypes not included in the 7-valent conjugate vaccine (PCV7): marked differences between two ethnic populations in southern Israel.

This study aimed to compare the clonal distribution of common pneumococcal strains not included in the 7-valent pneumococcal conjugate vaccine (PCV7) that were isolated from cases of acute otitis media (AOM) and invasive pneumococcal disease (IPD) in two distinct ethnic populations in southern Israel during the decade (1999 to 2008) preceding PCV7 implementation. Isolates recovered from Jewish and Bedouin children <5 years old were characterized by antibiotic resistance and molecular epidemiology using pulsed-field gel electrophoresis and multilocus sequence typing. Of 5,236 AOM and 425 IPD isolates, 43% and 57% were from Jewish and Bedouin children, respectively. PCV7 accounted for 54% and 45% of the AOM and IPD episodes, respectively. Eleven major non-PCV7 serotypes (1, 3, 5, 6A, 7F, 12F, 15B/C, 19A, 21, 33F, and 35B) constituted 31% and 42% of the AOM and IPD episodes, respectively. The clonal distributions of the 11 non-PCV7 serotypes and their antibiotic susceptibilities were significantly different among the two ethnic populations in both the AOM and IPD groups. About half of the AOM and IPD cases resulted from non-PCV7 pneumococci, even before PCV7 implementation. The significant differences between the two ethnic populations suggest that lifestyle and microenvironment are major determinants in the clonal distribution of disease-causing pneumococci. Post-PCV7 surveillance is important in understanding non-PCV7 clonal expansion in the two distinct populations.

Prevalence of Streptococcus pneumoniae in respiratory samples from patients with tracheostomy in a long-term-care facility.

We aimed to study the prevalence of Streptococcus pneumoniae in respiratory samples from institutionalized patients with chronic tracheostomy. A total of 264 pairs of nasopharyngeal and endotracheal cultures were collected. There was no difference in the proportion of positive cultures between children (21%) and adults (18%). However, the proportion of positive endotracheal cultures was higher than that of nasopharyngeal cultures in adults (18% versus 3%, respectively; P < 0.001) but not in children (17% in both sites).

Endogenous H2O2 produced by Streptococcus pneumoniae controls FabF activity.

FabF elongation condensing enzyme is a critical factor in determining the spectrum of products produced by the FASII pathway. Its active site contains a critical cysteine-thiol residue, which is a plausible target for oxidation by H2O2. Streptococcus pneumoniae produces exceptionally high levels of H2O2, mainly through the conversion of pyruvate to acetyl-P via pyruvate oxidase (SpxB). We present evidence showing that endogenous H2O2 inhibits FabF activity by specifically oxidizing its active site cysteine-thiol residue. Thiol trapping methods revealed that one of the three FabF cysteines in the wild-type strain was oxidized, whereas in an spxB mutant, defective in H2O2 production, none of the cysteines was oxidized, indicating that the difference in FabF redox state originated from endogenous H2O2. In vitro exposure of the spxB mutant to various H2O2 concentrations further confirmed that only one cysteine residue was susceptible to oxidation. By blocking FabF active site cysteine with cerulenin we show that the oxidized cysteine was the catalytic one. Inhibition of FabF activity by either H2O2 or cerulenin resulted in altered membrane fatty acid composition. We conclude that FabF activity is inhibited by H2O2 produced by S. pneumoniae.

Differential circulation of Streptococcus pneumoniae serotype 6C clones in two Israeli pediatric populations.

We genotyped Streptococcus pneumoniae serotype 6C (Sp6C) isolates collected from Jewish and Bedouin children in southern Israel during the decade before vaccination. Sp6C constituted 8.2% of the presumed Sp6A isolates. All of the Sp6C clonal clusters were associated with serogroup 6, mainly Sp6A. Different clonal distributions were found in the two subpopulations.

Validation of factor 6d antiserum for serotyping Streptococcus pneumoniae serotype 6C.

Factor 6d antiserum reacts with the new Streptococcus pneumoniae serotype 6C. Serogroup 6 isolates, consisting of 49 6A, 42 6B and 98 6C strains from the United States and Israel, serotyped in parallel by PCR and capsular swelling methods, were all identified correctly. The new factor 6d antiserum accurately identifies serotype 6C.

Pyruvate formate lyase is required for pneumococcal fermentative metabolism and virulence.

