In some people, the associated failure of breathing can lead to death. The infectious agents
that cause pneumonia are many and varied, including many types of viruses, bacteria, and
fungi. Certain microbes are more prevalent at particular ages; in neonates E. coli is a
common pathogen, whereas in adults Pneumococcusis more common. There is also a dis-
tinction between community-acquired and hospital-acquired (nosocomial) pneumonias;
they may be caused by different microbes. In people who are immunocompromised (due
to AIDS or cancer chemotherapy) unusual organisms may cause pneumonia, including
viruses (cytomegalovirus), fungi (cryptococcus), or even protozoa (Pneumocystis carinii).
The treatment of pneumonia is determined by the type of microbial agent.
The treatment of infectious diseases such as pneumonia is dictated more by the
nature of the microbe than by the location of the infection. For example, a staphylo-
coccal pneumonia is treated with the same antibacterial drugs as a staphylococcal infec-
tion elsewhere in the body. This tends to be different from other forms of pathology. For
example, an adenocarcinoma tumor of the lung is treated differently from adenocarci-
nomas elsewhere in the body. When given for a localized infection, antibiotics are not
“smart bombs”; they are not tissue-specific and are widely distributed throughout the
entirety of the body. This accounts for some of the side effects seen with antibacterial
agents. An antibiotic given for a pneumonia will just as easily kill bacteria in the
patient’s gastrointestinal tract, permitting undesirable microorganisms to overgrow and
produce side effects such as diarrhea.
9.8 The Clinical–Molecular Interface: Meningitis and Encephalitis
Meningitis is an infection of the meninges, the membranes that cover the surface of the
brain. Infectious causes of meningitis may be bacteria, viruses, fungi, or parasites. If
untreated, bacterial meningitis is uniformly fatal; with treatment, the mortality rate is
20–25%. Encephalitis is an inflammation, usually secondary to infection, of the sub-
stance of the brain. Whereas numerous viral, bacterial, fungal or parasitic agents are
capable of producing the encephalitis syndrome, viral causes are the most frequent. The
mortality and long-term morbidity rate of encephalitis is dependent upon the causative
agent. The following two patients recently presented to an emergency room within min-
utes of each other.
Patient 1.This 24-year-old male university student was brought to the emergency
department at 1600 h by his roommate. He was delirious and had a depressed level of con-
sciousness. Although he had been well the previous day, that morning he had complained
of a fever, severe headache, severe neck and back stiffness, nausea, and vomiting. He had
become progressively unwell over 7–8 hours. On physical examination he was acutely ill
with a temperature of 40°C. He was delirious and had neck rigidity with severe resistance
to any attempt to passively flex his neck. A CT scan of his brain was normal. A spinal tap
was performed and cerebrospinal fluid (CSF) was removed; it was cloudy.
A clinical diagnosis of bacterial meningitis was made. Therapy was started immedi-
ately because of the life-threatening nature of the illness. He was empirically treated
with ceftriaxone and vancomycin, intravenously. A short time later, a Gram stain of his
CSF revealed that the bacteria were Gram-positive cocci. Accordingly, the empiric
592 MEDICINAL CHEMISTRY