Gastroenteritis: This is the most likely diagnosis given the presence of bacterial pathogens commonly associated with gastrointestinal infections in infants, such as Campylobacter coli, jejuni, and upsaliensis. The symptoms would typically include diarrhea, possibly bloody, abdominal cramps, and fever.

Infectious Diarrhea: Caused by other bacterial, viral, or parasitic pathogens, which could present similarly to Campylobacter infections.
Food Poisoning: If the infant was exposed to contaminated food or water, other pathogens like Salmonella, E. coli, or Listeria could be responsible.
Intussusception: Although more commonly associated with viral infections, bacterial infections can occasionally lead to intussusception, especially if there's a lead point like a lymphoid hyperplasia.

HUS (Hemolytic Uremic Syndrome): A complication of certain bacterial infections, notably E. coli, but potentially other bacteria as well. It's crucial to monitor for signs of HUS, such as hemolytic anemia, acute kidney injury, and thrombocytopenia.
Sepsis: Bacterial infections can lead to sepsis, a life-threatening condition that requires immediate recognition and treatment.
Meningitis: Although less common, certain bacterial pathogens can cause meningitis, especially in young infants. Campylobacter species are not typically associated with meningitis, but the differential for a febrile infant includes this diagnosis.

Immunodeficiency: Recurrent or severe infections could indicate an underlying immunodeficiency.
Congenital Anomalies of the GI Tract: Conditions like intestinal malrotation or Hirschsprung's disease could predispose to infections or mimic their symptoms.
Tuberculosis: Although rare in infants, especially in areas with low TB prevalence, it can cause gastrointestinal symptoms among other systemic manifestations.