Knowledge of the in vivo physiology and metabolism of Streptococcus pneumoniae is limited, even though pneumococci rely on efficient acquisition and metabolism of the host nutrients for growth and survival. Because the nutrient-limited, hypoxic host tissues favor mixed-acid fermentation, we studied the role of the pneumococcal pyruvate formate lyase (PFL), a key enzyme in mixed-acid fermentation, which is activated posttranslationally by PFL-activating enzyme (PFL-AE). Mutations were introduced to two putative pfl genes, SPD0235 and SPD0420, and two putative pflA genes, SPD0229 and SPD1774. End-product analysis showed that there was no formate, the main end product of the reaction catalyzed by PFL, produced by mutants defective in SPD0420 and SPD1774, indicating that SPD0420 codes for PFL and SPD1774 for putative PFL-AE. Expression of SPD0420 was elevated in galactose-containing medium in anaerobiosis compared to growth in glucose, and the mutation of SPD0420 resulted in the upregulation of fba and pyk, encoding, respectively, fructose 1,6-bisphosphate aldolase and pyruvate kinase, under the same conditions. In addition, an altered fatty acid composition was detected in SPD0420 and SPD1774 mutants. Mice infected intranasally with the SPD0420 and SPD1774 mutants survived significantly longer than the wild type-infected cohort, and bacteremia developed later in the mutant cohort than in the wild type-infected group. Furthermore, the numbers of CFU of the SPD0420 mutant were lower in the nasopharynx and the lungs after intranasal infection, and fewer numbers of mutant CFU than of wild-type CFU were recovered from blood specimens after intravenous infection. The results demonstrate that there is a direct link between pneumococcal fermentative metabolism and virulence.

Pharyngeal colonization by Kingella kingae in children with invasive disease.

Kingella kingae organisms isolated from the blood of 3 children with invasive infections were identical by pulsed field gel electrophoresis and random amplified polymorphic DNA-polymerase chain reaction analysis to those recovered from the patients' pharynx, demonstrating the likely role of upper respiratory tract colonization in the pathogenesis of the disease caused by this bacterium.

Serotype coverage of invasive and mucosal pneumococcal disease in Israeli children younger than 3 years by various pneumococcal conjugate vaccines.

BACKGROUND: : Since the introduction of the 7-valent pneumococcal conjugate vaccine (PCV7) in the United States, the need for additional serotype coverage has become clear. Our objective was to assess the potential serotype coverage of PCV7 and of the 2 experimental conjugate vaccines, 10-valent (PCV10) and 13-valent (PCV13), against invasive pneumococcal disease (IPD), acute otitis media (AOM), acute conjunctivitis (AC), and pneumococcal carriage in southern Israel, where PCV7 had not yet been introduced at the time of the study. METHODS: : Data on isolates were obtained prospectively from children <36 months during 2000-2004. The potential coverage of the PCVs was calculated and analyzed separately for antibiotic-resistant strains. RESULTS: : A total of 5497 isolates were collected: 189 from blood or cerebrospinal fluid, 3197 from middle ear fluid, 348 from the conjunctiva, and 1763 from the nasopharynx of healthy children. The serotype coverage of PCV7 for IPD, AOM, AC, and carriage was 44%, 54%, 37%, and 46%, respectively. Serotypes included in PCV7 caused 47 IPD cases per 100,000 children <3 years (54 per 100,000 if serotype 6A is included). PCV10 extended mainly the coverage of IPD, while addition of serotypes 6A and 19A to PCV13 increased the coverage substantially in all entities (84%, 79%, 54%, and 67% in IPD, AOM, AC, and carriage, respectively). PCV13 could prevent >90% of penicillin-, macrolide-, and multidrug-resistant strains associated with IPD and AOM. CONCLUSIONS: : PCV7 can substantially decrease pneumococcal disease and carriage in Israel, but PCV10 and PCV13 have a significant added benefit. Moreover, PCV13 has an important potential added benefit over PCV7 and PCV10 in reducing disease by drug-resistant Streptococcus pneumoniae.

Dissemination of Kingella kingae in the community and long-term persistence of invasive clones.

