Live attenuated influenza vaccine enhances colonization of Streptococcus pneumoniae and Staphylococcus aureus in mice - PubMed

Michael J Mina  et al. mBio . 2014 .

Free PMC article

. 2014 Feb 18;5(1):e01040-13. doi: 10.1128/mBio.01040-13.

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Abstract

Community interactions at mucosal surfaces between viruses, like influenza virus, and respiratory bacterial pathogens are important contributors toward pathogenesis of bacterial disease. What has not been considered is the natural extension of these interactions to live attenuated immunizations, and in particular, live attenuated influenza vaccines (LAIVs). Using a mouse-adapted LAIV against influenza A (H3N2) virus carrying the same mutations as the human FluMist vaccine, we find that LAIV vaccination reverses normal bacterial clearance from the nasopharynx and significantly increases bacterial carriage densities of the clinically important bacterial pathogens Streptococcus pneumoniae (serotypes 19F and 7F) and Staphylococcus aureus (strains Newman and Wright) within the upper respiratory tract of mice. Vaccination with LAIV also resulted in 2- to 5-fold increases in mean durations of bacterial carriage. Furthermore, we show that the increases in carriage density and duration were nearly identical in all aspects to changes in bacterial colonizing dynamics following infection with wild-type (WT) influenza virus. Importantly, LAIV, unlike WT influenza viruses, had no effect on severe bacterial disease or mortality within the lower respiratory tract. Our findings are, to the best of our knowledge, the first to demonstrate that vaccination with a live attenuated viral vaccine can directly modulate colonizing dynamics of important and unrelated human bacterial pathogens, and does so in a manner highly analogous to that seen following wild-type virus infection.

Importance: Following infection with an influenza virus, infected or recently recovered individuals become transiently susceptible to excess bacterial infections, particularly Streptococcus pneumoniae and Staphylococcus aureus. Indeed, in the absence of preexisting comorbidities, bacterial infections are a leading cause of severe disease during influenza epidemics. While this synergy has been known and is well studied, what has not been explored is the natural extension of these interactions to live attenuated influenza vaccines (LAIVs). Here we show, in mice, that vaccination with LAIV primes the upper respiratory tract for increased bacterial growth and persistence of bacterial carriage, in a manner nearly identical to that seen following wild-type influenza virus infections. Importantly, LAIV, unlike wild-type virus, did not increase severe bacterial disease of the lower respiratory tract. These findings may have consequences for individual bacterial disease processes within the upper respiratory tract, as well as bacterial transmission dynamics within LAIV-vaccinated populations.

Figures

FIG 1

LAIV is safe, effective, replicates…

FIG 1

LAIV is safe, effective, replicates well within the URT, and elicits a robust…

FIG 1

LAIV is safe, effective, replicates well within the URT, and elicits a robust cytokine response. (A) WT and LAIV HK/Syd viruses were grown in MDCK cells at 37°C and LAIV virus was grown at 33°C, and viral titers were measured via the median TCID50 (n = 3 per group). (B) Groups of 12 to 14 8-week-old BALB/c mice were inoculated with 2e6 TCID50 LAIV, WT HK/Syd virus, or PBS and monitored for weight loss. Three of 12 mice and 2/12 mice died at 4 and 7 days postinfection with WT HK/Syd virus, respectively, while no mice died following LAIV or PBS inoculation. (C) Groups of 8 4-week-old BALB/c mice were inoculated with 2e6 TCID50 of LAIV (2 of the 3 groups) or PBS and 4 weeks later infected with a lethal dose (5e7 TCID50) of WT HK/Syd virus or the PBS control. Infection was considered lethal if body weight fell below 70% of the initial body weight. (D) Four groups of 5 mice each were vaccinated with LAIV, and whole lung and NP viral titers were measured at 1, 3, 5, and 7 days postvaccination. (E) Four groups of 5 mice were vaccinated with LAIV, and NP and BAL specimen cytokines were measured at day 0 (unvaccinated mice) and days 3, 5, and 7 following vaccination. Error bars represent standard errors (SE) of the mean. Asterisks indicate statistically significant differences from controls by two-sided Student’s t test. *, P

