This neonate with respiratory distress (eg, tachypnea, grunting, subcostal retractions) and gram-positive rods on blood culture most likely has neonatal sepsis due to infection with Listeria monocytogenes.  L monocytogenes is a facultative intracellular anaerobe that typically causes outbreaks via ingestion of contaminated foods (eg, unpasteurized milk, deli meats).  The bacteria can replicate at cold temperatures (eg, refrigeration) and can invade the intestinal mucosa once ingested, causing gastroenteritis (eg, fever, vomiting, diarrhea).  Most cases in healthy patients are self-limited; however, pregnant women, neonates, elderly patients, and immunocompromised individuals are at increased risk for invasive disease (eg, bacteremia, meningitis).

Neonatal listeriosis may be acquired during or after delivery or by transplacental transmission of the bacteria to the fetus.  Infection in late pregnancy can cause fetal distress, premature delivery, or signs of neonatal sepsis (eg, respiratory distress, temperature instability) within the first few hours of life, as seen in this patient.  Maternal infection in early pregnancy can be more damaging to the fetus, causing granulomatosis infantiseptica (ie, skin lesions, disseminated abscesses/granulomas) and/or fetal demise.

(Choices A and B)  Clostridium tetani and Corynebacterium species (eg, C diphtheriae) are also gram-positive rods.  However, tetanus usually presents with hypertonicity and spasms, while diphtheria typically causes severe pharyngitis; neonatal infection with either is uncommon in resource-rich countries due to transplacental transfer of neutralizing antibodies from immunized mothers.  In addition, neither pathogen causes early-onset neonatal sepsis.

(Choices C and E)  Escherichia coli and Streptococcus agalactiae (group B streptococcus) are the most common causes of neonatal sepsis.  However, E coli is a gram-negative rod, and S agalactiae appears as gram-positive cocci in chains.

(Choice F)  Streptococcus pneumoniae is a gram-positive diplococcus and a common cause of bacteremia and meningitis in infants age ≥1 month.

Educational objective:
Listeria monocytogenes is a gram-positive rod associated with outbreaks of gastroenteritis via ingestion of contaminated foods (eg, unpasteurized milk, deli meats).  It can cause sepsis in susceptible patients, including neonates, older adults, pregnant women, and immunocompromised individuals.