BACKGROUND: Although Kingella kingae is being increasingly recognized as an important pediatric pathogen, our current understanding of the transmission of the organism is limited. The dissemination of K. kingae in the community was studied in 2 ethnic groups living side-by-side in Southern Israel. METHODS: Organisms recovered from oropharyngeal cultures, obtained from healthy young Jewish and Bedouin children during a 12-month period, were typed by pulsed-field gel electrophoresis and compared. RESULTS: Isolates from Bedouin children usually differed from those derived from Jews, confirming the relative social isolation of the 2 populations and the importance of close mingling in the spread of K. kingae. Significant clustering of genotypic clones in households and Bedouin neighborhoods was observed, indicating person-to-person transmission through intimate contact. Organisms detected in the study were identical to historical isolates recovered over the last 15 years from respiratory carriers and patients with bacteremia or skeletal infections. CONCLUSIONS: The present study demonstrates that children may be asymptomatically colonized in the respiratory tract by virulent K. kingae clones. The organism is transmitted from child-to-child through intimate contact. Some strains exhibit increased fitness and are maintained in the population for prolonged periods.

Streptococcus pneumoniae serotype 3 among Costa Rican children with otitis media: clinical, epidemiological characteristics and antimicrobial resistance patterns.

BACKGROUND: After the introduction of the seven valent-pneumococcal conjugated vaccine into our National Immunization Program, it is important to establish and track local serotype distribution in order to evaluate its impact specially because serotype replacement phenomena has been described.To describe the clinical, epidemiological and antimicrobial resistance patterns of Costa Rican children with otitis media caused by Streptococcus pneumoniae serotype 3. METHODS: Middle ear fluid samples were obtained from Costa Rican children with otitis media who participated in various antimicrobial clinical trials between 1992 and 2007. Streptococcus pneumoniae was identified according to laboratory standard procedures. Strains were serotyped and antimicrobial susceptibility to penicillin, amoxicillin, cefuroxime, ceftriaxone, azithromycin and levofloxacin was determined by E-test. RESULTS: Throughout 1992-2007 a total of 1919 tympanocentesis were performed in children with otitis media (median age: 19 months) and yielded a total of 1208 middle ear isolates. The most common pathogens were: Streptococcus pneumoniae, 511 isolates (49%); Non-Typable Haemophilus influenzae, 386 isolates (37%); Moraxella catarrahalis, 100 isolates (9.5%); and Streptococcus pyogenes, 54 isolates (5%). Streptococcus pneumoniae serotyping was performed in 346/511 isolates (68%) recovered during years 1999-2006. The most common serotypes were 19F (101/30.0%), 14 (46/13.7%), 3 (34/10.1%), 6B (30/8.9%) and 23F (23/6.8%). Analysis performed per years showed a higher prevalence of serotype 3 Streptococcus pneumoniae during the study period 2004 and 2005. During the entire study period (1999-2006) serotype 3 was most commonly isolated in children older than 24 months (61.2% vs 40.6%;P = 0.05) and showed a lower rate of penicillin non-susceptibility (4.0% vs 18%; P = 0.003). CONCLUSION: Streptococcus pneumoniae serotype 3 is an important pathogen in Costa Rican children with otitis media, especially in children older than 24 months of age (P = 0.05). Most serotype 3 isolates were susceptible to penicillin, cephalosporins, macrolides and quinolones.

Effect of hydrogen peroxide production and the Fenton reaction on membrane composition of Streptococcus pneumoniae.

As part of its aerobic metabolism, Streptococcus pneumoniae generates high levels of H(2)O(2) by pyruvate oxidase (SpxB), which can be further reduced to yield the damaging hydroxyl radicals via the Fenton reaction. A universal conserved adaptation response observed among bacteria is the adjustment of the membrane fatty acids to various growth conditions. The aim of the present study was to reveal the effect of endogenous reactive oxygen species (ROS) formation on membrane composition of S. pneumoniae. Blocking carbon aerobic metabolism, by growing the bacteria at anaerobic conditions or by the truncation of the spxB gene, resulted in a significant enhancement in fatty acid unsaturation, mainly cis-vaccenic acid. Moreover, reducing the level of OH(.) by growing the bacteria at acidic pH, or in the presence of an OH(.) scavenger (salicylate), resulted in increased fatty acid unsaturation, similar to that obtained under anaerobic conditions. RT-PCR results demonstrated that this change does not originate from a change in mRNA expression level of the fatty acid synthase II genes. We suggest that endogenous ROS play an important regulatory role in membrane adaptation, allowing the survival of this anaerobic organism at aerobic environments of the host.