FIG 2

LAIV and WT influenza virus…

FIG 2

LAIV and WT influenza virus infection similarly enhance 19F pneumococcal carriage density and…

FIG 2

LAIV and WT influenza virus infection similarly enhance 19F pneumococcal carriage density and duration of colonization. Groups of 12 to 14 mice were vaccinated with LAIV and infected with WT influenza virus or PBS vehicle at 7 days following colonization with 19F pneumococcus (A to C) or 7 days prior to colonization with 19F (D to F). Bacterial strains constitutively expressed luciferase, and nasopharyngeal carriage density was measured via in vivo imaging (IVIS) at 12 h postbacterial infection and daily thereafter (B and E). Duration of colonization (C and F) was measured via bacterial plating of nasal washes taken daily after carriage density decreased below the limit of detection for IVIS imaging (~1e4 CFU/ml). Asterisks indicate significant differences between vaccinated (black asterisks in panels B and E) or WT influenza virus-infected (white asterisks in panels B and E) versus control groups (P

FIG 3

LAIV enhancement of pneumococcal density…

FIG 3

LAIV enhancement of pneumococcal density is time dependent and long lasting. Groups of…

FIG 3

LAIV enhancement of pneumococcal density is time dependent and long lasting. Groups of 12 to 14 mice were vaccinated with LAIV or PBS vehicle at 1 or 7 days prior to colonization with pneumococcal (pneumo) serotype 7F. Bacterial strains constitutively expressed luciferase, and bacterial NP density was measured via IVIS in vivo imaging (A and B). Mean cumulative bacterial titers in panel B were calculated by first calculating the cumulative bacterial titers per individual mouse NP at each time point and then calculating the average and SE across the individual cumulative titers per time point, rather than simply averaging the areas under the mean density curves shown in panel A. Asterisks indicate significant differences in bacterial densities between the vaccinated and PBS control groups (dark green indicates LAIV given 7 days prior and red indicates LAIV given 1 day prior to 7F inoculation; P < 0.05 by two-tailed Student’s t test). (C) Groups of mice were vaccinated with LAIV (n = 20) or PBS vehicle control (n = 30), respectively, at 28 days prior to colonization with 19F pneumococcus. Fold differences per day between mean bacterial densities measured in mice treated 28 days prior with LAIV versus PBS are reported. Error bars indicate standard errors of the mean and asterisks indicate significant differences (P < 0.05) from PBS controls (by two-tailed single-sample t test).

FIG 4

LAIV enhances bacterial load and…

FIG 4

LAIV enhances bacterial load and duration of staphylococcal carriage. Groups of 12 to…

FIG 4

LAIV enhances bacterial load and duration of staphylococcal carriage. Groups of 12 to 14 mice were vaccinated with LAIV or PBS vehicle 7 days prior to colonization with S. aureus (S.A.) strain Wright (A and B) or Newman (C and D). S. aureus constitutively expressed luciferase, and bacterial density was measured via IVIS in vivo imaging. Duration of colonization (B and D) was measured via bacterial plating of nasal washes taken daily after the carriage density decreased below the limit of detection for IVIS imaging. Asterisks indicate significant differences between vaccinated and control groups (P < 0.05 by two-sided Student’s t test), and error bars represent standard errors around the mean.

FIG 5

LAIV does not increase severe…

FIG 5

LAIV does not increase severe bacterial disease or mortality. Groups of mice received…

FIG 5

LAIV does not increase severe bacterial disease or mortality. Groups of mice received intranasal LAIV vaccination (solid red curves), sublethal infection with WT influenza virus (broken black curves), or PBS (broken blue curves) 7 days prior to inoculation with a sublethal dose of Streptococcus pneumoniae type 2 (1e5 CFU D39; n = 20 per group) (B) or type 3 (1e3 CFU A66.1; n = 12 to 15 per group) (C), and body weight and mortality were observed at least every 12 h for the first 4 days postpneumococcal inoculation and daily thereafter. Kaplan-Meier survival curves with 95% confidence intervals (CI) were constructed, and asterisks indicate statistically significant differences (P < 0.05 by log rank test) between LAIV- or WT virus-infected groups versus PBS controls.

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