By Carol A. Kemper, MD, FACP

House Mice as Vectors?

SOURCE: Williams SH, Che X, Paulick A, et al. New York City house mice (Mus musculus) as potential reservoirs for pathogenic bacteria and antimicrobial resistance determinants. MBio 2018;9. doi: 10.1128/mBio.00624-18.

House mice may have become permanent house guests, cohabiting your space and sharing your food. I remember as a kid at the cabin, they would run across our pillows at night while we were sleeping, getting caught in my hair. These researchers investigated whether these little pests may contribute to the spread of pathogenic bacteria and bacterial resistance in the home environment. They collected 416 house mice from the trash compactor area in the subbasement of several multifamily residential buildings in four different New York City boroughs, as well as from the kitchen and food storage area of a commercial building.

Researchers used a two-tiered approach, including bacterial 16S rRNA sequencing and commercial multiplexed anti-microbial resistance (AMR) gene marker PCR arrays of pooled fecal samples, followed by targeted PCR of anal swabs. In addition, they assessed the kidneys for Leptospira DNA, since the organism is concentrated more in the urinary tract than the gastrointestinal tract.

Bacterial 16S rRNA sequencing identified Bacteroidetes, Firmicutes, and Proteobacteria as the dominant bacteria of the house mouse fecal biome. Multiple pathogens also were identified, including Shigella/EIEC (14%), Clostridium perfringens (12%), atypical enteropathogenic Escherichia coli (4%) and Salmonella spp. (3%). Clostridium difficile cytotoxin genes were found in 18 mice (4.3%). One of the ribotypes identified (RT106) was the most common cause of community-acquired C. difficile in a 2014 surveillance study.

Further, AMR genes encoding resistance to quinolones, macrolides, and beta lactams (bla and OXA-24) were common. Of the house mice sampled, 153 (37%) harbored at least one potential pathogen and 96 (23%) harbored at least one AMR gene. One juvenile male mouse harbored five different potential pathogens, including C. difficile, Shigella/EIEC, atypical EPEC, C. perfringens, and Klebsiella pneumoniae.

Leptospirosis DNA was detected in 14/378 (4%) kidneys. Sequencing demonstrated two genotypes that most closely resembled L. interrogans and L. kirschneri, and the nearly complete 16S rRNA genes clustered within a larger complex of pathogenic Leptospira strains. House mice harboring Leptospira were found in Manhattan, Queens, and the Bronx. These data suggest that house mice may not only serve as a marker of increasing bacterial resistance in the community, but may contribute directly to the circulation of potential pathogens and increasing resistance in a large urban area.

Eat Your Fruits and Vegetables — or You Might Get TB!

SOURCE: Aibana O, Franke MF, Huang CC, et al. Impact of vitamin A and carotenoids on the risk of tuberculosis progression. Clin Infect Dis 2017;65:900-909.

For years, nutritional status has been linked to the risk of developing tuberculosis (TB) disease. Two studies suggested that children and adult smokers with high intake of fruits and vegetables had a decreased risk of TB. Recently, vitamin A has been found to affect the immune system in myriad ways: retinoic acid helps to control transcriptional expression of important target genes, and retinol modulates the T-cell priming function of dendritic cells, as well as the function of T regulatory cells, including T-helper 1 cells, a critical part of the immune system response to TB.

These researchers followed a longitudinal cohort of household contacts of pulmonary TB cases in Lima, Peru. Case patients were defined as HIV-negative persons who developed active TB more than 15 days after identification of an index case. In all, 6,751 household contacts were followed for one year, and their vitamin A and carotenoid levels were determined. Two-hundred fifty-eight of these people were diagnosed with TB, although 66 cases were believed to be concurrent with an index case and not included in the analysis. Of the remaining 180 patients, 82% were microbiologically confirmed; 92% had pulmonary TB and 6% had extra-pulmonary TB. They were matched to 709 controls based on year of birth and gender.

Following adjustments for body mass index (BMI), alcohol intake, and socioeconomic status, logistic regression analysis demonstrated that diminished vitamin A levels were associated with a 10-fold increase in the risk for active TB (P < 0.001). This risk appeared to increase with diminishing vitamin A levels, such that the lowest quartile had six times the risk of those in the highest quartile.

Young age also was a significant factor. In those with vitamin A deficiency, the risk of developing TB disease in 10- to 19-year-olds was nearly 20-fold higher (adjusted odds ratio [OR], 18.58, P = 0.001) and 10-fold higher for those older than 20 years of age. In addition, adolescents in the lowest quartile of carotenoid levels were at higher risk for TB disease. Lower levels of beta-cryptoxanthin also was associated with an increased risk of TB disease, as were combined vitamin A and vitamin D deficiencies.

Low vitamin A levels were a strong predictor of developing TB in household contacts, especially in younger people. Routine vitamin supplementation might be a simple, low-cost strategy for reducing the risk of developing TB.